Mitchell SJ, Cronjé FJ, Meintjes WAJ, Britz HC. Fatal respiratory failure during a “technical” rebreather dive at extreme pressure. Aviat Space Environ Med 2007; 78:81–86. A diving fatality at the extreme depth of 264 m fresh water is described. The diver was equipped with an underwater video camera which recorded events leading to his death. These events corroborated predictions about respiratory complications at extreme pressure made by early researchers. Review of the video and relevant literature resulted in the following physiological interpretation: an increase in respired gas density during descent caused a progressive increase in resistance to flow in both the airways and the breathing circuit. Initially, this was associated with a shift to ventilation at higher lung volumes, a relative degree of hypoventilation, and mild permissive hypercapnia. The promotion of turbulent airway flow by increasing gas density resulted in effort-independent expiratory flow at lower flow rates than usual. The consequent inability to match ventilation to the demands of physical work at the bottom precipitated a spiraling crisis of dyspnea, increasing PaCO₂, and wasted respiratory effort, thus producing more CO₂. Extreme hypercapnia eventually led to unconsciousness. This tragic case provides a timely and salient lesson to a growing population of deep “technical” divers that there are physiological limitations that must be understood and considered when planning extreme dives.

Montcalm-Smith E, Caviness J, Chen Y, McCarron RM. Stress biomarkers in a rat model of decompression sickness. Aviat Space Environ Med 2007; 78:8793. Introduction: Immune reactivity, stress responses, and inflammatory reactions may all contribute to pathogenic mechanisms associated with decompression sickness (DCS). Currently, there are no biomarkers for DCS. This research examined if DCS is associated with increased levels of biomarkers associated with vascular function, early/non-specific stress responses, and hypothalamic-pituitary-adrenal (HPA) axis stress responses. Methods: Rats undergoing a test dive to 175 ft of seawater (fsw) (6.2 ATA) for 60 min with a rapid decompression were observed for DCS (ambulatory deficit). Animals exercised on a rotating cage (∼3 m · min⁻¹) throughout the dive and subsequent 30-min observation period. All animals were euthanized and blood and tissue samples (brain, liver, lung) were collected for analysis of CRP and ET-1 by ELISA and stress markers by PCR. Results: HO-1 and HSP-70 increased in the brain, and HO-1, Egr-1, and iNOS increased in the lungs of animals with DCS. There was no difference in any stress marker in the liver, or in serum levels of CRP or ET-1. Conclusions: The results demonstrate that < 30 min after surfacing, there are genomic changes in animals with DCS compared with animals not showing signs of DCS. Identification of specific markers of DCS may permit use of such biomarkers as predictors of DCS susceptibility and/or occurrence.

Eftedal OS, Tjelmeland H, Brubakk AO. Validation of decompression procedures based on detection of venous gas bubbles: a Bayesian approach. Aviat Space Environ Med 2007; 78:94–99. Introduction: Verification of new decompression procedures has traditionally been based on observing the occurrence of decompression sickness (DCS) in test dives. Several hundred exposures are required to determine the safety of a procedure with any degree of certainty. The number of venous gas emboli (VGE) corresponds with the risk of getting DCS and detection of VGE has been used as an alternative method for validation of decompression procedures. We propose a new and improved method for validation based on detection of VGE. Methods: Our Bayesian statistics method combines results from ultrasound detection of VGE in test dives with knowledge about the correspondence between VGE and DCS risk obtained from a large number of previous experimental studies. Our algorithm is implemented in a computer program; it estimates DCS risk and 95% credible intervals for the tested procedure. Results: We have applied the method to available VGE data from tested air diving procedures with between 7 and 14 test dives for each procedure. The estimated credible intervals correspond to confidence intervals from 130–250 dives using the binomial distribution of the traditional “DCS observation validation.” Discussion: We conclude that, compared with previous methods, the proposed method can greatly reduce the number of dives required to validate or reject new decompression procedures.

Lu H-B, Zhang L-F, Bai J, Liu X, Zhang G. Mathematical modeling of high G protection afforded by various anti-G equipment and techniques. Aviat Space Environ Med 2007; 78:100–109. Background: It is difficult to assess how different combinations of recently developed anti-G protective equipment will affect +Gz tolerance and central hemodynamics during high G solely by centrifuge experiments. In this paper we report a mathematical model simulating the effects of various combinations on human circulatory response and +Gz tolerance, and its validation with published centrifuge data. Methods : A structurally based mechanistic model incorporating cardio-pulmonary function, as well as a more detailed modeling of vessel segments for different anatomic regions, was established to simulate hemodynamic responses during high-G exposure and the protection afforded by various protective modalities, such as tilt-back seats, extended coverage anti-G suits (ECGS), and positive pressure breathing for +Gz (PBG). Results : There were 43 pairs of human data from centrifuge trials and model outputs under the same or similar conditions that were compared. This comparison indicated that in 86% of cases the differences were less than 15%. From the model outputs, the best combinations which satisfied different protective needs, such as protection to +9 Gz, +10 Gz, and +12 Gz, respectively, could be discovered. They also suggested that while the combined protection of ECGS with PBG may be expressed as a simple addition of the two effects, the combined effect of the tilt-back seat with ECGS and/or PBG seemed to be better fitted by a synergistic model. Conclusions: Comparisons with published centrifuge data have suggested the validity and confidence of the model developed. The benefits and limitations of the model for future high-G physiology and protection are discussed.

Harrison MF, Neary JP, Albert WJ, Veillette DW, McKenzie NP, Croll JC. Trapezius muscle metabolism measured with NIRS in helicopter pilots flying a simulator. Aviat Space Environ Med 2007; 78:110–116. Introduction: This study examined metabolic and hemodynamic responses during night vision goggle (NVG) induced neck strain among military helicopter pilots. We hypothesized that near infrared spectroscopy (NIRS) would be capable of identifying metabolic differences in the trapezius muscles of pilots between simulated flights with and without NVG. Methods: There were 33 pilots who were monitored on consecutive days during Day and NVG flight simulator missions. NIRS probes were attached bilaterally to the trapezius muscles at the C7 level to record total oxygenation index (TOI, %), total hemoglobin (tHb), oxyhemoglobin (HbO₂), and deoxyhemoglobin (HHb). Results: Significant differences in tHb were found between Day (0.51 ± 2.31 μmol · cm⁻¹) and NVG (4.14 ± 2.74 μmol · cm⁻¹) missions, and for HbO₂ (Dayend 2.63 ± 1.64 μmol · cm⁻¹; NVGend 5.77 ± 1.98 μmol · cm⁻¹). Significant left and right side differences between Day and NVG were found for tHb (NVGleft −1.83 ± 2.55; NVGright 10.45 ± 2.86 μmol · cm⁻¹), HbO₂ (NVGleft 1.77 ± 1.90; NVGright 9.95 ± 2.07 μmol · cm⁻¹), and HHb (Dayleft −1.84 ± 0.95; Dayright −2.32 ± 0.87 μmol · cm⁻¹; NVGleft −3.60 ± 1.05 μmol · cm⁻¹; NVGright 0.49 ± 1.16 μmol · cm⁻¹). Discussion: These results support NIRS’s utility in assessing the significant metabolic and hemodynamic effects of NVG on neck musculature during real-time missions for 1) left and right side differences; and 2) Day vs. NVG missions. The additional mass of the NVG equipment does increase the metabolic stress of these muscles during simulated missions.

de Voogt AJ, van Doorn RRA. Approaches and landings at wrong airports: analysis of 54 incidents and 11 accidents, 1981–2004. Aviat Space Environ Med 2007; 78:117–120. Background: Inadvertent approaches and landings at airports other than the intended destination are instances of pilot disorientation. The circumstances that lead to such navigational errors point toward preventive measures. The objective was to gain insight into the circumstances of a wrong airport approach or landing as well as the moment at which the navigation error became apparent to the pilot. Methods: Accident reports published by the National Safety Transportation Board for the period 1981 through 2004 were studied in combination with Federal Aviation Administration incident reports of the same period. Results: In the studied period there were 54 incidents and 11 accidents. There were 15 pilots who tried to avoid a landing, which in 5 cases led to an accident. All other pilots made a full-stop landing at the wrong airport. Damage to the aircraft was significantly more likely during night flights and in flights with a student or pilot with a private pilot license. Corrective measures during the landing procedure, such as a go-around or a touch-and-go landing, accounted for 42% of the accidents. Eighty percent of the cases were reported in the first 12 yr of the studied period and 20% in the last 12 yr. Conclusions: A further implementation of GPS receivers in all aircraft could further reduce the number of incidents and accidents. Pilots need to be made aware of the dangers of a visual approach after an IFR flight without following an airport identification procedure. Recommendations include a comparison of airports in the vicinity of a destination airport and the use of GPS to assist in an identification procedure.

Krijn M, Emmelkamp PMG, Ólafsson RP, Bouwman M, van Gerwen LJ, Spinhoven P, Schuemie MJ, van der Mast CAPG. Fear of flying treatment methods: virtual reality exposure vs. cognitive behavioral therapy. Aviat Space Environ Med 2007; 78:121–128. Introduction: Fear of flying (FOF) can be a serious problem for individuals who develop this condition and for military and civilian organizations that operate aircraft. The aim of this study was to compare the effectiveness of three treatments: bibliotherapy (BIB) without therapist contact; individualized virtual reality exposure therapy (VRE); and cognitive behavior therapy (CB). In addition, we evaluated the effect of following up VRE and CB with 2 d of group cognitive-behavioral training (GrCB). Methods: There were 86 subjects suffering from FOF who entered the study; 19 BIB, 29 VRE, and 16 CB subjects completed the treatment protocols. The BIB subjects were then treated with VRE (n = 7) or CB (n = 12). There were 59 subjects who were then trained with GrCB. Results: Treatment with VRE or CB was more effective than BIB. Both VRE and CB showed a decline in FOF on the two main outcome measures. There was no statistically significant difference between those two therapies. However, effect sizes were lower for VRE (small to moderate) than for CB (moderate) and the addition of GrCB had less effect for VRE than for CB. Discussion: VRE holds promise as treatment for FOF, but in this trial CB followed by GrCB showed the largest decrease in subjective anxiety. The results suggest that future research should focus on comparing the effectiveness of VRE vs. VRE plus cognitive techniques or measure the effectiveness of each component of treatment. Moreover, the effectiveness of the GrCB as stand-alone treatment should be investigated, which might even be superior in cost-effectiveness.

Edmonds JL, Jarchow T, Young LR. A stair-stepper for exercising on a short-radius centrifuge. Aviat Space Environ Med 2007; 78:129–134. Introduction: One requirement for long-duration spaceflight is provisions for exercise to prevent deconditioning. We evaluated the feasibility of using a stair-stepper on a short-radius centrifuge for this purpose. Methods: A stair-stepper was implemented on a centrifuge with a 2-m radius. There were 13 subjects who performed stepping exercise in a supine horizontal position while spinning at 0, 12.5, 23, and 30 rpm. They were instructed to step as fast and hard as possible during each 2-min session. We measured the forces on the feet, the heart rate, BP, stepping cadence, and medial-lateral deflections of the knees due to Coriolis forces. Results: Subjects completed the 2-min sessions successfully. Voluntary cadence of exercise and foot forces increased as rotation rate increased (average of 68 steps · min⁻¹ at 0 rpm and 91 steps · min⁻¹ at 30 rpm). Foot forces during exercise increased from an average of 43% bodyweight at 0 rpm to 84% bodyweight at 30 rpm. Heart rate and systolic BP increased with exercise compared with rest at each rotation rate, but the change was smaller as rotation rate increased (average of 134 bpm at 0 rpm and 128 bpm at 30 rpm). Medial-lateral deflections of the knee during exercise while spinning were significantly greater than when not spinning in some cases. Discussion: Presumably heart rate and BP were higher during exercise on a static centrifuge due to the muscular work required to pull with one foot while stepping with the other in a supine position. Subjects can sustain greater ground reaction forces when exercising than when lying still on the centrifuge (in some cases, greater than the full bodyweight). Medial-lateral knee deflections are a potential problem and should be monitored in future rotation studies.

Weber F, Goriup A. Prevalence of right-to-left shunts in active fighter pilots. Aviat Space Environ Med 2007; 78:135–136. Background: Patent foramen ovale (PFO) is a risk factor for cerebrovascular accidents and provides a potential mechanism for paradoxical systemic embolization of venous gas bubbles produced after altitude decompression. The objective of the study is to describe the prevalence of PFO and of possible subsequent brain lesions in active military fighter pilots. Methods: A sample of 52 healthy active fighter pilots was assessed with transcranial Doppler sonography, transesophageal echocardiography, and cranial MRI. Results: Significant right to left shunting occurred in 17% (9/52; 95% CI 8.7% to 30.8%); all shunts were due to a PFO. Cranial MRI was normal in each case. Conclusion: In this sample, prevalence of PFO lies within the expected range. There is no evidence that military flying in pilots who carry PFOs leads to brain damage. Screening for PFO is not recommended.

Lurie O, Zadik Y, Einy S, Tarrasch R, Raviv G, Goldstein L. Bruxism in military pilots and non-pilots: tooth wear and psychological stress. Aviat Space Environ Med 2007; 78:137–139. Background: Bruxism is the diurnal or nocturnal para-functional habit of clenching or grinding the teeth and affects 5–10% of the general western population. Bruxism can cause pain and irreversible damage to the teeth, periodontium, masticatory muscles, and temporo-mandibular joint. Variables such as general stress, work-related stress, and personality traits have been increasingly considered as initiating, predisposing, and perpetuating factors for bruxism. We sought to evaluate the potential of work-related stress and personality factors to induce bruxism among military pilots and non-pilot officers. Methods: Subjects were 57 healthy male Israel Air Force officers (mean age 25.8 ± 4.3 yr). Of these, 17 were jet-pilots, 18 helicopter-pilots, and 22 non-pilot officers. Tooth-wear was classified according to a six-point scale. In addition, the subjects responded to a battery of psychological questionnaires for self-assessment of stress at the workplace and their coping behavior. Results: Bruxism of clinical importance (i.e., with dentin exposure) was found in 69% of the aircrew members but only 27% of the non-pilot group. No difference was found between groups regarding stress levels. Discussion: Military aircrews may be relatively vulnerable to deleterious bruxism as well as other signs of chronic stress. Among bruxers, pilots tended to show coping strategies that were significantly more emotional and less task-oriented than non-pilots, whereas non-bruxers showed no significant differences in coping behavior. This study suggest that integrating dental and psychological preventive intervention may be helpful.

Van Camp RO, Ortega Jr HJ. Hand sanitizer and rates of acute illness in military aviation personnel. Aviat Space Environ Med 2007; 78:140–142. Introduction: Alcohol-based hand sanitizer (HS) kills most organisms that cause acute illness, an important cause of lost duty time among aviation personnel. This preliminary study observed the impact on the acute illness rate when HS was made readily accessible to pilots. Methods: Wall-mounted HS dispensers were placed in two fighter squadron operations buildings during November 2005 and various media were used to alert all base personnel to the importance of hand hygiene and cough hygiene. Data were obtained for two groups of personnel on the same base: 1) pilots who worked in the two HS-equipped buildings (Squadron) (n = 56); and 2) pilots and air traffic controllers who worked at other locations (Non-Squadron) (n = 61). The incidence of acute illness and the cumulative number of duty days lost was determined in each group for the winters of 2004–05 (no HS) and 2005–06 (HS available). Results: For the Squadron group, the acute illness rates were 2.4% in 2004–5 (210 duty days lost) (no HS) compared with 0.9% in 2005–6 (78 duty days lost) when HS was provided. No year-to-year difference was apparent for the Non-Squadron group, where the illness rates were 2.4% in 2004–5 (229 duty days lost) and 2.3% in 2005–6 (221 duty days lost). Discussion: Making HS readily available at locations frequented by pilots together with educating them regarding hand hygiene may reduce the occurrence of acute illness and number of duty days lost.

Dillard TA, Bansal AK. Commentary: pulse oximetry during airline travel. Aviat Space Environ Med 2007; 78:143–144. This is an invited commentary on the article “Normobaric hypoxia inhalation test vs. response to airline flight in healthy passengers” by Kelly et al. Aviat Space Environ Med 2006; 77:1143–7.

Connolly K. Antisocial personality disorder and medical certification. Aviat Space Environ Med 2007; 78:145–146. This case of Antisocial Personality Disorder (APD) highlights typical historical, physical, and test findings. For certification consideration, APD cases must be deferred to FAA’s Aerospace Medical Certification Division. APD is a chronic disease without effective treatments, likely to result in medical certificate denial.