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BACKGROUND: Unexplained physiological events (PE), possibly related to hypoxia and hyperventilation, are a concern for some air forces. Physiological monitoring could aid research into PEs, with measurement of arterial oxygen saturation (Spo2) often suggested despite potential limitations in its use. Given similar physiological responses to hypoxia and hyperventilation, the present study characterized the cardiovascular and respiratory responses to each.METHODS: Ten healthy subjects were exposed to 55 mins of normobaric hypoxia simulating altitudes of 0, 8000, and 12,000 ft (0, 2438, and 3658 m) while breathing normally and voluntarily hyperventilating (doubling minute ventilation). Respiratory gas analysis and spirometry measured end-tidal gases (PETo2 and PETco2) and minute ventilation. Spo2 was assessed using finger pulse oximetry. Mean arterial, systolic, and diastolic blood pressure were measured noninvasively. Cognitive impairment was assessed using the Stroop test.RESULTS: Voluntary hyperventilation resulted in a doubling of minute ventilation and lowered PETco2, while altitude had no effect on these. PETo2 and Spo2 declined with increasing altitude. However, despite a significant drop in PETo2 of 15.2 mmHg from 8000 to 12,000 ft, Spo2 was similar when hyperventilating (94.7 ± 2.3% vs. 93.4 ± 4.3%, respectively). The only cardiovascular response was an increase in heart rate while hyperventilating. Altitude had no effect on cognitive impairment, but hyperventilation did.DISCUSSION: For many cardiovascular and respiratory variables, there is minimal difference in responses to hypoxia and hyperventilation, making these challenging to differentiate. Spo2 is not a reliable marker of environmental hypoxia in the presence of hyperventilation and should not be used as such without additional monitoring of minute ventilation and end-tidal gases.Haddon A, Kanhai J, Nako O, Smith TG, Hodkinson PD, Pollock RD. Cardiorespiratory responses to voluntary hyperventilation during normobaric hypoxia. Aerosp Med Hum Perform. 2023; 94(2):59–65.

INTRODUCTION: Recently developed wearable monitoring devices can provide arterial oxygen saturation (Spo2) measurements, offering potential for use in aerospace operations. Pilots and passengers are already using these technologies, but their performance has not yet been established under conditions experienced in the flight environment such as environmental hypoxia and concurrent body motion.METHODS: An initial evaluation was conducted in 10 healthy subjects who were studied in a normobaric chamber during normoxia and at a simulated altitude of 15,000 ft (4572 m; 11.8% oxygen). Spo2 was measured simultaneously using a standard pulse oximeter and four wearable devices: Apple Watch Series 6; Garmin Fēnix 6 watch; Cosinusso Two in-ear sensor; and Oxitone 1000M wrist-worn pulse oximeter. Measurements were made while stationary at rest, during very slight body motion (induced by very low intensity cycling at 30 W on an ergometer), and during moderate body motion (induced by moderate intensity cycling at 150 W).RESULTS: Missed readings, defined as failure to record an Spo2 value within 1 min, occurred commonly with all wearables. Even with only very slight body motion, most devices missed most readings (range of 12–82% missed readings) and the rate was higher with greater body motion (range 18–92%). One device tended to under-report Spo2, while the other devices tended to over-report Spo2. Performance decreased across the devices when oxygenation was reduced.DISCUSSION: In this preliminary evaluation, the wearable devices studied did not perform to the same standard as a traditional pulse oximeter. These limitations may restrict their utility in flight and require further investigation.Hearn EL, Byford J, Wolfe C, Agyei C, Hodkinson PD, Pollock RD, Smith TG. Measuring arterial oxygen saturation using wearable devices under varying conditions. Aerosp Med Hum Perform. 2023; 94(1):42–47.

BACKGROUND: High-G acceleration experienced during launch and re-entry of suborbital spaceflights may present challenges for older or medically susceptible participants. A detailed understanding of the associated physiological responses would support the development of an evidence-based medical approach to commercial suborbital spaceflight.METHODS: There were 24 healthy subjects recruited into ‘younger’ (18-44 yr), ‘intermediate’ (45-64 yr) and ‘older’ (65-80 yr) age groups. Cardiovascular and respiratory variables were measured continuously during dynamic combinations of +Gx (chest-to-back) and +Gz (head-to-foot) acceleration that simulated suborbital G profiles for spaceplane and rocket/capsule platforms. Measurements were conducted breathing air and breathing 15% oxygen to simulate a cabin pressure altitude of 8000 ft.RESULTS: Suborbital G profiles generated highly dynamic changes in heart rate, blood pressure, and cardiac output. G-induced hypoxemia was observed, with minimum arterial oxygen saturation < 80% in a quarter of subjects. Increased age was associated with greater hypoxemia and reduced cardiac output responses but did not have detrimental cardiovascular effects. ECG changes included recurrent G-induced trigeminy in one individual. Respiratory and visual symptoms were common, with 88% of subjects reporting greyout and 29% reporting blackout. There was one episode of G-induced loss of consciousness (G-LOC).DISCUSSION: Suborbital acceleration profiles are generally well tolerated but are not physiologically inconsequential. Marked hemodynamic effects and transient respiratory compromise could interact with predisposing factors to precipitate adverse cardiopulmonary effects in a minority of participants. Medically susceptible individuals may benefit from expanded preflight centrifuge familiarization that includes targeted physiological evaluation in the form of a ‘G challenge test’.Smith TG, Pollock RD, Britton JK, Green NDC, Hodkinson PD, Mitchell SJ, Stevenson AT. Physiological effects of centrifuge-simulated suborbital spaceflight. Aerosp Med Hum Perform. 2022; 93(12):830–839.

INTRODUCTION: Women of child-bearing age make up an ever-increasing element of the aeromedical workforce in Australia and the UK. However, policy relating to the management of risk for pregnant employees in this sector is often missing or inadequate, with many women facing detrimental impacts on their career progression and financial well-being. For women who choose to continue flying, there is a lack of transparent guidance about the risks of flying within a helicopter in an aeromedical role. While grounding pregnant employees removes some risks, it is at the cost of autonomy and brings other adverse effects for the employee and employer. Updated reflections on this important topic will empower the audience to make informed discussions around pregnancy in aeromedical roles.TOPIC: Applying principles from literature surrounding commercial, military, and medical aviation, the risks to pregnant employees and the fetus are reviewed. These risks are complex and dynamic depending on gestation and underlying medical problems; thus, individualization of risk management is of key importance. In low-risk pregnancies, incapacitation risk is below the usual threshold adopted for safety-sensitive aviation activities. Based on available evidence we have quantified risks where possible and provide guidance on the relevant factors to consider in creating a holistic risk-management framework. The greatest unknown surrounds the risk from vibration, noise, and winching. These are reviewed and suggestions given for discussing this risk. We also highlight the need for policy providing acceptable nonflying options to remove the pressure to continue flying in pregnancy.APPLICATION: Based on a literature review we have generated a framework for understanding and assessing risk relating to pregnant employees in the aeromedical sector. This is intended for use by aeromedical organizations, pregnant employees, and their treating medical practitioners to provide rational and sensible policy and guidance.Storey HM, Austin J, Davies-White NL, Ransley DG, Hodkinson PD. Navigating pregnancy for employees in civilian rotary-wing aeromedicine. Aerosp Med Hum Perform. 2022; 93(12):866–876.

INTRODUCTION: Flight-related neck pain (FRNP) is a frequently reported musculoskeletal complaint among military helicopter aircrew. However, despite its prevalence and suspected causes, little is known of the underpinning pain mechanisms or the impact of neck pain on aircrews in-flight task performance. The biopsychosocial (BPS) approach to health, combined with the contemporary conceptualization of musculoskeletal pain, in which injury and pain are not necessarily synonymous, provides a relatively new holistic framework within which to consider the problem of FRNP in military helicopter aircrew. Combining these concepts, a new conceptual model is proposed to illustrate how biopsychosocial factors may influence pain perception, potentially affecting aircrews capacity to process information and, therefore, threatening in-flight task performance. Recommendations are made for considering the underlying pain mechanisms of FRNP to aid prognoses and guide the development of holistic evidence-based countermeasures for FRNP in military helicopter aircrew. Development of instruments able to measure psychosocial factors, such as self-efficacy and functional ability, validated in the military helicopter aircrew population, would assist this task.Vail RE, Harridge SDR, Hodkinson PD, Green NDC, Pavlou M. A novel biopsychosocial approach to neck pain in military helicopter aircrew. Aerosp Med Hum Perform. 2021; 92(5):333341.

BACKGROUND: Members of the public will soon be taking commercial suborbital spaceflights with significant Gx (chest-to-back) acceleration potentially reaching up to 6 Gx. Pulmonary physiology is gravity-dependent and is likely to be affected, which may have clinical implications for medically susceptible individuals.METHODS: During 2-min centrifuge exposures ranging up to 6 Gx, 11 healthy subjects were studied using advanced respiratory techniques. These sustained exposures were intended to allow characterization of the underlying pulmonary response and did not replicate actual suborbital G profiles. Regional distribution of ventilation in the lungs was determined using electrical impedance tomography. Neural respiratory drive (from diaphragm electromyography) and work of breathing (from transdiaphragmatic pressures) were obtained via nasoesophageal catheters. Arterial blood gases were measured in a subset of subjects. Measurements were conducted while breathing air and breathing 15 oxygen to simulate anticipated cabin pressurization conditions.RESULTS: Acceleration caused hypoxemia that worsened with increasing magnitude and duration of Gx. Minimum arterial oxygen saturation at 6 Gx was 86 1 breathing air and 79 1 breathing 15 oxygen. With increasing Gx the alveolar-arterial (A-a) oxygen gradient widened progressively and the relative distribution of ventilation reversed from posterior to anterior lung regions with substantial gas-trapping anteriorly. Severe breathlessness accompanied large progressive increases in work of breathing and neural respiratory drive.DISCUSSION: Sustained high-G acceleration at magnitudes relevant to suborbital flight profoundly affects respiratory physiology. These effects may become clinically important in the most medically susceptible passengers, in whom the potential role of centrifuge-based preflight evaluation requires further investigation.Pollock RD, Jolley CJ, Abid N, Couper JH, Estrada-Petrocelli L, Hodkinson PD, Leonhardt S, Mago-Elliott S, Menden T, Rafferty G, Richmond G, Robbins PA, Ritchie GAD, Segal MJ, Stevenson AT, Tank HD, Smith TG. Pulmonary effects of sustained periods of high-G acceleration relevant to suborbital spaceflight. Aerosp Med Hum Perform. 2021; 92(7):633641.

NEW FINDINGS What is the topic of this review? This review focuses on the main physiological challenges associated with exposure to acceleration in the Gx, Gy and Gz directions and to microgravity. What advances does it highlight? Our current understanding of the physiology of these environments and latest strategies to protect against them are discussed in light of the limited knowledge we have in some of these areas. ABSTRACT The desire to go higher, faster and further has taken us to environments where the accelerations placed on our bodies far exceed or are much lower than that attributable to Earth's gravity. While on the ground, racing drivers of the fastest cars are exposed to high degrees of lateral acceleration (Gy) during cornering. In the air, while within the confines of the lower reaches of Earth's atmosphere, fast jet pilots are routinely exposed to high levels of acceleration in the head-foot direction (Gz). During launch and re-entry of suborbital and orbital spacecraft, astronauts and spaceflight participants are exposed to high levels of chest-back acceleration (Gx), whereas once in space the effects of gravity are all but removed (termed microgravity, μG). Each of these environments has profound effects on the homeostatic mechanisms within the body and can have a serious impact, not only for those with underlying pathology but also for healthy individuals. This review provides an overview of the main challenges associated with these environments and our current understanding of the physiological and pathophysiological adaptations to them. Where relevant, protection strategies are discussed, with the implications of our future exposure to these environments also being considered.

BackgroundWith the “Artemis”-mission mankind will return to the Moon by 2024. Prolonged periods in space will not only present physical and psychological challenges to the astronauts, but also pose risks concerning the medical treatment capabilities of the crew. So far, no guideline exists for the treatment of severe medical emergencies in microgravity. We, as a international group of researchers related to the field of aerospace medicine and critical care, took on the challenge and developed a an evidence-based guideline for the arguably most severe medical emergency – cardiac arrest.MethodsAfter the creation of said international group, PICO questions regarding the topic cardiopulmonary resuscitation in microgravity were developed to guide the systematic literature research. Afterwards a precise search strategy was compiled which was then applied to “MEDLINE”. Four thousand one hundred sixty-five findings were retrieved and consecutively screened by at least 2 reviewers. This led to 88 original publications that were acquired in full-text version and then critically appraised using the GRADE methodology. Those studies formed to basis for the guideline recommendations that were designed by at least 2 experts on the given field. Afterwards those recommendations were subject to a consensus finding process according to the DELPHI-methodology.ResultsWe recommend a differentiated approach to CPR in microgravity with a division into basic life support (BLS) and advanced life support (ALS) similar to the Earth-based guidelines. In immediate BLS, the chest compression method of choice is the Evetts-Russomano method (ER), whereas in an ALS scenario, with the patient being restrained on the Crew Medical Restraint System, the handstand method (HS) should be applied. Airway management should only be performed if at least two rescuers are present and the patient has been restrained. A supraglottic airway device should be used for airway management where crew members untrained in tracheal intubation (TI) are involved.DiscussionCPR in microgravity is feasible and should be applied according to the Earth-based guidelines of the AHA/ERC in relation to fundamental statements, like urgent recognition and action, focus on high-quality chest compressions, compression depth and compression-ventilation ratio. However, the special circumstances presented by microgravity and spaceflight must be considered concerning central points such as rescuer position and methods for the performance of chest compressions, airway management and defibrillation.

Space medicine is fundamental to the human exploration of space. It supports survival, function and performance in this challenging and potentially lethal environment. It is international, intercultural and interdisciplinary, operating at the boundaries of exploration, science, technology and medicine. Space medicine is also the latest UK specialty to be recognized by the Royal College of Physicians in the UK and the General Medical Council. This review introduces the field of space medicine and describes the different types of spaceflight, environmental challenges, associated medical and physiological effects, and operational medical considerations. It will describe the varied roles of the space medicine doctor, including the conduct of surgery and anaesthesia, and concludes with a vision of the future for space medicine in the UK. Space medicine doctors have a responsibility to space workers and spaceflight participants. These ‘flight surgeons' are key in developing mitigation strategies to ensure the safety, health and performance of space travellers in what is an extreme and hazardous environment. This includes all phases from selection, training and spaceflight itself to post-flight rehabilitation and long-term health. The recent recognition of the speciality provides a pathway to train in this fascinating field of medicine and is a key enabler for the UK Government's commercial spaceflight ambition.

Objective. During launch and atmospheric re-entry in suborbital space flights, astronauts are exposed to high G-acceleration. These acceleration levels influence gas exchange inside the lung and can potentially lead to hypoxaemia. The distribution of air inside the lung can be monitored by Electrical Impedance Tomography (EIT). This imaging technique might reveal how high gravitational forces affect the dynamic behavior of ventilation and impair gas exchange resulting in hypoxaemia. Approach. We performed a trial in a long-arm centrifuge with ten participants lying supine while being exposed to +2, +4 and +6\,Gx (chest-to-back acceleration) to study the magnitude of accelerations experienced during suborbital spaceflight. Main results. First, the tomographic images revealed that the dorsal region of the lung emptied faster than the ventral region. Second, the ventilated area shifted from dorsal to ventral. Consequently, alveolar pressure in the dorsal area reached the pressure of the upper airways before the ventral area emptied completely. Finally, the upper airways collapsed and the end-expiratory volume increased. This resulted in ventral gas trapping with restricted gas exchange. Significance. At +4x changes in ventilation distribution varied considerably between subjects potentially due to variation in individual physical conditions. However, at +6\,Gx all participants were affected similarly and the influence of high gravitational conditions was pronounced.

Background The World Health Organization (WHO) recommends following up passengers following possible exposure to a case of infectious tuberculosis (TB) during air travel. This is known to be time consuming and difficult, and increasingly so with higher numbers of flights and passengers to and from countries with high TB endemicity each year. Objectives This paper systematically reviews the literature on contact tracing investigations following a plane exposure to active pulmonary TB. Evidence for in-flight transmission was assessed by reviewing the positive results of contacts without prior risk factors for latent TB. Data sources & Eligibility A search of Medline, EMBASE, BIOSIS, Cochrane Library and Database of Systematic Reviews was carried out, with no restrictions on study design, index case characteristics, duration of flight or publication date. Results Twenty-two papers were included, with a total of 469 index cases and 15 889 contacts. Only 26.4% of all contacts identified completed screening following exposure. The yield of either a single positive tuberculin skin test (TST) or a TST conversion attributable to in-flight transmission is between 0.19% (95%CI 0.13–0.27) and 0.74% (95%CI 0.61–0.88) of all contacts identified (0.00%, 95%CI 0.00–0.00 and 0.13%, 95%CI 0.00–0.61 in random effects meta-analysis). Limitations The main limitation is heterogeneity of reporting. Conclusions and implications of key findings The evidence behind the criteria for initiating investigations is weak and it has been widely demonstrated that active screening of contacts is labour intensive and unlikely to be effective. Based on our findings, formal comprehensive contact tracing may be of limited utility following a plane exposure.

INTRODUCTION Magnetic resonance imaging (MRI) brain scans of U.S. Air Force (USAF) altitude workers show increased white matter hyperintensities (WMH) that appear related to decompression stress. Relevant exposure thresholds are unknown. This MRI survey compares the white matter status of UK participants (UKP) in altitude chamber research and training with USAF cohorts having background and increased WMH. METHODS UKP (N = 20) comprised 13 research subjects and 7 military altitude chamber instructors ages 33 to 50 yr (16 men, 4 women), encompassing 1417 decompressions over a 15,000-ft (4572 m) pressure altitude (range 11-189; median 50). High resolution MRI reproduced USAF sequences and data were analyzed at the University of Maryland to validate comparison with age-matched USAF control (DOC; N = 85) and aerospace operational physiologist (PHY; N = 55) cohorts. RESULTS UKP data are dichotomous: 17 subjects (85%) had normal scans (total 19 WMH) and three outliers had excess (>15) WMH (total of 83 lesions). WMH were not associated with metrics of decompression history (total exposures, rapid decompression, pressure breathing, hypoxia familiarization, decompression sickness, or exposure intensity). Ranked data indicate that UKP have fewer WMH than PHY but not DOC. UKP outliers' excess WMH are attributable to past mild traumatic brain injury. CONCLUSIONS WMH in UKP are unrelated to subjects' low intensity (brief, infrequent) experience of altitude chamber decompression, encompassing occasional hypobaric hypoxia and mild decompression sickness, even with cumulative experience over many years. Such low intensity hypobaric exposure appears 'subthreshold' for promotion of WMH.Connolly DM, Lee VM, Hodkinson PD. White matter status of participants in altitude chamber research and training. Aerosp Med Hum Perform. 2018; 89(9):777-786.

Hypoxia-induced elevation in pulmonary artery pressure during air travel may contribute to the worldwide burden of in-flight medical emergencies. The pulmonary artery pressure response may be greater in older passengers, who are more likely to require flight diversion due to a medical event. Understanding these effects may ultimately improve the safety of air travel.We studied 16 healthy volunteers, consisting of a younger group (aged25 yr) and an older group (aged60 yr). Using a hypobaric chamber, subjects undertook a 2-h simulated flight at the maximum cabin pressure altitude for commercial airline flights (8000 ft; 2438 m). Higher and lower altitudes within the aeromedical range were also explored. Systolic pulmonary artery pressure (sPAP) was assessed by Doppler echocardiography.There was a progressive increase in sPAP which appeared to be biphasic, with a small initial increase and a larger subsequent rise. Overall, sPAP increased by 5±1 mmHg from baseline to 35±1 mmHg at 8000 ft, an increase of 18%. The sPAP response to 8000 ft was greater in the older group than the younger group.This study confirms that pulmonary artery pressure increases during simulated air travel, and provides preliminary evidence that this response is greater in older people. Advancing age may increase in-flight susceptibility to adverse pulmonary vascular responses in passengers, aircrew, and aeromedical patients.

Introduction Evidence supports the efficacy of incorporating select recognized aviation practices and procedures into healthcare. Incident analysis, debrief, safety brief, and crew resource management (CRM) have all been assessed for implementation within the UK healthcare system, a world leader in aviation-based patient safety initiatives. Mindful application, in which aviation practices are specifically tailored to the unique healthcare setting, show promise in terms of acceptance and long-term sustainment. Methods In order to establish British healthcare applications of aviation practices, a PubMed search of UK authored manuscripts published between 2005-2016 was undertaken using search terms 'aviation,' 'healthcare,' 'checklist,' and 'CRM.' A convenience sample of UK-authored aviation medical conference presentations and UK-authored patient safety manuscripts were also reviewed. Results A total of 11 of 94 papers with UK academic affiliations published between 2005-2016 and relevant to aviation modeled healthcare delivery were found. The debrief process, incident analysis, and CRM are the primary practices incorporated into UK healthcare, with success dependent on cultural acceptance and mindful application. CRM training has gained significant acceptance in UK healthcare environments. Discussion Aviation modeled incident analysis, debrief, safety brief, and CRM training are increasingly undertaken within the UK healthcare system. Nuanced application, in which the unique aspects of the healthcare setting are addressed as part of a comprehensive safety approach, shows promise for long-term success. The patient safety brief and aviation modeled incident analysis are in earlier phases of implementation, and warrant further analysis.Powell-Dunford N, Brennan PA, Peerally MF, Kapur N, Hynes JM, Hodkinson PD. Mindful application of aviation practices in healthcare. Aerosp Med Hum Perform. 2017; 88(12):1107-1116.

Purpose To investigate whether there is a differential response at rest and following exercise to conditions of genuine high altitude (GHA), normobaric hypoxia (NH), hypobaric hypoxia (HH) and normobaric normoxia (NN). Method Markers of sympathoadrenal and adrenocortical function (plasma normetanephrine [PNORMET], metanephrine [PMET], cortisol), myocardial injury (highly sensitive cardiac troponin T [hscTnT]) and function (N-terminal brain natriuretic peptide [NT-proBNP]) were evaluated at rest and with exercise under NN, at 3375 m in the Alps (GHA) and at equivalent simulated altitude under NH and HH. Participants cycled for 2 hours {15 minute warm-up, 105 minutes at 55% Wmax (maximal workload)} with venous blood samples taken prior (T0), immediately following (T120) and 2 hours post-exercise (T240). Results Exercise in the three hypoxic environments produced a similar pattern of response with the only difference between environments being in relation to PNORMET. Exercise in NN only induced a rise in PNORMET and PMET. Conclusion Biochemical markers that reflect sympathoadrenal, adrenocortical and myocardial responses to physiological stress demonstrate significant differences in the response to exercise under conditions of normoxia versus hypoxia while NH and HH appear to induce broadly similar responses to GHA and may therefore be reasonable surrogates.

Future spacecraft and crew habitats are anticipated to use a moderately hypobaric and hypoxic cabin atmosphere to reduce the risk of decompression sickness associated with extravehicular activity. This has raised concerns about potential hypoxia-mediated adverse effects on astronauts. Noninvasive technology for measuring tissue oxygen saturation (StO2) has been developed for clinical use and may be helpful in monitoring oxygenation during spaceflight. We conducted a technical evaluation of a handheld StO2 monitor during a series of parabolic flights, and then undertook a preliminary analysis of the data obtained during the flights from six individuals. The StO2 monitor operated normally in all gravity conditions. There was considerable variability in StO2 between and within individuals. Overall, transition to microgravity was associated with a small decrease in StO2 of 1.1±0.3%. This evaluation has established the basic function of this technology in microgravity and demonstrates the potential for exploring its use in space.

Starkey et al provide a thorough and welcomed analysis of injuries sustained during a large airborne parachuting exercise, focusing on the traumatic injuries sustained.[1][1] While the altitude of despatch in this paper is not quoted, it is assumed to be low altitude (less than 10 000 ft), which

Unpressurized aircraft routinely operate at altitudes where hypoxia may be of concern. A systematic literature review was conducted regarding hypoxic impairment, including mental functions, sensory deficits, and other pertinent research findings that may affect aviation-related duties at moderate altitude (8000 to 15,000 ft/2438 to 4572 m). The results of this review suggest that cognitive and psychomotor deficits may include learning, reaction time, decision-making, and certain types of memory. However, results are difficult to quantify and reliably reproduce. Inconsistency of results may be related to the subtlety of deficits compared to high altitude, differences among individual compensatory mechanisms, variation in methodology or sensitivity of metrics, presence or absence of exercise, heterogeneous neuronal central nervous system (CNS) response, and interindividual variation. Literature regarding hypoxic visual decrements is more consistent. Rod photoreceptors are more susceptible to hypoxia; visual degradation has been demonstrated at 4000 to 5000 ft (1219 to 1524 m) under scotopic and 10,000 ft (3048 m) under photopic conditions. Augmented night vision goggle resolution demonstrates more resilience to mild hypoxic effects than the unaided eye under starlight conditions. Hypocapnia enhances visual sensitivity and contrast discrimination. Hyperventilation with resulting respiratory alkalosis and cerebral vasoconstriction may confound both cognitive/ psychomotor and visual experimental results. Future research should include augmentation of validated neuropsychological metrics (surrogate investigational end points) with actual flight metrics, investigation of mixed gas formulations, contribution of hypocapnic vasoconstrictive effects on hypoxic performance, and further investigation into cellular- and systems-level approaches for heterogeneous CNS response. Research is also required into the contribution of mild-moderate hypoxia in human factors- and spatial disorientation-related mishaps.

Acute exposure to altitude principally encompasses aviation and space activities. These environments can be associated with very acute changes in pressure, oxygenation and temperature due to rates and magnitude of ascent that are not experienced in more chronic exposure such as mountaineering. The four key physiological challenges during acute exposure to altitude are: hypoxia (and hyperventilation), gas volume changes, decompression sickness and cold. The brief nature of aviation exposure to altitude provides little opportunity for acclimatisation, leading to markedly different effects when an individual is exposed to the same altitude acutely compared with an acclimatised individual climbing an 8000m (26 347ft) peak. Challenges such as hypobaric decompression sickness are not considered a hazard for chronic altitude exposure but are routine considerations for those flying to high altitude. Protective systems are essential for aircrew and passengers to survive and function during acute exposure to altitude.

SummaryObjectiveMechanical stress above the physiological range can profoundly influence articular cartilage causing matrix damage, changes to chondrocyte metabolism and cell injury/death. It has also been implicated as a risk factor in the development of osteoarthritis (OA). The mechanism of cell damage is not understood, but chondrocyte volume could be a determinant of the sensitivity and subsequent response to load. For example, in OA, it is possible that the chondrocyte swelling that occurs renders the cells more sensitive to the damaging effects of mechanical stress. This study had two aims: (1) to investigate the changes to the volume and viability of in situ chondrocytes near an injury to cartilage resulting from a single blunt impact, and (2) to determine if alterations to chondrocyte volume at the time of impact influenced cell viability.MethodsExplants of bovine articular cartilage were incubated with the fluorescent indicators calcein-AM and propidium iodide permitting the measurement of cell volume and viability, respectively, using confocal laser scanning microscopy (CLSM). Cartilage was then subjected to a single impact (optimally 100g from 10cm) delivered from a drop tower which caused areas of chondrocyte injury/death within the superficial zone (SZ). The presence of lactate dehydrogenase (LDH; an enzyme released following cell injury) was used to determine the effects of medium osmolarity on the response of chondrocytes to a single impact.ResultsA single impact caused discrete areas of chondrocyte injury/death which were almost exclusively within the SZ of cartilage. There appeared to be two phases of cell death, a rapid phase lasting ∼3min, followed by a slower progressive ‘wave of cell death’ away from the initial area lasting for ∼20min. The volume of the majority (88.1±5.99% (n=7) of the viable chondrocytes in this region decreased significantly (P