When the Mercury program began, continuous monitoring of physiological data while a pilot performed his flight mission was a new concept. Consequently, there were no off-the-shelf items for continuous and reliable monitoring. When it was decided to attempt to monitor body temperature, chest movement, and heart action (ECG), equipment standards were established: The sensors and equipment must be comfortable, reliable, and compatible with other spacecraft s stems, and must. not interfere with the pilot's primary mission. Biomedical sensors were used primarily to assist the flight surgeon in determining whether the astronaut was physiologically capable of continuing the mission.
Considerable experience was gained through the use of range simulations
as well as actual flight. It was soon apparent that the medical flight
controller was an extremely important member of the flight control team.
The development of mission rules to aid in flight control was necessary
in the medical area as well in the many engineering areas. As experience
was gained, the evaluation and judgment of the medical flight controller
prime determinants in making a decision. According to Dr. Berry, the "condition of the astronaut as determined by voice and interrogation rather than physical parameters alone became a key factor in the aeromedical advice. to continue or terminate. The mission."9
The physiological parameters monitored were modified as experience was gained. Body temperature was monitored with a rectal thermistor in all missions. The thermistor would be modified for oral use in future missions of longer duration. Respiration was measured initially by an indirect method through the use of a linear potentiometer and carbon-impregnated rubber. Soon this method was replaced by a thermistor kept at 200° F and placed on the microphone pedestal of the helmet. Since neither gave reliable respiration traces, a change was made to the impedance pneumograph for pneumograph for the MA-8 and MA-9 flights. This device provided accurate respiration information during most of the flight.
Electrocardiographic electrodes of a low impedance to match the spacecraft amplifier were required to record during body movements and to stay effective during flight durations of over 30 hours. These electrodes, Dr. Berry notes, functioned well and provided excellent information on cardiac rate and rhythm.
Not until the MA-6 mission of Astronaut Glenn had blood pressure readings been taken, because until that time no satisfactory system had been developed. As early as the MR-3 flight, however, definitive work had begun with an automatic system using a uni-directional microphone and cuff. The system without the automatic feature was used on the MA-6 mission. During MA-7, all the inflight blood pressure readings obtained were elevated. An extensive postflight evaluation determined that instrument error had probably caused this result. Suggested remedies included considerable preflight calibration and matching of the settings to the individual astronaut along with the cuff and microphone. Excellent blood pressure tracings were obtained in both the MA-8 and MA-9 flights.
Voice transmissions were a valuable source, and the normal flight reports -and answers to queries were used for evaluation of the pilot. (To insure that the medical monitors were familiar tasks with the astronautís voice, tapes of mission simulations were dispatched to all range stations.)
Inflight photography and television proved of little value in medical monitoring because of the poor positioning of the cameras and the varying lighting conditions that resulted from the operational situation.
9. Ibid., p. 204