Cabin Altitude Research Articles

Exposure to Non-Steady-State Oxygen Is Reflected in Changes to Arterial Blood Gas Values, Prefrontal Cortical Activity, and Systemic Cytokine Levels.

Onboard oxygen-generating systems (OBOGSs) provide increased inspired oxygen (FiO2) to mitigate the risk of neurologic injury in high altitude aviators. OBOGSs can deliver highly variable oxygen concentrations oscillating around a predetermined FiO2 set point, even when the aircraft cabin altitude is relatively stable. Steady-state exposure to 100% FiO2 evokes neurovascular vasoconstriction, diminished cerebral perfusion, and altered electroencephalographic activity. Whether non-steady-state FiO2 exposure leads to similar outcomes is unknown. This study characterized the physiologic responses to steady-state and non-steady-state FiO2 during normobaric and hypobaric environmental pressures emulating cockpit pressures within tactical aircraft. The participants received an indwelling radial arterial catheter while exposed to steady-state or non-steady-state FiO2 levels oscillating ± 15% of prescribed set points in a hypobaric chamber. Steady-state exposure to 21% FiO2 during normobaria produced arterial blood gas values within the anticipated ranges. Exposure to non-steady-state FiO2 led to PaO2 levels higher upon cessation of non-steady-state FiO2 than when measured during steady-state exposure. This pattern was consistent across all FiO2 ranges, at each barometric condition. Prefrontal cortical activation during cognitive testing was lower following exposure to non-steady-state FiO2 >50% and <100% during both normobaria and hypobaria of 494 mmHg. The serum analyte levels (IL-6, IP-10, MCP-1, MDC, IL-15, and VEGF-D) increased 48 h following the exposures. We found non-steady-state FiO2 levels >50% reduced prefrontal cortical brain activation during the cognitive challenge, consistent with an evoked pattern of neurovascular constriction and dilation.

Literature Review on Air Conditioning Heat load Analysis of a Cabin

Abstract: Air conditioning system is necessary in automobile to maintain the comfort condition. Therefore, it is important to study transient response of vehicle under real driving conditions. The Heat Balance Method (HBM) is used for estimating the heating and cooling loads which develops inside the vehicle cabin. The Load Calculation of Automobile Air Conditioning System is calculated and presented. An hourly cooling load is calculated in Tirunelveli region with respect to its latitude. Tons of refrigeration required is also found out from the cooling load calculation and a review on cooling load calculation is also presented. This study gives overall cooling load and AC power consumption which can be used by HVAC engineers to design more efficient car AC systems. Only by knowing the cooling load and source of thermal load, we can develop intelligent system to reduce AC consumption. Environmental Control System (ECS) is a generic term used in aircraft industry for maintaining the required air temperature and pressure inside passenger and crew compartment. The real challenge for an ECS is to operate and supply adequate cooling over a wide range of ground and flight conditions in a most reliable and efficient manner. The most important aspect of ECS is to know the cabin heat loads during air cooling or air heating phases. A precise calculation of aircraft heat load would be a long process requiring detailed knowledge of the aircraft structure and of the quantities involved in the mechanism of heat pick up and interchange in the cabin. This paper describes a method that may be applied in calculating the heat load for any aircraft and calculations are shown for a typical light transport aircraft under the conditions that, the cabin altitude is maintained within 0 ft to 8000 ft (2438.4m) for the aircraft altitude of 0 ft to 25000ft (7620m). The system shall be capable of maintaining temperatures within 59°F to 75°F (15°C to 30°C).

Crush Injury and Simulated Flight Effects on Muscle Gene Expression in Female Mice.

Aeromedical evacuation provides critical care during long-distance transport of injured victims between medical facilities. Often, these victims sustain muscle trauma related to mechanical insults, such as crush. Understanding the effects of flight on injured muscle is important because the aircraft cabin represents an external environment with mild hypoxia-the cabin's altitude is 2,438 m instead of sea level. Because mild hypobaric hypoxia can alter gene expression in normal muscle and affect recovery patterns, it is beneficial to examine whether this type of hypoxia may also alter injury-related genes. The objective of this study was to verify the hypothesis that differential gene expression occurs in response to mild hypobaric hypoxia exposure in crush-injured muscle during two early recovery (preregeneration stage) time points. Twenty-four female mice were anesthetized, and the right gastrocnemius muscle underwent crush injury. Approximately 24 hours later, mice were exposed to normobaric normoxia or hypobaric hypoxia for 8-9 hours. After 32 or 48 hours of recovery, the mice were euthanized, and the right and left lateral gastrocnemius muscles were collected for microarray and bioinformatics analyses. The study hypothesis was verified. There were 353 highly upregulated, differentially expressed genes identified in the injured muscle compared to the uninjured muscle. Mid1 was upregulated in both pressure conditions regardless of injury status. There were 52 and 15 differentially expressed genes at 32 and 48 hours postinjury, respectively, in the hypobaric hypoxia-exposed, injured muscle compared to the normobaric normoxia-exposed, injured muscle. The macrophage gene Cd68 correlated with other leukocyte-related genes. These findings expand our understanding of the genetic changes that occur in muscle in response to a crush injury, including those related to the macrophage protein CD68. Nursing interventions addressing adequate functioning after crush muscle injury may need to consider the effects on Cd68 and its closely related genes. In addition, our results suggest a responsiveness of the gene Mid1 to flight-relevant hypobaric hypoxia. Changes in the expression of Mid1 may be appropriate in assessing the long-term health of flight crew members.

Cabin Pressure Altitude Effect on Acceleration Atelectasis After Agile Flight Breathing 60% Oxygen.

INTRODUCTION: A flight trial was conducted to determine whether breathing 60% oxygen during high performance flight maneuvers using contemporary pilot flight equipment induces atelectasis and to explore whether cabin altitude had any influence on the extent of atelectasis identified.METHODS: On 2 separate days, 14 male aircrew flew as passengers at High [14,500-18,000 ft (4420-5486 m)] and Low [4000-6000 ft (1219-1829 m)] cabin pressure altitude in a Hawk T Mk1 aircraft breathing 60% oxygen. Sorties comprised 16 maneuvers at +5 Gz, each sustained for 30 s. Lung volumes (spirometry), basal lung volume (electrical impedance tomography, EIT), and peripheral oxygen saturation during transition from hyperoxia to hypoxia (pulmonary shunt fraction) were measured in the cockpit immediately before (Pre) and after (Post) flight.RESULTS: Forced inspiratory vital capacity (FIVC) was significantly lower Postflight after High (-0.24 L) and Low (-0.38 L) sorties, but recovered to Preflight values by the fourth repeat (FIVC4). EIT-derived measures of FIVC decreased after High (-3.3%) and Low (-4.4%) sorties but did not recover to baseline by FIVC4. FIVC reductions were attributable to decreased inspiratory capacity. Spo₂ was lower Postflight than Preflight in High and Low sorties.DISCUSSION: Breathing 60% oxygen during flight results in a 3.8-4.9% reduction in lung volume associated with a small decrease in blood oxygenation and an estimated pulmonary shunt of up to 5.7%. EIT measures suggest persisting airway closure despite repeated FIVC maneuvers. There was no meaningful influence of cabin pressure altitude. The operational consequence of the observed changes is likely to be small.Tank H, Kennedy G, Pollock R, Hodkinson P, Sheppard-Hickey R-A, Woolford J, Green NDC, Stevenson A. Cabin pressure altitude effect on acceleration atelectasis after agile flight breathing 60% oxygen. Aerosp Med Hum Perform. 2023; 94(1):3-10.

Pressurization System on Aircraft Boeing 737-300F, Aircraft MSN: 28567 During Flight Hanoi to Bangkok: Problem Solving and Root Cause Analysis

The aircraft, with type Boeing 737-300 freighter, Serial Number: 28567, Flight number: TMG-918, with a flight route from Hanoi International (HAN) to Bangkok International airport (BKK) on the date of 12 April 2021, with a take-off time of 22.00 UTC and landing time 22.25 UTC, is operated by PT XYX Airlines on a non-schedule flight. After taking off from Hanoi to Bangkok (HAN – BKK), with an altitude of nearly 10.000 ft flight level, the aircraft got a problem with the pressurization system in auto mode (auto system), and the cabin altitude indicator was shown 10.000 ft; cabin rate altitude indication at 2000 – 300 ft/minute (in normal rate 200 – 300 ft/minute). The pilot was unable to control the pressurization system in the auto system; in this condition, the Pilot followed the procedure for selecting the pressurization system from auto mode to manual mode, and after that, the cabin altitude indicator suddenly was shown fluctuated or became unstable. After the pressurization system operates in Manual mode and all conditions control by the flight crew, the captain makes the decision to aircraft return to base (RTB) flight back to Hanoi International airport (HAN) and land safely at 22.25 UTC. The author wants to analyse the root cause of the pressurization system problem by using several methods, as per 5 whys, fishbone diagrams, and fault tree analysis. Then the author compares the root cause results of each method to take corrective and preventive actions to solve the problems. All these cases were in Reference to SDR Report Control Number: 012/SDR-YGH/TMG/IV/2021. The report submitted by PT.Tri M.G. Intra Asia Airlines on 12 April 2021 and the Flight Log Manual (FML) Page No: 03232, dated 12 April 2021. The purpose of this research is to identify the problem and determine the root cause of the problem's inability to control the pressurization system and make a plan for corrective action and preventive action; then, the team will implement the corrective action and preventive action. Quality Division will check and monitor the effectiveness of corrective and preventive action in three months. After that, the team &amp; Quality Division create the procedure and policy for the company standard. The author and team used the methodology 5 why (cause and effect diagram), Fishbone diagram (Ishikawa Diagram), and Fault Tree Analysis (FTA), and from each method will be found the root cause analysis. Then the author combines all root cause analyses to identify the problem and create problem-solving. The main result of this research was that the company was able to determine and implement the corrective action and preventive action for the uncontrollable problem pressurization system. The problem of the pressurization system that cannot be controlled causes the aircraft to return to base or cancel a flight to be expected not to happen again in all aircraft operated by PT. XYX company in the future.

High-altitude decompression strain can be reduced by an early excursion to moderate altitude while breathing oxygen

Recent observations suggest that development of venous gas emboli (VGE) during high-altitude flying whilst breathing hyperoxic gas will be reduced by intermittent excursions to moderate altitude. The present study aimed to investigate if an early, single excursion from high to moderate altitude can be used as an in-flight means to reduce high-altitude decompression strain. Ten healthy men were investigated whilst breathing oxygen in a hypobaric chamber under two conditions, once during a 90-min continuous exposure to a simulated cabin altitude of 24,000 ft (High; H) and once during 10 min at 24,000 ft, followed by 30 min at 15,000 ft and by 80 min at 24,000 ft (high–low–high; H–L–H). VGE scores were assessed by cardiac ultrasound, using a 6-graded scale. In H, VGE increased throughout the course of the sojourn at 24,000 ft to attain peak value [median (range)] of 3 (2–4) at min 90, just prior to descent. In H–L–H, median VGE scores were 0 throughout the trial, except for at min 10, just prior to the excursion to 15,000 ft, whence the VGE score was 1.5 (0–3). Thus, an early, single excursion from high to moderate cabin altitude holds promise as an in-flight means to reduce the risk of altitude decompression sickness during long-duration high-altitude flying in aircraft with limited cabin pressurization. Presumably, such excursion acts by facilitating the gas exchange in decompression bubbles from a predomination of nitrogen to that of oxygen.

Hyperoxic Effects on Decompression Strain During Alternating High and Moderate Altitude Exposures.

INTRODUCTION: In fighter aircraft, long-duration high-altitude sorties are typically interrupted by refueling excursions to lower altitude. In normoxia, excursions to moderate cabin altitude may increase the occurrence of venous gas emboli (VGE) at high cabin altitude. The aim was to investigate the effect of hyperoxia on VGE and decompression sickness (DCS) during alternating high and moderate altitude exposure.METHODS: In an altitude chamber, 13 healthy men were exposed to three different conditions: A) 90 min at 24,000 ft (7315 m) breathing normoxic gas (54% O₂; H-NOR); B) 90 min at 24,000 ft breathing hyperoxic gas (90% O₂; H-HYP); and C) three 30-min exposures to 24,000 ft interspersed by two 30-min exposures to 18,000 ft (5486 m) breathing 90% O₂ (ALT-HYP). VGE occurrence was evaluated from cardiac ultrasound imaging. DCS symptoms were rated using a scale.RESULTS: DCS occurred in all conditions and altogether in 6 of the 39 exposures. The prevalence of VGE was similar in H-NOR and H-HYP throughout the exposures. During the initial 30 min at 24,000 ft, the prevalence of VGE was similar in ALT-HYP as in the other two conditions, whereas, after the first excursion to 18,000 ft, the VGE score was lower in ALT-HYP than in H-NOR and H-HYP.DISCUSSION: Hyperoxic excursions from 24,000 to 18,000 ft reduces VGE occurrence, presumably by facilitating diffusive gas exchange across the bubble surfaces, increasing the share of bubble content contributed by oxygen. Still, the excursions did not abolish the DCS risk.Ånell R, Grönkvist M, Gennser M, Eiken O. Hyperoxic effects on decompression strain during alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2021; 92(4):223230.

Medical Events on Board Aircraft: Reducing Confusion and Misinterpretation in the Scientific Literature

INTRODUCTION: A topic in aviation medicine that attracts much attention from the scientific community as well as from the media concerns medical incidents on board commercial airline flights. It was noticed that many papers on the subject were written by authors whose specialization was outside that of aviation medicine and that they sometimes made basic errors concerning the application of scientific principles of the subject. A review was undertaken to determine if there were any patterns to the observed errors and, if so, to consider whether recommendations might be provided that could reduce their frequency.METHOD: A literature search was undertaken of MEDLINE using PubMed for English-only articles published between January 1, 1974, and February 1, 2019, employing the following search terms: air emergency, air emergencies, air passenger, air travel, aircraft, airline, aviation, commercial air, flight, and fitness to fly. In addition, other relevant papers held in the personal collection of the authors were reviewed.RESULTS: Many cases of misinterpretation or misunderstanding of aviation medicine were found, which could be classified into eight main categories: references; cabin altitude; pressure/volume relationship; other technical aspects of aircraft operations; regulations; medical events; in-flight deaths; and automated external defibrillator.CONCLUSION: Papers were identified as having questionable statements of fact or of emphasis. Such instances often appeared to result from authors being unfamiliar with the subject of aviation medicine and/or the commercial aviation environment. Simple steps could be taken by authors to reduce the future rate of such instances and recommendations are provided.Thibeault C, Evans AD. Medical events on board aircraft: reducing confusion and misinterpretation in the scientific literature. Aerosp Med Hum Perform. 2021; 92(4):265273.

Computer Simulation Research on Flow Field of SRM High Altitude Simulation Test

The simulation test of passive ejection type high-altitude solid rocket motor (SRM) was simulated by computer. For SRM passive ejector type high-altitude test, the tempering in the process of engine ignition and flameout poses a serious threat to the nozzle of the engine test device and circuit arrangement in the upper compartment. Using the N-S equation and Spalart-Allmaras model: numerical simulation on the flow structure of engine pressurize, decompression and stratochamber air phase in the testing process, and flow field of the diffuser and the cabin altitude simulation, analyzing the flow field structure of high-altitude experiment stages. The results showed the rough coincidence between the simulation curve and the measured data, with slight difference at the initial stage of air supply, the measured data and the simulation data reach the overall high degree of coincidence. During the process of building a compression and decompression, the adiabatic measures should be taken to prevent high temperature gas from damaging the engine, especially the nozzle and the head ring, in addition, the reasonable design of the nozzle contour surface can control gas separation tempering, reducing the influence caused by tempering. Stability of the flow field in the high altitude chamber of the pressure will not affect the engine.

Aircraft Cabin Pressurization and Concern for Non-Arteritic Anterior Ischemic Optic Neuropathy.

BACKGROUND: Cabin pressurization is the process by which aircraft maintain a comfortable and safe environment for passengers flying at high altitudes. At high altitudes, most patients can tolerate changes in pressurization; however, passengers at high risk of hypoxia may experience ischemic events. The purpose of this study was to evaluate variations in pressurization of commercial aircraft at cruising altitude and describe its relevance in relation to patients with non-arteritic anterior ischemic optic neuropathy (NAION).METHODS: Altimeters were used to measure altitude and cabin altitude at cruising altitude aboard 113 commercial flights, including 53 narrow-body and 60 wide-body aircraft.RESULTS: Cabin altitude ranged from 4232 ft to 7956 ft at cruising altitudes ranging from 30,000 ft to 41,000 ft. The mean cabin altitude for all flights was 6309 876 ft. Narrow-body aircraft had a significantly higher mean cabin altitude (6739 829 ft) compared to wide-body aircraft (5929 733 ft). For all flights, the mean cruising altitude was 35,369 2881 ft with narrow-body aircraft cruising at a lower altitude of 34,238 2389 ft compared to wide-body aircraft at 36,369 2925 ft. Newer generation aircraft had a mean cabin altitude of 6066 837 ft, which was lower than the mean cabin altitude of older aircraft (6616 835 ft).DISCUSSION: Innovation in flight design has offered the ability for aircraft to fly at greater altitudes while maintaining lower cabin altitude. Those at high risk of hypoxia-induced complications may consider aircraft type when air travel is required.Nazarali S, Liu H, Syed M, Wood T, Asanad S, Sadun AA, Karanjia R. Aircraft cabin pressurization and concern for non-arteritic anterior ischemic optic neuropathy. Aerosp Med Hum Perform. 2020; 91(9):715719.

Patients With Traumatic Brain Injury Transported by Critical Care Air Transport Teams: The Influence of Altitude and Oxygenation during Transport.

Traumatic brain injuries (TBIs) are life-threatening, and air transport of patients with TBI requires additional considerations. To mitigate the risks of complications associated with altitude, some patients fly with a cabin altitude restriction (CAR) to limit the altitude at which an aircraft's cabin is maintained. The goal of this study was to examine the effects of CARs on patients with TBI transported out of theater via Critical Care Air Transport Teams. We conducted a retrospective chart review of patients with moderate-to-severe TBI evacuated out of combat theater to Landstuhl Regional Medical Center via Critical Care Air Transport Teams. We collected demographics, flight and injury information, procedures, oxygenation, and outcomes (discharge disposition and hospital/ICU/ventilator days). We categorized patients as having a CAR if they had a documented CAR or maximum cabin altitude of 5,000feet or lower in their Critical Care Air Transport Teams record. We calculated descriptive statistics and constructed regression models to evaluate the association between CAR and clinical outcomes. We reviewed the charts of 435 patients, 31% of which had a documented CAR. Nineteen percent of the sample had a PaO2 lower than 80mm Hg, and 3% of patients experienced a SpO2 lower than 93% while in flight. When comparing preflight and in-flight events, we found that the percentage of patients who had a SpO2 of 93% or lower increased for the No CAR group, whereas the CAR group did not experience a significant change. However, flying without a CAR was not associated with discharge disposition, mortality, or hospital/ICU/ventilator days. Further, having a CAR was not associated with these outcomes after adjusting for additional flights, injury severity, injury type, or preflight head surgery. Patients with TBI who flew with a CAR did not differ in clinical outcomes from those without a CAR.

Assessment of portable oxygen concentrators in infants undergoing hypoxic challenge testing. A randomised controlled crossover trial.

Due to reduced PaO2 , aircrafts at cruising altitudes are pressurised to a cabin altitude of 2438m, equivalent to breathing FiO2 0.15. Portable oxygen concentrators (POCs) are approved for onboard oxygen supply with lack of evidence, especially in infants. We assessed POCs (continuous-flow cPOC vs. pulsed-flow pPOC) under simulated altitude conditions performing Hypoxic Challenge Testing (HCT). In a randomised controlled crossover trial, we included patients <1year born prematurely. In incidents of hypoxia (SpO2 ≤85%), oxygen was administered through POC. In patients with a positive hypoxia reversal, HCT was repeated 24hours later. If hypoxia occurred during the second testing, oxygen was given using the alternative POC. We randomised 26 patients; 22 patients received allocated intervention (4 dropped out). Mean gestational age 30.4weeks, mean corrected age 38.2weeks. Both POCs achieved immediate hypoxia reversal in all cases (SpO2 cPOC/pPOC 98%/99.4% (95%CI -2.91, 0.01)) without any adverse events. No significant difference was observed in patients with BPD. Both POCs generated sufficient oxygen to reverse HCT induced hypoxia. Although pPOCs are not recommended in paediatric age, our data suggest their effectiveness even in neonates without any associated adverse events. Future research on pPOCs safety is required to establish recommendations for their use.

Chronic decompression illness cognitive dysfunction improved with hyperbaric oxygen: a case report

Altitude chamber exposures are used for training to allow aircrew to experience their hypoxia and pressure effect symptoms. Decompression illness (DCI) can occur subsequent to altitude chamber training or in operational aircraft when the cabin altitude is at least 18,000 feet. Definitive emergent treatment is hyperbaric oxygen (HBO2) to decrease bubble size, dissipate excess nitrogen, hyperoxygenate tissue and reduce inflammation. A 27-year-old female underwent altitude chamber training to 25,000 feet. She developed tingling in both legs and left arm, headache, dizziness, malaise, then difficulty talking. She underwent two HBO2 treatments. Over the next 12 months, she had paresthesia, decreased memory and cognitive function similar to symptoms seen following traumatic brain injury. She was referred 14 months after the event for evaluation. Using pre-deployment Automated Neuropsychological Assessment Metrics (ANAM) and serial tests over 58 HBO2 treatments, the patient demonstrated near-return to her pre-deployment test scores.. The reason for HBO2 treatment was based on previous experience with chronic traumatic brain injury subjects where HBO2 improved outcome. The patient's chronic neurological symptoms mimicked chronic TBI. The patient was unique in that baseline cognitive tests existed that could be used to monitor her changes during the treatment series.

Evolution and Preservation of Venous Gas Emboli at Alternating High and Moderate Altitude Exposures.

INTRODUCTION: The evolution and preservation of venous gas emboli (VGE), as markers of decompression stress, were investigated during alternating high- and moderate altitude exposures, thus, simulating a fighter aircraft high-altitude flight, interrupted by refueling excursions to lower altitudes.METHODS: Eight men served as subjects during three normoxic simulated altitude exposures: High = 90 min at 24,000 ft; High-Low = three × 30 min at 24,000 ft, interspersed by two 30-min intervals at 15,000 ft; Low = 90 min at 15,000 ft. VGE scores were assessed by cardiac ultrasound, using a 5-grade scale. Respiratory nitrogen exchange was measured continuously using a modified closed-circuit electronic rebreather.RESULTS: Both High and High-Low induced persistent VGE, with no inter-condition difference either at rest [median (range): High: 1 (0-3), High-Low: 2 (0-3)] or during unloaded knee-bends [High: 3 (1-4), High-Low: 3 (0-4)], whereas VGE was considerably less in Low, both at rest [0 (0-1)] and during knee-bends [0 (0-2)]. In High-Low, VGE decreased temporarily during the 15,000-ft excursions, but resumed pre-excursion values upon return to 24,000 ft. During the final descent to ground level, VGE were more persistent following High-Low than High. In both High and Low, nitrogen was continuously washed out at altitude, whereas in High-Low, the washout at 24,000 ft was interrupted by nitrogen uptake at 15,000 ft.DISCUSSION: In normoxic conditions, long-duration flying at a cabin altitude of 24,000 ft is associated with substantial VGE occurrence, which is not abolished by intermittent excursions to a cabin altitude of 15,000 ft.Ånell R, Grönkvist M, Gennser M, Eiken O. Evolution and preservation of venous gas emboli at alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2020; 91(1):11-17.

Risks from Breathing Elevated Oxygen.

INTRODUCTION: Effects of breathing gas with elevated oxygen partial pressure (Po₂) and/or elevated inspired oxygen fraction (FIo₂) at sea level or higher is discussed. High FIo₂ is associated with absorption problems in the lungs, middle ear, and paranasal sinuses, particularly if FIo₂ > 80% and small airways, Eustachian tubes, or sinus passages are blocked. Absorption becomes faster as cabin altitude increases. Pulmonary oxygen toxicity and direct oxidative injuries, related to elevated Po₂, are improbable in flight; no pulmonary oxygen toxicity has been found when Po₂ < 55 kPa [418 Torr; 100% O₂ higher than 15,000 ft (4570 m)]. Symptoms with Po₂ of 75 kPa [520 Torr; 100% O₂ at 10,000 ft (3050 m)] were reported after 24 h and the earliest signs at Po₂ of 100 kPa (760 Torr, 100% O₂ at sea level) occurred after 6 h. However, treatment for decompression sickness entails a risk of pulmonary oxygen toxicity. Elevated Po₂ also constricts blood vessels, changes blood pressure control, and reduces the response to low blood sugar. With healthy lungs, gas transport and oxygen delivery are not improved by increasing Po₂. Near zero humidity of the breathing gas in which oxygen is delivered may predispose susceptible individuals to bronchoconstriction.Shykoff BE, Lee RL. Risks from breathing elevated oxygen. Aerosp Med Hum Perform. 2019; 90(12):1041-1049.

Interface design on cabin pressurization system affecting pilot's situation awareness: The comparison between digital displays and pointed displays

AbstractThe fundamental approach to improve pilots’ situation awareness (SA) would be to reorganize and restructure the presentation of information to fit pilot's cognitive model on the flight deck. This would facilitate pilots’ perception, understanding, and projection, hence making it easier to find the relevant targets. Sixty pilots (30 B‐737 pilots and 30 B‐777 pilots) participated in this study to investigate pilots’ SA while interacting with digital displays and moving pointed needle displays on cabin pressurization system. The results have shown significant differences on pilots’ perception, understanding, and overall SA between digital display and pointed display on the flight deck. Pilots significantly preferred the digital design cabin pressurization system, which is consistent with the proximity compatibility principle, and the position of the display on the center instrument panel is easily accessible to both pilots and does not require large head movements. There are some recommendations on the cabin pressurization design including the size of outflow valve position indicator, which should be significantly increased to provided saliency of information; color coding should be used on cabin altitude and differential pressure indicator to mark critical cabin altitude; and standard operating procedures shall include cabin altitude and differential pressure reading by pilot monitoring. The final and completed solution to the issues on the cabin pressurization system is to redesign the scattered pointed displays as integrated digital displays to fit the human‐centered principle.

Changes in Heart Rate and Rhythm During a Crossover Study of Simulated Commercial Flight in Older and Vulnerable Participants.

Objectives: Elderly passengers and those with preexisting disease are flying with increasing frequency and in-flight cardiac emergencies are a more frequent occurrence. We conducted a study of the physiological effects of simulated cabin altitudes and resulting lower oxygen levels among such passengers.Methods: We monitored 41 participants in a hypobaric chamber for 2 days, one at an equivalent of 7,000 feet altitude (regulations limit pressurization to 8,000 feet) for a 4–5 h simulated flight and the other at ground level using generalized least squares models to account for repeated measures. We evaluated associations between simulated flight, heart rate (HR) and measures of heart rate variability(HRV) (root mean square of successive R-R interval differences [RMSSD], standard deviation of normal-to-normal intervals [SDNN], high-frequency power [HF], and low-frequency power [LF]).Results: Heart rate was 3.9% (95% CI: 2.1, 5.8) higher on simulated flight days compared with non-flight days. The RMSSD was 10.6% (95% CI: −21.3, 0.05) lower during simulated flight days, indicative of reduced HRV. The remaining HRV measures were also lower on simulated flight days, though associations were less precise.Conclusion: We report that typical simulated flight conditions elicit changes in cardiac autonomic control, suggesting sympathetic arousal or reductions in parasympathetic drive. Our findings, if confirmed, may suggest the need for guidelines to protect vulnerable passengers including prescreens, symptom evaluation after air travel, the use of oxygen concentrators, and education about healthy behaviors in flight.

131 Patients With Traumatic Brain Injury Transported by Critical Care Air Transport Teams: The Influence of Altitude and Oxygenation During Transport

Moderate and severe traumatic brain injuries (TBI) are life-threatening, necessitating prompt evaluation and intervention. The safe air transport of patients with TBI to a higher level of care requires additional considerations. Patients with TBI are susceptible to complications related to altitude, including hypobaria and hypoxia. To mitigate this risk, some patients are transported with a cabin altitude restriction (CAR), which limits the altitude at which an aircraft’s cabin is maintained. The goal of this study was to examine the effects of altitude and oxygenation on patients with TBI transported via critical care air transport teams (CCATT) from a Role III medical treatment facility (MTF) to Landstuhl Regional Medical Center (LRMC). We conducted a retrospective chart review of patients with moderate to severe TBI evacuated out of combat theater via CCATT. Data abstractors collected data on demographics, flight information (including CAR), injury type, injury severity, pre-flight procedures, in-flight oxygenation, in-flight complications, and outcomes (mortality, hospital days, ICU days, and ventilator days). We calculated descriptive statistics and conducted Cox proportional hazards regression analyses to evaluate the association between CAR and clinical outcomes. We reviewed the CCATT charts of 435 patients with TBI transported via CCATT from a Role III MTF to LRMC. Eighty-one patients (19%) had a recorded CAR. About 19% of the sample had a PaO2 lower than 80 mmHg and 5% of patients experienced an in-flight SpO2 of 93% or lower. Flying without a CAR was not significantly associated with increased mortality or more hospital days, ICU days, or ventilator days. Further, having a CAR was not significantly associated with hospital days, ICU days, or ventilator days after adjusting for additional flights, injury severity, and injury type. Patients with moderate or severe TBI who were flown with a recorded CAR did not significantly differ from those who flew without a CAR in mortality rates, hospital days, ICU days, or ventilator days. Funding support: Air Force Medical Service (AFMS) Disclaimer: The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Air Force, Department of the Army, Department of Defense, or US Government.

Should I stay or should I go? COPD and air travel.

Chronic obstructive pulmonary disease (COPD) is a challenging respiratory problem throughout the world. Although survival is prolonged with new therapies and better management, the magnitude of the burden resulting from moderate-to-severe disease is increasing. One of the major aims of the disease management is to try to break the vicious cycle of patients being homebound and to promote an active lifestyle. A fundamental component of active daily life is, of course, travelling. Today, the world is getting smaller with the option of travelling by air. Air travel is usually the most preferred choice as it is easy, time saving, and relatively inexpensive. Although it is a safe choice for many passengers, the environment inside the aeroplane may sometimes have adverse effects on health. Hypobaric hypoxaemia due to cabin altitude may cause health risks in COPD patients who have limited cardiopulmonary reserve. Addressing the potential risks of air travel, promoting proactive strategies including pre-flight assessment, and education of COPD patients about the "fitness to fly" concept are essential. Thus, in this narrative review, we evaluated the current evidence for potential risks of air travel in COPD and tried to give a perspective for how to plan safe air travel for COPD patients.

Clinical Impact of Cabin Altitude Restriction Following Aeromedical Evacuation.

Combat medical care relies on aeromedical evacuation (AE). Vital to AE is the validating flight surgeon (VFS) who warrants a patient is "fit to fly." To do this, the VFS considers clinical characteristics and inflight physiological stressors, often prescribing specific interventions such as a cabin altitude restriction (CAR). Unfortunately, limited information is available regarding the clinical consequences of a CAR. Consequently, a dual case-control study (CAR patients versus non-CAR patients and non-CAR patients flown with a CAR versus non-CAR patients) was executed. Data on 1,114 patients were obtained from TRANSCOM Regulating and Command and Control Evacuation System and Landstuhl Regional Medical Center trauma database (January 2007 to February 2008). Demographic and clinical factors essentially showed no difference between groups; however, CAR patients appeared more severely injured than non-CAR patients. Despite being sicker, CAR patients had similar clinical outcomes when compared with non-CAR patients. In contrast, despite an equivocal severity picture, the non-CAR patients flown with a CAR had superior clinical outcomes when compared with non-CAR patients. It appeared that the CAR prescription normalized severely injured to moderately injured and brought moderately injured into a less morbid state. These results suggest that CAR should be seriously considered when evacuating seriously ill/injured patients.