Cabin Altitude Research Articles

A Retrospective Cohort Analysis of Battle Injury Versus Disease, Non-Battle Injury-Two Validating Flight Surgeons' Experience.

Today, military combat medical care is the best it has ever been. Regulated U.S. Air Force aeromedical evacuation (AE) is one important reason. The Theater Validating Flight Surgeon (TVFS) validates that a patient is ready for flight. Two TVFSs' experiences, successively deployed in 2007, are the focus of this study. A unique operational worksheet used to manage the AE queue was used for approximately 5 months. A descriptive analysis of the worksheet's 1,389 patients found the majority male (94%), median age 30 years, and mostly Army enlisted soldiers (63%). U.S. civilians made up 9%. Battle Injury (55%) surpassed Disease, Non-Battle Injury (45%); most frequently seen were extremity injuries (73%) and cardiac illness (31%), respectively. Common to both Battle Injury and Disease, Nonbattle Injury were several TVFS prescriptions including no "remain overnights" (79%), head of bed elevation (78%), cabin altitude restriction (57%), no stops (44%), Critical Care Air Transport Team (27%), and supplemental oxygen (22%). This study is a first look at the TVFS experience and it offers up an initial accounting of the TVFS clinical and prescriptive practices. It is also a jumping point for future TVFS investigations using the available AE databases.

Pre-flight evaluation of adult patients with cystic fibrosis: a cross-sectional study

BackgroundAir travel may imply a health hazard for patients with cystic fibrosis (CF) due to hypobaric environment in the aircraft cabin. The objective was to identify pre-flight variables, which might predict severe hypoxaemia in adult CF patients during air travel.MethodsThirty adult CF-patients underwent pre-flight evaluation with spirometry, arterial oxygen tension (PaO2), pulse oximetry (SpO2) and cardiopulmonary exercise testing (CPET) at sea level (SL). The results were related to the PaO2 obtained during a hypoxia-altitude simulation test (HAST) in which a cabin altitude of 2438 m (8000 ft) was simulated by breathing 15.1% oxygen.ResultsFour patients fulfilled the criteria for supplemental oxygen during air travel (PaO2 HAST < 6.6 kPa). While walking slowly during HAST, another eleven patients dropped below PaO2 HAST 6.6 kPa. Variables obtained during CPET (PaO2 CPET, SpO2 CPET, minute ventilation/carbon dioxide output, maximal oxygen uptake) showed the strongest correlation to PaO2 HAST.ConclusionsExercise testing might be of value for predicting in-flight hypoxaemia and thus the need for supplemental oxygen during air travel in CF patients.Trial registration The study is retrospectively listed in the ClinicalTrials.gov Protocol Registration System: NCT01569880 (date; 30/3/2012)

An algebraic model of high-altitude aircraft decompression and emergency descent

An emergency descent maneuver initiated by pilots shortly after the onset of the decompression recognition was developed for subsonic, supersonic and hypersonic cruisers. Among other findings, the times when a passenger cabin is exposed to altitudes above 25,000 and 40,000 ft and the maximum cabin altitude reached are estimated. An airplane descent aerodynamic model was incorporated for high-speed and low-speed high-drag emergency descents. Airplane cabin atmosphere is assumed to be isothermal. The environmental atmosphere is simulated using the NLPAM nonlinear atmospheric model valid up to 47 geopotential kilometers. Rapid and slow decompressions at several discrete cruising altitudes ranging from 12 to 40 km and varying pilot reaction times in initiating the emergency descent were simulated. The main motivation for this work was to estimate times and altitudes a cabin reaches during depressurization for various flight conditions. This model can be utilized in optimizing the emergency-descent piloting techniques, calculating oxygen supplies, evaluating aeromedical factors, estimating harmful exposures to low pressures, and for other important high-altitude aircraft operations.

Cognitive Performance Effects of Bilastine 20 mg During 6 Hours at 8000 ft Cabin Altitude.

Bilastine is a new oral, second generation antihistamine used in the symptomatic treatment of allergic rhinoconjunctivitis and urticaria. It is considered a nonsedating antihistamine and might be recommended for use in pilots, pending research on the effects on flying-related performance under hypobaric conditions that prevail in an airliner. We assessed the effects of a single dose of bilastine 20 mg on alertness and complex task performance of healthy volunteers in a hypobaric chamber at 75.2 kPa (8000 ft/2438 m cabin altitude). In a randomized, double-blind, crossover study, 24 volunteers received a single dose of bilastine 20 mg, hydroxyzine 50 mg (active control), and placebo. Using the Vigilance and Tracking Task, Multi-Attribute Task Battery, and Stanford Sleepiness Scale, assessments were made before and up to 6 h after intake of the study medication. Bilastine 20 mg had no impairing effects on sleepiness levels, vigilance, or complex task performance for up to 6 h post-dose. Hydroxyzine 50 mg (active control) was associated with significant sleepiness and impaired performance across this time period, confirming the sensitivity of the tests. Bilastine 20 mg did not cause sleepiness or impaired performance on tasks related to flying. It is anticipated that a single dose of bilastine 20 mg will not affect flying performance. Bilastine may provide a safe therapeutic alternative for pilots suffering from allergic rhinitis or urticaria. Our findings might also have implications for the treatment of allergic disorders of personnel involved in other safety-sensitive jobs. Valk PJL, Simons R, Jetten AM, Valiente R, Labeaga L. Cognitive performance effects of bilastine 20 mg during 6 hours at 8000 ft cabin altitude. Aerosp Med Hum Perform. 2016; 87(7):622-627.

Complication Rates in Altitude Restricted Patients Following Aeromedical Evacuation.

Military aeromedical evacuation, especially that associated with the present Middle East conflict, is seeing increasing research. This ecological study initiates research into the validating flight surgeon by looking at cabin altitude restriction (CAR), arguably the validating flight surgeon's prescription with the highest patient-mission impact, and its association with postflight complications. CAR rates from January 2006 through February 2008 were determined from the U.S. Transportation Command Regulating and Command and Control Evacuation System database. Postflight complication rates-the rate of patients with postflight complications (PFC) and the postflight complications per 100 patients (PFC-100)-from January 2007 through June 2008 were calculated from the Landstuhl Regional Medical Center trauma database. CAR and complication rates were examined before, during, and after the authors' deployment. In addition, the relationship between CAR and postflight complication rates was investigated; as the rates were nonlinear, a Spearman correlation was performed. CAR rates during the authors' deployments were significantly up compared to the authors' predecessors or successors; their predecessors and successors did not differ statistically. Likewise, the PFC rate during the authors' deployments was significantly lower than that of the before or after time frames. Furthermore, a statistically significant inverse relationship between CAR and PFC rates (Spearman rho = -0.587) as well as CAR and PFC-100 rates (Spearman rho = -0.568) was demonstrated. CAR rate was inversely correlated to PFC and PFC-100 rates. This finding suggests that aggressive prescribing of CARs may have a salutary effect on postflight complication rates and bears further investigation.

AsMA Medical Guidelines for Air Travel: Fitness to Fly and Medical Clearances.

Medical Guidelines for Airline Travel provide information that enables healthcare providers to properly advise patients who plan to travel by air. Not everyone is fit to travel by air and physicians should advise their patients accordingly. They should review the passenger's medical condition, giving special consideration to the dosage and timing of any medications, contagiousness, and the need for special assistance during travel. In general, an individual with an unstable medical condition should not fly; cabin altitude, duration of exposure, and altitude of the destination airport are all considerations when recommending a passenger for flight.

Description of the AeroForm CO2-Based Tissue Expander and Assessment of the Effect of Pressurized Cabin Air Travel

Background: Tissue expanders are used in breast reconstruction after mastectomy to create a space for placement of permanent breast implants. The AeroForm™ Tissue Expander, developed by AirXpanders™ Inc., utilizes carbon dioxide released from an internal reservoir to inflate the expander. The released gas is contained within a high barrier material pre-formed into a breast shaped shell of the desired volume. During patient travel to higher altitude, a partially inflated expander will increase in volume proportionately to the gas fill volume. At volume levels near full, expansion is governed by the compliance of the inner gas barrier and silicone shell. Therefore, the assessment of the expander performance at altitude consists of the analysis of two operating regimes. The first regime is fill levels &amp;lt; 70% full where the implant, when exposed to cabin pressure, expands without significantly stressing the inner gas barrier. The second is fill levels ~&amp;gt;70% where the response of the inner gas barrier is important, both in terms of structural capability and determination of the volume increase. We assessed the impact of pressurized flight on expander performance in both operating regimes. Findings: The volume increase associated with altitude increase to 8000 feet (maximum cabin altitude per FAA) is typically within the range administered during post-operative fills of saline expanders. Although assessment must be conducted by a clinician, a patient can be typically expected to tolerate the increased volume with some minor discomfort, such as a feeling of tightness. At higher fill levels, the structural capability of shell has been demonstrated to withstand the additional pressure loading. At these fill levels, the expander does not expand as much, due to the structural restraint of the shell. To date, 7 subjects have flown with the expander in situ during clinical trials. All subjects were required to temporarily cease dosing up to two weeks prior. Flight travel was completed uneventfully and they reported discomfort levels ranging from none to moderate. The recommendation to cease dosing two weeks prior to flying was made to allow the expected 1 cc per day of CO2 permeation to occur, which will result in slight deflation to accommodate for the expansion of the CO2 when flying. As expected, subjects reported a sensation of pressure upon ascent which subsided on descent.

A Thermodynamic Analysis of Three and Four-Wheel Air Cycle Machines for Aeronautical Applications

Air cycle refrigeration is an attractive alternative that has been employed to provide aircraft cabin cooling. The primary function of the cabin air conditioning and pressurization system is to maintain an aircraft environment that will ensure safety and comfort of the passengers and crew during all fly operational conditions and provide adequate avionics cooling. The energy to drive these machines comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Usually, Air Cycle Machine (ACM) architecture includes mainly two compact air-to-air heat exchangers, a compressor and a expander with one or two expansion stages (called three-wheel or four-wheel configuration, respectively). In this context, this work focuses on a comparative thermodynamic study of three and four-wheels air-conditioning aircraft air cycle machines. This comparison will be performed taking account some design features that affect the ACM performance as: aircraft flight Mach number, cabin altitude, heat exchanger effectiveness and compressed bleed air conditions. Results showed that the second level of expansion from four-wheel air cycle machine increases its thermodynamic efficiency. As the amount of rejected heat in the secondary heat exchanger (SHX) is greater for the 4-wheel architecture, it is possible to have the same cooling effect than the 3-wheel machine but with a more compact SHX. Moreover, the implemented computational tool to solving the air cycle refrigeration mathematical model allows a better understanding of the ACM performance.

A Thermodynamic Study of Air Cycle Machine for Aeronautical Applications

This work focuses on a thermodynamic study of an air cycle machine (ACM) for aircraft air-conditioning purposes. The ACM configuration mainly includes two compact heat exchangers, a compressor and an expander. The energy to drive this machine comes from the compressed air bleed from the compressor of the aircraft propulsion turbine. Some design features that affect the ACM performance will be studied: aircraft Mach number, cabin altitude, cabin recirculated air temperature and the percentage of the turbine work absorbed by the exhaust fan. Results showed that the computational tool implemented to solve the ACM mathematical model allows an understanding of the air cycle machine performance when flight aircraft and cabin human comfort parameters are changed to attain an optimized aircraft environmental control system (ECS) design

Effect of Mild Hypoxia on Working Memory, Complex Logical Reasoning, and Risk Judgment

Mild hypoxia, typically equivalent to a pressurized aircraft cabin altitude of 2,438 m (8,000 ft), does not generally affect well-learned cognitive, vigilance, and perceptual-motor performance. Learning and novel and complex cognitive tasks involving multiple demands, however, might be impaired. This study evaluated whether complex cognition—as assessed by complex reasoning, multiple memory, and risk judgment—was impaired during mild hypoxia. Using a normobaric single-blind crossover design, 25 healthy nonsmoking male participants breathed normoxic (FiO2 = 0.206) or hypoxic air (FiO2 = 0.143) equivalent to 2,438 m for 2 hr and performed the following tasks at baseline, 30 min, and 90 min: (a) a complex logical reasoning task that assessed accuracy, response time, and a reasoning quality index for easy (nonconflict valid), difficult (nonconflict invalid), fairly difficult (conflict valid), and very difficult (conflict invalid) syllogisms; (b) a multiple memory test that assessed sentence judgment error, working memory span, and prospective memory; and (c) a simple vigilance psychomotor task that assessed the frequency and mean time that a disc was outside a target area and braking reaction time. They also completed a self-perceived risk judgement questionnaire near the end of each exposure. After 90 min, the mean change in working memory span for mild hypoxia (M = 0.9, SD = 4.6) was significantly less than for normoxia (M = 4.4, SD = 7.2). The reasoning quality index for conflict invalid syllogisms for mild hypoxia (M = 0.22, SD = 0.29) was marginally significantly less than for normoxia (M = 0.39, SD = 0.35). The chances of these findings occurring by chance cannot be discounted, but are small. Although this study suggests that mild hypoxia might impair working memory and complex logical reasoning involving difficult conflicts, further studies using more discerning tests of cognition are warranted.

Physiological consequences of rapid or prolonged aircraft decompression: evaluation using a human respiratory model.

Aircraft passengers and crew may be subjected to rapid or prolonged decompression to high cabin altitude when an aircraft develops a hole in the fuselage. The accepted measure of neurological damage due to the hypobaric hypoxia produced is the subjective 'time of useful consciousness' (TUC) measure, which is appropriate for pilots and crew who perform their given tasks, however, TUC is measured under conditions different than the decompression scenarios that passengers undergo in today's aircraft. Ernsting proposed that prolonged exposure to alveolar O2 pressures less than 30 mmHg (P30) causes neurological damage. The current study proposes that a critical value of arterial O2 saturation of 70% (S70) can be used in place of P30 and that this physiological measure is more suited for determination of hypobaric hypoxia in passengers. The study shows the equivalence of model-predicted P30 and S70 values in the Ernsting-decompression scenarios. The model is also used to predict values of these physiological measures in actual aircraft-decompression scenarios. The model can be used by others to quantitatively predict the degree of hypobaric hypoxia for virtually any kind of decompression scenario, including those where supplemental O2 is used. Use of this tool avoids the prohibitive costs of human-subject testing for new aircraft and the potential danger inherent in such tests.

Air Travel and Pneumothorax

The number of medical emergencies onboard aircraft is increasing as commercial air traffic increases and the general population ages, becomes more mobile, and includes individuals with serious medical conditions. Travelers with respiratory diseases are at particular risk for in-flight events because exposure to lower atmospheric pressure in a pressurized cabin at cruising altitude may result in not only hypoxemia but also pneumothorax due to gas expansion within enclosed pulmonary parenchymal spaces based on Boyle's law. Risks of pneumothorax during air travel pertain particularly to those patients with cystic lung diseases, recent pneumothorax or thoracic surgery, and chronic pneumothorax. Currently available guidelines are admittedly based on sparse data and include recommendations to delay air travel for 1 to 3 weeks after thoracic surgery or resolution of the pneumothorax. One of these guidelines declares existing pneumothorax to be an absolute contraindication to air travel although there are reports of uneventful air travel for those with chronic stable pneumothorax. In this article, we review the available data regarding pneumothorax and air travel that consist mostly of case reports and retrospective surveys. There is clearly a need for additional data that will inform decisions regarding air travel for patients at risk for pneumothorax, including those with recent thoracic surgery and transthoracic needle biopsy.

Flying with a Pneumothorax: A Model of Altitude Limitations Due to Gas Expansion

Pneumothorax(PTX) is considered an absolute contraindication to flying. Guidelines for recovery time are arbitrary and fail to acknowledge that some passengers with PTX have flown without incident. One concern is pleural air expansion, causing extrinsic lung compression, increased intrathoracic pressure, and the subsequent risk of tension pneumothorax. We used a model to investigate critical endpoints resulting from PTX expansion at altitude. Pneumothorax expansion was investigated using physiological simulation in the form of a mathematical model comprising elastic lungs, rib cage, hemidiaphragms, mediastinum, and abdomen. Compliance curves were assigned to each compartment based on published data. Cyclical muscle pressures drive normal ventilation. Initial sea-level pleural air volumes were set in the range from 10 to 60% pneumothorax. Pressures, volumes, and mediastinal shift were tracked during ascent to cruising altitude at 8000 ft (2438 m) and during cabin depressurization to 30,000 ft (9144 m). Pleural pressure oscillations during normal breathing became less negative during ascent. Positive pleural pressure was encountered at cabin altitude only if sea-level PTX exceeded 45%. Corresponding peak pressure gradient across the mediastinum did not exceed 5 cm H2O. Our results provide insight into the mechanics of pneumothorax expansion during flight. Sea-level PTX up to 45% would be tolerable in otherwise healthy persons if positive intrathoracic pressure is the dominant mechanism causing respiratory discomfort. Critical limitation in our model is more likely due to hypoxemia caused by altitude and pulmonary shunt from lung collapse. Studies of PTX tolerance to altitude should be conducted with caution.

Lung Volumes, Pulmonary Ventilation, and Hypoxia Following Rapid Decompression to 60,000 ft (18,288 m)

Rapid decompressions (RD) to 60,000 ft (18,288 m) were undertaken by six subjects to provide evidence of satisfactory performance of a contemporary, partial pressure assembly life support system for the purposes of flight clearance. A total of 12 3-s RDs were conducted with subjects breathing 56% oxygen (balance nitrogen) at the base (simulated cabin) altitude of 22,500 ft (6858 m), switching to 100% oxygen under 72 mmHg (9.6 kPa) of positive pressure at the final (simulated aircraft) altitude. Respiratory pressures, flows, and gas compositions were monitored continuously throughout. All RDs were completed safely, but one subject experienced significant hypoxia during the minute at final altitude, associated with severe hemoglobin desaturation to a low of 53%. Accurate data on subjects' lung volumes were obtained and individual responses post-RD were reviewed in relation to patterns of pulmonary ventilation. The occurrence of severe hypoxia is explained by hypoventilation in conjunction with unusually large lung volumes (total lung capacity 10.18 L). Subjects' lung volumes and patterns of pulmonary ventilation are critical, but idiosyncratic, determinants of alveolar oxygenation and severity of hypoxia following RD to 60,000 ft (18,288 m). At such extreme altitudes even vaporization of water condensate in the oxygen mask may compromise oxygen delivery. An altitude ceiling of 60,000 ft (18,288 m) is the likely threshold for reliable protection using partial pressure assemblies and aircrew should be instructed to take two deep 'clearing' breaths immediately following RD at such extreme pressure breathing altitudes.

Managing patients with stable respiratory disease planning air travel: a primary care summary of the British Thoracic Society recommendations

Air travel poses medical challenges to passengers with respiratory disease, principally because of exposure to a hypobaric environment. In 2002 the British Thoracic Society published recommendations for adults and children with respiratory disease planning air travel, with a web update in 2004. New full recommendations and a summary were published in 2011, containing key recommendations for the assessment of high-risk patients and identification of those likely to require in-flight supplemental oxygen. This paper highlights the aspects of particular relevance to primary care practitioners with the following key points: (1) At cabin altitudes of 8000 feet (the usual upper limit of in-flight cabin pressure, equivalent to 0.75 atmospheres) the partial pressure of oxygen falls to the equivalent of breathing 15.1% oxygen at sea level. Arterial oxygen tension falls in all passengers; in patients with respiratory disease, altitude may worsen preexisting hypoxaemia. (2) Altitude exposure also influences the volume of any air in cavities, where pressure x volume remain constant (Boyle's law), so that a pneumothorax or closed lung bulla will expand and may cause respiratory distress. Similarly, barotrauma may affect the middle ear or sinuses if these cavities fail to equilibrate. (3) Patients with respiratory disease require clinical assessment and advice before air travel to: (a) optimise usual care; (b) consider contraindications to travel and possible need for in-flight oxygen; (c) consider the need for secondary care referral for further assessment; (d) discuss the risk of venous thromboembolism; and (e) discuss forward planning for the journey.

Air transport monitoring

I read with interest the article by McMahon et al. 1. It is pleasing to see both research and publication in the field of transport medicine given their rightful place at the table of informed debate. The study presented has the potential to influence clinicians involved in transport medicine in a pragmatic way. In relation to this, I have one question: was there any difference in the limits of agreement when controlled for/analysed by: (a) type of aircraft used; and (b) altitude of the readings? The fixed wing aircraft quoted has the potential for a pressurised cabin altitude. Although the measurements are taken simultaneously, the non-linear change in cabin pressure with altitude/pressurisation may have affected the calibration differentially.

Altitude Exposures During Commercial Flight: A Reappraisal

Hypobaric hypoxia during commercial air travel has the potential to cause or worsen hypoxemia in individuals with pre-existing cardiopulmonary compromise. Knowledge of cabin altitude pressures aboard contemporary flights is essential to counseling patients accurately about flying safety. The objective of the study was to measure peak cabin altitudes during U.S. domestic commercial flights on a variety of aircraft. A handheld mountaineering altimeter was carried by the investigators in the plane cabin during commercial air travel and peak cabin altitude measured. The values were then compared between aircraft models, aircraft classes, and distances flown. The average peak cabin altitude on 207 flights aboard 17 different aircraft was 6341 +/- 1813 ft (1933 m +/- 553 m), significantly higher than when measured in a similar fashion in 1988. Peak cabin altitude was significantly higher for flights longer than 750 mi (7085 +/- 801 ft) compared to shorter flights (5160 +/- 2290 ft/1573 +/- 698 m). Cabin altitude increased linearly with flight distance for flights up to 750 mi in length, but was independent of flight distance for flights exceeding 750 mi. Peak cabin altitude was less than 5000 ft (1524 m) in 70% of flights shorter than 500 mi. Peak cabin altitudes greater than 8000 ft (2438 m) were measured on approximately 10% of the total flights. Peak cabin altitude on commercial aircraft flights has risen over time. Cabin altitude is lower with flights of shorter distance. Physicians should take these factors into account when determining an individual's need for supplemental oxygen during commercial air travel.

Endotracheal Tube Cuff Pressure before, during, and after Fixed-Wing Air Medical Retrieval

Background. Increased endotracheal tube (ETT) cuff pressure is associated with compromised tracheal mucosal perfusion and injuries. No published data are available for Australia on pressures in the fixed-wing air medical retrieval setting. Objective. After introduction of a cuff pressure manometer (Mallinckrodt, Hennef, Germany) at the Royal Flying Doctor Service (RFDS) Base in Dubbo, New South Wales (NSW), Australia, we assessed the prevalence of increased cuff pressures before, during, and after air medical retrieval. Methods. This was a retrospective audit in 35 ventilated patients during fixed-wing retrievals by the RFDS in NSW, Australia. Explicit chart review of ventilated patients was performed for cuff pressures and changes during medical retrievals with pressurized aircrafts. Pearson correlation was calculated to determine the relation of ascent and ETT cuff pressure change from ground to flight level. Results. The mean (± standard deviation) of the first ETT cuff pressure measurement on the ground was 44 ± 20 cmH2O. Prior to retrieval in 11 patients, the ETT cuff pressure was >30 cmH2O and in 11 patients >50 cmH2O. After ascent to cruising altitude, the cuff pressure was >30 cmH2O in 22 patients and >50 cmH2O in eight patients. The cuff pressure was reduced 1) in 72% of cases prior to take off and 2) in 85% of cases during flight, and 3) after landing, the cuff pressure increased in 85% of cases. The correlation between ascent in cabin altitude and ETT cuff pressure was r = 0.3901, p = 0.0205. Conclusions. The high prevalence of excessive cuff pressures during air medical retrieval can be avoided by the use of cuff pressure manometers. Key words: cuff pressure; air medical retrieval; prehospital

Pulmonary Artery Pressure Increases During Commercial Air Travel in Healthy Passengers

It is not known whether the mild hypoxia experienced by passengers during commercial air travel triggers hypoxic pulmonary vasoconstriction and increases pulmonary artery pressure in flight. Insidious pulmonary hypertensive responses could endanger susceptible passengers who have cardiopulmonary disease or increased hypoxic pulmonary vascular sensitivity. Understanding these effects may improve pre-flight assessment of fitness-to-fly and reduce in-flight morbidity and mortality. Eight healthy volunteers were studied during a scheduled commercial airline flight from London, UK, to Denver, CO. The aircraft was a Boeing 777 and the duration of the flight was 9 h. Systolic pulmonary artery pressure (sPAP) was assessed by portable Doppler echocardiography during the flight and over the following week in Denver, where the altitude (5280 ft/1610 m) simulates a commercial airliner environment. Cruising cabin altitude ranged between 5840 and 7170 ft (1780 to 2185 m), and mean arterial oxygen saturation was 95 +/- 0.6% during the flight. Mean sPAP increased significantly in flight by 6 +/- 1 mmHg to 33 +/- 1 mmHg, an increase of approximately 20%. After landing in Denver, sPAP was still 3 +/- 1 mmHg higher than baseline and remained elevated at 30 +/- 1 mmHg for a further 12 h. Pulmonary artery pressure increases during commercial air travel in healthy passengers, raising the possibility that hypoxic pulmonary hypertension could develop in susceptible individuals. A hypoxia altitude simulation test with simultaneous echocardiography ('HAST-echo') may be beneficial in assessing fitness to fly in vulnerable patients.

Aeromedical transfer of women at risk of preterm delivery in remote and rural Western Australia: Why are there no births in flight?

For more than three decades, women at imminent risk of preterm birth (PTB) in Western Australia have been transferred by small aircraft over long distances to the single tertiary level perinatal centre in Perth, with no known case of birth during the flight. We aimed to review recent experience to understand how aircraft travel may delay PTB. Retrospective observational study of 500 consecutive Royal Flying Doctor Service (RFDS) transfers of women at risk of preterm labour to the tertiary referral centre, from September 2007 to December 31, 2009. In-flight delivery, complications associated with transfer and factors associated with delay in preterm delivery. There were no in-flight deliveries or serious complications associated with the aeromedical transfer of these patients. In a multivariable Cox proportional hazards regression analysis, clinical factors in the presentation that were associated with a shorter time from landing to subsequent delivery included cervical dilatation ≥ 4 cm, ruptured membranes, gestational age > 32 weeks and nulliparity. The aircraft reaching an ambient altitude > 14,000 feet, or cabin altitude above zero (sea level), was associated with a delay in time from landing to delivery for women who were not in spontaneous preterm labour. Our findings add to a 30-year experience that women at risk of preterm labour do not deliver during aeromedical transfer. Ambient and cabin altitude of the aircraft were associated with an extension in the time to delivery after arrival. The mechanisms underpinning this effect warrant further investigation.