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

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 (Pco₂) in a pressurized spacesuit. We applied the methodology to characterize Pco₂ for the extravehicular mobility unit (EMU).

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

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.

A Systematic Review and Meta-Analysis of Decompression Sickness in Altitude Physiological Training.

A review of decompression sickness (DCS) cases associated with the NASA altitude physiological training (APT) program at the Johnson Space Center (JSC) motivated us to place our findings into the larger context of DCS prevalence from other APT centers. We reviewed JSC records from 1999 to 2016 and 14 publications from 1968 to 2004 about DCS prevalence in other APT programs. We performed a meta-analysis of 15 APT profiles (488 cases / 385,116 exposures).

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.

Venous Gas Emboli and Ambulation at 4.3 psia.

Introduction: Ambulation during extravehicular activity on Mars may increase the risk of decompression sickness through enhanced bubble formation in the lower body.

Hypotheses: walking effort (ambulation) before an exercise-enhanced denitrogenation (prebreathe) protocol at 14.7 psia does not increase the incidence of venous gas emboli (VGE) at 4.

Equivalent Air Altitude and the Alveolar Gas Equation.

It is expedient to use normobaric hypoxia (NH) as a surrogate for hypobaric hypoxia (HH) for training and research. The approach matches inspired oxygen partial pressure (P(I)o₂) at the desired altitude to that at site pressure (PB) by reducing the inspired fraction of oxygen (FIo₂) to <0.21 using the equation: PIo₂= (PB - 47) × FIo₂, where 47 mmHg is the vapor pressure of water at 37°C.

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.

Probability of hypobaric decompression sickness including extreme exposures.

Introduction: The fitting of probabilistic decompression sickness (DCS) models is more effective when data encompass a wide range of DCS incidence. We obtained such data from the Air Force Research Laboratory Altitude Decompression Sickness Research Database. The data are results from 29 tests comprising 708 human altitude chamber exposures (536 men and 172 women).

Protective mechanisms in hypobaric decompression.

Background: To reduce bubble formation and growth during hypobaric exposures, a denitrogenation or nitrogen "washout" procedure is performed. This procedure consists of prebreathing oxygen fractions as close to one as possible (oxygen prebreathe) prior to depressurization before ascending to the working altitude or low spacesuit pressures. During the NASA prebreathe reduction program (PRP), it was determined that the addition of a light arm exercise to short, individually designed, performance-based heavy exercise (dual cycle ergometry) during an abbreviated 2-h prebreathe (F1O2 - 1.

PH2O and simulated hypobaric hypoxia.

Some manufacturers of reduced oxygen (O2) breathing devices claim a comparable hypobaric hypoxia (HH) training experience by providing F1O2 < 0.209 at or near sea level pressure to match the ambient oxygen partial pressure (iso-PO2) of the target altitude. I conclude after a review of literature from investigators and manufacturers that these devices may not properly account for the 47 mmHg of water vapor partial pressure that reduces the inspired partial pressure of oxygen (P1O2), which is substantial at higher altitude relative to sea level.

Decompression sickness after air break in prebreathe described with a survival model.

Introduction: A perception exists in aerospace that a brief interruption in a 100% oxygen prebreathe (PB) by breathing air has a substantial decompression sickness (DCS) consequence. The consequences of an air break during PB on the subsequent hypobaric DCS outcomes were evaluated. The hypothesis was that asymmetrical and not symmetrical nitrogen (N2) kinetics was best to model the distribution of subsequent DCS survival times after PBs that included air breaks.

Air break during preoxygenation and risk of altitude decompression sickness.

Introduction: To reduce the risk of decompression sickness (DCS), current USAF U-2 operations require a 1-h preoxygenation (PreOx). An interruption of oxygen breathing with air breathing currently requires significant extension of the PreOx time. The purpose of this study was to evaluate the relationship between air breaks during PreOx and subsequent DCS and venous gas emboli (VGE) incidence, and to determine safe air break limits for operational activities.

Critique of the equivalent air altitude model.

The adverse effects of hypoxic hypoxia include acute mountain sickness (AMS), high altitude pulmonary edema, and high altitude cerebral edema. It has long been assumed that those manifestations are directly related to reduction in the inspired partial pressure of oxygen (P(I)O2). This assumption underlies the equivalent air altitude (EAA) model, which holds that combinations of barometric pressure (P(B)) and inspired fraction of O2 (F(I)O2) that produce the same P(I)O2 will result in identical physiological responses.

A latent class model to assess error rates in diagnosis of altitude decompression sickness.

Background: Prospective testing of denitrogenation protocols to reduce the risk of decompression sickness (DCS) in astronauts requires pre-defined accept and reject criteria. We assume that the end-point of a test, the presence or absence of signs and symptoms attributable to DCS, is unequivocal. However, diagnosis of DCS is not perfect, nor is there is a gold standard to assess diagnosis error rates.

Age affects severity of venous gas emboli on decompression from 14.7 to 4.3 psia.

Introduction: Variables that define who we are, such as age, weight and fitness level influence the risk of decompression sickness (DCS) and venous gas emboli (VGE) from diving and aviation decompressions. We focus on age since astronauts that perform space walks are approximately 10 yr older than our test subjects. Our null hypothesis is that age is not statistically associated with the VGE outcomes from decompression to 4.

Improved pulmonary function in working divers breathing nitrox at shallow depths.

Introduction: There is limited data about the long-term pulmonary effects of nitrox use in divers at shallow depths. This study examined changes in pulmonary function in a cohort of working divers breathing a 46% oxygen enriched mixture while diving at depths less than 12 m.

Methods: A total of 43 working divers from the Neutral Buoyancy Laboratory (NBL), NASA-Johnson Space Center completed a questionnaire providing information on diving history prior to NBL employment, diving history outside the NBL since employment, and smoking history.