Following space flight, the ability to remain upright (standing) or egress from the space vehicle after landing may be compromised by an inability to maintain adequate arterial pressure and cerebral perfusion. Many astronauts experience postflight orthostatic intolerance, and its severity and incidence appear to increase as the length of microgravity exposure is extended. Approximately 20 – 60 percent of astronauts returning from short-duration space flights (4-18 days) and up to 83% of astronauts returning from long-duration space flights (greater than one month) become presyncopal during post-flight orthostatic challenges. Reduced postflight plasma volume and altered distribution of blood, particularly to the abdomen and lower body, while upright is thought to contribute to postflight orthostatic intolerance.
To provide protection against space flight-induced orthostatic intolerance during re-entry and landing, both NASA and the Russian Federal Space Agency require that astronauts and cosmonauts wear compression garments. During Space Shuttle landings, NASA astronauts used an inflatable anti-gravity suit (AGS) that consisted of five interconnected bladders that cover the abdomen, thigh, and calf. The Russian Kentavr is a non-inflatable compression garment made of a resilient elastic fabric. It consists of bicycle-type shorts that extend to the knee and a pair of gaiters that cover the calves. Each component of the Kentavr has lacing to allow adjustments, and the optimal pressure produced by the Kentavr is 30 ± 5 mmHg. One disadvantage of the Kentavr is that uncovered areas of the body (e.g. knees, ankle, and feet) tend to swell if the garment is worn for an extended period of time, such as when cosmonauts continue to wear the Kentavr as they re-adapt to Earth gravity in the first few days following flight.
Due to the limitations of the AGS and Kenavr, the investigators initiated a series of studies to evaluate the efficacy of various configurations of compression garments with the intent of identifying a new garment which could be integrated into advanced exploration suits with little to no complication. BSN-Medical, Inc. manufactures commercial-off-the-shelf and custom-fit compression garments that are available in a variety of styles and pressures. The garments are made from a blend of nylon and spandex to provide mechanical compression and are used clinically to treat vascular disorders and orthostatic hypotension. Working with materials experts at BSN-Medical, Inc. the investigators developed individually-fitted, abdomen-high compression garments which were custom-designed to combine the positive features of the AGS and Kentavr, while eliminating most of the negative features. These garments provide a gradient compression along the length of the leg rather than static pressures; do not require a pressurized air source from the vehicle or other external source; provide complete coverage from the toes to the abdomen so as to prevent uncomfortable swelling in tissue in the uncompressed areas as in other garments; and do not increase the physical effort associated with ambulation experienced while wearing the AGS. Furthermore, these lightweight piece garments are easy to don, relatively inexpensive to produce, and require minimal stowage and maintenance in flight.
The investigators previously showed that thigh-high garments were effective in preventing post-space flight symptoms of orthostatic intolerance but evidence from other studies suggests that abdominal compression improves efficacy of the garments. The purpose of this study was to evaluate a more advanced compression garment, a three-piece abdomen-high garment, as a countermeasure to post-space flight orthostatic intolerance. We hypothesized that these garments would prevent the tachycardia and the reduction in stroke volume and cardiac output normally seen during orthostatic stress after space flight. Furthermore, they hypothesized that this novel design would be easy to don and comfortable to wear.
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Fifteen Space Shuttle astronauts (8 treatment, 7 controls) volunteered to participate in this study. Astronauts in both groups participated in a short 3.5-minute stand test before flight without compression garments as a measure of the preflight baseline condition. Seven of the eight treatment astronauts completed the same stand test on landing day (R+0), but one astronaut in the treatment group withdrew from the study on R+0. Five of these astronauts participated in testing on the day after landing (R+1). Seven astronauts served as control subjects by not wearing the compression garments during an identical stand test protocol on R+0 and R+1. Control astronauts completed the stand test as participants in a separate study, the Functional Task Test (FTT), who consented to share those test results. Testing protocol and procedures, as well as requests for data sharing, were reviewed and approved by NASA’s Johnson Space Center’s Committee for the Protection of Human Subjects (CPHS). Subjects received written and oral explanations of the test protocols before providing signed informed consent.
Approximately 30 days before launch (L-30), on R+0, and R+1, astronauts participated in a short 3-minute stand test. Preflight and postflight testing was conducted in the Cardiovascular Laboratory at Johnson Space Center, TX. Stand tests were conducted under standard laboratory conditions. Testing on R+0 was conducted approximately 2 hours after landing.
On the last day of the Shuttle flight, astronauts donned the Advanced Crew Escape Suit (ACES) with the standard NASA AGS, were prescribed to participate in the standard fluid-loading protocol, and inflated their AGS according to NASA Flight Rules. Following re-entry, landing, and wheelstop, the astronauts egressed the Shuttle and boarded NASA’s Crew Transport Vehicle (CTV). Astronauts removed the ACES and AGS in the CTV. Some of the treatment subjects donned the compression garments at this time, wearing the garment under their flight suits during the Shuttle “walk around” and media events before transport to the BDCF. Other treatment subjects chose to don the garments after arriving at the data collection facility.
Approximately 60 days before the scheduled launch, each astronaut was measured for the individualized construction of the garment. A trained fitter measured the circumference of each crewmember’s legs every 1.5 inches from the feet to the top of the thigh. Additional measurements were taken along the torso ending just below the breast-line. The manufacturer used these measurements to design and construct customized graded compression garments which produced a pressure of 55 mmHg at the ankle, decreasing to approximately 35 mmHg at the knee and 18 mmHg at the thigh. The pressure in the abdominal region was a consistent 16 mmHg. This garment was designed after consultation with the manufacturer and based upon several ground-based pilot studies conducted in our laboratory and other published reports that suggested that both leg and abdominal compression were required for the best outcome.
During the measurement session, two-dimensional echocardiography was used to obtain the aortic annulus diameter from the parasternal long axis for use during calculation of cardiac output based upon the stroke velocity integral measured during the subsequent stand test sessions. This was done to minimize the time requirement for each testing session. Abdomen, thigh, calf, and ankle measurements were also measured during each testing session to track changes in body segments which might influence fit of the garments. During the pre-flight stand test data collection session at L-30, a fit check of the customized garment was performed. Test operators queried the astronauts regarding garment comfort and fit while the astronauts were wearing the garments on R+0 and R+1.
No subjects in either the ACG or control group became presyncopal during the stand test preflight or on R+0. The change in heart rate from prone to standing was lower in the ACG subjects on R+0 than in the control subjects. Postflight stroke volume and cardiac output were not different than preflight in the ACG subjects, but total peripheral resistance was higher on R+0. The ACG prevented the tachycardia and decrease in stroke volume normally associated with standing after space flight. Further evaluation of this garment after long-duration space flight is warranted as this garment shows promise as a countermeasure which protects against blood pooling, can be donned in weightlessness, and is relatively comfortable to wear.
The majority of the astronauts described the shorts and thigh-high garments as being comfortable on landing day. Specifically, five of the seven astronauts described the shorts as being comfortable or very comfortable, while two of the seven described them as being uncomfortable. Of the seven astronauts, six reported the thigh high garments as comfortable or very comfortable. The lowest comfort rating for the thigh-highs was 3, which would be neither comfortable nor uncomfortable (“neutral”). None of the astronauts described the garments as being very uncomfortable.