Relative Severity of Human Performance Decrements Recorded in Rapid vs. Gradual Decompression.

INTRODUCTION: Cabin decompression presents a threat in high-altitude-capable aircraft. A chamber study was performed to compare effects of rapid (RD) vs. gradual decompression and gauge impairment at altitude with and without hypoxia, as well as to assess recovery.METHODS: There were 12 participants who completed RD (1 s) and Gradual (3 min 12 s) ascents from 2743-7620 m (9000-25000 ft) altitude pressures while breathing air or 100% O2. Physiological indices included oxygen saturation (SPo2), heart rate (HR), respiration, end tidal O2 and CO2 partial pressures, and electroencephalography (EEG). Cognition was evaluated using SYNWIN, which combines memory, arithmetic, visual, and auditory tasks. The study incorporated ascent rate (RD, gradual), breathing gas (air, 100% O2) and epoch (ground-level, pre-breathe, ascent-altitude, recovery) as factors.RESULTS: Physiological effects in hypoxic "air" ascents included decreased SPo2 and end tidal O2 and CO2 partial pressures (hypocapnia), with elevated HR and minute ventilation (V˙E); SPo2 and HR effects were greater after RD (-7.3% lower and +10.0 bpm higher, respectively). HR and V˙E decreased during recovery. SYNWIN performance declined during ascent in air, with key metrics, including composite score, falling further (-75% vs. -50%) after RD. Broad cognitive impairment was not recorded on 100% O2, nor in recovery. EEG signals showed increased slow-wave activity during hypoxia.DISCUSSION: In hypoxic exposures, RD impaired performance more than gradual ascent. Hypobaria did not comprehensively impair performance without hypoxia. Lingering impairment was not observed during recovery, but HR and V˙E metrics suggested compensatory slowing following altitude stress. Participants' cognitive strategy shifted as hypoxia progressed, with efficiency giving way to "satisficing," redistributing effort to easier tasks.Beer J, Mojica AJ, Blacker KJ, Dart TS, Morse BG, Sherman PM. Relative severity of human performance decrements recorded in rapid vs. gradual decompression. Aerosp Med Hum Perform. 2024; 95(7):353-366.

Variations on Ernsting's Post-Decompression Hypoxia Prevention Model.

INTRODUCTION: In the event of decompression using an isobaric differential cockpit pressurization system, oxygen concentration breathed pre-decompression must be greater than required for the given cockpit altitude in order to prevent hypoxia. The model for determining oxygen concentration requirements advanced by Dr. John Ernsting, when graphed against cockpit altitude, creates a hypoxia safety "notch" which has become a standard requirement for aircraft oxygen systems. Although variables in the Ernsting notch model are not fixed, they are often presented as such.METHODS: Model equations are presented to evaluate the effects of different cockpit pressurization, oxygen regulator PBA schedules, and changes to the physiological state of the aircrew.RESULTS: Increased cockpit differential pressure, regulator breathing pressure, and aircrew respiratory quotient decreased pre-decompression oxygen concentration requirements by up to 6%, eliminating the hypoxia safety "notch." Although effects were small, reducing alveolar carbon dioxide pressure decreased oxygen concentration requirements while reducing respiratory quotient increased oxygen concentration requirements. A 10-mmHg increase in the minimal oxygen hypoxia threshold increased the pre-decompression oxygen concentration requirement 8 to 12% depending on cockpit altitude.CONCLUSION: Variation in cockpit and regulator pressure schedules which stray outside the parameters used by Ernsting need to be independently calculated. During flight, an individual's physiological "notch" will be dynamic, wavering in response to changes in metabolic load, respiratory dynamics, and environmental conditions. Consideration of aircrew activity should be factored in when considering minimal oxygen concentration for pre-decompression hypoxia protection in the design of aircrew life support systems.Dart TS, Morse BG. Variations on Ernsting's post-decompression hypoxia prevention model. Aerosp Med Hum Perform. 2022; 93(2):99-105.

Pulmonary Effects from a Simulated Long-Duration Mission in a Confined Cockpit.

INTRODUCTION: A recent U-2 fatigue study, in which 10 subjects completed 2 simulated long-duration missions breathing either 100% oxygen or air in a hypobaric chamber, offered an opportunity to compare subjects' pulmonary function before and after remaining seated in a confined cockpit for 12 h. METHODS: In one U-2 mission configuration, the subject wore a full pressure suit and breathed aviator's breathing oxygen while chamber pressure was maintained at 4572 m (15,000 ft) above mean sea level. In the second mission configuration, subjects wore standard aircrew flight equipment and breathed air while chamber pressure was maintained at 2438 m (8000 ft) above mean sea level. Subjects' pulmonary function was assessed before and after the mission using four metrics: forced vital capacity, forced expiratory volume in 1 s, peak expiratory flow, and forced expiratory volume in 1 s/forced vital capacity ratio. RESULTS: Subjects showed significant declines for all four pulmonary metrics (2.7%, 6.4%, 13.9%, and 3.5%, respectively) after 12 h seated in the cockpit in both full pressure suit and aircrew flight equipment conditions. DISCUSSION: While the declines at both altitudes amounted to modest percentages of subjects' total pulmonary capacities, they emerged after a single, acute sedentary exposure and appear to be unrelated to the percentage of oxygen in the breathing gas. This might have operational implications in confined mission environments where physiological demands are interspersed with long periods of inactivity.Beer J, Dart TS, Fischer J, Kisner J. Pulmonary effects from a simulated long-duration mission in a confined cockpit. Aerosp Med Hum Perform. 2017; 88(10):952-957.

Cognitive Deterioration in Moderate and Severe Hypobaric Hypoxia Conditions.

BACKGROUND: Hypoxia continues to present risks in military aviation. Hypoxia symptoms include sensory and cognitive effects; of these, it is important to identify which components of operator performance are most vulnerable to hypoxia-induced decline in order to determine which sensory modality is most effective for alerting an impaired aviator of an imminent hypoxic episode. METHODS: A study was performed in a hypobaric chamber to characterize deterioration of cognitive performance under moderate (MH) and severe (SH) hypoxia conditions, culminating in subjects' inability to perform tasks. Subjects operated a synthetic workstation, performing multiple simultaneous tasks during hypobaric exposures equivalent to 5486 m (18,000 ft) MH and 7620 m (25,000 ft) SH ascents. Performance was compared across baseline, altitude exposure, and recovery periods within MH vs. SH altitude profiles. Ascents lasted until at least one of a list of termination criteria was met, at which point the chamber was returned to ground level pressure and the subject resumed workstation performance during recovery. RESULTS: SH conditions generated greater deficits than MH conditions, and these more severe effects hastened the termination of exposures (5 vs. 18 min mean duration, respectively). Workstation performance collapsed rapidly on SH exposure, with Mathematics and Auditory Monitoring tasks proving vulnerable to breakdown. In MH exposures, these tasks exhibited impaired accuracy (declining 11% and 9%, respectively) and speed, with declines in Auditory Monitoring lingering into recovery. DISCUSSION: The relative robustness of memory and visual monitoring vs. the vulnerability of mathematical and auditory processing suggest that care should be taken designing purely auditory cockpit hypoxia warning alerts.Beer JMA, Shender BS, Chauvin D, Dart TS, Fischer J. Cognitive deterioration in moderate and severe hypobaric hypoxia conditions. Aerosp Med Hum Perform. 2017; 88(7):617-626.

USAF treatment table 8: treatment for altitude decompression sickness.

INTRODUCTION: Altitude decompression sickness (DCS) has been treated with hyperbaric therapy since 1941. Treatment has essentially followed the diving DCS paradigm. Expanding space operations and higher flying, more remotely placed military aircraft have stimulated a re-examination of this paradigm. Can the oxygen and pressure-producing resources in these austere environs be reduced without sacrificing treatment efficacy? METHOD: A prospective series of 12 patients was treated with a new treatment table. USAF Treatment Table 8 (TT8) consists of 100% oxygen delivered at 2 ATA for four 30-min periods with intervening 10-min air breaks (a total oxygen dose of 2 h). Inclusion spanned 1985-1989. RESULTS: There were 10 patients who were treated 11 times for Type I altitude decompression sickness. Treatment was successful in 91%. There was one failure (a recurrence of elbow pain) requiring further therapy. Two patients were treated for Type II altitude decompression sickness. Treatment was successful in 50%. There was one failure (incomplete clearance of sensory deficits and weakness in the shoulder) requiring further therapy. CONCLUSION: Although TT8 had two failures, its successes suggest that a new protocol for the treatment of altitude decompression sickness is viable. In addition, its successes further suggest that a more extensive clinical trial is in order.