Modeling Occupational Fingernail Onycholysis Disorders in the Population of US Astronauts Who Have Engaged in Extravehicular Activity.

OBJECTIVES: Spacesuits are designed to be reliable personal spacecraft that preserve the life and well-being of the astronaut from the extremes of space. However, materials, operating pressures, and suit design requirements often result in a risk of musculoskeletal discomfort and injury to various areas of the body. In particular, this investigation looked at fingernails and their risk of developing onycholysis. METHODS: An onycholysis literature review was followed by a retrospective analysis of injury characteristics, astronaut suited training and spaceflight events, hand anthropometry, glove sizing, and astronaut demographics. Multiple logistic regression was used to assess the likelihood of onycholysis occurrence by testing potential risk variables against the dataset compiled from the retrospective data mining. RESULTS: The duration of event exposure, type of glove used, distance (delta) between the fingertip and the tip of the glove, sex, and age were found to be significantly related to occurrence of onycholysis (whether protective or injurious). CONCLUSION: An initial risk formula (model) for onycholysis was developed as a result of this investigation. In addition to validation through a future study, further improvement to this onycholysis equation and spacesuit discomfort and injury in general can be aided by future investigations that lead to better definition of the threshold between safe and risky exposure for each type of risk factor. APPLICATION: This work described a potential method that can be used for EVA spacesuit glove onycholysis injury risk analysis for either iterative glove design or between glove comparisons, such as during a product downselect process.

The Partial Pressure of Inspired Carbon Dioxide Exposure Levels in the Extravehicular Mobility Unit.

BACKGROUND: NASA has been making efforts to assess the carbon dioxide (CO2) washout capability of spacesuits using a standard CO2 sampling protocol. This study established the methodology for determining the partial pressure of inspired CO2 (PIco2) in a pressurized spacesuit. We applied the methodology to characterize PIco2 for the extravehicular mobility unit (EMU).METHODS: We suggested an automated and mathematical algorithm to find the end-tidal CO2 and the end of inspiration. We provided objective and standardized guidelines to identify acceptable breath traces, which are essential to accurate and reproducible calculation of the in-suit inhaled and exhaled partial pressure of CO2 (Pco2). The mouth guard-based method for measurement of inhaled and exhaled dry-gas Pco2 was described. We calculated all individual concentrations of PIco2 inhaled by 19 healthy subjects classified into 3 fitness groups. The transcutaneous Pco2 was monitored as a secondary measure to validate washout performance.RESULTS: Mean and standard deviation values for the data collection performance and the CO2 metrics were presented (e.g., minimum time weighted average Pco2 at suited workloads of resting, 1000, 2000, and 3000 (BTU h1) were 4.75 1.03, 8.09 1.39, 11.39 1.26, and 14.36 1.29 (mmHg s1). All CO2 metrics had a statistically significant association and all positive slopes with increasing metabolic rate. No significant differences in CO2 metrics were found between the three fitness groups.DISCUSSION: A standardized and automated methodology to calculate PIco2 exposure level is presented and applied to characterize CO2 washout in the EMU. The EMU has been operated successfully in over 400 extravehicular activities (EVAs) and is considered to provide acceptable CO2 washout performance. Results provide a basis for establishing verifiable Pco2 requirements for current and future EVA spacesuits.Kim KJ, Bekdash OS, Norcross JR, Conkin J, Garbino A, Fricker J, Young M, Abercromby AFJ. The partial pressure of inspired carbon dioxide exposure levels in the extravehicular mobility unit. Aerosp Med Hum Perform. 2020; 91(12):923931.

Carbon Monoxide Levels in the Extravehicular Mobility Unit by Modeling and Operational Testing.

INTRODUCTION: Carbon monoxide (CO) is a toxic gas with potential for detriment to spaceflight operations. An analytical model was developed to investigate if a maximum CO contamination of 1 ppm in the oxygen (O2) supply reached dangerous levels during extravehicular activity (EVA). Occupational monitoring pre- and postsuited exposures provided supplementary data for review.METHODS: The analytical model estimated O2 and CO concentrations in the extravehicular mobility unit (EMU) based on O2 and CO flow rates into and out of the system. The model was based on 3 h of prebreathe at 15.2 psia, 8 h of EVA at 4.3 psia, and 1 h at 15.2 psia for suit doffing. The Coburn-Forster-Kane equation was used to calculate crewmember carboxyhemoglobin saturation (COHb%) as a function of time. Monitoring of hemoglobin CO saturation (Spco) with a CO-oximeter was conducted pre- and post-EVA during operations on the International Space Station and in ground-based analog environments.RESULTS: The model predicted a maximum PCO in the EMU of 0.061 mmHg and a maximum crewmember COHb% of 2.1%. Operational Spco measurements in mean ± SD during ground-based analog testing were 0.7% ± 1.8% pretest and 0.5% ± 1.5% posttest. Spco values on the ISS were 1.5% ± 0.7% pre-EVA and 1.1% ± 0.3% post-EVA.DISCUSSION: The model predicted that astronauts are not exposed to toxic levels of CO during EVA and operational measurements did not show significant differences between Spco levels between pre- and post-EVA.Makowski MS, Norcross JR, Alexander D, Sanders RW, Conkin J, Young M. Carbon monoxide levels in the extravehicular mobility unit by modeling and operational testing. Aerosp Med Hum Perform. 2019; 90(2):84-91.

Retrospective Evaluation of Clinical Symptoms Due to Mild Hypobaric Hypoxia Exposure in Microgravity.

INTRODUCTION: A habitat atmosphere of 34% oxygen (O2) and 66% nitrogen (N2) at 8.2 psia (56.5 kPa) is proposed to minimize the risk of decompression sickness during extravehicular activity. The resulting inspired O2 partial pressure (PIo2) of 128 mmHg is similar to that experienced during portions of 41 Space Shuttle missions that used a "staged" denitrogenation (prebreathe) protocol with an atmosphere of 26.5% O2 and 73.5% N2 at 10.2 psia (70.3 kPa). We evaluated symptoms possibly linked to mild hypoxia in astronauts breathing a PIo2 of 127 mmHg. METHODS: Environmental data were used to determine time in the shuttle at 10.2 psia and time at 14.7 psia (101.3 kPa). A total of 14 possible hypoxia symptoms were compared with symptoms collected during normoxic shuttle operations at 14.7 psia using logistic regression. RESULTS: There were 134.1 d (788.8 person days) under the 10.2 psia staged condition with a mean of 3.17 ± 2.2 SD d/mission. There were 258.81 d at 14.7 psia (2192.95 person days). An average of 4.31 potentially hypoxia-related symptoms per mission day was documented under the staged condition compared with 4.08 per mission day during the normoxic condition. Logistic regression showed no symptoms were significantly associated with just the 10.2 psia condition. DISCUSSION: Chronic exposure to a PIo2 of 127 mmHg is well-tolerated by healthy humans on Earth. A similar short-duration exposure on the shuttle resulted in no increased reporting of possible hypoxia-related symptoms. However, chronic mild hypoxia interactions with physiological changes due to microgravity adaptations remain unclear.Wessel JH III, Schaefer CM, Thompson MS, Norcross JR, Bekdash OS. Retrospective evaluation of clinical symptoms due to mild hypobaric hypoxia exposure in microgravity. Aerosp Med Hum Perform. 2018; 89(9):792-797.

Hemoglobin Oxygen Saturation with Mild Hypoxia and Microgravity.

INTRODUCTION: Microgravity (µG) exposure and even early recovery from µG in combination with mild hypoxia may increase the alveolar-arterial oxygen (O2) partial pressure gradient. METHODS: Four male astronauts on STS-69 (1995) and four on STS-72 (1996) were exposed on Earth to an acute sequential hypoxic challenge by breathing for 4 min 18.0%, 14.9%, 13.5%, 12.9%, and 12.2% oxygen-balance nitrogen. The 18.0% O2 mixture at sea level resulted in an inspired O2 partial pressure (PIo2) of 127 mmHg. The equivalent PIO2 was also achieved by breathing 26.5% O2 at 527 mmHg that occurred for several days in µG on the Space Shuttle. A Novametrix CO2SMO Model 7100 recorded hemoglobin (Hb) oxygen saturation through finger pulse oximetry (Spo2, %). There were 12 in-flight measurements collected. Measurements were also taken the day of (R+0) and 2 d after (R+2) return to Earth. Linear mixed effects models assessed changes in Spo2 during and after exposure to µG. RESULTS: Astronaut Spo2 levels at baseline, R+0, and R+2 were not significantly different from in flight, about 97% given a PIo2 of 127 mmHg. There was also no difference in astronaut Spo2 levels between baseline and R+0 or R+2 over the hypoxic challenge. CONCLUSIONS: The multitude of physiological changes associated with µG and during recovery from µG did not affect astronaut Spo2 under hypoxic challenge.Conkin J, Wessel JH III, Norcross JR, Bekdash OS, Abercromby AFJ, Koslovsky MD, Gernhardt ML. Hemoglobin oxygen saturation with mild hypoxia and microgravity. Aerosp Med Hum Perform. 2017; 88(6):527-534.

Hypobaric Decompression Sickness Treatment Model.

INTRODUCTION: The Hypobaric Decompression Sickness (DCS) Treatment Model links a decrease in computed bubble volume from increased pressure (ΔP), increased oxygen (O2) partial pressure, and passage of time during treatment to the probability of symptom resolution [P(SR)]. The decrease in offending volume is realized in two stages: 1) during compression via Boyles law; and 2) during subsequent dissolution of the gas phase via the oxygen window. METHODS: We established an empirical model for the P(SR) while accounting for multiple symptoms within subjects. The data consisted of 154 cases of hypobaric DCS symptoms with ancillary information from tests on 56 men and 18 women. RESULTS: Our best estimated model is P(SR)=1/(1+exp(-(ln(ΔP)-1.510+0.795×AMB-0.00308×Ts)/0.478)), where ΔP is pressure difference (psid); AMB=1 if ambulation took place during part of the altitude exposure, otherwise AMB=0; and Ts is the elapsed time in minutes from the start of altitude exposure to recognition of a DCS symptom. DISCUSSION: Values of ΔP as inputs to the model would be calculated from the Tissue Bubble Dynamics Model based on the effective treatment pressure: ΔP=P2-P1|=P1×V1/V2-P1, where V1 is the computed volume of a bubble at low pressure P1 and V2 is computed volume after a change to a higher pressure P2. If 100% ground-level oxygen was breathed in place of air, then V2 continues to decrease through time at P2 at a faster rate.

The preferred walk to run transition speed in actual lunar gravity.

Quantifying the preferred transition speed (PTS) from walking to running has provided insight into the underlying mechanics of locomotion. The dynamic similarity hypothesis suggests that the PTS should occur at the same Froude number across gravitational environments. In normal Earth gravity, the PTS occurs at a Froude number of 0.5 in adult humans, but previous reports found the PTS occurred at Froude numbers greater than 0.5 in simulated lunar gravity. Our purpose was to (1) determine the Froude number at the PTS in actual lunar gravity during parabolic flight and (2) compare it with the Froude number at the PTS in simulated lunar gravity during overhead suspension. We observed that Froude numbers at the PTS in actual lunar gravity (1.39±0.45) and simulated lunar gravity (1.11±0.26) were much greater than 0.5. Froude numbers at the PTS above 1.0 suggest that the use of the inverted pendulum model may not necessarily be valid in actual lunar gravity and that earlier findings in simulated reduced gravity are more accurate than previously thought.