Cognition Effects of Low-Grade Hypoxia.

Introduction: The effects of low-grade hypoxia on cognitive function are reported in this paper. The study compared cognitive function during short exposures at four different altitudes.

Methods: Ninety-one subjects were exposed to simulated altitudes of ground level, 1524, 2438, and 3658 m (5000, 8000, and 12,000 ft) in the Brooks City-Base altitude pressure chamber in a balanced design.

Inferior g protection with an electrical muscle stimulation suit compared to a standard g-suit.

Background: At +1 Gz, electrical muscle stimulation (EMS) has been shown to increase systemic blood pressure similarly to a standard G-suit or lower body muscle straining. It was hypothesized that EMS might improve G protection at increased G levels.

Methods: An EMS suit was developed with electrodes over the calves, thighs, gluteal, and abdominal muscles.

Acceleration endurance with pressure breathing during G with and without a counterpressure vest.

Introduction: The purpose of this study was to test whether pressure breathing during G (PBC) without a counterpressure vest negatively influences G endurance or increases breathing fatigue during extended duration high-G exposures.

Methods: While using PBG, 10 subjects underwent 2 trials of +3 Gz exposures: once when wearing a counterpressure vest and once without. The exposures consisted of a relaxed, gradual G onset run until peripheral or central light loss, a straining rapid onset GC run to +6 Gz for 15 s, and a simulated aerial combat maneuver (SACM) G profile consisting of 10-s periods varying between +5 Gz and +9 Gz, during which subjects executed a hand-eye tracking task.

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.

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.

Partial pressure of nitrogen in breathing mixtures and risk of altitude decompression sickness.

Background: Many aircraft oxygen systems do not deliver 100% O2. Inert gases can be present at various levels. The purpose of this study was to determine the effect of these inert gas levels on decompression sickness (DCS).

Altitude decompression sickness susceptibility: influence of anthropometric and physiologic variables.

Introduction: There is considerable variability in individual susceptibility to altitude decompression sickness (DCS). The Air Force Research Laboratory Altitude DCS Research Database consists of extensive information on 2980 altitude exposures conducted with consistent procedures and endpoint criteria. We used this database to quantify the variation in susceptibility and determine if anthropometric and/or physiologic variables could be used to predict DCS risk.

Pressure breathing without a counter-pressure vest does not impair acceleration tolerance up to 9 G.

Introduction: This study was to determine whether safe and adequate G-protection by pressure breathing during G (PBG) could be maintained if the COMBAT EDGE counter-pressure vest were eliminated to ensure aircrew do not unnecessarily endure a possible in-flight discomfort or distraction.

Methods: Centrifuge exposures up to +9 Gz were completed by 11 subjects, including 5 F-15 aircrew, using PBG at 60 mmHg pressure with and without the counter-pressure vest. Additional G-exposures using pressures of 0, 30, and 45 mmHg were performed without the vest.

Central nervous system decompression sickness and venous gas emboli in hypobaric conditions.

Introduction: Altitude decompression sickness (DCS) that involves the central nervous system (CNS) is a rare but potentially serious condition. Identification of early symptoms and signs of this condition might improve treatment.

Methods: We studied data from 26 protocols carried out in our laboratory over the period 1983-2003; all were designed to provoke DCS in a substantial proportion of subjects.

Altitude decompression sickness at 7620 m following prebreathe enhanced with exercise periods.

Introduction: Over 80% altitude decompression sickness (DCS) was reported during a 4-h exposure with mild exercise to 7620 m (25,000 ft) without prebreathe. Prebreathe for more than 1 h would be necessary to reduce the DCS risk below 40%. Use of a single period of exercise to enhance prebreathe effectiveness has been successfully tested and used during some U-2 operations.

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.

The risk of altitude decompression sickness at 12,000 m and the effect of ascent rate.

Introduction: Loss of aircraft cabin pressurization can result in very rapid decompression rates. The literature contains reports of increased or unchanged levels of altitude decompression sickness (DCS) resulting from increasing the rate of decompression. We conducted two prospective exposure profiles to quantify the DCS risk at 12,192 m (40,000 ft), and to determine if there was a greater DCS hazard associated with a much higher rate of decompression than typically used during past DCS studies.

Muscle activity in pilots with and without pressure breathing during acceleration.

Background: Fighter pilots are frequently exposed to high acceleration (+Gz) forces during sorties. To counter these forces the pilots wear anti-G ensembles, use positive pressure breathing for G protection (PBG), and perform anti-G straining maneuvers (AGSMs). The purpose of this study was to analyze the muscle activity during sustained high G when no positive pressure breathing was used (control) compared with that during the use of PBG.

Pulmonary decompression sickness at altitude: early symptoms and circulating gas emboli.

Introduction: Pulmonary altitude decompression sickness (DCS) is a rare condition. 'Chokes' which are characterized by the triad of substernal pain, cough, and dyspnea, are considered to be associated with severe accumulation of gas bubbles in the pulmonary capillaries and may rapidly develop into a life-threatening medical emergency. This study was aimed at characterizing early symptomatology and the appearance of venous gas emboli (VGE).

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.

Heat stress effects for USAF anti-G suits with and without a counter-pressure vest.

Background: Aircrew have reported increased heat stress when wearing the USAF Combined Advanced Technology Enhanced Design G-Ensemble or COMBAT EDGE (CE). The perceived thermal burden has been attributed to the fact that CE includes an inflatable counter-pressure vest to ease the work of positive pressure breathing during G (PBG). This study compared the heat load of CE with that of the standard USAF anti-G system (STD) without the vest, and measured heat stress effects on G-tolerance in both suits.

Non-invasive measurement of pulmonary artery pressure in humans with simulated altitude-induced venous gas emboli.

Background: Decompression to simulated altitude causes super-saturation of nitrogen desolved in body tissues and can result in venous gas emboli (VGE), which are usually "cleared" in the lung. Large intravenous boli of air administered to animals increase pulmonary artery pressure (PAP), and may induce cross-over of gas to the left side of the heart (creating dangerous arterial gas emboli). This study was conducted to determine whether high VGE grades induced at simulated altitude elevate PAP in humans.