Electrical Shock Hazard Severity Estimation During Extravehicular Activity for the International Space Station.

INTRODUCTION: Research has shown that astronauts performing extravehicular activities may be exposed, under certain conditions, to undesired electrical hazards. This study used computer models to determine whether these undesired induced electrical currents could be responsible for involuntary neuromuscular activity caused by either large diameter peripheral nerve activation or reflex activity from cutaneous afferent stimulation.METHODS: A multiresolution variant of the admittance method along with a magnetic resonance image millimeter resolution model of a male human body were used to calculate the following: 1) induced electric fields; 2) resistance between contact areas in a Extravehicular Mobility Unit spacesuit; 3) currents induced in the human body; 4) the physiological effects of these electrical exposures; and 5) the risk to the crew during extravehicular activities.RESULTS: Using typical EMU shock exposure conditions, with a 15V source, the current density magnitudes and total current injected are well above previously reported startle reaction thresholds. This indicates that, under the considered conditions during a spacewalk in the charged ionospheric plasma of space, astronauts could experience possibly harmful involuntary motor response and sensory pain nerve activation.Hamilton DR. Electrical shock hazard severity estimation during extravehicular activity for the International Space Station. Aerosp Med Hum Perform. 2021; 92(4):231239.

Implications of Space Suit Injury Risk for Developing Computational Performance Models.

INTRODUCTION: Although a space suit is a technological feat sustaining human life outside the spacecraft, working in the space suit environment can lead to musculotendon and soft tissue injuries in astronauts. In this literature review, we consider the injury risk mechanisms for human-space suit interactions. We first present a review of space suit injury risk founded in empirical, statistical, and experimental studies. We then review efforts in computational modeling of a human and space suit. As the interpretation of models for injury risk has not previously been defined, a review is presented of biomechanical considerations of injury risk to the tissue and joints based on previously observed space suit injuries. A review of risk assessment in occupational health in the workplace is then presented, an adjacent area that informs relevant measures of consideration for human-space suit applications. Finally, we discuss how the work-to-date can inform continued efforts in minimizing risk of musculoskeletal injury to the human when using a space suit. From the literature, this review concludes space suits cause biomechanical alterations, inducing musculoskeletal injury. Combining occupational health kinematic constraints with computational models could enable a trade space evaluation on space suited biomechanics to reduce risk mechanisms. Future work, though, is required to enable computational models to be predictive of individual injury risk. Our findings show there are significant gaps in our current knowledge on tissue injuries that preclude biomechanical models from being used directly as an injury risk assessment model. This review identifies how risk factor monitoring and modeling will enable improved space suit design and evaluation.Stirling L, Arezes P, Anderson A. Implications of space suit injury risk for developing computational performance models. Aerosp Med Hum Perform. 2019; 90(6):553-565.

[Analysis of the importance of cosmonaut's location and orientation onboard the International space station to levels of visceral irradiation during traverse of the region of the South Atlantic Anomaly].

Parametric analysis of absorbed radiation dose to the cosmonaut working in the Service module (SM) of the International space station (ISS) was made with allowance for anisotropy of the radiation field of the South Atlantic Anomaly. Calculation data show that in weakly shielded SM compartments the radiation dose to poorly shielded viscera may depend essentially on cosmonaut's location and orientation relative to the ISS shell. Difference of the lens absorbed dose can be as high as 5 times depending on orientation of the cosmonaut and the ISS. The effect is less pronounced on the deep seated hematopoietic system; however, it may increase up to 2.5 times during the extravehicular activities. When the cosmonaut is outside on the ISS SM side presented eastward, the absorbed dose can be affected noticeably by remoteness from the SM. At a distance less than 1.5 meters away from the SM east side in the course of ascending circuits, the calculated lens dose is approximately half as compared with the situation when the cosmonaut is not shielded by the ISS material.

[Radiation effect on cosmonauts during extravehicular activities in 2008-2009].

The geometrical model of suited cosmonaut's phantom was used in mathematical modeling of EVAs performed by cosmonauts with consideration of changes in the ISS Russian segment configuration during 2008-2009 and the dependence of space radiation absorbed dose on EVA scene. Influence of spatial position of cosmonaut on absorbed dose value was evaluated with the EVA dosimeter model reproducing the actually determined weight and dimension. Calculated absorbed dose values are in good agreement with experimental data. Absorbed doses imparted to body organs (skin, lens, hemopoietic system, gastrointestinal tract, central nervous system, gonads) were determined for specific EVA events.

Venous gas emboli and exhaled nitric oxide with simulated and actual extravehicular activity.

The decompression experienced due to the change in pressure from a space vehicle (1013hPa) to that in a suit for extravehicular activity (EVA) (386hPa) was simulated using a hypobaric chamber. Previous ground-based research has indicated around a 50% occurrence of both venous gas emboli (VGE) and symptoms of decompression illness (DCI) after similar decompressions. In contrast, no DCI symptoms have been reported from past or current space activities. Twenty subjects were studied using Doppler ultrasound to detect any VGE during decompression to 386hPa, where they remained for up to 6h. Subjects were supine to simulate weightlessness. A large number of VGE were found in one subject at rest, who had a recent arm fracture; a small number of VGE were found in another subject during provocation with calf contractions. No changes in exhaled nitric oxide were found that can be related to either simulated EVA or actual EVA (studied in a parallel study on four cosmonauts). We conclude that weightlessness appears to be protective against DCI and that exhaled NO is not likely to be useful to monitor VGE.

[Theoretical evaluation of the risk of decompression illness during simulated extravehicular activity].

Theoretical analysis of the risk of decompression illness (DI) during extravehicular activity following the Russian and NASA decompression protocols (D-R and D-US, respectively) was performed. In contrast to the tradition approach to decompression stress evaluation by the factor of tissue supersaturation with nitrogen, our probabilistic theory of decompression safety provides a completely reasoned evaluation and comparison of the levels of hazard of these decompression protocols. According to this theory, the function of cumulative DI risk is equal to the sum of functions of cumulative risk of lesion of all body tissues by gas bubbles and their supersaturation by solute gases. Based on modeling of dynamics of these functions, growth of the DI cumulative risk in the course of D-R and D-US follows essentially similar trajectories within the time-frame of up to 330 minutes. However, further extension of D-US but not D-R raises the risk of DI drastically.

[The heart in extreme sports: hyperbaric activity and microgravity]. / II cuore nello sport estremo: attività iperbarica e microgravità.

The study of the cardiovascular and respiratory modifications in extreme environments could be useful for the understanding of the adaptive mechanisms of the body in particular conditions. The knowledge of how different environmental conditions in terms of extreme pressure, temperature and gravity modify the neurovegetative and cardiovascular system could be useful in daily practice for hypobaric and hyperbaric sports.

Gas embolism and surfactant-based intervention: implications for long-duration space-based activity.

Intravascular gas embolism can occur with decompression in space flight, and it commonly occurs during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. Surfactant-based intervention is a novel treatment for gas embolism. Intravascular surfactant can adsorb onto the gas-liquid interface and compete with blood-borne macromolecules for interfacial occupancy. Surfactants can retard the progress of pathophysiological molecular and cellular events stimulated by the bubble surface, including endothelial cell injury and initiation of blood clotting. Bulk and surface transport of a surfactant to provide competition for interfacial occupancy is a therapeutic strategy because surfactant adsorption can dominate protein (or other macromolecule) adsorption. The presence of surfactant along the gas-liquid interface also induces variation in the interfacial tension, which in turn affects the blood flow and the bubble motion. We describe the interplay between biological transport processes and physiological events occurring and the cellular and molecular level in vascular gas embolization. Special consideration is given to modeling the transport and hydrodynamic interactions associated with surfactant-based intervention.

Finger heat flux/temperature as an indicator of thermal imbalance with application for extravehicular activity.

The designation of a simple, non-invasive, and highly precise method to monitor the thermal status of astronauts is important to enhance safety during extravehicular activities (EVA) and onboard emergencies. Finger temperature (Tfing), finger heat flux, and indices of core temperature (Tc) [rectal (Tre), ear canal (Tec)] were assessed in 3 studies involving different patterns of heat removal/insertion from/to the body by a multi-compartment liquid cooling/warming garment (LCWG). Under both uniform and nonuniform temperature conditions on the body surface, Tfing and finger heat flux were highly correlated with garment heat flux, and also highly correlated with each other. Tc responses did not adequately reflect changes in thermal balance during the ongoing process of heat insertion/removal from the body. Overall, Tfing/finger heat flux adequately reflected the initial destabilization of thermal balance, and therefore appears to have significant potential as a useful index for monitoring and maintaining thermal balance and comfort in extreme conditions in space as well as on Earth.

Decompression sickness during simulated extravehicular activity: ambulation vs. non-ambulation.

BACKGROUND: Extravehicular activity (EVA) is required from the International Space Station on a regular basis. Because of the weightless environment during EVA, physical activity is performed using mostly upper-body movements since the lower body is anchored for stability. The adynamic model (restricted lower-body activity; non-ambulation) was designed to simulate this environment during earthbound studies of decompression sickness (DCS) risk. DCS symptoms during ambulatory (walking) and non-ambulatory high altitude exposure activity were compared. The objective was to determine if symptom incidences during ambulatory and non-ambulatory exposures are comparable and provide analogous estimates of risk under otherwise identical conditions. METHODS: A retrospective analysis was accomplished on DCS symptoms from 2010 ambulatory and 330 non-ambulatory exposures. RESULTS: There was no significant difference between the overall incidence of DCS or joint-pain DCS in the ambulatory (49% and 40%) vs. the non-ambulatory exposures (53% and 36%; p > 0.1). DCS involving joint pain only in the lower body was higher during ambulatory exposures (28%) than non-ambulatory exposures (18%; p < 0.01). Non-ambulatory exposures terminated more frequently with non-joint-pain DCS (17%) or upper-body-only joint pain (18%) as compared with ambulatory exposures, 9% and 11% (p < 0.01), respectively. DISCUSSION: These findings show that lower-body, weight-bearing activity shifts the incidence of joint-pain DCS from the upper body to the lower body without altering the total incidence of DCS or joint-pain DCS. CONCLUSIONS: Use of data from previous and future subject exposures involving ambulatory activity while decompressed appears to be a valid analogue of non-ambulatory activity in determining DCS risk during simulated EVA studies.

The main results of EVA medical support on the Mir Space Station.

The aim of this paper is to review the main results of medical support of 78 two-person extravehicular activities (EVAs) which have been conducted in the Mir Space Program. Thirty-six male crewmembers participated in these EVAs. Maximum length of a space walk was equal to 7 h 14 min. The total duration of all space walks reached 717.1 man-hours. The maximum frequency of EVA's execution was 10 per year. Most of the EVAs (67) have been performed at mission elapsed time ranging from 31 to 180 days. The oxygen atmosphere of the Orlan space suit with a pressure of 40 kPa in combination with the normobaric cabin environment and a short (30 min) oxygen prebreathe protocol have minimized the risk of decompression sickness (DCS). There has been no incidence of DCS during performed EVAs. At the peak activity, metabolic rates and heart rates increased up to 9.9-13 kcal/min and 150-174 min-1, respectively. The medical problems have centred on feeling of moderate overcooling during a rest period in a shadow after the high physical loads, episodes with tachycardia accompanied by cardiac rhythm disorders at the moments of emotional stress, pains in the muscles and general fatigue after the end of a hard EVA. All of the EVAs have been completed safely.

Patent foramen ovale and paradoxical systemic embolism: a bibliographic review.

A patent foramen ovale (PFO) has been reported to be an important risk factor for cardioembolic cerebrovascular accidents through paradoxical systemic embolization, and it provides one potential mechanism for the paradoxical systemic embolization of venous gas bubbles produced after altitude or hyperbaric decompressions. Here, we present in a single document a summary of the original findings and views from authors in this field. It is a comprehensive review of 145 peer-reviewed journal articles related to PFO that is intended to encourage reflection on PFO detection methods and on the possible association between PFO and stroke. There is a heightened debate on whether aviators, astronauts, and scuba divers should go through screening for PFO. Because it is a source of an important controversy, we prefer to present the findings in the format of a neutral bibliographic review independent of our own opinions. Each cited peer-reviewed article includes a short summary in which we attempt to present potential parallels with the pathophysiology of decompression bubbles. Two types of articles are summarized, as follows. First, we report the original clinical and physiological findings which focus on PFO. The consistent reporting sequence begins by describing the method of detection of PFO and goal of the study, followed by bulleted results, and finally the discussion and conclusion. Second, we summarize from review papers the issues related only to PFO. At the end of each section, an abstract with concluding remarks based on the cited articles provides guidelines.

The effect of simulated weightlessness on hypobaric decompression sickness.

BACKGROUND: A discrepancy exists between the incidence of ground-based decompression sickness (DCS) during simulated extravehicular activity (EVA) at hypobaric space suit pressure (20-40%) and crewmember reports during actual EVA (zero reports). This could be due to the effect of gravity during ground-based DCS studies. HYPOTHESIS: At EVA suit pressures of 29.6 kPa (4.3 psia), there is no difference in the incidence of hypobaric DCS between a control group and group exposed to simulated weightlessness (supine body position). METHODS: Male subjects were exposed to a hypobaric pressure of 29.6 kPa (4.3 psi) for up to 4 h. The control group (n = 26) pre-oxygenated for 60 min (first 10 min exercising) before hypobaric exposure and walking around in the altitude chamber. The test group (n = 39) remained supine for a 3 h prior to and during the 60-min pre-oxygenation (also including exercise) and at hypobaric pressure. DCS symptoms and venous gas emboli (VGE) at hypobaric pressure were registered. RESULTS: DCS occurred in 42% in the control and in 44% in simulated weightlessness group (n.s.). The mean time for DCS to develop was 112 min (SD +/- 61) and 123 min (+/- 67), respectively. VGE occurred in 81% of the control group subjects and in 51% of the simulated weightlessness subjects (p = 0.02), while severe VGE occurred in 58% and 33%, respectively (p = 0.08). VGE started after 113 min (+/- 43) in the control and after 76 min (+/- 64) in the simulated weightlessness group. CONCLUSIONS: No difference in incidence of DCS was shown between control and simulated weightlessness conditions. VGE occurred more frequently during the control condition with bubble-releasing arm and leg movements.

The effect of staged decompression while breathing 100% oxygen on altitude decompression sickness.

INTRODUCTION: Space Shuttle extravehicular activity (EVA) requires decompression from sea level pressure (14.7 psia) to a 4.3 psia (30,300 ft) pressure suit. The transition currently involves altering the shuttle atmosphere to allow shirt-sleeve denitrogenation to occur during a 12 to 36-h staged decompression (SD) at 10.2 psia (9,800 ft) with an oxygen-enriched breathing gas (26.5% oxygen, 73.5% nitrogen). The denitrogenation provides protection from decompression sickness (DCS) during EVA in a 4.3 psia pressure suit. Our goal was to determine the highest altitude at which SD while breathing 100% oxygen (SD100) could provide effective protection from development of DCS symptoms after further decompression to 29,500 ft (4.5 psia). METHODS: There were 30 male subjects exposed to at least 6 of 11 conditions in random order on successive months to 29,500 ft for 4 h while performing mild exercise and being monitored for venous gas emboli (VGE) with an echo-imaging system. The subjects received 15 min of ground-level (GL) preoxygenation and an additional 60 or 120 min of SD100 at one of four altitudes between 8,000 ft (10.9 psia) and 18,000 ft (7.3 psia). Control exposures followed a 75- or 135-min ground-level preoxygenation. RESULTS: During SD100, one case of DCS occurred at 18,000 ft, but not at lower staging altitudes. Higher levels of VGE were observed during SD100 at 18,000 ft than during SD100 at any lower altitude. CONCLUSION: Staged decompression at 16,000 ft and below results in decompression risk during subsequent decompression to 29,500 ft similar to that following equivalent periods of ground-level preoxygenation.

Effects of heterogeneous structure and diffusion permeability of body tissues on decompression gas bubble dynamics.

To gain insight into the special nature of gas bubbles that may form in astronauts, aviators and divers, we developed a mathematical model which describes the following: 1) the dynamics of extravascular bubbles formed in intercellular cavities of a hypothetical tissue undergoing decompression; and 2) the dynamics of nitrogen tension in a thin layer of intercellular fluid and in a thick layer of cells surrounding the bubbles. This model is based on the assumption that, due to limited cellular membrane permeability for gas, a value of effective nitrogen diffusivity in the massive layer of cells in the radial direction is essentially lower compared to conventionally accepted values of nitrogen diffusivity in water and body tissues. Due to rather high nitrogen diffusivity in intercellular fluid, a bubble formed just at completion of fast one-stage reduction of ambient pressure almost instantly grows to the size determined by the initial volume of the intercellular cavity, surface tension of the fluid, the initial nitrogen tension in the tissue, and the level of final pressure. The rate of further bubble growth and maximum bubble size depend on comparatively low effective nitrogen diffusivity in the cell layer, the tissue perfusion rate, the initial nitrogen tension in the tissue, and the final ambient pressure. The tissue deformation pressure performs its conservative action on bubble dynamics only in a limited volume of tissue (at a high density of formed bubbles). Our model is completely consistent with the available data concerning the random latency times to the onset of decompression sickness (DCS) symptoms associated with hypobaric decompressions simulating extravehicular activity. We believe that this model could be used as a theoretical basis for development of more adequate methods for the DCS risk prediction.

Thermoregulation and heat exchange in a nonuniform thermal environment during simulated extended EVA. Extravehicular activities.

BACKGROUND: Nonuniform heating and cooling of the body, a possibility during extended duration extravehicular activities (EVA), was studied by means of a specially designed water circulating garment that independently heated or cooled the right and left sides of the body. The purpose was to assess whether there was a generalized reaction on the finger in extreme contradictory temperatures on the body surface, as a potential heat status controller. METHOD: Eight subjects, six men and two women, were studied while wearing a sagittally divided experimental garment with hands exposed in the following conditions: Stage 1 baseline--total body garment inlet water temperature at 33 degrees C; Stage 2--left side inlet water temperature heated to 45 degrees C; right side cooled to 8 degrees C; Stage 3--left side inlet water temperature cooled to 8 degrees C, right side heated to 45 degrees C. RESULTS: Temperatures on each side of the body surface as well as ear canal temperature (Tec) showed statistically significant Stage x Side interactions, demonstrating responsiveness to the thermal manipulations. Right and left finger temperatures (Tfing) were not significantly different across stages; their dynamic across time was similar. Rectal temperature (Tre) was not reactive to prevailing cold on the body surface, and therefore not informative. Subjective perception of heat and cold on the left and right sides of the body was consistent with actual temperature manipulations. CONCLUSIONS: Tec and Tre estimates of internal temperature do not provide accurate data for evaluating overall thermal status in nonuniform thermal conditions on the body surface. The use of Tfing has significant potential in providing more accurate information on thermal status and as a feedback method for more precise thermal regulation of the astronaut within the EVA space suit.

Cardiovascular and hormonal changes induced by a simulation of a lunar mission.

BACKGROUND: This is the first simulation of a 14-d lunar mission including 6 d on the Moon. HYPOTHESIS: We hypothesized that a lunar gravity simulation in the middle of a head-down tilt (HDT) might result in some reversal of body fluid/hormonal responses, and influence cardiovascular deconditioning. METHODS: Six men (28 +/- 2.5 yr) were placed in bed rest (BR): in (HDT) (-6 degrees) to simulate microgravity during the travel (two 4-d periods), and in head-up tilt (HUT) (+10 degrees) (6-d period) to simulate lunar gravity (1/6 g). Muscular exercise was performed during the HUT period to simulate 6 h of lunar EVA. Heart rate variability (HRV) and hormonal responses were studied. RESULTS: An orthostatic arterial hypotension was observed after the BR (tilt test) in 4 of the 6 subjects. Plasma volume measured at D14 decreased by -11.1% (vs. D-3, sitting position). A decrease in atrial natriuretic peptide (26 +/- 3.5 pg.ml-1 (D14) vs. 37.9 +/- 3.5 pg.ml-1 (D-3, sitting) and an increase in plasma renin activity (198 +/- 9.2 mg.L-1.min-1 (D14) vs. 71 +/- 9.2 mg.L-1.min-1 (D-3, sitting) were observed during the BR, more pronounced in HUT at 7:00 p.m. Sympathetic-parasympathetic balance (HRV) at rest showed a decrease in parasympathetic indicator and an increase in sympathetic indicator in BR (p < 0.05), without differences within HDT and HUT periods. CONCLUSION: These changes were mostly similar to those reported in spaceflights, and HDT. Although the exposure to 1/6 g with exercise modified some hormonal and body fluid responses, this partial gravity simulation was not sufficient to prevent the decrease in orthostatic tolerance observed here as well as after Apollo lunar missions.