The primary objective of the Apollo Flight Crew Cardiovascular Evaluations was to determine the response of the cardiovascular system to weightlessness. The results of postflight tests were expected to show differences in cardiovascular responsiveness between crewmen who walked on the moon and those who remained in weightlessness. These speculations and 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 1-G. Then, as a countermeasure to orthostatic intolerance, a supplemental objective was addressed on the last two Apollo missions This objective was to evaluate the efficacy of an experimental antihypotensive garment. Though the Gemini and early Apollo missions revealed no need for such postflight support, planners of the 28- and 56-day Skylab missions envisioned the possible need for such postflight protection.
Lower Body Negative Pressure (LBNP) Protocol:
The LBNP consisted of a chamber of sufficient size to accommodate the lower body, an airtight waist seal and a regulated vacuum source. The types of physiological measurements taken during the LBNP protocol differed slightly from mission to mission. Measurements made in conjunction with the Apollo 7 through 9 missions included continuous axillary and sternal lead electrocardiograms (ECG) and indirect blood pressure taken every 30 seconds by the Korotkoff Sound techniques. Changes in calf circumference were measured by double-strand, mercury-in-Silastic strain gauges. The calf measurements were taken at the maximum girth during supine rest for the Apollo 7-11 and 15-17 missions. 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 ankle to the groin with the crew man in the supine position and the leg extended and slightly elevated.
For the Apollo 15 to 17 evaluations, the limited two-lead electrocardiogram 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, Ca.). The respiration rates of the Apollo 16 and 17 crewmen were measured with a mercury strain gauge attached to the lower thorax. The carotid pulse trace was recorded for Apollo 17 crewmen. Other data considered in evaluating the test results included blood volume, exercise response, and vasoactive hormones.
Orthostatic intolerance evaluations were performed as part of major medical examinations conducted approximately 30,15, and 5 days before flight. The preflight (baseline) evaluations were compared to postflight evaluation results which were performed shortly after splashdown and at intervals of 24 hours thereafter. The number of postflight evaluations and the time at which they were performed were dictated by operational constraints and partly by the length of time required for individual crewmembers to regain their preflight status.
The supine LBNP was used with a five-minute rest control period, followed by 15-minute reduced pressure period, followed by a five-minute recovery period. The 15 minutes under reduced pressure utilized five different pressure levels:
1 minute at -8 mm Hg
1 minute at -16 mm Hg
3 minutes at -30 mm Hg
5 minutes at -40 mm Hg
5 minutes at -50 mm Hg
Passive Stand Test Protocol:
The Passive Stand protocol consisted of a five-minute supine resting period followed by a five-minute passive stand. The subject would lean against a wall in a relaxed manner with heels spaced 15 cm (6 inches) away from the wall. The physiological measurements made during this protocol included continuous sternal and axillary lead ECGs and indirect blood pressure taken by the Korotkoff sound technique at 30-second intervals.
Antihypotensive Garment Test:
On the Apollo 16 and 17 missions, the experimental antihypotensive garments were tested. These garments were to be worn during postflight orthostatic evaluations to assess their antihypotensive effect. A Jobst waist-length elastic leotard was used in conjunction with the Apollo 16 mission. A garment employing the capstan principle for the application of pressure to the lower limbs was designed to be worn by the Apollo 17 subject during postflight tests.
The Apollo 16 tests, utilizing the Jobst leotard, were performed pre- and postflight. Passive stand tests were performed 15 days before flight on the Apollo 16 subject and his backup, then repeated on the Apollo 16 subject and the ground control subjects during their respective recovery day examinations. This test 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 leotard was then put on and, after a ten-minute period of supine rest, the stand test was repeated. Blood pressure and heart-rate data were obtained using the instrumentation of the LBNP test.
For the Apollo 17 test, the subject wore the antihypotensive garment approximately one-half hour prior to deorbit. After splashdown, while still reclining in the couch, he inflated the capstan to a pressure of 130 mm Hg and thus furnished 65 mm Hg pressure over the ankle region. This pressure was maintained until the stand test could be performed. The suit was tested by performing a stand test four hours after splashdown and before LBNP testing. Crew time constraints prevented repetition of the preflight protocol, which included 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 garment inflated, five minutes passive standing with the capstan garment inflated, five minutes standing with the garment depressurized and four minutes standing with the garment reinflated to the original pressure of 130 mm Hg. The total duration of the continuous stand test was 15 minutes, including approximately 45 seconds for reinflation of the capstan garment. Heart rate was obtained continuously from the VCG; blood pressure was measured every 30 seconds by a Skylab automatic blood pressure measuring system.
Physiological measurements were recorded real-time on a strip chart recorder and on frequency modulated (FM) magnetic tape. The strip chart data was used real-time for assessment of crewmember well-being and safety. In the event of manifestation of presyncopal symptoms during orthostatic stress, the protocol was terminated. Minute heart rates were derived from an analysis of ECG or VCG R-R intervals. 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 each crewmember at his last major preflight medical examination and first postflight evaluation.
Data Collection and Reduction:
For each crewman evaluation, heart rate, blood pressure (systolic and diastolic), pulse pressure, and stroke volume values were averaged within each of the five minute LBNP periods and within the two five-minute passive stand periods to produce the respective mean values for each of these periods. These mean values for each crew member, 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 LBNP was used.
Individual and group mean data was determined. For individual crewmembers, the mean and standard deviation of the preflight values of each measurement in each distinct protocol condition were calculated. From these values, fiducial limits of the normal range at the 95-percent confidence level were determined. Individual postflight values lying outside these limits were defined as statistically significant. It should be noted that 4 of the crewmen flew two Apollo missions each.
Heart rate statistics can be divided into three stressor categories: 1) during resting supine control, 2) during the highest pressure level (-50 mm Hg) of LBNP, and 3) during passive standing. Of the 24 crewmen tested, 13 (or 54%) experienced elevated resting supine heart rates on the first postflight day. By the third postflight evaluation, only 3 of 15 crewmen (20%) showed significant elevations in supine resting heart rate. With the application of -50 mm Hg pressure during LBNP, 82% (14 of 17) experienced elevated heart rates at the first postflight evaluation. One crewman experienced presyncopal symptoms during the last seconds of the -40 mm Hg pressure level and therefore was not tested at the -50 mm Hg level during the first evaluation period. Five other crewmen experienced presyncopal symptoms at the -50 mm Hg level prior to completion of the protocol.
Immediately postflight, more crewmembers experienced a larger heart rate increase over preflight values during LBNP stress than during the rest control period, however statistically significant group differences disappeared by the third postflight evaluation. Results of the passive stand test yielded similar results with the increased heart rate immediately postflight. Eight of 9 (89%) crewmen experienced heart rates above their 95-percent preflight envelope.
Accompanying each postflight evaluation group mean is the t-test probability that it differs for the preflight summary group mean. During the first and second evaluations, resting supine control showed significantly elevated heart rates, the reciprocal response for stroke volume and no significant change in systolic, diastolic, and pulse pressures. LBNP results at -30, -40 and -50 mm Hg levels showed elevated heart rates during the first postflight evaluation period, with a trend toward preflight values at subsequent evaluations. Reciprocal stroke volume data was again noted. Significant decreases in systolic and pulse pressures were noted during the first evaluation period of LBNP. The passive stand test results paralleled the LBNP results.
No significant postflight calf volume changes were observed during the three conditions of reduced-pressure stress at any of the postflight evaluations. Seven of the 17 crewmen (41%) tested showed calf volume changes were significantly decreased postflight under the LBNP stress at -50 mm Hg as compared to the preflight results. The first postflight group mean weight showed a 3.4 kg (4.4%) decrease that was not regained at 90 to 160 hours after splashdown by the Apollo 15 to 17 crewmen. Also, at the first postflight evaluation, results during the resting supine control condition showed that 16 of 24 crewmen (67 %) had significantly reduced calf circumferences. Total leg volume, calculated for the Apollo 16 and 17 crewmen, showed a 1-liter decrement, though this result is not considered statistically significant.
To determine whether heart size changes had occurred, cardiothoracic (C/T) ratios were calculated. Posterior-anterior chest X-rays were taken once before and once after flight. Twenty-four of 30 crewmen (80%) showed a highly significant decreased group mean in C/T ratios of .021 (5%). Vectorcardiographic data showed no significant clinical changes.
Efficacy of Antihypotensive Garment:
The Apollo 16 subject underwent orthostatic evaluations 7 hours after splashdown wearing the Jobst waist-length elastic leotard. The garment was .5 cm smaller than the one used during preflight evaluations in anticipation of decreased limb girth after flight. The leotard, although it appeared to furnish moderate protection against orthostatic hypotension, was unsuitable for the operational setting because the Apollo 16 subject was unable to put on the suit in the confined volume of the spacecraft. Consequently, any benefits the suit provided were not available until the postflight testing phase. This option proved untenable because of the problems associated with obtaining a proper fit. The decline of limb girth postflight was neither uniformly distributed nor predictable in magnitude.
The design of the pressurized garment included features intended to overcome the difficulty of predicting change in limb girth during flight. The Apollo 17 subject was able to put on the pressurized suit while still in the spacecraft. Results showed that heart rate, while reclining with the suit inflated, was 10 beats per minute slower than during preflight testing 15 days before flight. With the garment deflated, heart rate increased and was still increasing after five minutes. Reinflating the garment, which lasted about 40 seconds, was associated with a modest reduction in heart rate and thus suggested a protective effect from the garment. Worth noting is that the Apollo 17 subject was the only one of 18 crewmen tested whose mean heart rate at the first evaluation was within the preflight envelope and who showed no decrement of performance during bicycle ergometry as compared to preflight values. Prior to deflation of the garment, the Apollo 17 subject showed an increased C/T ratio postflight as compared to the 20 Apollo crewmen who experienced continuous weightlessness.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Apollo 10||05/18/1969||05/26/1969||8 days|
|Apollo 11||07/16/1969||07/24/1969||8 days|
|Apollo 12||11/14/1969||11/24/1969||10 days|
|Apollo 13||04/11/1970||04/17/1970||6 days|
|Apollo 14||01/31/1971||02/09/1971||9 days|
|Apollo 15||07/26/1971||08/07/1971||12 days|
|Apollo 16||04/16/1972||04/27/1972||11 days|
|Apollo 17||12/07/1972||12/19/1972||12 days|
|Apollo 7||10/11/1968||10/22/1968||11 days|
|Apollo 8||12/21/1968||12/27/1968||6 days|
|Apollo 9||03/03/1969||03/13/1969||10 days|