Abel SM, Odell P. Sound attenuation from earmuffs and earplugs in combination: maximum benefits vs. missed information. Aviat Space Environ Med 2006; 77:899–904. Introduction: Noise levels from military aircraft range from 100–130 dBA. Peak pressure levels from large caliber weapons may reach 180 dB SPL. To protect against hearing loss, individuals are encouraged to wear double hearing protection. This study determined ways to maximize benefit. Method: Hearing thresholds from 0.25–8 kHz and consonant discrimination were assessed in normal-hearing subjects with ears unoccluded and fitted with highly rated earmuffs and earplugs, singly or in combination. The earplugs were available in two sizes. Selection was based on best fit. Attenuation values were derived from the threshold measurements. Results: With the muff, plug, and muff and plug in combination, thresholds ranged from 35–48 dB SPL, 40–55 dB SPL, and 44–66 dB SPL, respectively, across the frequencies tested. The combination (without regard to size of plug) resulted in attenuation values of 38–54 dB. With the smaller of the two plugs, low-frequency values as high as 53–61 dB were realized. Consonant discrimination decreased by 6–8% with the devices worn singly and by 22% with the devices in combination, relative to unoccluded listening. Discussion: Sufficient low-frequency attenuation may be achieved with muffs and plugs in combination to prevent hearing loss from operational noise. Attenuation may be maximized by choosing a smaller earplug to achieve a better fit. Possible downsides are reduced detection of warning sounds and speech intelligibility. To be heard warning sounds should surpass protected thresholds by at least 5 dB. Choosing devices which provide somewhat less attenuation may be necessary to preserve communication capability.

Løset A, Møllerløkken A, Berge V, Wisløff U, Brubakk A.O. Post-dive bubble formation in rats: effects of exercise 24 h ahead repeated 30 min before the dive. Aviat Space Environ Med 2006; 77:905–908. Introduction: Recent studies have shown that a nitric oxide releasing agent or a single bout of high-intensity exercise 20–24 h before a dive can prevent bubble formation following decompression. The aim of this study was to determine whether high-intensity exercise immediately prior to a dive eliminates the protective effect of a single bout of high-intensity exercise 24 h before the dive. Methods: Twelve female Sprague-Dawley rats were randomly divided into two equal groups. Group 1 performed 90 min of exercise twice, beginning 24.5 h and again 2.0 h before compression. Group 2 performed 90 min of exercise beginning at 25.5 h before compression. The standardized exercise protocol was 7 × 8 min at 85–90% maximal oxygen uptake ([V-dot]o₂max) followed by 2 min at 50% [V-dot]o₂max for a total of 90 min including a 20 min warm-up at 40–50% of [V-dot]o₂max. All rats were exposed to a pressure of 700 kPa (7 ATA) for 45 min in a dry hyperbaric chamber followed by decompression to the surface at 100 kPa (1 ATA) at a rate of 50 kPa · min⁻¹ (0.5 atm · min⁻¹) breathing air. Results: Bubble formation was significantly higher in rats that had exercised 24 h and 30 min prior to dive than rats that had only exercised 24 h prior to the dive (median bubble grade 4.5 vs. 0.5). Conclusion: This study demonstrated that acute exercise prior to a dive eliminated the protection against bubble formation found 24 h after high-intensity exercise in rats.

Cloutier A, Watt DGD. Motion sickness provoked by torso rotation predicts that caused by head nodding. Aviat Space Environ Med 2006; 77:909–914. Introduction: Some degree of space motion sickness is experienced by at least 50% of astronauts early in flight. It is unpleasant and could be hazardous during an extravehicular activity or urgent re-entry in the first few days after launch. To date, there is no reliable ground-based test to predict who will be affected. Methods: Head nodding (HN) in a supine position was used as a model of motion sickness caused by an unusual gravito-inertial environment. Torso rotation (TR) was used as a means of predicting susceptibility to development of symptoms caused by HN. Motion sickness was quantified in 26 subjects (5 men, 21 women, age range 18–52) using numerical estimates of discomfort and a more detailed questionnaire. Susceptibility to TR and HN was determined on three occasions for each stimulus, with test sessions at least 1 mo apart. Results: Subjects reached their stopping point at a mean duration of 13.72 min (± 1.06 CI) for TR and 11.31 min (± 0.38 CI) for HN. When susceptibility to HN was plotted as a function of susceptibility to TR and a linear regression line was added, the correlation coefficient was 0.744. Discussion: Susceptibility to TR predicts susceptibility to HN. The method may be useful as a screening test for potential astronauts.

Bruce-Low SS, Cotterrell D, Jones GE. Heart rate variability during high ambient heat exposure. Aviat Space Environ Med 2006; 77:915–920. Introduction: This study observed heart rate variability (HRV) measured in order to detect the changes in sympathovagal activity during high ambient (74°C) temperature. HRV is a measure of heart rate (HR) fluctuations around the mean HR and has been used to indicate the balance between parasympathetic and sympathetic function of the autonomic nervous system in medicine and exercise, but not in extreme environments. Methods: There were 10 healthy male subjects who wore Polar HR monitors (PE 5000) during a 15-min exposure (74.3 ± 5.9 °C). Results: HR increased significantly (p < 0.05) from 66.5 bpm pre-exposure to 106.0 bpm during exposure to the dry heat. A significant decrease in parasympathetic drive was indicated by: 1) a reduction of 89.1 ± 31.3% in the proportion of interval differences between two normal R-R intervals that were in excess of 50 ms in length (pNN50); 2) an 83.4 ± 7.0% decrease in the root mean square of successive R-R differences (RMSSD); and 3) an 82.7 ± 11.4% decrease in the normalized high-frequency (HF norm) values. An increase in a sympathetic drive was indicated by a significant increase in: 1) the normalized low-frequency (LF norm) values (of 84.5 ± 19.4%); and 2) the LF:HF ratio (10.9 ± 10.8%). Discussion: The results from this study show that exposure to high ambient temperature produces a significant increase in HR through an increase in sympathetic and decrease in parasympathetic drive.

Goodman LS, Grosman-Rimon L, Mikuliszyn R. Carotid sinus pressure changes during push-pull maneuvers. Aviat Space Environ Med 2006; 77:921–928. Introduction: The push-pull maneuver (PPM) is defined as a reduction in G-tolerance when positive acceleration (+Gz) immediately follows negative acceleration (−Gz) exposure, with the carotid baroreceptors presumably playing a dominant role in the ensuing BP (SBP) responses. The objective of this study was to determine whether application of neck pressure (NP) during the preceding −Gz phase maintains +Gz tolerance during subsequent +Gz. Methods: There were 10 experienced men who were exposed to 3 centrifuge run types using a multi-axis centrifuge: a relaxed control run from +1.4 baseline to visual tolerance; a relaxed control PPM run (PPM-C) consisting of 5 s of −1 Gz followed by 15 s of +Gz to visual tolerance; and an experimental PPM run performed with pressurized neck (PPM-NP) consisting of −1 Gz for 5 s followed by 15 s of +Gz at the previous PPM-C G-tolerance level. Results: Relaxed control G tolerance (3.6 ± 0.26 Gz) was greater vs. the PPM-C (3.0 ± 0.21 Gz) and PPM-NP (3.1 ± 0.20 Gz) conditions, but the two PPM conditions did not differ significantly. During −Gz, mean R-R interval for PPM-NP was significantly shorter than in the PPM-C from second 1 to second 3. During the +Gz phase, however, R-R interval responses between PPM-C and PPM-NP differed only at seconds 8 and 9. There were no differences in carotid sinus SBP between PPM-C and PPM-NP during −Gz. During +Gz, carotid sinus SBP was significantly depressed in PPM-NP and PPM-C conditions vs. Control. Discussion: Application of NP during the −Gz phase, despite altering R-R interval, did not ameliorate SBP responses or reductions in G tolerance during subsequent +Gz exposure. Despite neck compression counteracting increased carotid hydrostatic pressure during −Gz, the carotid baroreceptor response is likely opposed by the aortic or other baroreceptors.

Lieberman HR, Niro P, Tharion WJ, Nindl BC, Castellani JW, Montain SJ. Cognition during sustained operations: comparison of a laboratory simulation to field studies. Aviat Space Environ Med 2006; 77:929–935. Introduction: Military operations, especially combat, expose individuals to multiple stressors, including sleep loss, food deprivation, and sustained physical activity. Civilians, such as woodland firefighters, disaster victims, and relief workers, are also exposed to such environments. Our laboratory developed a brief, intense, laboratory-based simulation of a multistressor environment which included sleep loss, continuous physical activity, and food deprivation. Methods: During this sustained operations (SUSOPS) scenario, and a control period, cognitive performance and mood were measured in 13 volunteers. The scenario included road marches, battle drills, and land navigation. Physical activity and sleep were assessed with actigraphs. Results: Significant decrements in visual vigilance, choice reaction time, and matching-to-sample, a test of short-term memory, were observed. Marksmanship was stable and physical activity significantly increased. Mood states assessed by the Profile of Mood States (POMS: Tension, Depression, Anger, Vigor, Fatigue and Confusion) also significantly deteriorated. Discussion: Cognitive function declined more extensively and rapidly than physical performance. Decrements in cognitive performance were comparable to those in a field study conducted for an equivalent period of time in uncontrolled conditions. This demonstrates that decrements in cognitive function and increased physical activity, similar to those in highly stressful field environments, can be duplicated under controlled conditions. The simulated SUSOPS scenario is an appropriate paradigm for assessment of adverse effects of military and civilian multistressor environments on human performance, physiology, and interventions designed to mitigate them.

Lewis ME. Survivability and injuries from use of rocket-assisted ejection seats: analysis of 232 cases. Aviat Space Environ Med 2006; 77:936–943. Introduction: Ejection injury has been documented with respect to non-rocket-assisted seats, but there is little information on injuries associated with rocket-assisted seats. This study analyses the survivability of military accidents and the injuries associated with rocket-assisted ejection. Methods: A total of 232 Royal Air Force accident reports were accessed and aircrews’ injuries were related to the aircraft parameters of ejection, aircrew anthropometry, and the ejection seat and parachute dynamics. Ejection sequences were simulated using a computerized modeling tool to provide information relating to the dynamic response index, acceleration of the ejection seats, and performance of the parachutes. Results: Ejection survival was 89.2% overall, 95.7% for within envelope ejections and 23.8% for out of envelope ejections. There were 29.4% of aircrew who sustained spinal fractures. Another 14.2% of aircrew sustained a head injury and the incidence of head injury in Tornado ejectees was higher than the other aircraft types. Compared with 5.8% of ejectees from aircraft with an arm restraint system, 11.2% of aircrew sustained upper limb flail injuries from ejecting from aircraft without an arm restraint system. Arm flail injuries occurred at a higher aircraft speed at ejection compared with ejections where no arm flail injuries were sustained. There was also 18% of aircrew who sustained lower limb parachute landing injuries. Discussion: Information from this study has lead to a redesign of the Tornado ejection seat headbox, an improvement in the Tornado ejection catapult dynamics, an upgrade of escape system parachutes, and provided evidence that future aircraft should be fitted with an arm restraint system.

Duflou J, Nickols G, Waite P, Griffiths R, Sage M. Artefactual contraction band necrosis of the myocardium in fatal air crashes. Aviat Space Environ Med 2006; 77:944–949. Background : The detection of conditions associated with possible medical incapacitation is a crucial component of the aviation autopsy. Acute myocardial ischemia is notoriously difficult to diagnose at autopsy, although various pathological markers may strongly support a diagnosis of acute myocardial infarction occurring just prior to the crash. Hypothesis: Contraction band necrosis may not be a reliable indicator of acute myocardial ischemia in aircraft crashes because of the forces on myocardial tissue sustained in the crash. Methods: Microscopic examination of the myocardium of fatal air crash occupants was compared with a control group of suicidal hanging deaths. This study examined 80 air crash fatalities and 44 age and sex matched suicidal ligature hanging controls. We assessed both the presence and extent of contraction band necrosis type lesions in both groups and scored the lesions. Results: Contraction band lesions were seen in the left ventricular myocardium of all study groups. There was no significant difference between the contraction band score for crash victim deaths and hanging deaths. However, widespread contraction banding was significantly more common in air crash victims (p = 0.032). There was no significant difference between contraction banding in victims of impacts without a post-crash fire compared with those in crashes with a post-crash fire. Conclusions: Contraction band necrosis-like lesions in isolation should not be considered as evidence of acute myocardial ischemia in cases of massive trauma. Severe trauma, possibly as a result of sudden stretching of the cardiac myocytes, may cause a microscopic lesion which is indistinguishable from contraction band necrosis.

Pagán BJ, de Voogt AJ, van Doorn RRA. Ultralight aviation accident factors and latent failures: a 66-case study. Aviat Space Environ Med 2006; 77:950–952. Introduction: Little research has been done on ultralight aviation accidents. A better understanding of accident factors allows for better development of preventive measures. This study analyzes ultralight accidents with respect to significant factors related to active and latent failures, as referred to in Reason’s Swiss cheese model of human error. Methods: There were 66 National Transportation Safety Board (NTSB) ultralight accident reports that were examined from 1985–2004. Contextual information about active and latent failures was identified, compiled, and cross-referenced with pilot, aircraft, and accident information for evidence of significant relationships. Results: Pilots with less than 40 make/model-specific flying hours were significantly more likely to crash fatally (χ² = 9.07; p < 0.005; df = 1) than other pilots and/or because of losing control (χ² = 7.24; p < 0.05; df = 1) than other accident causes. In contrast, pilots with 40 or more make/model-specific flying hours were significantly more likely to crash as a result of engine failure (χ² = 9.33; p < 0.005; df = 1). Loss of control as an active failure was usually associated with such latent failures as strong winds and insufficient mission planning, while the engine failure accidents involved inadequate maintenance. Conclusion: In order to reduce accident prevalence, ultralight self-regulation organizations should focus on training in mission planning, aircraft familiarity, and proper maintenance procedures. Further research should concentrate on explaining the prevalence of the active and latent failures shown here and determining the effects of the FAA’s new light sport aircraft category.

Cook SB, Clark BC, Ploutz-Snyder LL. Accelerometry as a measure of subject compliance in unilateral lower limb suspension. Aviat Space Environ Med 2006; 77:953–956. Introduction: Human unilateral lower limb suspension (ULLS) is a commonly used model to study the effects of disuse and unweighting of human skeletal muscle. ULLS requires subjects to ambulate on crutches with an elevated shoe on the weight-bearing limb or a strap on the unloaded limb for prolonged periods of time (i.e., 4–5 wk). Ensuring compliance during ULLS participation is critical to the integrity of the study. Purpose: The purpose of this study was to determine the accuracy of an accelerometer to detect steps taken while walking and to measure the effectiveness of an accelerometer to monitor compliance during ULLS. Methods: There were 10 subjects (26.2 ± 3.6 yr; 170.9 ± 6.9 cm; 68.0 ± 9.6 kg) who participated in two conditions: normal walking and ULLS (left leg was unweighted via an elevated shoe on the contralateral limb) at various speeds. Additionally, subjects completed an obstacle course to simulate daily activities. During these activities, subjects wore a planar accelerometer on their left ankle to measure acceleration. The mean peak axial acceleration (MPAA) of the leg in the swing phase of walking was determined by the accelerometer and a step was detected during ULLS if the MPAA was greater than or equal to the minimum MPAA observed during walking. From this, the sensitivity of the accelerometer was determined. During ULLS, the number of steps detected by the accelerometer with an MPAA ≥ the minimum MPAA during walking was computed and the specificity of the accelerometer was determined. Results: The sensitivity of the accelerometer during walking was 96% and the specificity during ULLS was 97%. Conclusion: An accelerometer is an accurate tool to quantify the number of steps taken during walking and it may be used to measure subject compliance during ULLS.

Tufan K, Ademoglu A, Kurtaran E, Yildiz G, Aydin S, Egi SM. Automatic detection of bubbles in the subclavian vein using Doppler ultrasound signals. Aviat Space Environ Med 2006; 77:957–962. Introduction: It is possible to detect venous gas bubbles by listening to the Doppler audio signals. However, a serious disadvantage of the audio evaluation is the inability of continuous monitoring and the inter-rater agreement. Several researchers have worked on the automated detection of emboli, but no current system has the required sensitivity and specificity for clinical use. Method: We developed software that integrated frequency filtering, processing, and detection phases of microemboli into a graphical user interface. The detection algorithm consists of a rule-based criterion with a user-defined threshold sliding in-time axis that estimates the duration of the embolic event. Subclavian Doppler audio recordings obtained from a high altitude diving expedition were analyzed using digital filtering and non-linear operator combinations of the software. The data set includes 43 embolic events in 9 recordings from 4 different subjects. Results: It was determined that embolic signals are best differentiated from the background signal at the 4500–8000-Hz frequency band. By using the non-linear “Teager Energy Operator,” embolic signals were amplified against their background and a high level of sensitivity and specificity was obtained (83.7% and 97.3%, respectively). The duration of the detected emboli was estimated as 12.17 ± 4.36 ms (mean ± SD). Discussion: The optimal frequency band for the detection of subclavian emboli is significantly higher than previous findings for the transcranial site. The duration output of the software can be used to estimate the size and the composition of emboli. Successful integration of the software into an ambulatory detection system may provide important site-specific bubble size distribution data for decompression modeling.

Armentrout JJ, Holland DA, O’Toole KJ, Ercoline WR. Fatigue and related human factors in the near crash of a large military aircraft. Aviat Space Environ Med 2006; 77:963–970. Introduction: During approach to a remote island location, a U.S. Air Force heavy-airlift aircraft was flown into an aerodynamic stall, resulting in the loss of more than 4000 ft of altitude, with the crew recovering the aircraft just before impact would have occurred. Methods: An analysis of the mishap was conducted through a review of non-privileged USAF mishap data, cockpit voice recordings, flight data records, and interviews of the aircrew involved. A thorough examination of fatigue-related factors was conducted, including computerized fatigue modeling. Results: The crew traveled over 11,000 mi in a westward direction over a 6-d period. They had been on duty for nearly 21 h on the day of the mishap, with minimal in-flight rest. The pilots were late beginning their descent for landing, and a minor aircraft malfunction distracted the crew, contributing to channelized attention and degraded situational awareness. A breakdown in crew communication and failure to adequately monitor and interpret true aircraft state culminated in loss of aircraft control. Analysis of the crew’s work/rest schedule confirmed that multiple elements of fatigue were present during this mishap, including acute and cumulative fatigue, circadian disruptions, and sleep inertia. Additionally, reduced situational awareness and spatial disorientation, exacerbated by the underlying fatigue, were causal in this mishap. Discussion: This mishap highlights the importance of maintaining a high degree of situational awareness during long-haul flights with a continuing need to address issues regarding spatial disorientation, proper application of human engineering principles in modern cockpits, and mitigation of aircrew fatigue factors.

Gempp E, Blatteau J-E. Neurological disorders after repetitive breath-hold diving. Aviat Space Environ Med 2006; 77:971–973. We report a case of transient neurological disorder compatible with cerebral decompression illness in a breath-hold diver. A large right-to-left shunt was later detected with contrast transcranial Doppler ultrasound. While the mechanism of brain damage is unclear, this observation highlights the need for breath-hold divers to avoid excessive nitrogen loading and to refrain from forceful Valsalva maneuvers that may contribute to the opening of a patent foramen ovale and lead to paradoxical cerebral embolism. Because decompression illness is a possibility, anyone who experiences unusual symptoms after breath-hold diving should seek immediate medical attention.

Evans A, Finkelstein S, Singh J, Thibeault C. Pandemic influenza: a note on international planning to reduce the risk from air transport. Aviat Space Environ Med 2006; 77:974–976. The rapid and intercontinental spread of avian influenza in 2005 and the potential for human pandemic influenza caused preparedness plans for such an event to be highlighted. The World Health Organization (WHO) has developed a global influenza preparedness plan, but this document does not address in detail the contribution necessary by the aviation community. The International Civil Aviation Organization, with assistance from WHO, the Airports Council International, and the International Air Transport Association, and others, has developed preparedness guidelines that are in accord with those of WHO but which are focused on the aviation aspects. Effective communication between stakeholders is the single most important issue that is addressed in the preparedness guidelines. States are recommended to appoint a clear contact point at the national aviation level that has responsibility for ensuring that all stakeholders are adequately consulted in the development of an aviation preparedness plan and that the relevant communication links are established. It is also important that the aviation preparedness plan is incorporated into the State’s general preparedness plan, which demands efficient collaboration between the departments of health and transport at the government level. Communication with passengers, and those considering traveling, is important so that individuals are made aware of the risks associated with travel to particular parts of the globe and of the risk-reduction measures they may experience, or can take themselves, at airports and on aircraft. The guidelines will be web-based and will evolve as more knowledge becomes available.

Mohler SR, Day PC. The Annual Awards of the Aerospace Medical Association. Aviat Space Environ Med 2006; 77:977–980. The following summary of information on each of the Association's 15 awards has been assembled at the request of Richard T. Jennings, M.D., M.S., who assumed the Association Presidency during the period May 2006-May 2007. Dr. Jennings tasked the Chair of the History and Archives Committee with preparing a readable summary of some highlights in the lives of the award namesakes.

McCleod S. Prostate cancer. Aviat Space Environ Med 2006; 77:984–986. Prostate cancer is the most common malignancy in American men and second only to lung cancer in deaths. The American Cancer Society estimates that there will be about 232,090 new cases of prostate cancer in the United States in 2005, and about 30,350 men will die of this disease (1). Over the past 15 yr, research has expanded our knowledge of this cancer, its risk factors, treatments, and the potential screening tools. Yet, there is no clear consensus of how to deal with every man who comes in for aeromedical certification, how to screen for it, and how to treat it. No man is the same when it comes to prostate cancer. It is the responsibility of the aviation medical examiner to evaluate the unique aspects of every case for aeromedical implications.