BACKGROUND: It remains unknown whether brain perfusion is preserved and mirrored by middle cerebral blood flow velocity (MCA BFV) during prolonged changes in body posture. Herein, we examined the impact of sustained (180 min) 30° head-up (HUT) and head-down (HDT) tilt on brain perfusion, as determined by MCA BFV and blood flow in the extracranial arteries.METHODS: In 10 healthy male subjects, arterial diameters, BFVs, and blood flows were determined in the left internal carotid (ICA) and vertebral (VA) arteries using duplex Doppler ultrasound in supine rest, and 5, 20, 60, 120, and 180 min following 30° HUT and HDT. MCA BFV was recorded throughout with transcranial Doppler ultrasound.RESULTS: ICA as well as VA diameters and blood flows were unaltered during HUT. Likewise, brain blood flow and MCA BFV were preserved with HUT. In the HDT protocol, ICA and VA diameters were gradually increased, although ICA, VA, and brain blood flows were preserved. MCA BFV was progressively reduced during HDT. In addition, MCA BFV was positively associated with ICA BFV (β = 0.9) and negatively associated with ICA diameter (β = –125.5). MCA BFV was positively associated with brain blood flow during HUT (β = 0.2) but not HDT.CONCLUSIONS: Brain perfusion is preserved whereas MCA BFV is progressively decreased and associated with extracranial arterial BFV during sustained 30° HDT. Therefore, MCA BFV may not be a surrogate of brain perfusion in conditions including prolonged HDT.Montero D, Rauber S. Brain perfusion and arterial blood flow velocity during prolonged body tilting. Aerosp Med Hum Perform. 2016; 87(8):682–687.

BACKGROUND: Bed rest studies have shown that high load (HL) resistance training can mitigate the loss of muscle size and strength during musculoskeletal unloading; however, not all individuals are able to perform HL resistance exercise. Blood flow restricted (BFR) resistance exercise may be a novel way to prevent maladaptation to unloading without requiring HL exercise equipment. This study evaluated the muscular training adaptations to HL and BFR resistance training during unilateral lower limb suspension (ULLS), a human limb unloading model. ULLS allows for evaluation of exercise training in both weight-bearing and nonweight-bearing legs within the same individual.METHODS: There were 13 participants who completed 25 d of ULLS and were counterbalanced to: 1) HL, N = 6; or 2) BFR, N = 7, training groups. During ULLS, HL and BFR performed unilateral leg press and heel raise exercise (3 d/wk).RESULTS: In weight-bearing legs, both HL and BFR increased knee extensor muscle cross-sectional area (CSA) and strength. In nonweight-bearing legs, knee extensor CSA and strength increased only in HL and decreased with BFR.CONCLUSION: HL and BFR resistance exercise were both effective exercise programs for the weight-bearing leg. However, BFR exercise was not as effective as HL resistance exercise in the nonweight-bearing leg. These data show that exercise that improved muscle CSA and strength in ambulatory weight-bearing conditions was not sufficient to maintain muscle function during unloading. For the preservation of muscle CSA and strength, BFR exercise should be considered an adjunct but not a primary exercise countermeasure for future space missions.Hackney KJ, Downs ME, Ploutz-Snyder L. Blood flow restricted exercise compared to high load resistance exercise during unloading. Aerosp Med Hum Perform. 2016; 87(8):688–696.

INTRODUCTION: Despite significant investment into the development and improvement of military helicopter seat systems, military aviators continue to report seat system related pain and discomfort during prolonged missions.METHODS: Using a factorial repeated measures design, 15 healthy subjects completed the study, in which focal pressure was applied to two locations on the sitting surfaces of the body (ischial tuberosity and middle of the posterior thigh). Pressure was applied using a purpose-built pressure application system allowing subjects to sit in a position mimicking the sitting position in the UH-60 Black Hawk helicopter. The researchers measured pain using the Category Partitioning Scale and McGill Pain Questionnaire and vascular function using dynamic infrared thermography in the lower leg and pulse oximetry at the great toe. Data were collected before and during a 10-min application of focal pressure applied to either the ischial tuberosity or middle of the posterior thigh and at two different pressure magnitudes (36 or 44 kPa).RESULTS: We found that during a 10-min pressure application, superficial skin temperature increased by 0.61°C, suggesting a decreased venous return during pressure application. We found that lower extremity blood oxygenation remained unchanged during pressure application. Subjects’ reported pain increased during pressure application and was greater with 44 kPa of application compared to 36 kPa.DISCUSSION: These results support the hypothesis that locally high pressure creates symptoms of discomfort and paresthesia. Research examining the effects of local pressure application on physiological and neurological function is needed.Games KE, Lakin JM, Quindry JC, Weimar WH, Sefton JM. Local pressure application effects on discomfort, temperature, and limb oxygenation. Aerosp Med Hum Perform. 2016; 87(8):697–703.

BACKGROUND: Climbing and trekking at altitude are common recreational and military activities. Physiological effects of altitude are hypoxia and hyperventilation. The hyperventilatory response to altitude may cause respiratory muscle fatigue and reduce sustained submaximal exercise. Voluntary isocapnic hyperpnea respiratory muscle training (VIHT) improves exercise endurance at sea level and at depth. The purpose of this study was to test the hypothesis that VIHT would improve exercise time at altitude [3600 m (11,811 ft)] compared to control and placebo groups.METHODS: Subjects pedaled an ergometer until exhaustion at simulated altitude in a hypobaric chamber while noninvasive arterial saturation (S_ao₂), ventilation (V_E), and oxygen consumption (Vo₂) were measured.RESULTS: As expected, S_ao₂ decreased to 88 ± 4% saturation at rest and to 81 ± 2% during exercise, and was not affected by VIHT. VIHT resulted in a 40% increase in maximal training V_E compared to pre-VIHT. Exercise endurance significantly increased 44% after VIHT (P = <0.001). Vo₂ (30 ± 3 ml · kg⁻¹ · min⁻¹) and heart rate (177 ± 10 bpm) did not change during exercise and were not affected by VIHT (P = 0.531). Pre-VIHT V_E increased 21–27% during the initial 12 min of exercise, after which it decreased 17% at 17.7 ± 6.0 min. V_E at altitude post-VIHT increased more (49%) for longer (21 min) and decreased less (11% at 25.4 ± 6.7 min).DISCUSSION: VIHT improved exercise time at altitude and sustained V_E. This suggests that VIHT reduced respiratory muscle fatigue and would be useful to trekkers and military personnel working at altitude.Helfer S, Quackenbush J, Fletcher M, Pendergast DR. Respiratory muscle training and exercise endurance at altitutde. Aerosp Med Hum Perform. 2016; 87(8):704–711.

INTRODUCTION: Previous studies found that aircraft maintenance workers may be exposed to organophosphates in hydraulic fluid and engine oil. Studies have also illustrated a link between long-term low-level organophosphate pesticide exposure and depression.METHODS: A questionnaire containing the Patient Health Questionnaire 8 depression screener was e-mailed to 52,080 aircraft maintenance workers (with N = 4801 complete responses) in a cross-sectional study to determine prevalence and severity of depression and descriptions of their occupational exposures.RESULTS: There was no significant difference between reported depression prevalence and severity in similar exposure groups in which aircraft maintenance workers were exposed or may have been exposed to organophosphate esters compared to similar exposure groups in which they were not exposed. However, a dichotomous measure of the prevalence of depression was significantly associated with self-reported exposure levels from low (OR: 1.21) to moderate (OR: 1.68) to high exposure (OR: 2.70) and with each exposure route including contact (OR: 1.68), inhalation (OR: 2.52), and ingestion (OR: 2.55). A self-reported four-level measure of depression severity was also associated with a self-reported four-level measure of exposure.DISCUSSION: Based on self-reported exposures and outcomes, an association is observed between organophosphate exposure and depression; however, we cannot assume that the associations we observed are causal because some workers may have been more likely to report exposure to organophosphate esters and also more likely to report depression. Future studies should consider using a larger sample size, better methods for characterizing crew chief exposures, and bioassays to measure dose rather than exposure.Hardos JE, Whitehead LW, Han I, Ott DK, Waller DK. Depression prevalence and exposure to organophosphate esters in aircraft maintenance workers. Aerosp Med Hum Perform. 2016; 87(8):712–717.

INTRODUCTION: Cognitive performance is crucial during military operations. It is suggested that impaired cognitive performance accounts for most of the accidents during training courses and actual battle. There is a need to define when soldiers’ operational readiness becomes impaired. The objective of this systematic review was to investigate the effects of sustained military operations (SUSOPS) on vigilance, reaction time, working memory, and reasoning in order to select good indicators for performance impairment.METHODS: A systematic literature search was performed using publicly accessible databases (IngentaConnect, PubMed, Science Direct, and Defense Technical Information Center online) that were screened until July 2015. Keywords were military, sustained operations, (cognitive) performance, soldier, and training.RESULTS: Only 7 out of 589 studies met the inclusion criteria. Selected studies were difficult to compare due to different methodologies, cognitive tasks, and military courses. Vigilance, reaction time, and working memory were affected after only a few hours, showing severe impairment. They are linearly related to military stress up to 80 h of SUSOPS. These three indicators needed little recovery time to return to baseline levels. After more than 80 h of SUSOPS, no significant impairments of those indicators were observed. Reasoning becomes impaired after high stress levels of relatively short duration and can remain affected after more than 80 h of SUSOPS.DISCUSSION: Vigilance, reaction time, and working memory are affected after only a few hours while little recovery time is needed. For reasoning to return to baseline values, longer recovery is needed than the time available during SUSOPS.Vrijkotte S, Roelands B, Meeusen R, Pattyn N. Sustained military operations and cognitive performance. Aerosp Med Hum Perform. 2016; 87(8):718–727.

BACKGROUND: Identify challenges and best practices in the development of an austere air ambulance transfusion program.METHODS: A search of PubMed using combinations of the key terms ‘prehospital,’ ‘blood product,’ ‘red blood cells,’ ‘damage control resuscitation,’ ‘transfusion,’ ‘air ambulance,’ ‘medical evacuation,’ and ‘medevac’ yielded 196 articles for further analysis, with 14 articles suitable for addressing the background of prehospital transfusion within a helicopter. Retrospective analysis of unclassified briefs, after action reports, and procedures was also undertaken along with interview of subject matter experts. The initial series of 15 transfusions were discussed telephonically among flight crew, trauma surgeons, and lab specialists. Review of Joint Theater System data was readily available for 84 U.S. Army air ambulance transfusions between May-December 2012, with December marking the redeployment of the 25^th Combat Aviation Brigade.RESULTS: Standardized implementation enabled safe blood product administration for 84 causalities from May-December 2012 without blood product shortage, expiration, or transfusion reaction. Challenges included developing transfusion competency, achieving high quality blood support, countering the potential for anti-U.S. sentiment, and diversity in coalition transfusion practices.DISCUSSION: Blood product administration aboard the air ambulance is logistically complex, requiring blood bank integration. Repetitive training enabled emergency medical technicians (EMTs) with basic medical training to safely perform transfusion in accordance with clinical operating guidelines. In the austere environment, logistic factors are significant challenges and political sensitivities are important considerations. Best practices may facilitate new en route transfusion programs.Powell-Dunford N, Quesada JF, Gross KR, Shackelford SA. Army air ambulance blood product program in the combat zone and challenges to best practices. Aerosp Med Hum Perform. 2016; 87(8):728–734.

BACKGROUND: Inner ear decompression sickness (IEDCS) in scuba diving results in residual vestibulocochlear deficits with a potential impact on health-related quality of life. The aim of this study was to determine the predictive factors for poor clinical recovery and to try to establish a prognostic score on initial physical examination.METHODS: The medical records of injured divers with IEDCS treated in our facility between 2009 and 2014 were retrospectively analyzed. The clinical severity of the deficit was evaluated on admission using a numerical scoring system taking into account the intensity of vestibular symptoms and the presence of cochlear signs. The clinical outcome was assessed at 3 mo by telephone interview. After multivariate analysis of potential risk factors for sequelae, the discriminating value of the score and these prognostic reliability indices were calculated.RESULTS: Among the 99 patients included in the study, 24% still had residual symptoms. Statistical analysis revealed that only a high clinical score [OR = 1.39 (95% CI 1.13-1.71)] and a delay in hyperbaric recompression >6 h [OR = 1.001 (95% CI 1-1.003)] were independently associated with incomplete recovery. The advantage of the score lay in its highly specific nature (92%) rather than its sensitivity (48%) for a threshold of 10.CONCLUSION: Results suggest that the severity of IEDCS can be easily determined by a clinical score during the acute phase. Recompression treatment should not be delayed.Gempp E, Louge P, de Maistre S, Morvan J-B, Vallée N, Blatteau J-E. Initial severity scoring and residual deficit in scuba divers with inner ear decompression sickness. Aerosp Med Hum Perform. 2016; 87(8):735–739.

INTRODUCTION: Supersonic, high altitude aviation places its pilots and aircrew in complex environments, which may lead to injury that is not easily diagnosed or simply treated. Decompression illness (either venous or arterial) and environmental conditions (e.g., abnormal gases and pressure) are the most likely adverse effects aircrew often face. Though symptomatic aircrew personnel may occasionally require hyperbaric oxygen treatment, it is rare to require more than one treatment before returning to baseline function.CASE REPORT: This challenging aviation case details the clinical course and discusses the salient physiological factors of an F/A-18D pilot who presented with neurological symptoms following loss of cabin pressure at altitude.DISCUSSION: Most crucial to this discussion was the requirement for multiple hyperbaric oxygen treatments over several days due to recurrence of symptoms. The likelihood of recurrence during and after future flights cannot be estimated with accuracy. This case illustrates a degree of recurrences for neurological symptoms in aviation (hypobaric exposure to hyperbaric baseline environment) that has not previously been described.Robinson T, Evangelista JS III, Latham E, Mukherjee ST, Pilmanis A. Recurrence of neurological deficits in an F/A-18D pilot following loss of cabin pressure at altitude. Aerosp Med Hum Perform. 2016; 87(8):740–744.

Bozung TK. You’re the flight surgeon: venous thoracic outlet syndrome. Aerosp Med Hum Perform. 2016; 87(8):748–751.