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.

Initial Investigation of a Grating Stimulus as a Visual Endpoint for Human Centrifuge Research.

INTRODUCTION: G tolerance has been widely assessed using Peripheral Light Loss (PLL), but this approach has several limitations and may lack sensitivity. The aim of this study was to investigate the use of a foveal visual endpoint for centrifuge research (Grating Loss; GL) and assess its repeatability, reliability, and usability with PLL as a reference.METHODS: A total of 11 subjects undertook centrifuge assessment. Gradual onset sessions (GOR; 0.1 G · s-1) measured both endpoints simultaneously and were performed twice, consisting of six determinations with anti-G suits activated (GOR-On) and six without (GOR-Off). Four determinations of each endpoint were also taken during rapid onset runs (ROR; 3 G · s-1). Usability was scored subjectively.RESULTS: The GL endpoint was reached 0.3-0.5 Gz lower than PLL with each endpoint correlating strongly in GOR-Off (r = 0.93), GOR-On (r = 0.95), and ROR (r = 0.86). The GL had excellent test-retest repeatability (intraclass correlation coefficient: GOR-Off/On = 0.99, ROR = 0.92) and low within-subject variability. Between-subject variance equaled PLL in all conditions. Subjective usability endpoint ratings were equal for all conditions.DISCUSSION: For the 11 individuals tested, the GL was a reliable, repeatable, and usable endpoint, with similar performance to PLL. GL may prove useful as a supplementary endpoint for human centrifuge research as a secondary data point or to reduce fatigue in repeated measurements. The foveal GL stimulus was lost before PLL, contrary to popular models of visual changes under +Gz.Britton J, Connolly DM, Hawarden DE, Stevenson AT, Harridge SDR, Green NDC, Pollock RD. Initial investigation of a grating stimulus as a visual endpoint for human centrifuge research. Aerosp Med Hum Perform. 2023; 94(12):894-901.

Physiological Effects of Centrifuge-Simulated Suborbital Spaceflight.

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.

A Novel Biopsychosocial Approach to Neck Pain in Military Helicopter Aircrew.

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.

Hypoxia-Like Events in UK Typhoon Aircraft from 2008 to 2017.

INTRODUCTION: Recent reports of in-flight, hypoxia-like events have prompted concern that aircraft life support systems (LSS) may not always provide effective altitude protection. An analysis was undertaken of hypoxia-like incidents reported in a UK front-line combat aircraft.METHODS: A search of the UK Aviation Safety Information Management System database identified all Typhoon Defense Air Safety Occurrence Reports (DASORs) notifying in-flight symptoms over the decade 20082017. Qualitative analysis focused on the event narrative, altitude profile, timeline, symptom description, sortie characteristics, LSS function, postflight engineering investigation, and training implications. The plausibility and likelihood of hypobaric hypoxia were assessed, and the probable cause of symptoms ascribed.RESULTS: There were 18 DASORs with notified symptoms of suspected in-flight hypoxia, 13 in solo pilots and 5 reports of symptoms affecting 7 of 10 aircrew in 2-seat aircraft. Two cases of probable hypoxia comprised one oxygen bottle failure and one mask-off cabin depressurization. In one report, hypoxia was assessed as plausible but unlikely, following birdstrike with failure of cabin pressurization during climb. Symptoms were explained by hyperventilation in 13 cases (65%) and twice by minor constitutional upset. Suspected hypoxia was managed by immediate selection of emergency oxygen and expedited descent in 10 of 18 occurrences (56%).CONCLUSIONS: Only 2 cases of probable hypoxia have been reported in over 150,000 Typhoon flying hours. The Typhoon LSS has provided effective altitude protection including during cases of cabin depressurization. Symptom occurrences in Typhoon are idiosyncratic and unrelated; hyperventilation probably accounts for two-thirds of reports.Connolly DM, Lee VM, McGown AS, Green NDC. Hypoxia-like events in UK Typhoon aircraft from 2008 to 2017. Aerosp Med Hum Perform. 2021; 92(4):257264.

Hemodynamic Responses and G Protection Afforded by Three Different Anti-G Systems.

BACKGROUND: UK Royal Air Force fast jet aircrew use three different anti-G systems, however, little objective comparison of the G protection they provide exists. The G-protection afforded by each system and associated hemodynamic responses were investigated.METHODS: Ten subjects performed centrifuge acceleration exposures using Mk-10 (S1) and Mk-4 (S2) five-bladder anti-G trousers (AGT) and full coverage AGT plus pressure breathing for G-protection (PBG; S3). Measurements of relaxed G tolerance (RGT), eye-level blood pressure (BPeye), lower body blood volume (LBV), stroke volume (SV) and total peripheral resistance (TPR) were made during gradual onset runs (GOR) and rapid onset runs (ROR). The subjective effort required to maintain clear vision at +7 and +8 Gz provided an indication of the protection provided by the system.RESULTS: All systems moderated decreases in SV and BPeye and increases in LBV under increased +Gz. S3 provided the greatest mean RGT during GOR (+6.2 Gz) and ROR (+6 Gz), reduced the effort required to maintain clear vision at up to +8 Gz, prevented venous pooling and afforded the greatest rise in TPR. The majority of indices revealed no difference between S1 and S2 although RGT during the ROR was greater with S2 (+0.25 Gz).DISCUSSION: S3 effectively prevented pooling of blood in the lower limbs under +Gz, despite the use of PBG, and offers an advantage over five-bladder AGT. Given the similarities of S1 and S2, it was unsurprising that the majority of indices measured were similar. The objective measurement of hemodynamic parameters provides useful information for comparing the G-protection provided by anti-G systems.Pollock RD, Firth RV, Storey JA, Phillips KE, Connolly DM, Green NDC, Stevenson AT. Hemodynamic responses and G protection afforded by three different anti-G systems. Aerosp Med Hum Perform. 2019; 90(11):925-933.

Aircrew Conditioning Programme Impact on +Gz Tolerance.

INTRODUCTION: Physical conditioning may improve aircrew performance during exposure to high +Gz acceleration, although few studies have directly assessed this. The present study investigated the effects of a 12-wk Aircrew Conditioning Programme (ACP) on markers of G tolerance. The ACP comprises aerobic and muscle strengthening exercise performed twice weekly and targets improved fitness and reduced injury risk.METHODS: There were 36 UK Royal Air Force and Royal Navy aircrew who volunteered; 17 performed the ACP (Ex) and 19 acted as a control group (Con). Centrifuge testing was performed before and after the intervention. Relaxed G tolerance (RGT) and straining G tolerance (SGT), which had the addition of muscle tensing, were assessed. G endurance was also determined via repeated simulated air combat maneuvers (SACMs). During these centrifuge runs a number of physiological variables were recorded.RESULTS: During the G profile to determine RGT, neither RGT, HR, nor blood pressure responses were affected by the ACP. During SGT profiles, a lower HR at a given +Gz (+5.5 Gz) level following the ACP was observed (Ex: pre 146.0 ± 4.4, post 136.9 ± 5.6 bpm; Con: pre 148.0 ± 3.2, post 153.1 ± 3.3 bpm). BP was maintained and there was a tendency toward an improved SGT. The ACP increased the proportion of individuals completing the number of SACM profiles, although no meaningful differences were found between groups in other variables.CONCLUSION: Overall the ACP has no negative effect on RGT, reduced the physiological strain associated with a given level of +Gz (during SGT), and tended to improve the ability to tolerate repeated Gz exposure.Slungaard E, Pollock RD, Stevenson AT, Green NDC, Newham DJ, Harridge SDR. Aircrew conditioning programme impact on +Gz tolerance. Aerosp Med Hum Perform. 2019; 90(9):764-773.

Content Validity of Level Two of the Royal Air Force Aircrew Conditioning Programme.

INTRODUCTION: The prevalence of flight-related neck pain in all Royal Air Force (RAF) aircrew is 66% and 70% in UK fast-jet aircrew. The RAF Aircrew Conditioning Programme (ACP) has been designed to enhance pilot performance through reducing fatigue and strain injuries, particularly to the neck. Content validity of the ACP was assessed to determine the appropriateness for delivery to aircrew. METHODS: Six international medical experts reviewed level two of the ACP, which is delivered to student aircrew who have completed basic instruction in cervical spine stability, core stability and initial technique instruction for strength training. Content validity on overall exercise approach (5 items) and specific exercise session (24 items) was rated on a 4-point Likert-type ordinal scale for Relevance and Simplicity. Four reviewers had experience of delivering an exercise program to aircrew. The item-content validity index (I-CVI) was the proportion of experts rating an item/exercise as acceptable (score 3-4) while protocol-CVI was the average I-CVI across items. RESULTS: Of the suggested exercise sessions, 20 reached an excellent I-CVI (1.00) for Relevance (4 reached acceptable I-CVI (0.83)), and 21 reached an excellent I-CVI (1.00) for Simplicity (3 reached acceptable I-CVI (0.83)). Protocol-CVI for the ACP was excellent for Relevance (0.90) and good for Simplicity (0.83). The need for sufficient supervision during the exercises was recommended for safe exercise execution and to maintain adherence. CONCLUSION: The ACP demonstrated excellent relevance for the target population. The aircrew require additional supervision with the more complex neck exercises to enhance simplicity with the ACP.Slungaard E, Green NDC, Newham DJ, Harridge SDR. Content validity of level two of the Royal Air Force Aircrew Conditioning Program. Aerosp Med Hum Perform. 2018; 89(10):896-904.

Incidence of G-Induced Loss of Consciousness and Almost Loss of Consciousness in the Royal Air Force.

INTRODUCTION: Exposure to sustained +Gz acceleration with inadequate G protection can result in G-induced loss of consciousness (G-LOC) or almost loss of consciousness (A-LOC). The UK Royal Air Force (RAF) last conducted a survey of G-LOC within their military aircrew in 2005 with interventions subsequently introduced. The aim of this study was to repeat the 2005 survey in order to evaluate the impact of those interventions. METHODS: An anonymous questionnaire requesting details of G-LOC and A-LOC events was mailed to all RAF pilots (N = 1878) and weapons systems operators (WSOs) (N = 473), irrespective of aircraft currently flown. RESULTS: The questionnaire was returned by 809 aircrew (34.4% response rate). There were 120 (14.8%) aircrew who reported at least one episode of G-LOC and 260 (32.2%) reported at least one episode of A-LOC. The reported prevalence of G-LOC in the previous 2005 survey was 20.1% (N = 454). There was an increased reporting of G-LOC in the Hawk, Tucano, and Grob Tutor aircraft, with 5 G-LOC and 19 A-LOC events reported in the Grob Tutor compared to none in 2005. DISCUSSION: The prevalence of reported G-LOC has decreased in the surveyed populations, which may be due to the introduction of centrifuge training, but also may be influenced by patterns of G exposure and other factors. Scope for further reduction remains through correct execution of the anti-G straining maneuver (AGSM) with centrifuge training early in flying training and use of a structured conditioning program to increase the general strength of muscles involved in the AGSM.Slungaard E, McLeod J, Green NDC, Kiran A, Newham DJ, Harridge SDR. Incidence of G-induced loss of consciousness and almost loss of consciousness in the Royal Air Force. Aerosp Med Hum Perform. 2017; 88(6):550-555.

Pneumopericardium and pneumomediastinum in a passenger on a commercial flight.

Pneumopericardium and pneumomediastinum are rare presentations seen most commonly in the context of chest trauma or mechanical ventilation. Here we present a case of a spontaneous pneumopericardium and pneumomediastinum, which occurred in a young man with a recent coryzal illness and multiple Valsalva maneuvers in flight. Although the etiology of pneumopericardium and pneumomediastinum are well described in the literature, possible acute risks to flight personnel have not been previously documented.

G-induced loss of consciousness: retrospective survey results from 2259 military aircrew.

INTRODUCTION: Prevalence of G-induced loss of consciousness (G-LOC) in the United Kingdom Royal Air Force (RAF) was found to be 19.3% in 1987. With the introduction of the Typhoon, a fourth generation aircraft, the prevalence of G-LOC has been re-assessed to determine the effectiveness of current G tolerance training. METHOD: A survey was sent to 4018 RAF aircrew, irrespective of their current role. Information was requested on G-LOC, role and aircraft type, experience, and attitudes toward G-LOC prevention. RESULTS: Responses were received from 2259 (56.2%) individuals, 882 (39%) of whom were current fast jet aircrew. At least one episode of G-LOC was reported by 20.1% of all respondents. In front line aircraft, prevalence of G-LOC among the 882 fast jet aircrew who responded was 6%. In the whole group, G-LOC was reported most commonly in aircrew under training (70.9%), and was most prevalent in training aircraft (77.4% of G-LOC events). At the time of the G-LOC, 64% of aircrew had less than 100 h total flying time. G-LOC was reported most frequently between +5 to +5.9 Gz, and "push-pull" maneuvers were associated with 31.3% of G-LOC events. Pulling G was not considered a problem by 50.6% of respondents, although over 80% recognized the value of flying currency, use of an anti-G suit, and physical fitness, and 55.6% felt that centrifuge training would be valuable. DISCUSSION: The prevalence of G-LOC in the RAF has changed little since 1987, and there remains considerable scope for aircrew education, particularly with the introduction of the Typhoon.

Head positioning and neck muscle activation during air combat.

INTRODUCTION: Specific mechanisms leading to acute neck injury in flight as a result of +Gz exposure remain unclear. In this study, head positions adopted by aircrew in air combat have been quantified, and the associated levels of cervical muscle activation have been determined. METHOD: Six fast jet aircrew subjects were instrumented with surface electromyography (EMG) electrodes, and activation potentials from neck erector spinae (ES) and sternocleidomastoid (SC) muscles were logged on a data recorder. EMG signal was normalized to preflight maximum voluntary contraction (MVC). All subjects flew a one-on-one air combat sortie in a Hawk T1 aircraft comprising at least four air combat engagements. In-cockpit video and +Gz acceleration were recorded. Time-synchronized analysis of video, EMG, and acceleration were conducted for head position and normalized muscle activation (%MVC). RESULTS: During air combat, the head was away from neutral for 68% of the time, predominantly in extension, or rotation plus extension. During neck extension under G, 40-80% MVC occurred in the ES: this was reduced by half when the canopy was used as a support. Similar activation occurred in the SC in neck extension plus rotation. The ES was activated at over 40% MVC for 25% of the engagement duration. Postsortie, 35% reduction in neck muscle strength occurred. CONCLUSIONS: Extreme neck extension +/- rotation is very common in air combat and is associated with high levels of muscle activation and fatigue. This information can be used to help devise targeted neck conditioning and positioning strategies in order to reduce injury risk.