SP-368 Biomedical Results of Apollo

 

CHAPTER 4

APOLLO FLIGHT CREW CARDIOVASCULAR EVALUATIONS

 

by

G. W. Hoffler, M.D.
Robert L. Johnson, M.D.
Lyndon B. Johnson Space Center
 

Introduction

 

[227] The Apollo Program was designed to fulfill the specific operational goals of landing man safely on the moon, enabling him to explore the lunar surface, and successfully returning him to Earth. The engineering and operational complexity of this effort necessarily limited inflight physiological studies of man to those measurements considered vital to crew safety and health assessment. Limited availability of astronaut time during busy preflight and postflight periods constrained evaluations significantly; therefore, only examinations believed to have the greatest relevance to the understanding of man's physiological responses to the space flight environment were undertaken.

Reductions in orthostatic tolerance following space flight were first observed with the late flights of Project Mercury. Tilt table tests revealed moderate orthostatic hypotension in the Mercury-Atlas 9 Pilot after only 34 hours of orbital flight. Because of this finding, tilt table tests for orthostatic tolerance were incorporated into routine preflight and postflight evaluations and continued throughout the Gemini Program. The results of these tests confirmed consistent but variable losses of orthostatic tolerance following three- to fourteen-day flights. Elevated heart rate, reduced pulse pressure, and increased pooling of fluid in the lower extremities were found consistently during 70° upright tilts in the early postflight period. Responses to this stress usually returned to normal within 50 hours after splashdown, regardless of flight duration (NASA, 1963; 1967).

The advent of the Apollo Program presented new questions and uncertainties. Fundamental differences in the Apollo spacecraft, in its operational environment, and in program goals were expected to produce physiological responses that differed from those [228] seen after the Gemini flights. The two-gas (oxygen and nitrogen) atmosphere and the capability to move about in the spacecraft led to speculation that returning Apollo crewmen might show little or no change in orthostatic tolerance. On the other hand, there was some concern regarding the ability of the cardiovascular system to withstand acceleration stresses associated with lunar descent and ascent. Headward acceleration (+Gz) was imposed during the Lunar Module descent after three to four days of weightlessness, and a near one-g (+Gz) force was produced by the ascent profile after a day or more of 1/6-g exposure. Also, the results of postflight tests were expected to show important differences in cardiovascular responsiveness between crewmen who walked on the moon and those who remained in weightless flight. These speculations and many other unanswered questions emphasized the need to gain as much understanding as possible about the cardiovascular system and its adaptation, first to zero g and, later, to one g.

For several years before the first manned Apollo flight, investigators had studied the effects on the cardiovascular system of the application of lower body negative pressure (LBNP). Lower body negative pressure involves the application of reduced pressure usually to that portion of the body below the level of the iliac crests. Evaluations of its use as a simulator of orthostatic stress (Samueloff et al., 1966; Brown et al., 1966; Gilbert et al., 1966; Murray et al., 1967) and as a preventer of cardiovascular deconditioning (Stevens et al., 1966a; 1966b) bad been made. Lower body negative pressure, at levels ranging from 40 to 60 mm Hg (-53 x 102 to -80 x 102 N/m2) ) as determined by individual tolerance, produced changes in heart rate and blood pressure similar to those resulting from upright tilting. Clearly, the cardiovascular responses initially induced by either stress procedure depended primarily on displacement of blood, chiefly from central blood volume reservoirs, to the lower extremities.

Although qualitatively alike, differences in the magnitude of cardiovascular compensatory responses induced by LBNP have been reported. Stevens (1966) and Stevens and Lamb (1965) found a greater increase in heart rate during upright tilting than during LBNP adjusted to produce the same cardiac output reduction (-19 percent). Later, Musgrave and co-workers (1969; 1971) reported that even though LBNP at 40 mm Hg (-53 x 102 N/m2) ) and the upright posture displaced essentially equal volumes of blood to the lower extremities, negative pressure levels of -SO mmHg (-67 x 102 N/m2) ) were required to produce equivalent elevations of heart rate. Both groups of investigators attributed the smaller heart rate response during LBNP to the absence of stimulation of carotid and other baroceptors by gravity-induced hydrostatic pressure and flow changes. Further, the absence of hydrostatic pressure gradients along the lower extremities during LBNP caused displaced blood to be distributed differently than during tilt.

In addition to the capability to induce cardiovascular responses similar to those resulting from orthostasis, several advantages over the tilt table test were offered by the LBNP procedure. No movement of the subject was required; therefore, instrumentation was easier to apply and maintain, and physiological signals remained more stable. Stress could be applied at several levels and the magnitude of stress could be adjusted with greater ease and precision with the LBNP procedure. Because it could be used in weightless conditions and tilt table testing could not, LBNP testing of Apollo crewmen [229] furnished a valuable data base for future application to the understanding of Skylab results. LBNP studies were performed for most Apollo crewmen for missions not encumbered by postflight quarantine restrictions. In some instances, a static stand procedure was performed in conjunction with, or instead of LBNP evaluations. Admittedly, these techniques had limitations. The response of the cardiovascular system during weightlessness can only be inferred from studies performed before and after flight. In addition, many variables, including climatic and emotional factors, complicated interpretation of the results (Hoffler et al., 1974).

On the last two Apollo missions, experimental antihypotensive garments were tested. Although the Gemini and earlier Apollo missions revealed no need for such postflight support, planners of the 28- and 56-day Skylab flights envisioned the possible need for such postflight protection. This concern was in part engendered by reports that crewmen of the 18-day Soyuz 9 orbital mission had to be assisted from their spacecraft after flight because of difficulty standing, and that anti-G suits had been provided for Soyuz 11/Salyut crewmen for use following flight if necessary.

In this chapter, the results of the lower body negative pressure and passive stand tests are presented, and the efficacy of the experimental antihypotensive garments is evaluated. Many answers will be required before the entire picture. of man's cardiovascular adaptation to weightlessness can be clarified and understood. The Apollo cardiovascular studies constitute a small but important step in the acquisition of this knowledge.

 

Methods and Conditions

 

As noted previously, an LBNP protocol was used in conjunction with missions not encumbered by postflight quarantine restrictions. To assess the comparability of the LBNP and passive stand procedures, both tests were performed on the Apollo 9 crewmen. The passive stand protocol alone was used for evaluating the orthostatic tolerance of the Apollo 10 and 11 crewmen. The Apollo 10 to 14 missions included postflight quarantine, which precluded use of the LBNP. The types and durations of each of the eleven manned Apollo missions and the orthostatic evaluation techniques employed for each are described in table 1. Total mission duration varied from 143 to 302 hours; for the lunar landing missions, the length of crew time in 1/6 g varied from 22 to 75 hours.

The Command Module Pilot (CMP), his backup crewmember, and two control subjects were fitted for Jobst waist-length leotards before the flight of Apollo 16. These garments were to be donned during postflight orthostatic evaluations to assess their antihypotensive effect. A garment employing the capstan principle for the application of lower body positive pressure was designed to be worn by the Apollo 17 CMP during postflight tests.

The following subsections will describe the methodological aspects and conditions affecting orthostatic evaluation with and without the use of countermeasure garments.

 

Equipment and Measures

Lower Body Negative Pressure Device. The device for accomplishing LBNP consisted of a chamber of sufficient size to accommodate the lower body, an airtight waist seal, and....

 


[
230] Table 1

Apollo Mission Characteristics and Orthostatic Evaluation Techniques Employed

Apollo Mission

Type of Mission

Time From Lift-off to Lunar Landing, Hr

Length of Lunar Stay, Hr

Time From Lunar Lift-off to Splash-down, Hr

Total Mission Duration

Type of Orthostatic Evaluation Parformed

Hours

Days

.

7

Earth orbital

-

-

-

260.1

10.8

LBNP

8

Lunar orbital

-

-

-

147.0

6.1

LBNP

9

Earth orbital

-

-

-

241.0

10.0

LBNP, Stand

10

Lunar orbital

-

-

-

192.0

8.0

Stand

11

Lunar landing

102.7

22.2

70.9

194.0

8.1

Stand

12

Lunar landing

110.5

31.5

102.0

244.5

10.2

-

13

Lunar abort

-

-

-

142.9

6.0

-

14

Lunar landing

108.2

33.5

74.3

216.0

9.0

-

15

Lunar landing

104.7

67.0

123.6

295.0

12.3

LBNP

16

Lunar landing

104.5

71.0

90.3

265.8

11.1

LBNP

17

Lunar landing

110.3

75.0

116.5

301.8

12.6

LBNP


 

[231] ....a regulated vacuum source (Wolthuis et al., 1970; Wolthuis et al., 1972). The LBNP device is shown in figure 1. The type of physiological measurements taken during the LBNP protocol varied slightly from mission to mission. Measurements made in conjunction with the Apollo 7 to 9 missions included continuous axillary and sternal lead electrocardiograms, indirect blood pressure taken every 30 seconds by the Korotkov sound technique [using the NASA Gemini blood pressure measuring system (NASA, 1968)], and changes in calf circumference measured by double-strand, mercury-in-Silastic strain gages.

 


Figure 1. Subject underground test in lower body negative pressure device.

Figure 1. Subject underground test in lower body negative pressure device.

 

For the Apollo 15 to 17 evaluations, the limited two-lead electrocardiogram (ECG) was replaced with a modified Frank lead vectorcardiogram (VCG), and wide-band precordial heart sounds (vibrocardiogram) were recorded with a capacitance microphone system (LTV Research Center, Anaheim, Calif.). The respiration rates of the Apollo 16 and 17 crewmen were measured with a mercury strain gage attached to the lower thorax. The carotid pulse trace was recorded for Apollo 17 crewmen.

Antihypotension Garments. A Jobst waist-length elastic leotard was used in conjunction with the Apollo 16 mission. This garment was designed to produce a pressure [232] at the ankle of 40 to 45 mm Hg (53 x 102 to 60 x 102 N/m2) that decreased linearly to approximately 10 mm Hg (13 x 102 N/m2) ) at the waist. To accommodate the reduction in limb size expected to occur during flight, garments in three separate sizes were made for the CMP. They were, respectively, 0.5, 1, and 1.5 cm smaller in circumference at the calf with proportionate reductions throughout the lower limbs.

A lower body garment using the capstan principle to apply pressure to the lower limbs was designed, fabricated, and sized for the Apollo 17 CMP to use following splashdown. The garment is pictured diagrammatically in figure 2. Capstan pressure was read from an aneroid gage and the capstan was inflated with a hand bulb, both of which were concealed in a zippered pocket. The capstan exerted the pressure of the garment over the skin at the ankle m a 2:1 ratio. This pressure diminished linearly to approximately 10 mm Hg (13 x 102 N/m2) ) at the waist. Preflight testing with pressure sensors between the garment and the skin verified the ratio and the diminishing gradient of pressure from ankle to waist. To accommodate anticipated loss of limb girth, laces were provided for reducing the garment size slightly before stowage in the Command Module. The capstan itself accommodated moderate changes (±2.5 cm) in limb girth.

 

Physical Examinations

Major medical examinations of space flight crewmembers were performed at approximately 30, 15 and 5 days before flight (F-30, F-15 and F-5, respectively). Orthostatic tolerance evaluations performed as an integral part of these medical examinations provided baseline information for comparison with postflight evaluation results. These preflight orthostatic tolerance evaluations took place at the NASA Lyndon B. Johnson Space Center (JSC) Cardiovascular Laboratory, Houston, Texas, and at the NASA John F. Kennedy Space Center (KSC) Medical Operations Facility, Kennedy Space Center, Florida. As part of the major medical examinations, postflight orthostatic tolerance evaluations were performed shortly after splashdown and at intervals of approximately 24-hours thereafter. The number of postflight evaluations and the time at which they were performed (table 2) were dictated partly by operational constraints and partly by the length of time required for individual crewmembers to regain their preflight status. As indicated in table 2, either two or three postflight orthostatic evaluations were completed on each crewman; a fourth evaluation of the Apollo 15 to 17 crewmembers differed in that it did not necessarily include orthostatic stress tests. Immediately postflight, the first evaluations took place on the recovery ship; subsequent postflight evaluations were performed on the recovery ship, at KSC, or at the JSC Cardiovascular Laboratory.

 

Control Subjects

To ensure comparability of test conditions and operability of test equipment, several members of the attending support team assigned to each Apollo mission participated in preflight and postflight orthostatic evaluations identical to those used on crewmembers. These control subjects were evaluated a day or two before the Apollo crewmen were evaluated. The data collected helped ensure the validity of postflight changes observed in space flight crewmembers and the operational readiness of test teams and equipment.

 


[
233]

Figure 2. Lower body positive pressure garment employing the capstan principal.

Figure 2. Lower body positive pressure garment employing the capstan principal.


[234] Table 2

Time of Apollo Postflight Orthostatic Tolerance Evaluations

Apollo Mission

Crewmember

Time of Postflight Evaluations (hours following splashdown)

First

Second

Third

Fourth

.

7

CDR

3

34

.

.

CMP

2

35

.

.

LMP

5

32

.

.

8

CDR

3

26

51

.

CMP

4

27

53

.

LMP

5

26

52

.

9

CDR

2

31

53

.

CMP

4

33

55

.

LMP

3

32

54

.

10

CDR

2

26

.

.

CMP

3

27

.

.

LMP

2

28

.

.

11

CDR

6

25

.

.

CMP

7

25

.

.

LMP

8

26

.

.

15

CDR

3

43

73

122

CMP

4

42

71

121

LMP

5

44

72

137

16

CDR

4

24

68

162

CMP

6

26

70

162

LMP

5

25

71

162

17

CDR

6

24

48

90

CMP

5

26

50

91

LMP

7

25

51

91


 

Test Protocols

The protocols for the two orthostatic stress procedures are shown in figure 3. The supine LBNP protocol consisted of a five-minute resting control period, a five-minute period at each of three distinct reduced-pressure levels, and a five-minute recovery period. The first five-minute period of reduced pressure included one minute at -8 mm Hg (-11 x 102 N/m2) ) and one minute at -16 mm Hg (-21 x 102 N/m2) ), followed by three minutes at -30 mm Hg (-40 x 102 N/m2) ). The two short-duration, relatively low levels of reduced pressure were adopted to obtain additional information regarding the responsiveness of lower limb capacitance vessels. The three levels of sequentially applied reduced pressure used were chosen on the basis of previous experience in the JSC Cardiovascular Laboratory (Wolthuis et al., 1970). As reported, the use of an incremental LBNP protocol produced physiological responses for each level of reduced pressure [235] applied and ensured a measurable, quantitative stress response in both the normal preflight and the orthostatically intolerant postflight conditions.

 


Figure 3. Orthostatic stress procedure protocols.

Figure 3. Orthostatic stress procedure protocols.

 

The passive stand protocol consisted of a five-minute resting supine control period followed by a five-minute passive stand. For the passive stand, the subject leaned against a wall in a relaxed manner with his heels spaced 15 cm (6 in.) away from the wall. Physiological measurements made during this protocol included continuous sternal and axillary lead ECG's, and indirect blood pressure taken by the Korotkov sound technique at 30-second intervals.

[236] The Apollo 16 tests, utilizing the Jobst leotard, were performed pre and postflight. Passive stand tests were performed at the F-15 tests on the Command Module Pilot, the backup CMP, and the. two control subjects, and were repeated on the CMP and the controls at their respective recovery day examinations. The tests followed the LBNP test and consisted of a five-minute supine rest period followed by a five minute stand period in the manner of the earlier Apollo passive stand tests. The leotards were then donned, and, after a ten-minute period of supine rest, the stand test was repeated. Blood pressure and heart-rate data were obtained by using the instrumentation of the earlier LBNP test.

Approximately one-half hour before Apollo 17 deorbit, the Command Module Pilot donned but did not inflate the antihypotensive garment. After splashdown, while still reclining in the couch, he inflated the capstan to a pressure of 130 mm Hg (173 x 102 N/m2) ) and, thus, furnished 65 mm Hg (87 x 102 N/m2) ) pressure over the ankle region. This pressure was maintained until a stand test could be performed. The suit was tested by performing a stand test four hours after splashdown and before LBNP testing. Crew time restraints prohibited repetition of the preflight protocol, which included separate tests with and without the garment, each separated by an appropriate recovery period. Therefore, the crewman spent five minutes in the supine position with the capstan inflated, five minutes passive standing with the capstan inflated, five minutes standing with the garment depressurized, and four minutes standing with the capstan reinflated to the original capstan pressure of 130 mm Hg (173 x 102 N/m2) ). The total duration of the continuous stand was 15 minutes, including approximately 45 seconds for reinflation of the capstan. Heart rate was obtained continuously from the VCG; blood pressure was measured every 30 seconds by a Skylab automatic blood pressure measuring system.

 

Ancillary Indicators of Orthostatic Tolerance

Accessory cardiovascular and related measurements were made in conjunction with orthostatic evaluations. Before orthostatic evaluation of the Apollo 7 to 11 and 15 to 17 crewmen, the circumference of the calf at its maximum girth was measured during supine rest. An assessment of total lower limb volume made on the Apollo 16 and 17 crewmembers consisted of multiple leg circumference measurements at discrete intervals from the ankles to the groin while the crewman was supine with the legs extended and slightly elevated. Limb volume was computed by summing sequential, truncated, assumed circular cones. Standard 1.8-m (6-ft) posterior-anterior chest X-rays were taken of every crewmember at his last major preflight medical examination and first postflight evaluation The cardiothoracic (C/T) ratio was determined by standard clinical methods. The ambient temperature and the oral temperature and body weight of each crewman were recorded at each evaluation.

 

Ambient Conditions and Other Variables

Ambient temperatures and oral temperatures were recorded during preflight and postflight orthostatic evaluations because sufficiently high temperatures can affect orthostatic tests in an adverse way. While ambient temperatures during preflight orthostatic evaluations were acceptably low, temperatures during the first postflight [237] evaluations were generally markedly higher. Ambient temperatures during orthostatic evaluations for the Apollo 15 Commander are illustrative. During preflight testing, the mean ambient temperature derived from measurements made on three separate days of testing was 297°K (24°C). On the first postflight day, the ambient temperature during orthostatic evaluation was 301°K (28°C). The significant elevation in group mean ambient temperature at the first postflight evaluation reflected the recovery zone climate (usually tropical) and inadequate air conditioning of the recovery ships. Group mean ambient temperatures for subsequent postflight evaluations were not significantly different from preflight temperatures.

Preflight examinations employing the Apollo 16 antihypotensive garment were performed under adequately controlled temperatures of 295° to 296°K (22° to 23°C). However, environmental temperatures during the first and second postflight examinations were the highest of any encountered during the Apollo shipboard tests, ranging from 305° to 306°K (32° to 33°C) during the postflight stand tests of the CMP. Apollo 17 crewmen were exposed to high environmental temperatures during transfer to the recovery vessel and during subsequent ceremonies, but their tests were performed in the air conditioned Skylab Mobile Laboratory at a temperature of 296°K (23°C).

Table 3 is a tabulation of group mean oral temperature. Here, too, the preflight mean was based on three separate determinations, thirty, fifteen and five days before flight. The elevation in this parameter noted at the first postflight evaluation continued for succeeding postflight days.

The effects of elevated ambient and oral temperatures within the postflight evaluation periods may be altered by the presence of certain additional variables. For example, although most Apollo crewmembers reported a normal amount of sleep before each preflight evaluation, there was a significant group mean reduction in the amount of sleep on the night before splashdown. Further, the interval between venipuncture for biochemical analysis (30 to 80 cm3 withdrawn) and time of orthostatic evaluation varied widely (15 minutes to many hours) within preflight and postflight time frames. Finally, the interval between food ingestion and orthostatic evaluation also varied widely (15 minutes to 17 hours).

 

Data Collection and Reduction

The various physiological measurements were recorded in real time on a strip chart recorder and on frequency modulation magnetic tape. The strip chart data were used for real-time assessment of crewmember well-being and safety. The appearance of presyncopal symptoms in some crewmen during orthostatic stress caused early termination of the procedure. Analog tape data were subsequently converted to digital data and analyzed by specially developed software on a Sigma 3 computer system.

Minute heart rates were derived from an analysis of electrocardiogram or vectorcardiogram R-R intervals; systolic. blood pressure and diastolic blood pressure values were read at the appearance of the first and last Korotkov sounds, respectively, on the calibrated descending arm cuff pressure ramp. Percentage change in calf volume was measured by calculating the change from initial, resting-calf circumference and converting this value to percentage change in calf volume using the method of Eagan (1961) Two....

 


[
238] Table 3

Tabulation of Apollo Group Mean Oral Temperatures

(Arrows Indicate p<0.05)

 

Apollo Mission

Crewmember

Preflight Summary

Postflight Evaluations

Mean

± SD

First

Second

Third

°K

(°C)

°K

(°C)

°K

(°C)

°K

(°C)

.

7

CDR

309.6

(36.5)

0.12

310.7

(37.6)arrow pointing upward

309.9

(36.8)arrow pointing upward

.

.

CMP

309.8

(36.7)

0.12

309.7

(36.6)

310.1

(37.0)arrow pointing upward

.

.

LMP

309.6

(36.5)

0.38

310.5

(37.4)

308.9

(36.8)

.

.

8

CDR

309.6

(36.5)

0.17

310.2

(37.1)arrow pointing upward

309.7

(36.6)

309.9

(36.8)

CMP

309.9

(36.8)

0.32

310.2

(37.1)

310.2

(37.1)

310.0

(36.9)

LMP

309.7

(36.6)

0.25

309.9

(36.8)

309.7

(36.6)

309.8

(36.7)

9

CDR

309.6

(36.4)

0.15

309.5

(36.4)

309.3

(36.2)

310.3

(37.2)arrow pointing upward

CMP

309.4

(36.3)

0.15

309.7

(36.6)

309.3

(36.2)

309.6

(36.5)

LMP

309.7

(36.6)

0.21

309.9

(36.6)

310.3

(37.2)arrow pointing upward

309.9

(36.8)

10

CDR

309.6

(36.5)

0.36

309.3

(36.2)

309.4

(36.3)

-

-

CMP

309.8

(36.7)

0.31

309.9

(36.8)

309.9

(36.8)

-

-

LMP

309.6

(36.5)

0.15

310.2

(37.1)arrow pointing upward

309.7

(36.6)

-

-

11

CDR

309.6

(36.5)

0.12

309.5

(36.4)

-

-

-

.

CMP

309.6

(36.5)

0.49

309.8

(36.7)

-

-

-

.

LMP

309.8

(36.7)

0.06

310.2

(37.1)arrow pointing upward

-

-

-

.

15

CDR

309.4

(36.3)

0.23

-

(37.1)

309.2

(36.1)

309.4

(36.3)

CMP

309.6

(36.5)

0.17

-

(36.9)

-

-

310.4

(37.3)arrow pointing upward

LMP

309.6

(36.5)

0.21

-

(36.9)

309.8

(36.7)

309.7

(36 6)

16

CDR

308.9

(35.8)

0.40

-

(37.1)

-

-

309.6

(36.5)

CMP

309.1

(36.0)

0.10

-

(36.7)

-

-

309.7

(36.6)arrow pointing upward

LMP

308.8

(35.7)

0.46

-

(36.4)

-

-

310.2

(37.1)arrow pointing upward

17

CDR

309.8

(36.7)

0.40

309.8

(36.7)

308.7

(36.6)

309.8

(36.7)

CMP

310.0

(36.9)

0.35

310.4

(37.3)

309.8

(36.7)

310.5

(37.4)

LMP

309.4

(36.3)

0.46

308.9

(36.8)

310.0

(36.9)

309.3

(36.2)

.

Group Mean

± SD

309.64

(36.42)

.

310.01

(36.86)

309.81

(36.66)

309.92

(36.77)

0.334

0.345

0.316

0.353

t-Test

p>0.001

n.s.

p<0.005


 

[239] ...successive heart sound complexes were analyzed from the vibrocardiogram each minute; computation of stroke volume followed the method of Agress and co-workers (1967).

For each crewman evaluation, heart rate, systolic blood pressure, diastolic blood pressure, pulse pressure, and stroke volume values were averaged within each of the five five-minute LBNP periods and within the two five-minute passive stand periods to produce the respective mean values within each of these periods. These mean values for each crewmember, during each period and by each measurement, were subsequently used as the best estimate of measurement within that period in the compilation of data tables. In the case of percentage, maximal calf volume change rather than mean values within each level of LPNP was used.

 

Data Analysis

Data were analyzed statistically by individual crewmember and by group mean. For individual crewmembers, the mean and the standard deviation of the three preflight values for each measurement in each distinct protocol condition were calculated (preflight summary). From these values, fiducial limits of the normal range at the 95-percent confidence level were determined. Individual postflight values Iying outside these limits were defined as statistically significant changes and are indicated appropriately in the tables. Group means and standard deviations were calculated for each discrete measurement within each protocol condition for every evaluation day and for the preflight summaries. Preflight summary group means were compared with each postflight counterpart by using the independent t-test.

It should be noted that four astronauts flew two Apollo missions each. The Apollo 8 Command Module Pilot (CMP) flew as the Apollo 13 Commander (CDR); the Apollo 9 CMP flew as the Apollo 15 CDR; the Apollo 10 CMP flew as the Apollo 16 CDR; and the Apollo 10 Lunar Module Pilot (LMP) flew as the Apollo 17 Commander.

 

Results

 

Heart Rates

Of the various cardiovascular measurements obtained from Apollo crewmembers during their evaluations, heart rate was the most easily measured and yielded the most accurate and predictable values. Table 4 contains heart-rate data on individual crewmembers during three conditions of orthostatic stress evaluations: (1) resting supine control, (2) the highest level of LBNP [-SO mm Hg (-67 x 102 N/m2)], and (3) passive standing. Resting supine heart rate is elevated significantly in 13 of 24 crewmen (54 percent) at the first postflight evaluation; the group response is elevated at the two-percent level of confidence. A trend toward preflight values is subsequently evident. By the third postflight evaluation, only three of fifteen individuals (20 percent) show significant elevations in resting supine heart rate, and the group mean value is not statistically different from the preflight group mean heart rate (n = 15, paired).

Following the same comparisons, the application of -50 mm Hg (-67 x 102 N/m2) LBNP produced significantly elevated heart rates in 14 of 17 Apollo crewmen (82 percent) at the first postflight evaluation, with a group elevation significant at the O.1-percent level. The Apollo 15 LMP experienced presyncope during the last seconds of....

 


[240] Table 4

Individual Apollo Crewmember Heart Rate Data (Arrows Indicate p < 0.05)

 

Protocol Condition

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

.

Resting Supine Control Period

7

CDR

56

59

54

56

2.6

77upward arrow

59

.

CMP

81

74

78

78

3.1

78

76

.

LMP

57

64

66

62

4.4

75upward arrow

70

.

8

CDR

74

69

70

71

2.6

87upward arrow

70

80upward arrow

CMP

84

69

66

73

9.7

94

76

66

LMP

77

74

71

74

2.4

91upward arrow

81upward arrow

71

9

CDR

76

63

68

69

6.8

64

78

80

CMP

56

59

58

57

2.0

57

54

53

LMP

59

55

57

57

2.1

50downward arrow

50downward arrow

50downward arrow

10

CDR

62

70

59

64

5.7

81upward arrow

73

-

CMP

65

59

55

60

5.0

65

62

-

LMP

59

62

52

58

5.1

80upward arrow

79upward arrow

-

11

CDR

61

62

67

63

3.2

69

79upward arrow

-

CMP

53

46

51

50

3.6

67upward arrow

65upward arrow

-

LMP

68

69

70

69

1.0

62downward arrow

81upward arrow

-

15

CDR

51

50

55

52

2.6

54

50

52

CMP

66

69

70

68

2.1

83upward arrow

84upward arrow

73

LMP

52

56

57

55

2.6

66upward arrow

66upward arrow

66upward arrow

16

CDR

57

57

55

56

1.2

70upward arrow

60upward arrow

61upward arrow

CMP

49

49

45

48

2.1

56upward arrow

48

56upward arrow

LMP

60

53

54

56

3.9

57

61

60

17

CDR

55

62

59

59

3.2

67upward arrow

70upward arrow

64

CMP

78

76

68

74

5.1

67

64

69

LMP

50

50

51

50

0.6

55upward arrow

56upward arrow

52

.

.

Group Mean

62.8

61.5

60.7

61.6

.

69.7

67.2

63.5

±SD

10.47

8.53

8.41

8.60

12.13

10.90

9.88

LMP

.

.

.

t-Test

p < 0.02

n.s.

n.s.

 

[241] Table 4 (Continued) Individual Apollo Crewmember Heart Rate Data

(Arrows Indicate p<0.05)

 

Protocol Condition

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

.

-50mm Hg* LBNP

7

CDR

72

61

59

64

6.7

90upward arrow

67

-

CMP

94

92

90

92

2.1

137upward arrow

94

-

LMP

76

74

76

75

1.1

108upward arrow

87upward arrow

-

8

CDR

100

86

94

93

6.7

159upward arrow

108

101

CMP

116

89

94

99

14.5

129

121

88

LMP

97

105

106

103

48

146upward arrow

137upward arrow

102

9

CDR

82

67

78

76

7.9

100upward arrow

94

93

CMP

63

73

76

71

6.9

81

70

68

LMP

74

70

67

70

3.3

87upward arrow

75

65

15

CDR

62

59

61

61

1.5

76upward arrow

-

65

CMP

79

81

81

80

1.2

131upward arrow

109upward arrow

93upward arrow

LMP

58

56

64

59

4.2

-

84upward arrow

78upward arrow

16

CDR

79

71

72

74

4.1

109upward arrow

101upward arrow

83

CMP

62

67

58

62

4.2

99upward arrow

74upward arrow

79upward arrow

LMP

82

72

83

73

5.9

112 upward arrow

98upward arrow

98upward arrow

17

CDR

67

78

71

72

5.3

112upward arrow

91upward arrow

78

CMP

87

86

79

84

4.3

87

78

90

LMP

59

69

60

63

5.4

82upward arrow

80upward arrow

60

.

.

Group Mean

78.3

75.3

76.1

76.5

.

108.5

92.2

82.7

± SD

15.97

12.61

13.70

13.27

24.58

18.85

13.76

.

.

.

t-Test

p < 0.001

p < 0.02

n.s.

* -67 x 102 N/m2

 

[242] Table 4 (Continued) Individual Apollo Crewmember Heart Rate Data

(Arrows Indicate p<0.05)

 

Protocol Condition

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

.

Passive Stand

9

CDR

81

73

79

78

4.2

93up arrow

100up arrow

96up arrow

CMP

66

75

72

71

4.6

88up arrow

72

70

LMP

71

67

69

69

2.0

93up arrow

79up arrow

65

10

CDR

86

93

86

88

4.0

111up arrow

92

-

CMP

88

85

70

81

9.6

100

81

-

LMP

80

74

70

75

5.0

121up arrow

109up arrow

-

11

CDR

73

83

85

80

6.4

112up arrow

105up arrow

-

CMP

76

69

65

70

5.6

91up arrow

88up arrow

-

LMP

73

76

79

76

3.0

89up arrow

100up arrow

-

.

.

Group Mean

77.1

77.2

75.0

76.4

.

99.8

91.8

77.0

± SD

7.22

8.29

7.48

6.11

11.99

12.71

16.64

.

.

.

.

t-Test

p< 0.001

p<0.001

n.s.


 

[243] -40 mm Hg (-53 x 102 N/m2) LBNP and was not tested at -50 mm Hg (-67 x 102 N/m2) LBNP on recovery day. Five other crewmembers (the Apollo 8 CMP, the Apollo 8 LMP, the Apollo 9 LMP, the Apollo 16 CMP, and the Apollo 16 LMP) developed presyncopal symptoms at some point before protocol completion during their immediate postflight 50 mm Hg (-67 x 102 N/m2) stress; the Apollo 15 Commander experienced similar symptoms during his second postflight evaluation. Although more crewmembers, immediately postflight, demonstrated a larger heart rate increment over preflight values during LBNP stress than during the resting control period, statistically significant group differences disappeared by the third postflight evaluation. Passive vertical standing results indicated a similar increase in heart rate immediately postflight, with eight of nine crewmembers (89 percent) having heart rates above their 95-percent preflight envelope, and the group mean value being elevated at the 0.1 percent level.

In table 5, heart rates of Apollo crewmembers are compared with those of control subjects for three protocol conditions. Significant "postflight" heart rate changes among the control subjects onboard the recovery ship were not observed. Although the control subjects were exposed to similar environmental conditions, all had a five- to ten-day acclimatization period onboard the recovery ship preceding their evaluations.

 


Table 5

Apollo Crewmember Versus Control Subject Heart Rate Data

Protocol Condition

Apollo Group

Preflight Summary

Postflight Evaluations

Response

First

Second

N

group mean

SDi

SDt

N

group mean

p

N

group mean

p

.

Resting supine

bracket

Crew

24

61.6

8.60

1.06

24

69.7

0.02

24

67.2

0.05

Controls

22

69.7

6.93

1.00

22

69.4

n.s.

10

70.4

n.s.

-50mm Hg* LBNP

bracket

Crew

18

76.5

13.27

1.55

17

108.5

0.001

17

92.2

0.02

Controls

16

85.1

8.14

1.49

14

87.3

n.s.

9

84.2

n.s.

Stand

bracket

Crew

9

76.4

6.11

1.24

9

99.8

0.001

9

91.8

0.01

Controls

7

79.6

6.40

2.72

7

81.1

n.s.

-

-

-

* -67 x 102N/m2
Note:
N = Number of subjects
group mean= Group mean
SDi = Standard deviation of crewmember preflight summary means
SDt = Standard deviation of three preflight group means
p = Probability level


 

Heart Rate and Other Measures During Several LBNP Protocols

Table 6 contains group mean values for several physiological measurements by protocol condition. Preflight summary group means are shown with two different standard deviations. The first (SDi) is an expression of variability between the crewmember preflight summary means; the second (SDt) is a measure of variability [244] among the three preflight group means. Accompanying each postflight evaluation group mean is the t-test probability that it differs from the preflight summary group mean. For the resting supine control condition, heart rate i8 significantly elevated at the first and second postflight evaluations. The reciprocal of this response is seen in the stroke volume data. No significant differences are noted after flight in the resting systolic, diastolic, or pulse pressures. During the three conditions of reduced pressure [-30, -40, and -SO mm Hg (-40 x 102, -53 x 102 and -67 x 102 N/m2) LBNP], heart rates are significantly elevated at the first postflight evaluation, with a trend toward preflight summary response values in subsequent postflight evaluations. Again, stroke volume followed a reciprocal pattern. Significant decreases in systolic and pulse pressures are seen during LBNP only in the first postflight evaluations. Changes during the passive stand condition parallel changes during LBNP. Postflight changes during the recovery condition are not significant. All postflight alterations return to preflight summary values by the third postflight evaluation.

 

Calf Volume Changes Induced by LBNP

No significant postflight changes in calf volume are observed during the three conditions of reduced-pressure stress at any of the postflight evaluations (table 6). Table 7, which includes data on individual calf volume change during Apollo LBNP maximal stress, is presented because plethysmographic data from Gemini tilt table tests indicated increased postflight calf volume during tilt stress. Seven of seventeen Apollo crewmembers (41 percent) showed significantly decreased postflight calf volume changes during the maximal [-50 mm Hg (-67 x 102 N/m2) ] LBNP level, and the total group mean also decreased from the preflight value, although not to a statistically significant degree

 

Body Weight Changes

Significant body weight changes occurred in virtually all astronauts regardless of flight duration If a significant part of the weight change is due to a reduction in blood volume or loss of body fluids, cardiovascular function might be affected. Consequently, weight changes were considered in conjunction with orthostatic evaluations. Table 8 contains data on individual body weights at each evaluation date. Preflight summary means are based on three weights taken on the days of the major medical examinations. Launch day (F-O) weight. are also listed because the postflight weight of United States space crewmen has been previously based on these data (Berry, 1973). The launch day group mean is clearly decreased (0.7 kg) from the preflight summary group mean. The t-test probability for postflight weight change is referenced to the preflight summary group mean rather than to the single launch day group mean, because the preflight mean is more representative of true crew weight change. The first postflight group mean weight shows a 3.4-kg (4.4 percent) decrement that is not regained at 90 to 160 hours after splashdown by the nine crewmen (Apollo 15 to 17 missions) weighed that long after recovery.

 

Resting Calf Circumference and Volume of the Lower Limbs

The simple and relatively accurate supine measurement of maximal calf circumference was performed before and after flight on 24 crewmen. The first section of table 9....

 


[245] Table 6

Apollo Group Mean Values for Preflight Summary and Postflight Orthostatic Evaluations

 

Measurement

Protocol Condition

Preflight Summary

Postflight Evaluations

Response

First

Second

Third

N

group mean

SDi

SDt

N

group mean

p

N

group mean

p

N

group mean

p

.

Heart rate (bpm)

Control

24

61.6

8.60

1.06

24

69.7

0.02

24

67.2

n.s.

15

63.5

n.s.

-30

bracket

mm Hg* LBNP

18

65.7

11.11

1.42

18

84.3

0.005

18

72.7

n.s.

15

68.5

n.s.

-40

18

70.7

11.20

1.40

18

96.7

0.001

18

79.8

0.05

15

74.5

n.s.

-50

18

76.5

13.27

1.55

17

108.5

0.001

17

92.2

0.02

15

82.7

n.s.

Recovery

18

59.1

8.66

1.08

18

67.4

n.s.

18

64.1

n.s.

15

60.5

n.s.

Stand

9

76.4

6.11

1.24

9

99.8

0.001

9

91.8

0.001

3

77.0

n.s.

Systolic blood pressure (mm Hg*)

Control

24

115.3

8.31

0.74

24

111.6

n.s.

24

118.0

n.s.

15

118.5

n.s.

-30

bracket

mm Hg* LBNP

18

110.5

10.04

1.86

18

101.5

0.02

18

112.3

n.s.

15

112.7

n.s.

-40

18

107.7

10.66

1.15

18

96.3

0.01

18

109.7

n.s.

15

109.3

n.s.

-50

18

104.8

11.09

1.86

17

91.5

0.01

17

107.4

n.s.

15

107.2

n.s.

Recovery

18

117.1

10.03

1.55

18

116.4

n.s.

18

123.2

n.s.

15

120.5

n.s.

Stand

9

118.8

6.24

3.40

9

105.8

0.001

9

123.9

n.s.

3

120.7

n.s.

Diastolic blood pressure (mm Hg*)

Control

24

67.0

6.61

1.51

24

67.1

n.s.

24

67.7

n.s.

15

66.3

n.s.

-30

bracket

mm Hg* LBNP

18

69.7

6.63

1.31

18

66.5

n.s.

18

67.4

n.s.

15

67.9

n.s.

-40

18

70.7

6.21

1.25

18

66.3

0.05

18

68.3

n.s.

15

70.0

n.s.

-50

18

71.8

6.84

2.01

17

66.6

n.s.

17

69.1

n.s.

15

70.9

n.s.

Recovery

18

71.0

6.32

0.89

18

73.4

n.s.

18

70.9

n.s.

15

69.4

n.s.

Stand

9

81.0

5.22

4.46

9

80.2

n.s.

9

82.8

n.s.

3

80.7

n.s.

 

*1 mm Hg = 1.33 x 102 N/m2
 
Note: N = Number of subjects
group mean= Group mean
SDi = Standard deviation of crewmember preflight summary means
SDt = Standard deviation of three preflight group means
p = Probability level


[246] Table 6 (Continued)

Apollo Group Mean Values for Preflight Summary and Postflight Orthostatic Evaluations

 

Measurement

Protocol Condition

Preflight Summary

Postflight Evaluations

Response

First

Second

Third

N

group mean

SDi

SDt

N

group mean

p

N

group mean

p

N

group mean

p

.

Pulse Pressure (mm Hg*)

Control

24

48.3

6.34

0.81

24

44.6

n.s.

24

50.2

n.s.

15

52.1

n.s.

-30

bracket

mm Hg* LBNP

18

40.9

6.09

0.61

18

35.2

0.01

18

44.8

n.s.

15

44.8

n.s.

-40

18

37.2

6.52

0.06

18

30.2

0.02

18

41.4

n.s.

15

39.4

n.s.

-50

18

33.1

6.59

0.06

17

24.8

0.02

17

38.2

n.s.

15

36.3

n.s.

Recovery

18

46.4

6.76

1.07

18

43.1

n.s.

18

52.2

0.05

15

51.0

n.s.

Stand

9

37.8

6.44

7.47

9

25.6

0.02

9

41.0

n.s.

3

40.0

n.s.

Calf circumference (cm)

Calf volume

Change (% delta)

Control

24

37.47

1.626

0.072

24

36.38

0.05

21

36.85

n.s.

15

37.05

n.s.

-30

bracket

mm Hg* LBNP

18

1.62

0.512

0.060

18

1.45

n.s.

18

1.49

n.s.

15

1.45

n.s.

-40

18

2.32

0.597

0.050

18

2.09

n.s.

18

2.26

n.s.

15

2.21

n.s.

-50

18

3.08

0.679

0.042

18

2.71

n.s.

17

3.04

n.s.

15

3.04

n.s.

Recovery

18

0.54

0.270

0.029

17

0.27

0.02

18

0.66

n.s.

15

0.53

n.s.

Stroke volume (ml)

Control

9

85.8

4.49

0.15

7

74.1

0.02

9

79.2

0.05

9

80.4

n.s.

-30

bracket

mm Hg* LBNP

9

73.7

6.00

1.05

7

60.3

0.01

9

64.9

0.05

9

66.3

n.s.

-40

9

63.8

6.96

1.58

6

49.3

0.025

9

56.4

n.s.

9

58.0

n.s.

-50

9

57.6

7.02

0.78

5

41.4

0.05

9

47.9

n.s.

9

50.2

0.05

Recovery

9

86.9

3.37

1.36

7

79.4

n.s.

9

81.6

n.s.

9

82.7

n.s.

 
*1 mm Hg = 1.33 x 102 N/m2
 
Note: N = Number of subjects
group mean= Group mean
SDi = Standard deviation of crewmember preflight summary means
SDt = Standard deviation of three preflight group means
p = Probability level


Table 7

Individual Calf Volume Percent Change Data During Apollo LBNP Maximal Stress. (Arrows Indicate p < O.05).

 

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

SD

First

Second

Third

.

7

CDR

1.74

1.73

2.24

1.90

0.294

2.21

2.01

.

CMP

2.49

2.30

2.50

2.43

0.120

1.96downward arrow

2.21

.

LMP

3.60

3.41

2.85

3.13

0.392

2.78

3.87

.

8

CDR

3.06

2.86

2.54

2.83

0.262

2.37

2.75

2.91

CMP

2.74

2.98

2.98

2.90

0.140

2.29downward arrow

2.54downward arrow

2.55

LMP

3.54

4.09

3.45

3.70

0.350

2.61downward arrow

4.25

3.34

9

CDR

2.45

2.16

2.42

2.34

0.159

2.72

2.53

2.40

CMP

2.59

3.86

2.16

2.87

0.884

3.40

2.83

2.71

LMP

2.90

-

3.50

3.20

0.424

2.31

2.59

2.55

15

CDR

4.16

3.93

4.28

4.12

0.178

3.55downward arrow

-

3.28downward arrow

CMP

2.71

2.85

3.03

2.86

0.160

3.27up arrow

3.50up arrow

2.91

LMP

3.98

3.86

4.28

4.04

0.216

-

3.90

3.94

16

CDR

4.02

4.02

3.90

3.98

0.069

3.37downward arrow

3.98

4.18up arrow

CMP

3.69

3.78

3.16

3.54

0.335

2.32downward arrow

3.11

4.03

LMP

3.89

3.94

3.68

3.83

0.135

2.99downward arrow

3.37downward arrow

3.71

17

CDR

2.47

2.81

3.08

2.79

0.306

2.71

2.85

2.84

CMP

1.97

1.84

2.13

1.98

0.145

2.37up arrow

2.44

1.58downward arrow

LMP

3.05

2.92

3.25

3.07

0.166

2.80

2.98

2.69

.

Group Mean

3.06

3.14

3.08

3.08

.

2.71

3.04

3.04

± SD

0.729

0.796

0.679

0.679

0.472

0.666

0.708

.

.

.

.

t-Test

n.s.

n.s.

n.s.

 


[248-249] Table 8

Individual Body Weights at Each Orthostatic Evaluation Date

(Arrows Indicate p < 0.05) (Values are in kg)

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Launch Day

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

Fourth

.

7

CDR

87.1

88.0

88.2

87.8

0.59

88.0

86.1 downward arrow

86.4

.

.

CMP

69.4

69.4

69.8

69.5

0.23

71.2up arrow

66.7 downward arrow

68.3

.

.

LMP

69.4

71.8

70.8

70.7

1.21

70.8

67.8

69.6

.

.

8

CDR

76.2

76.4

77.1

76.6

0.47

78.8

72.8downward arrow

74.0downward arrow

75.1downward arrow

.

CMP

76.4

77.6

76.4

76.8

0.69

78.0

74.4downward arrow

74.7downward arrow

75.2

.

LMP

66.0

67.1

66.0

66.4

0.64

64.4downward arrow

62.6downward arrow

62.8downward arrow

-

.

9

CDR

73.5

72.8

72.8

73.0

0.40

72.1

69.6downward arrow

70.9downward arrow

71.7downward arrow

.

CMP

82.8

82.5

80.7

82.0

1.14

80.7

78.2downward arrow

82.1

81.2

.

LMP

74.7

74.4

73.7

74.3

0.51

72.1downward arrow

69.4 downward arrow

71.3downward arrow

72.3downward arrow

.

10

CDR

80.1

79.4

78.9

79.5

0.60

77.6downward arrow

76.4downward arrow

77.4downward arrow

.

.

CMP

76.6

77.1

76.6

76.8

0.29

74.8downward arrow

72.3downward arrow

73.1downward arrow

.

.

LMP

79.4

79.5

79.4

79.4

0.06

78.5downward arrow

73.9downward arrow

74.6downward arrow

.

.

11

CDR

78.0

78.2

79.1

78.4

0.59

78.0

74.4downward arrow

77.1

.

.

CMP

74.4

75.3

77.1

75.6

1.37

75.3

72.1downward arrow

72.1downward arrow

.

.

LMP

77.6

78.9

77.9

78.1

0.68

75.7downward arrow

75.3downward arrow

77.1

.

.

12

CDR

66.2

-

66.9

66.6

0.49

67.7

65.8

66.7

66.7

.

CMP

71.0

70.3

-

70.7

0.49

70.4

67.1

68.9

68.9

.

LMP

69.4

-

70.3

69.9

0.64

69.1

63.5downward arrow

64.9

64.4

.

13

CDR

79.8

77.8

78.5

78.7

1.01

80.5

74.2downward arrow

.

.

.

CMP

89.1

-

89.7

89.4

0.42

89.3

84.4downward arrow

.

.

.

LMP

71.0

70.3

71.2

70.8

0.47

70.8

67.8downward arrow

.

.

.

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Launch Day

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

Fourth

.

14

CDR

78.0

78.5

78.7

78.4

0.36

76.2downward arrow

76.6downward arrow

77.1downward arrow

.

.

CMP

74.2

762.

75.5

75.3

1.01

74.8

96.4downward arrow

72.6downward arrow

.

.

LMP

83.5

83.1

83.2

83.2

0.26

79.8downward arrow

80.3downward arrow

80.7downward arrow

.

.

15

CDR

80.5

81.2

81.5

81.1

0.51

80.2

78.9downward arrow

-

81.0

80.7

CMP

73.7

73.2

74.0

73.6

0.40

73.5

72.1downward arrow

-

72.6

72.3downward arrow

LMP

74.3

73.9

74.8

74.3

0.45

73.2

70.8downward arrow

-

73.7

73.1downward arrow

16

CDR

80.8

80.5

78.9

80.1

1.02

78.9

75.5downward arrow

76.6downward arrow

-

76.4downward arrow

CMP

63.2

61.9

62.6

62.6

0.65

61.5

58.5downward arrow

59.9downward arrow

-

60.3downward arrow

LMP

73.1

73.8

72.6

73.2

0.60

73.

70.5downward arrow

71.7downward arrow

-

71.3downward arrow

17

CDR

81.0

80.3

80.7

80.7

0.35

80.3

76.1downward arrow

76.0downward arrow

78.0downward arrow

78.5downward arrow

CMP

78.2

76.6

77.0

77.3

0.83

75.7

74.6downward arrow

73.9downward arrow

73.9downward arrow

74.8downward arrow

LMP

76.0

76.6

75.3

76.0

0.65

74.8

72.9downward arrow

71.8downward arrow

73.4downward arrow

72.8downward arrow

.

Group Mean

75.90

75.09

76.12

75.96

.

75.26

72.45

73.05

73.44

73.36

± SD

5.849

5.213

5.786

5.792

5.727

5.866

5.763

4.781

5.787

.

.

.

.

t-Test

.

p< 0.02

n.s.

n.s.

n.s.


 

[250] ....contains values of the average of both calves for individual crewmembers at each test date. In the first postflight evaluation, 16 of 24 crewmembers (67 percent) showed significantly reduced calf circumference. Group mean values showed a statistically significant probability (p < 0.05) immediately postflight of a decrement of 1.1 cm (3 percent) that was not totally regained at approximately 120 hours after splashdown by two of the three crewmen tested at that time.

Total leg volume was calculated for the six crewmen of the last two Apollo missions (Apollo 16 and 17). The last section of table 9 contains data on total leg volume as the sum of both legs. Although not statistically significant, a one-liter (5.8 percent) group mean decrement was seen in the first two postflight evaluations. No clear trend toward restitution was seen as late as 90 to 160 hours after splashdown; subsequent measurements were not performed.

 

Cardiothoracic Ratios

To determine whether a change in heart size had occurred, cardiothoracic (C/T) ratios were calculated. Once before and once after flight, posterior-anterior chest X-rays were taken of each crewmember. The C/T ratios given in table 10 provided a measure of heart size to amplify the preceding weight and leg-size data. Accurate cardiothoracic ratios could not be obtained from three postflight films. Synchronization at peak systolic and peak diastolic cardiac phases for X-rays taken on the last six Apollo crewmembers (Apollo 16 and 17 missions) enabled achievement of greater accuracy by providing two films for each preflight and postflight comparison, and by eliminating random X-ray exposure in the cardiac cycle. Twenty-four of thirty crewmembers (80 percent) showed a decrease in postflight C/T ratios with a group mean cardiothoracic ratio decrement of 0.021 (5 percent), highly significant at p < 0.001. The Apollo 17 CMP, who showed a postflight increase in C/T ratio, wore a special antihypotensive pressure garment from splashdown until LBNP evaluation five hours later.

 

Special Measures for Apollo 15, 16, and 17

Vectorcardiographic data for Apollo 15, 16, and 17 crewmen showed no changes of clinical significance. An analysis of the phonocardiographic findings derived from the vibrocardiogram and of the systolic time intervals obtained with carotid pulse and VCG measurements was incomplete at the time of this writing.

 

Antihypotensive Garment Efficacy

Seven hours after splashdown, orthostatic evaluations were made of the Apollo 16 CMP wearing the antihypotensive garment. The garment was 0.5 cm smaller at the calf than the one worn during preflight testing to compensate for the expected loss of lower limb girth from disuse in zero g. The results are shown in table 11. Blood pressure and heart rate data are expressed as mean values with one standard deviation, for each five-minute period.

As noted earlier, ambient temperatures during postflight testing of Apollo 16 astronauts were high [305°K (32°C) to 306°K (33°C)]. During the same tests on two control subjects one day earlier, the temperature was somewhat lower: 301°K (28°C) for....

 


[251] Table 9

Individual Resting Supine Calf Circumference and Lower Limb Volume Data (Arrows Indicate p < O.O5)

 

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

Fourth

Resting Supine Mean Calf Circumference, cm

.

7

CDR

40.7

40.9

40.5

40.8

0.10

40.1 downward arrow

40.1downward arrow

-

-

CMP

35.9

35.9

35.9

35.9

0.00

34.7

35.5

-

-

LMP

36.6

36.9

36.1

36.5

0.40

35.1 downward arrow

36.0

-

-

8

CDR

35.2

35.3

35.4

35.3

0.10

34.9 downward arrow

35.2

34.4 downward arrow

-

CMP

39.7

39.4

39.4

39.5

0.17

39.1

39.1

39.1

-

LMP

37.3

36.8

37.2

37.1

0.26

36.8

36.7

37.2

-

9

CDR

37.0

37.0

36.8

36.9

0.12

35.2 downward arrow

35.9 downward arrow

36.4 downward arrow

-

CMP

40.5

40.2

40.1

40.3

0.21

38.9 downward arrow

40.2

40.4

-

LMP

36.4

-

36.2

36.3

0.14

34.7 downward arrow

38.1 upward arrow

36.1

-

10

CDR

36.3

35.1

35.9

35.8

0.61

34.6 downward arrow

35.6

-

-

CMP

37.8

37.1

37.0

37.3

0.44

36.2

37.1

-

-

LMP

38.1

37.5

37.0

37.5

0.55

35.6 downward arrow

36.5

-

-

11

CDR

36.6

36.0

36.2

36.3

0.31

35.6

-

-

-

CMP

37.2

36.8

38.1

37.4

0.67

37.0

-

-

-

LMP

37.9

38.3

37.6

37.9

0.35

37.6

-

-

-

15

CDR

40.3

40.5

40.5

40.4

0.12

39.3 downward arrow

39.4 downward arrow

40.1

40.8 upward arrow

CMP

36.5

36.3

36.5

36.4

0.12

35.6 downward arrow

35.1 downward arrow

35.9 downward arrow

35.9downward arrow

LMP

37.5

37.1

37.4

37.3

0.21

36.0 downward arrow

36.5 downward arrow

36.7 downward arrow

36.3 downward arrow

16

CDR

38.1

37.9

38.0

38.0

0.10

36.6 downward arrow

36.6 downward arrow

36.5 downward arrow

-

CMP

34.4

34.4

34.8

34.5

0.23

33.5 downward arrow

33.5 downward arrow

33.2 downward arrow

-

LMP

36.3

36.3

36.3

36.3

0.00

35.5

35.6

35.4

-


[252] Table 9 (Continued)

Individual Resting Supine Calf Circumference and Lower Limb Volume Data (Arrows Indicate p < O.O5)

 

Apollo Mission

Crewmember

Preflight Evaluations

Preflight Summary

Postflight Evaluations

F-30 Days

F-15 Days

F-5 Days

Mean

± SD

First

Second

Third

Fourth

Resting Supine Mean Calf Circumference, cm (continued)

.

17

CDR

38.0

38.2

38.5

38.2

0.25

37.3downward arrow

36.6downward arrow

38.1

37.3downward arrow

CMP

38.8

38.1

38.6

38.5

0.36

37.0downward arrow

37.0downward arrow

38.1

37.0downward arrow

LMP

38.6

39.1

38.9

38.9

0.25

37.4downward arrow

37.5downward arrow

38.1downward arrow

37.6downward arrow

.

Group Mean

37.57

37.44

37.45

37.47

.

36.43

36.85

37.05

37.48

± SD

1.621

1.724

1.625

1.634

1.688

1.719

1.995

1.743

.

.

.

.

t-Test

p < 0.05

n.s.

n.s.

n.s.

.

Lower Limb Volume, ml

.

16

CMP

15 929

15 485

15 669

15 694

223

14 108downward arrow

14 146downward arrow

13 770downward arrow

13 812downward arrow

LMP

12 577

12 492

12 798

12 622

158

12 150downward arrow

11 989downward arrow

12 005downward arrow

12 146downward arrow

CDR

14 556

14 794

14 741

14 697

125

14 482

14 033downward arrow

14 068downward arrow

13 806downward arrow

17

CMP

17 265

17 685

17 991

17 647

365

16 772

16 427downward arrow

17 238

16 706downward arrow

LMP

17 426

17 132

17 357

17 305

154

15 964downward arrow

16 366downward arrow

17 028

16 424downward arrow

CDR

17 944

18 452

18 030

18 172

323

17 084downward arrow

17 692

17 878

17 189downward arrow

.

Group Mean

15 950

16 022

16 098

16 023

.

15 093

15 094

15 331

15 014

± SD

2 059

2 218

2 089

2 113

1 873

2 116

2 371

2 035

.

.

.

.

t-Test

n.s.

n.s.

n.s.

n.s.


[253] Table 10

Apollo Crewmen Cardiothoracic Ratios During Orthostatic Evaluations (Ratios based on X-radiographs)

Apollo Mission

Crewmember

Preflight F-5 Days

First Postflight

Change in C/T

.

7

CDR

0.46

0.44

-0.02

CMP

0.45

0.41

-0.04

LMP

0.39

0.36

-0.03

8

CDR

0.44

0.40

-0.04

CMP

0.44

0.41

-0.03

LMP

0.38

0.32

-0.06

9

CDR

0.37

0.36

-0.01

CMP

0.43

0.39

-0.04

LMP

0.36

0.33

-0.03

10

CDR

0.43

0.39

-0.04

CMP

0.43

0.39

-0.04

LMP

0.50

0.40

-0.10

11

CDR

0.40

0.40

0.00

CMP

0.35

-

-

LMP

0.40

0.39

-0.01

12

CDR

0.37

0.39

+0.02

CMP

0.41

-

-

LMP

0.40

-

-

13

CDR

0.42

0.41

-0.01

CMP

0.43

0.42

-0.01

LMP

0.43

0.39

-0.04

14

CDR

0.39

0.42

+0.03

CMP

0.41

0.40

-0.01

LMP

0.46

0.44

-0.02

15

CDR

0.42

0.43

+0.01

CMP

0.40

0.37

-0.03

LMP

0.48

0.51

+0.03

16

CDR

0.41

0.40

-0.01

CMP

0.44

0.41

-0.03

LMP

0.36

0.34

-0.02

17

CDR

0.50

0.44

-0.06

CMP

0.43

0.45

+0.02

LMP

0.37

0.36

0.00

.

Group Mean

0.417

0.399

-0.021

± SD

0.0383

0.0384

0.0281

.

t-Test

n.s.

p < O.001


 

[254] ....control subject 3, and 303°K (30°C) for control subject 2. The results of their tests also appear in table 11.

 


Table 11

Preflight and Postflight Passive Stand Test Data With and Without Jobst Antihypotensive Garment

Subject Position

Measurement

Without Garment

With Garment

Preflight Mean ± SD

Postflight Mean ± SD

Preflight Mean ± SD

Postflight Mean ± SD

.

Apollo 16 Command Module Pilot

.

Supine

Heart rate, bpm

45.8 ± 0.96

57.8 ± 0.84

44.8 ± 0.84

54.6 ± 0.89

SBP, mm Hg*

113.5 ± 2.64

119.2 ± 4.80

117.9 ± 7.09

112.6 ± 6.17

DBP, mm Hg*

74.3 ± 2.00

80.8 ± 2.90

67.2 ± 4.21

67.5 ± 3.89

Erect

Heart rate, bpm

55.8 ± 1.79

87.6 ± 0.89

55.2 ± 3.56

78.4 ± 1.34

DBP, mm Hg*

121.6 ± 5.62

112.8 ± 6.17

117.8 ± 4.02

110.2 ± 5.24

DBP, mm Hg*

77.2 ± 4.37

67.5 ± 3.89

77.8 ± 5.27

75.2 ± 6.02

.

Control Subject 1

.

Supine

Heart rate, bpm

77.6 ± 0.89

60.2 ± 1.30

81.4 ± 1.52

63.4 ± 2.70

SBP, mm Hg*

118.0 ± 2.71

102.8 ± 4.77

118.4 ± 2.50

111.3 ± 4.47

DBP, mm Hg*

57.4 ± 2.95

62.1 ± 2.81

58.0 ± 4.45

58.4 ± 4:12

Erect

Heart rate, bpm

85.8 ± 0.84

78.8 ± 1.48

78.4 ± 2.70

70.4 ± 1.34

SBP, mm Hg*

119.1 ± 0.72

104.4 ± 8.38

122.7 ± 4.79

109.6 ± 3.95

DBP, mm Hg*

74.9 ± 2.66

75.8 ± 4.02

75.1 ± 3.60

76.5 ± 3.24

.

Control Subject 2

.

Supine

Heart rate, bpm

67.2 ± 0.84

72.4 ± 0.89

64.0 ± 1.87

71.2 ± 1.30

SBP, mm Hg*

134.3 ± 3.11

127.7 ± 5.58

137.1 ± 2.85

124.2 ± 5.55

DBP, mm Hg*

71.8 ± 5.03

74.9 ± 5.21

81.3 ± 5.01

75.0 ± 1.63

Erect

Heart rate, bpm

76.8 ± 2.05

92.2 ± 2.17

70.6 ± 1.95

85.0 ± 1.22

SBP, mm Hg*

145.0 ± 7.44

132.7 ± 8.74

149.7 ± 5.25

136.0 ± 8.01

DBP, mm Hg*

82.8 ± 2.57

81.4 ± 5.52

90.4 ± 3.47

84.4 ± 7.95

*1 mm Hg = 1.33 x 402 N/m2


 

The Apollo 17 CMP, as noted previously, inflated his antihypotensive garment one-half hour before deorbit and kept it inflated [which provided a pressure of 65 mm Hg (87 x 102 N/m2) over the ankle area] until a standard orthostatic evaluation could be made. Under the conditions of testing, his heart rate increased slightly and tended to climb after the garment was deflated. Heart rate declined slightly upon reinflation (figure 4). Heart rate and blood pressure data are shown in table 12 as mean values for the three five-minute periods and for the single four-minute period.

 


[
255]

Figure 4. Passive Stand test with antihypotenrive garnent-Apollo 17 CMP.

Figure 4. Passive Stand test with antihypotenrive garment-Apollo 17 CMP.


Table 12

Heart Rate and Blood Pressure Data for Apollo 17 Command Module Pilot During Passive Stand Test utilizing Antihypotensive Garment

Measurement

Supine

Erect

Garment Inflated

Garment Inflated

Garment Deflated

Garment Reinflated

Mean ± SD

Mean ± SD

Mean ± SD

Mean ± SD

.

Heart rate, bpm

70.1 ± 3.50

98.3 ± 3.43

105.2 ± 3.82

103.5 ± 3.72

SBP, mm Hg*

115.5 ± 8.28

128.8 ± 3.27

131.0 ± 3.89

129.1 ± 5.92

DBP, mm Hg*

64.6 ± 3.92

82.7 ± 4.22

54.4 ± 4.93

85.4 ± 2.88

Pulse pressure, mm Hg*

49.4 ± 6.90

48.9 ± 7.25

46.6 ± 5.46

43.3 ± 7.16

*1 mm Hg = 1.33 x 102 N/m2.


 

[256] Discussion

 

The objective of Apollo preflight and postflight cardiovascular evaluations was to determine the effects of space flight on human physiological functions. These studies were performed within the context of transporting man safely to the moon and returning him to Earth while ensuring his well-being and functional capability in an unnatural environment. It would be naive, however, to ascribe the cardiovascular findings reported here to the effects of weightlessness alone. The observed postflight cardiovascular changes reflect the total effect of the environmental conditions encountered by each crewman within a given space flight mission. In addition to stresses of the weightless state, these conditions included stresses of launch, inflight deviations from normal work and rest cycles, variations in duration and magnitude of lunar activity, changes in diet, and stresses of entry, splashdown, and recovery. Unfortunately, the relative contribution of each of these environmental conditions cannot be established.

Significant postflight changes in cardiovascular measurements have included elevated resting and orthostatically stressed heart rate, similar but reciprocal decreases in stroke volume, and decreases in pulse pressure during orthostatic stress caused almost exclusively by decreases in systolic blood pressure. These changes are characteristic of decreased orthostatic tolerance. In addition, several presyncopal episodes occurred postflight during orthostatic stress. To properly assess the postflight decrease in crew orthostatic tolerance, however, one must consider the set of variables that existed during the recovery period.

 

1. Crewmen were launched and maintained in a temperate environment but were recovered and evaluated immediately after flight at significantly elevated ambient temperatures (Apollo 10, 11, and 17 missions excepted).
 
2. Crewmen were physically more active in the time periods immediately preceding and following splashdown. This activity tended to augment any postflight thermal stress.
 
3. Preflight evaluations were always performed in the morning hours, whereas postflight evaluations were usually performed in the afternoon or evening hours with respect to the preflight work and rest cycles established at the Kennedy Space Center and normally maintained in flight. This change in the time of day postflight evaluations were performed could have produced diurnal variations in body temperature, heart rate, and orthostatic tolerance.
 
4. Returned crewmen were exposed for varying time periods to orthostatic stress in one-g prior to orthostatic testing.
 
5. Vestibular effects associated with readaptation to the one-g environment were compounded by sea motion (not expressly evaluated).
 
6. Neurohumoral forces were altered by the excitement and the emotion of return to Earth.

 

These stresses and uncontrolled variables undoubtedly affected the postflight cardiovascular changes reported here.

[257] Certain relationships suggest that all the. factors listed contributed significantly. A positive, though statistically insignificant, correlation (r = 0.27) exists between change (preflight to postflight) in resting heart rate and change in oral temperature (figure 5). Also, there is a significant positive correlation (r= 0.52) between postflight change in orthostatically stressed heart rate and postflight change in resting heart rate (figure 6). In concert with similar data from Gemini crew evaluations, these Apollo findings suggest that, for flights of eight to fourteen days, postflight resting or orthostatically stressed heart rates do not increase in conjunction with increasing mission duration.

 


Figure 5. Positive correlation between preflight to postflight change in oral temperature and change in resting heart rate.

Figure 5. Positive correlation between preflight to postflight change in oral temperature and change in resting heart rate.

 

Weight loss was a universal finding among Apollo flight crews, but the cause and the specific body tissues involved are not readily apparent. A positive correlation between weight loss and change in total blood volume (r = 0.77) was obtained from Apollo data. Fluid losses or changes, however, did not fully explain the weight loss. The relatively inactive role of the lower extremities during space flight predisposes them to significant loss of tissue substance, especially in muscle; consistent postflight reductions in maximal calf girth on 24 Apollo crewmen and in total leg volume on the last six Apollo crewmen showed significant soft-tissue decrements (table 9). The magnitude of these decrements in the maximal calf circumference measurement taken immediately after recovery showed a positive correlation (r= 0.42) with the time of the measurement following splashdown

[258] (figure 7). Assuming rapid changes to be due to fluid shifts to the lower extremities postflight, a better correlation would be expected had the physical activities of the crewmen between splashdown and time of calf measurement been controlled. Continued decrements in leg size for several days after splashdown indicate that they were not exclusively caused by fluid changes. On the other hand, a true flight-related issue deterioration was suggested by a negative and significant correlation (r = -0.47) between the decrement in calf size and the length of exposure to weightlessness (figure 8). When both Apollo data and Gemini data (from missions shorter and longer than Apollo missions) are used, weight loss reveals a leveling off with flight duration, if not a reversed trend, after a peak at approximately 200 hours of flight time (figure 9). The relative contributions of muscle, fatty, and interstitial tissues to weight loss have not yet been determined.

 


Figure 6. Positive correlation between postflight change in orthostatically stressed heart rate and postflight change in resting heart rate.

Figure 6. Positive correlation between postflight change in orthostatically stressed heart rate and postflight change in resting heart rate.

 

Perhaps more specific are data obtained from preflight and postflight chest roentgenograms. Although a decrease in the frontal plane cardiac silhouette size may...

 


[
259]

Figure 7. Positive correlation between maximal calf circumference taken immediately after recovery and time of measurement following splashdown.

Figure 7. Positive correlation between maximal calf circumference taken immediately after recovery and time of measurement following splashdown.

 


Figure 8. Negative correlation between decrement in calf size and length of exposure to weightlessness.

Figure 8. Negative correlation between decrement in calf size and length of exposure to weightlessness.

 

[260] ...represent either a decrement of myocardial tissue, a decrement of intrachamber blood content, or positional change such as rotation of the heart with reference to the chest wall, changes in the cardiothoracic ratio show a very definite rise and subsequent reversal with the duration of zero g exposure; the peak decrement occurs between 100 and 200 hours (figure 10). The relationship between the cardiothoracic ratio and the duration of zero-g exposure is definite, whereas correlations of the C/T ratio with weight loss or change in blood volume are only vaguely suggested. A most unexpected finding, however, is the significant difference (p<0.01) between the mean C/T ratio of the 12 lunar explorers and the mean of those Apollo crewmen who were continuously exposed to weightlessness. With 11 useful postflight data points, the lunar-walking group mean postflight cardiothoracic ratio was essentially unchanged from the preflight ratio, whereas the other 19 Apollo crewmen incurred a decrease in the group mean C/T ratio of -0.03. Because changes explicitly caused by exposure to the space environment are of great importance and concern, any opportunity to detect them is eagerly explored. Other similar comparisons between these same groups have revealed no difference in postflight weight loss or changes in resting and stressed postflight heart rate. Despite some use of the lower extremities on the lunar surface, no difference in resting-calf circumference changes was detected between the groups. These findings imply that exposure to the lunar environment somehow maintains the preflight cardiothoracic ratio.

 


Figure 9. Apollo and Gemini data indicating a leveling off of weight loss after 200 hours of flight.

Figure 9. Apollo and Gemini data indicating a leveling off of weight loss after 200 hours of flight.

 


[
261]

Figure 10. Roentgenogram showing peak decrement in cardiothoracic ratio.

Figure 10. Roentgenogram showing peak decrement in cardiothoracic ratio.

 

These Apollo data have also provided a comparison of cardiovascular responses to LBNP and to vertical passive standing (the true orthostatic stress reference). For 18 crewmen evaluated with -50 mm Hg (-67 x 102N/m2) LBNP and for nine tested with the passive stand (both procedures for three of each group), heart rates were almost identical before flight, and postflight values for LBNP stress were slightly greater. In contrast, and as noted in prior studies comparing orthostatic techniques, preflight and postflight systolic and diastolic. blood pressure values were higher during stand stress than during LBNP. Thoracic and carotid pressure sensors differentially responding to the two stressors may partly account for the difference. Pulse pressure during LBNP, however, differed very little from pulse pressure during passive stand. These findings supported the use of LBNP as an orthostatic stress procedure and provided a reference for the integration of data from the Skylab inflight LBNP evaluations.

Of the two garments designed to offer protection against orthostatic hypotension, the garment employing the capstan principle proved to be the more suitable for use in the space flight environment. Although the elastic garment worn by the Apollo 16 CMP appeared to furnish moderate protection against orthostatic hypotension following weightless flight and heat stress, this type of garment seemed to be unsuitable for use in the operational setting. The crewman was unable to don the leotards in zero g before reentry or following splashdown in the confined volume of the spacecraft. Consequently, any protection the garment afforded could not be made available until the posflight testing phase. It was also impossible to ensure a garment of proper fit for postflight use [262] because the decline in limb girth was neither uniformly distributed nor predictable in magnitude.

The design of the pressurized garment used by the Apollo 17 CMP included features intended to overcome the difficulty of predicting change in limb girth during flight. The CMP reported that the garment was easier to don in flight than he had anticipated, due in part perhaps to a relatively large reduction in limb girth. He wore the garment for more than four hours and reported it relatively comfortable.

The heart rate while reclining with the suit inflated was ten beats per minute slower than during the preflight test 15 days before launch (70.1 ±3.5 compared to 81 ± 2.12 beats per minute). Although uncommon, a reduction of the supine resting heart rate from preflight values had been seen previously in Apollo crewmen. Mean heart rate during the first five minutes of standing with the garment inflated after flight was 98.3 ± 3.43 beats per minute compared to 91 ± 2.35 beats per minute in the preflight test.

When the garment was deflated, heart rate increased and was still increasing after five minutes. Garment reinflation, which required approximately 40 seconds, was associated with an interruption of the rising slope of heart rate and a modest reduction of mean heart rate, suggesting a protective effect from the garment.

Aside from the antihypotensive effect of using the garment, other physiological processes that occurred during readaptation to one g may have been modified. The Apollo 17 CMP was the only crewman of the 18 tested whose mean heart rate at R+0 during exposure to a pressure of -50 mm Hg (-67 x 102N/m2) was within the preflight envelope. In the other stress procedure, bicycle ergometry, he again showed no decrement of performance from preflight levels. His pattern of postflight limb volume changes, estimated from multiple circumferential measurements, was somewhat different from that shown by the other five crewmen who received such measurements. Postflight X-rays, taken before deflation of the garment, showed an increased cardiothoracic ratio in contrast to the other 20 Apollo crewmen exposed to continuous weightlessness, for whom data exist demonstrating postflight decreases in C/T ratios.

 

Summary and Conclusions

 

In summary, postflight orthostatic evaluations during the Apollo Program appear to indicate that reduction in orthostatic tolerance is a consequence of space flight exposure. Heart rate, the most reliable index, was increased, while systolic and pulse pressures were decreased during immediate postflight evaluations using lower body negative pressure and passive standing as the orthostatic stress. Elevation in resting heart rate was a less frequent finding. There was considerable variability in the magnitude of these changes between individual crewmembers and in the persistence of the changes over subsequent postflight evaluations. Postflight changes in leg volume during LBNP were equal to or less than those seen during preflight baseline evaluations. Body weight, resting calf girth, supine leg volume, and cardiothoracic ratios were all diminished immediately postflight, and return to preflight values was not complete within the postflight testing time frame.

The reported changes in orthostatic tolerance and other related measurements must be interpreted with care in view of the conditions under which the data were obtained.

[263] The priority of operations during Apollo missions did not allow optimal control over a number of important variables during preflight and postflight evaluations. Preflight evaluations had to be scheduled and completed within narrow time limits and in competition with the training and launch preparation of crewmembers. Postflight evaluations were performed among intensive debriefing sessions, public appearances, and other ceremonies. Relative degrees of sleep loss and high ambient temperatures also undoubtedly influenced the findings.

Wearing of a lower body positive pressure garment during the reentry and immediate postflight period appeared to offer some protective benefit by way of reducing extravascular lower body pooling of fluid. It would, however, be premature to conclude that the garment was the primary factor responsible for improved orthostatic tests for the Apollo 17 Command Module Pilot. As was the case in all missions and for all crewmen, individual variables cloud interpretation of the data. Other studies will be necessary to determine the effects of such protective garments under space flight type readaptive conditions.

Man's physiological adaptation to the space environment and his readaptive alterations upon return to Earth are complex. The orthostatic evaluations performed in conjunction with the Apollo missions provide some insight into these changes. But a more complete understanding of the physiological role, especially for missions of longer duration, requires a thorough analysis of the effects of the space environment with special emphasis upon inflight evaluations, control of environmental conditions, and interrelating findings from many study disciplines.

 

References

 


The authors are grateful for the technical assistance of R. A. Wolthuis, J. T. Baker, M. E. Taylor, D. P. Golden, and M. M. Ward. The authors also thank T. A. Beale, S. A. Bergman, J. Day, J. A. Donaldson, J. G. Groves, M. M. Jackson, N. A. Lee, S. McKamie, A. E. Nicogossian, R. A. Schiffmam, and E. Sloan. All associates of various tenure were affiliated with the NASA Lyndon B. Johnson Space Center Cardiovascular Laboratory during the Apollo Program.


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