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PubMed1980

Automatic control of human thermal comfort by a liquid-cooled garment.

Astronauts utilize water cooling in a liquid-cooled garment to maintain thermal comfort during extravehicular activities (EVA's). In the Apollo and Skylab Programs, manual control of the cooling water was a necessary operation to ensure proper control of body heat storage for the EVA crewman. The development of an automatic thermal control system would be a valuable asset to the conduct of EVA, relieving the crewman of a task that can interfere with his EVA objectives. An analytical model of human thermoregulation was used to develop the equations governing the operation of such an automatic controller. A series of tests verified the feasibility of a controller utilizing only a measurement of the difference in coolant temperature into and out of the astronaut's liquid-cooled garment and an estimate of environmental heat loss to maintain the proper crewman thermal balance. Three test subjects performed over a wide range of metabolic rates, and the crewman heat balance was maintained well within allowable medical limits. This study demonstrates the use of a mathematical model to generate previously unknown physiological relationships between human thermal comfort and liquid cooled garment performance. In so doing, it quantitates physiological parameters that are difficult to relate directly by experiment. Index terms: body temperature regulation, space suit cooling, temperature control, human thermoregulation.

Aerospace Medicine↗
PubMed2004

Evaluation of shoulder integrity in space: first report of musculoskeletal US on the International Space Station.

Investigative procedures were approved by Henry Ford Human Investigation Committee and NASA Johnson Space Center Committee for Protection of Human Subjects. Informed consent was obtained. Authors evaluated ability of nonphysician crewmember to obtain diagnostic-quality musculoskeletal ultrasonographic (US) data of the shoulder by following a just-in-time training algorithm and using real-time remote guidance aboard the International Space Station (ISS). ISS Expedition-9 crewmembers attended a 2.5-hour didactic and hands-on US training session 4 months before launch. Aboard the ISS, they completed a 1-hour computer-based Onboard Proficiency Enhancement program 7 days before examination. Crewmembers did not receive specific training in shoulder anatomy or shoulder US techniques. Evaluation of astronaut shoulder integrity was done by using a Human Research Facility US system. Crew used special positioning techniques for subject and operator to facilitate US in microgravity environment. Common anatomic reference points aided initial probe placement. Real-time US video of shoulder was transmitted to remote experienced sonologists in Telescience Center at Johnson Space Center. Probe manipulation and equipment adjustments were guided with verbal commands from remote sonologists to astronaut operators to complete rotator cuff evaluation. Comprehensive US of crewmember's shoulder included transverse and longitudinal images of biceps and supraspinatus tendons and articular cartilage surface. Total examination time required to guide astronaut operator to acquire necessary images was approximately 15 minutes. Multiple arm and probe positions were used to acquire dynamic video images that were of excellent quality to allow evaluation of shoulder integrity. Postsession download and analysis of high-fidelity US images collected onboard demonstrated additional anatomic detail that could be used to exclude subtle injury. Musculoskeletal US can be performed in space by minimally trained operators by using remote guidance. This technique can be used to evaluate shoulder integrity in symptomatic crewmembers after strenuous extravehicular activities or to monitor microgravity-associated changes in musculoskeletal anatomy. Just-in-time training, combined with remote experienced physician guidance, may provide a useful approach to complex medical tasks performed by nonexperienced personnel in a variety of remote settings, including current and future space programs.

Humans↗
PubMed2000

A model for influence of exercise on formation and growth of tissue bubbles during altitude decompression.

In response to exercise performed before or after altitude decompression, physiological changes are suspected to affect the formation and growth of decompression bubbles. We hypothesized that the work to change the size of a bubble is done by gas pressure gradients in a macro- and microsystem of thermodynamic forces and that the number of bubbles formed through time follows a Poisson process. We modeled the influence of tissue O(2) consumption on bubble dynamics in the O(2) transport system in series against resistances, from the alveolus to the microsystem containing the bubble and its surrounding tissue shell. Realistic simulations of experimental decompression procedures typical of actual extravehicular activities were obtained. Results suggest that exercise-induced elevation of O(2) consumption at altitude leads to bubble persistence in tissues. At the same time, exercise-enhanced perfusion leads to an overall suppression of bubble growth. The total volume of bubbles would be reduced unless increased tissue motion simultaneously raises the rate of bubble formation through cavitation processes, thus maintaining or increasing total bubble volume, despite the exercise.

Altitude↗
PubMed1989

Energy and thermal regulation during bed rest and spaceflight.

In planning for long-duration (1- to 2-yr) space missions (microgravity), the availability of oxygen, water, and food is critical for survival. If astronauts would consume approximately 3,100 kcal and 2.2 liters of fluid per day, the requirements for a 2-yr flight would be 2,263,000 kcal and 1,606 liters for each astronaut. These estimates, based on limited microgravity simulation and flight data, include 1 h/day of moderate isotonic exercise. Each 30-min/day reduction in exercise training time would save 110,869 kcal and 91 liters of water per year. One daily 5-h extravehicular sortie at an average work rate of 1.7 l/min would require an additional 529,250 kcal and 1,095 liters of water per year. Results from microgravity simulation (bed rest) experiments suggest that 1) there is uncertainty whether basal metabolism is unchanged, 2) submaximal ergometer exercise oxygen uptake appears to be unchanged or lower, and 3) without vigorous exercise training near peak levels, the peak oxygen uptake is definitely reduced. In addition, the equilibrium level of exercise core temperature is elevated excessively by approximately 0.5 degrees C after bed-rest acclimation. Changes in the efficiency of work or metabolism in any or all of these conditions could affect nutritional requirements for long spaceflights. Further research is necessary to elucidate the metabolic factors that would be changed and the energy cost of intra- and extravehicular activity during prolonged exposure to microgravity.

Adult↗
PubMed1989

Exercise-training protocols for astronauts in microgravity.

The question of the composition of exercise protocols for use by astronauts in microgravity is unresolved. Based on our knowledge of physical working requirements for astronauts during intra- and extravehicular activity and on the findings from bed-rest studies that utilized exercise training as a countermeasure for the reduction of aerobic power, deterioration of muscular strength and endurance, decrements in mood and cognitive performance, and possibly for bone loss, two exercise protocols are proposed. One assumes that, during microgravity, astronaut exercise physiological functions should be maintained at 100% of ground-based levels; the other assumes that maximal aerobic power in flight can be reduced by 10% of the ground-based level. A recommended prescription for in-flight prevention or partial suppression of calcium (bone) loss cannot be written until further research findings are obtained that elucidate the site, the magnitude, and the mechanism of the changes. Hopefully these proposed exercise prescriptions will stimulate further research and discussion resulting in even more efficient protocols that will help ensure the optimal health and well-being of our astronauts.

Exercise↗
PubMed2001

Historical aspects of the early Soviet/Russian manned space program.

Human spaceflight was one of the great physiological and engineering triumphs of the 20th century. Although the history of the United States manned space program is well known, the Soviet program was shrouded in secrecy until recently. Konstantin Edvardovich Tsiolkovsky (1857-1935) was an extraordinary Russian visionary who made remarkable predictions about space travel in the late 19th century. Sergei Pavlovich Korolev (1907-1966) was the brilliant "Chief Designer" who was responsible for many of the Soviet firsts, including the first artificial satellite and the first human being in space. The dramatic flight of Sputnik 1 was followed within a month by the launch of the dog Laika, the first living creature in space. Remarkably, the engineering work for this payload was all done in less than 4 wk. Korolev's greatest triumph was the flight of Yuri Alekseyevich Gagarin (1934-1968) on April 12, 1961. Another extraordinary feat was the first extravehicular activity by Aleksei Arkhipovich Leonov (1934-) using a flexible airlock that emphasized the entrepreneurial attitude of the Soviet engineers. By the mid-1960s, the Soviet program was overtaken by the United States program and attempts to launch a manned mission to the Moon failed. However, the early Soviet manned space program has a preeminent place in the history of space physiology.

Astronauts↗
PubMed2006

Numerical modeling of the transport to an intravascular bubble in a tube with a soluble/insoluble surfactant.

Using a newly developed algorithm in conjunction with the front tracking scheme, we have evaluated the transport associated with a deformable bubble moving in a tube in the presence of a soluble or an insoluble surfactant. Such evaluations are useful to the understanding of gas embolism--a common syndrome for decompression sickness. Decompression sickness may be encountered in performing extravehicular activity during space exploration. The numerical evaluations indicate that as the location of the adsorptive interface gets closer to the vessel wall, the surfactant amount on the wall gets depleted. The implication is that the process by which a bubble occluding a vessel dislodges may depend both on the strength of the diffusivity of the surfactant and the adsorption process. More detailed study is needed to clarify this observation. The numerical results evaluated include Marangoni flow, which causes a bubble to propel out of its initial static location, and bubble motion in Poiseuille flow. The presence of a soluble/insoluble surfactant slows down the bubble motion. For identical surface concentrations of the surfactant, the effect of the presence of a soluble surfactant is more severe on the retardation of the bubble motion than that of an insoluble surfactant.

Algorithms↗
PubMed2001

[The assessment of the risk of altitude decompression sickness during simulation of repeated (with 12 hour interval) exits into open space].

Purpose of the investigation was to assess contribution of repeated (with a 12-hr interval) decompression to the risk of altitude decompression sickness (ADS) by simulation of 6-hr extravehicular activities (EVA) of space crewmembers in altitude chamber. The protocol included "ascents" of 6 essentially healthy male subjects at the age of 24 to 51 to the altitude of 7,600 m (37 kPa) following 30-min prebreathing (elimination of nitrogen from the body by breathing pure oxygen through a mask at the ambient pressure of 73 kPa = 2,600 m). Each subject participated in 2 experimental exposures: first initial and then repeated decompression. None of 24 "ascents" produced clinical signs of ADS. Comparison of the data concerning frequency and time points of detection by ultrasonic Doppler equipment of gas bubbles (GB) in the venous bed during decompression with initial, maximal and mean values of US signal intensity failed to state a significant difference between them. Data of the investigation were confronted with anticipated length of GB dispersion in body tissues.

Adult↗
PubMed2001

[Prevention of altitude decompression sickness during simulation of egress from the cabin of space vehicle with hypobaric artificial atmosphere].

Based on the proposed semiempiric nomograms, the study was aimed at selection and investigation of normoxic N2-O2 hypobaric atmosphere (HA) at 93-73 kPa, and evaluation of effectiveness of the gas mixture against the altitude decompression sickness (ADS) during 6-hr simulation of extravehicular activities at 37 kPa without prebreathing. Subjects were 22 healthy males from 20 to 50 yr. old. In all, 115 experiments were performed. Twenty-four hours in HA at 93 kPa and subsequent transition to 37 kPa led up to development of ADS symptoms by one subject in one of 27 experiments (3.7%), and emergence of venous gas bubbles (USI) with the intensity of 2, 70, and 19 points by the Spenser scale in 9 experiments (33.3%). Lower HA pressures (86 kPa, 80 kPa and 73 kPa) did not give rise to ADS though the occurrence of venous GB distinctly tended downward (30.6%, 14.3% and 11.8%) and so did the intensity of their entry into the pulmonary circulation (2, 40, 18 points; 1, 80, 19 points, and 2, 00, 15 points, respectively). Minimal ADS risk was observed in HA at 80 kPa and 73 kPa and did not reach 4% at the confidence level of 95%.

Adult↗
PubMedDate not supplied

[Hypobaric nitrogen-oxygen atmosphere as a method of preventing altitude decompression sickness].

It has been shown experimentally that the development of altitude decompression disease at 250 and 180 mm Hg can be prevented by preliminary desaturation in the nitrogen-oxygen hypobaric atmosphere (60% N2 and 40% O2 at 550 mm Hg). This has been demonstrated in 38 experiments on 21 test subjects. The use of this atmosphere in space cabin prevents the development of decompression disease upon a decrease of the cabin pressure to 250 mm Hg and upon extravehicular activity in a space suit with 180--200 mm Hg.

Adult↗
PubMed1970

Food technology problems related to space feeding.

The development of foods suitable for extraterrestrial consumption posed unique problems. Limitations on weight, volume and stability of space food together with the lack of refrigeration favored the use of dehydrated foods on Gemini and Apollo menus. Environmental constraints, cabin pressures of 1/3 atmosphere with exposure of the food assembly to the vacuum of space in conjunction with extravehicular activities and zero gravity required special packaging and adaptation of foods considered suitable for space flight use. Requirements for acceptable, familiar, crumb free, low residue, non-gas producing, stable foods added to the complexity of the developmental effort. Four basic approaches: semisolid foods in metal tubes, dehydrated bite-size foods to be eaten dry, dehydrated foods to be reconstituted before eating and flexibly packaged thermostabilized wet meat products have been utilized in the feeding systems developed for Projects Mercury, Gemini and Apollo. The development of each type posed many interesting technologic problems. Data from current Apollo flights have pointed to certain deficiencies which still remain to be corrected. Work is progressing to eliminate current problems and to provide feeding systems suitable for both short-term and long-term space flights.

Atmospheric Pressure↗
PubMedDate not supplied

[The ultrasonic location of gas bubbles in the human bloodstream during work in a spacesuit].

The results of testing a procedure of ultrasonic location of the gas bubbles (GB) in man during space suit operations to simulate an extravehicular activity (EVA) are presented. Doppler echotachocardiograph "Rhythm" operating at ultrasonic frequency of 1.76 mHz was used as a GB detector. The device "Rhythm" integrated with a special flat transducer of 23 mm in diameter and 4 mm in width was positioned on the subject chest above the pulmonary artery projection. During 4-6 hour human operations while wearing pressurized (276-290 mm Hg) space suit, in 7 of 12 tests performed a stable and qualitative signal of the arterial blood flow in the lungs was recorded. In case of an unstable signal, in order that its quality be improved the posture of test subject was changed and the signal was recorded during a short-term expired breath-holding. Cardiac GB formation was noted during 6 tests in 2 subjects. The first GBs appeared at the 30th, 33rd, 70th, 111th, 114th and 180th minute after producing an operating reduced pressure in space suit. The time of GB detection on the average was 89.7 min. The maximum intensity of GB signal was 3-4 scores on Spencer's scale, but altitude decompression sickness symptoms did not develop in the test subjects. The risk of developing the altitude decompression sickness as opposed to the results of control experiments without use of space suit is discussed.

Adult↗
PubMed1992

The influence of prior exercise at anaerobic threshold on decompression sickness.

This study was conducted to examine the effects of exercise prior to decompression on the incidence of altitude decompression sickness (DCS). In a balanced, two-period, crossover trial, 39 healthy individuals (29 males, 10 females) of mean (S.D.) age 32.5 (7.7) years and body mass index 23.7 (3.4) were each exposed twice, without denitrogenation, to an altitude of 6,400 m (21,000 ft) in a hypobaric chamber. Under the experimental condition, subjects exercised at their predetermined anaerobic threshold levels for 30 min each day for 3 d prior to altitude exposure; the other condition was a non-exercise control. Under both conditions, subjects performed exercise simulating space extravehicular activities at altitude for a period of 3 h, while breathing 100% oxygen. There were nine preferences (untied responses) for DCS, four under control and five under experimental conditions; all were Type I, pain-only bends. No carryover effect between exposures was detected, and the test for treatment differences showed p = 0.56 (95% confidence interval = 0.34-0.58) for symptoms. No significant difference in DCS preferences was found after subjects exercised up to their anaerobic threshold levels during the days prior to decompression.

Adult↗
PubMed1992

Time to detection of circulating microbubbles as a risk factor for symptoms of altitude decompression sickness.

This study investigated the association between time at onset of circulating microbubbles (CMB) and symptoms of altitude decompression sickness (DCS), using Cox proportional hazard regression models. The study population consisted of 125 individuals who participated in direct ascent, simulated extravehicular activities profiles. Using individual CMB status as a time-dependent variable, we found that the hazard for symptoms increased significantly (at the end of 180 min at altitude) in the presence of CMB (Hazard Ratio = 29.59; 95% confidence interval [95% CI] = 7.66-114.27), compared to no CMB. Further examination was conducted on the subgroup of individuals who developed microbubbles during the test (n = 49), by using Cox regression. Individuals with late onset of CMB (> 60 min at altitude) showed a significantly reduced risk of symptoms (hazard ratio = 0.92; 95% CI = 0.89-0.95), compared to those with early onset (< or = 60 min), while controlling for other risk factors. We conclude that time to detection of circulating microbubbles is an independent determinant of symptoms of DCS.

Adult↗
PubMed2003

Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures.

INTRODUCTION: The current extravehicular activity (EVA) space suit at 4.3 psia causes hand and arm fatigue and is too heavy for Martian EVA. A 3.5 psia EVA pressure suit requires increased preoxygenation time but would reduce structural complexity, leak rate, and weight while increasing mobility, comfort, and maintainability. On Mars, nitrogen and argon are available to provide the inert gas necessary for a fire-resistant habitat atmosphere, eliminating need for transport. This study investigated breathing argon/oxygen and 100% oxygen gas mixtures during staged decompression prior to exposure to 3.5 psia. METHOD: During this study, 40 subjects each completed 3 hypobaric exposures to 3.5 psia for 3 h in a reclined position: (A) a 4-h 25-min 14.7-psia (ground level) denitrogenation (100% oxygen breathing) prior to exposure to 3.5 psia; (B) the same as A, utilizing a 7.3-psia stage denitrogenation; and (C) the same as B, with 62% argon-38% oxygen (ARGOX) during the stage. Venous gas emboli (VGE) were monitored with echocardiography. RESULTS: Decompression sickness (DCS) incidence at 3.5 psia with ARGOX at 7.3 psia (C) was significantly higher than with oxygen breathing with or without staged decompression: there was 78% DCS for C compared with 33% and 55% DCS, respectively, for A and B. The corresponding VGE incidences were 73% (C) compared with 33% (A) and 45% (B). CONCLUSION: Preoxygenation at a 7.3-psia stage resulted in a higher DCS risk at 3.5 psia than ground level preoxygenation. It is suggested that an 8.0-psia stage pressure could eliminate this difference. Unfavorable results after preoxygenation with ARGOX indicate argon on-gassing was significant.

Adolescent↗
PubMed2004

Altitude decompression sickness symptom resolution during descent to ground level.

INTRODUCTION: Altitude decompression sickness (DCS) is a health risk associated with the conduct of high altitude airdrop operations, high altitude reconnaissance, future fighter operations, hypobaric chamber training, unpressurized flight, and extravehicular activity (EVA) in space. The treatment for DCS includes the provision of 100% oxygen (O2) at ground level (GLO) and/or hyperbaric oxygen therapy (HBO). In this paper we examine the effect of repressurization to ground level from hypobaric conditions on DCS symptoms. Timely recompression (descent at first recognition of any DCS symptom) may be a safe, effective treatment for the large majority of DCS symptoms. METHODS: Data from altitude chamber exposures recorded in the Air Force Research Laboratory (AFRL) Altitude DCS Database were reviewed to determine the level of recompression required for complete resolution of 1,699 observed symptoms. RESULTS: Of the 1,699 DCS symptoms reviewed, 66 (3.9%) resolved at altitude, 117 (6.9%) resolved at ground level, and 1,433 (84.3%) resolved during descent. Increasing the pressure by 138 mmHg from the altitude of exposure where symptoms occurred resolved roughly 50% of symptoms. Little resolution of symptoms was noted with recompressions of < 50 mmHg. The greatest rate of symptom resolution occurred with recompressions of 50-250 mmHg. CONCLUSION: These findings support the concept that descent and postflight, ground-level oxygen may be sufficient to relieve the majority of altitude DCS symptoms. HBO may be reserved for serious, recurring, delayed, or refractory symptoms. The findings also suggest a need for further study of DCS symptom resolution.

Aerospace Medicine↗
PubMed2006

Motion sickness provoked by torso rotation predicts that caused by head nodding.

INTRODUCTION: Some degree of space motion sickness is experienced by at least 50% of astronauts early in flight. It is unpleasant and could be hazardous during an extravehicular activity or urgent re-entry in the first few days after launch. To date, there is no reliable ground-based test to predict who will be affected. METHODS: Head nodding (HN) in a supine position was used as a model of motion sickness caused by an unusual gravito-inertial environment. Torso rotation (TR) was used as a means of predicting susceptibility to development of symptoms caused by HN. Motion sickness was quantified in 26 subjects (5 men, 21 women, age range 18-52) using numerical estimates of discomfort and a more detailed questionnaire. Susceptibility to TR and HN was determined on three occasions for each stimulus, with test sessions at least 1 mo apart. RESULTS: Subjects reached their stopping point at a mean duration of 13.72 min +/- 1.06 CI) for TR and 11.31 min (+/- 0.38 CI) for HN. When susceptibility to HN was plotted as a function of susceptibility to TR and a linear regression line was added, the correlation coefficient was 0.744. DISCUSSION: Susceptibility to TR predicts susceptibility to HN. The method may be useful as a screening test for potential astronauts.

Adolescent↗
PubMedDate not supplied

Preliminary results of medical research on board the "Mir" orbital complex during its second main mission.

In 1987 the USSR orbital complex "Mir" accomplished its space mission, crewed by Yu.V. Romanenko (326 days), and A.I. Laveykin (about 176 days), who was replaced on the orbit (in consequence of some cardiac function peculiarities revealed in exercise conditions) by A.P. Aleksandrov (about 160 days). During the flight, extravehicular activity in the open space was carried out three times, and conjoint programmes were conducted, over a period of seven days, with an international Soviet-Syrian crew. The most important, fundamental result of the medical studies carried out in this flight seems to be the noted fact that Yu.V. Romanenko's 326 days in-flight (which means 3 months in excess to the results obtained hitherto) and his activity was not accompanied by developing any quantitatively new functional shifts, when compared to other long-term flights. Besides that, the cosmonaut maintained his functional endurance and work capacity on satisfactory levels. These results are in apparent relation with the rationally composed crew complement, the contribution the ground services responsible for the work-rest regimen and the whole life activity on board the station, as well as with the systematic and sufficiently extensive use of preventive measures. The general feeling and work capacity of the other crew members were also good throughout the flight. However, the reactions observed in each cosmonaut showed their individual characteristics, which are discussed in the paper.

Adult↗