Goswami N, Loeppky JA, Hinghofer-Szalkay H. LBNP: past protocols and technical considerations for experimental design. Aviat Space Environ Med 2008; 79:459–71. Introduction: Lower body negative pressure (LBNP) has been used for decades to simulate orthostatic stress and the effects of blood loss in humans. Since the definitive review of LBNP in 1974, new applications have been developed and research has revealed conflicting cardiovascular and neurohormonal responses during and after LBNP. Methods: A search of the literature was conducted for 1964–2007 using the Web of Science and the search terms “cardiovascular system,” “orthostasis,” “spaceflight,” and “methodologies” to identify publications in English that describe human studies where LBNP was used to simulate orthostasis. Publications cited in the earlier review were excluded, leaving a total of 215 articles for consideration. Results: We divided the reported protocols into eight categories based on the pressure, pattern, and duration of the stimulus: 1) mild, constant, short; 2) mild, constant, long; 3) mild, ramp, short; 4) mild, ramp, long; 5) moderate-to-strong, constant, short; 6) moderate, constant, long; 7) moderate-to-strong, ramp, short; and 8) strong, ramp, long. The review showed that these protocols stimulate different reflexes and can be used to produce particular responses. Discussion: Based on the review, we developed guidelines for using LBNP in a predictable and reproducible manner. Variables that must be controlled include subject characteristics, procedures, and environmental conditions as well as specifications for the LBNP chamber and seal positioning. An understanding of the many technical details of such experiments and the nature of elicited cardiovascular and neurohormonal responses is required to design optimal protocols to address specific research questions.

Irwin DC, Subudhi AW, Klopp L, Peterson D, Roach R, Monnet E. Pulmonary edema induced by cerebral hypoxic insult in a canine model. Aviat Space Environ Med 2008; 79:472–8. Introduction: The mechanisms of noncardiogenic pulmonary edema syndromes, such as neurogenic and high-altitude pulmonary edema, remain unclear even after years of study. Previous attempts to develop an animal model for these illnesses have used increased intracranial pressure or whole-body hypoxia. We hypothesized that a cerebral insult induced with a venous hypoxic blood infusion to the brain would trigger neurogenic pulmonary edema in a canine model. Methods: We measured indices of pulmonary edema, hemodynamics, norepinephrine (NE), and epinephrine values in anesthetized adult Walker hounds in which the brain was perfused for 2 h with either venous blood (venous perfused brain, VPB) or arterial blood (arterial perfused brain, APB) while maintaining normoxic pulmonary and systemic circulations. Normal cerebral perfusion was then reinstated for an additional 2-h period before euthanasia. Results: VPB animals showed a greater fall in arterial Po₂ and S_ao₂ and higher peak plasma NE compared to APB. On necropsy, VPB animals had greater lung wet-to-dry weight ratios compared to APB. Histological analyses revealed areas of marked alveolar infiltration of neutrophils and macrophages, acute hemorrhage, congestion, and alveolar edema in the VPB animals. Discussion: This study supports the hypothesis that a cerebral insult from venous hypoxic blood can induce pulmonary edema. This method yields a promising approach to the study of noncardiogenic pulmonary edema syndromes.

Tribukait A, Bergsten E, Eiken O. Visual sensations of roll rotation during complex vestibular stimulation. Aviat Space Environ Med 2008; 79:479–87. Background: In aviation, vestibular-induced spatial disorientation is a significant cause of accidents. Recreating flight-like vestibular stimuli in simulators might be a means for training pilots to respond adequately in disorienting situations. Due to the physical constraints of land-based simulators, the question arises whether a given illusion may be created in different ways. For instance, is it possible to induce sensations of tilt by rotary stimuli? The present study concerns the relationship between sensations of rotation and tilt during complex vestibular stimulation. Methods: The visual sensation of roll rotation was quantified by means of a velocity-matching procedure. In a large gondola centrifuge eight subjects underwent four runs (2 G, 2 min) with different heading positions (forward, backward, centripetally, and centrifugally). The inclination of the gondola persistently corresponded with the vector sum of the Earth gravity force and the centrifugal force (60° at 2 G). Thus, the semicircular canal stimulus in roll was combined in different ways with stimuli in yaw and pitch, as well as with an increasing or decreasing G vector. Results: The magnitude of the responses was only dependent on the roll component of the stimulus. The gain, defined as the ratio between the response and the roll stimulus, was 7–10%. The responses decayed with a time constant ranging from 4 to 5.5 s. Conclusion: The visual sensation of roll rotation reflects the roll plane canal velocity stimulus independently of other stimulus components. This is in contrast to earlier findings on the sensation of changes in position (roll tilt).

Schellart NAM, Brandt Corstius J-J, Germonpré P, Sterk W. Bubble formation after a 20-m dive: deep-stop vs. shallow-stop decompression profiles. Aviat Space Environ Med 2008; 79:488–94. Objectives: It is claimed that performing a “deep stop,” a stop at about half of maximal diving depth (MDD), can reduce the amount of detectable precordial bubbles after the dive and may thus diminish the risk of decompression sickness. In order to ascertain whether this reduction is caused by the deep stop or by a prolonged decompression time, we wanted to test the “deep stop” theory without increasing the total decompression time. From a modeling point of view, Haldanian theory states that this situation would increase the probability of observable bubbles, because of a longer stay at depth. Under these conditions, we examined whether a “deep-stop dive” (DSD) produces more bubbles or less than a “shallow-stop dive” (SSD). Methods: Recreational divers performed either a DSD or a SSD. Both groups were matched biometrically. MDD was 20 msw, bottom time 40 min and total diving time 47 min. In DSD, the “deep” stop (10 msw) replaced 3 min of the 7 min stop at 4 msw of SSD. Results : DSD produced significantly more precordial bubbles than SSD after knee bends (P-values ranging from 0.00007 to 0.038). Discussion: Our results indicate that at least for the tested dive profile, the higher supersaturations after surfacing overruled any possible beneficial effects of the deep stop on bubble formation. The usefulness of substituting a shallow stop with a deep stop in dives up to 20 msw can be questioned; at the least, more research is needed.

Pretorius T, Cahill F, Kocay S, Giesbrecht GG. Shivering heat production and core cooling during head-in and head-out immersion in 17°C water. Aviat Space Environ Med 2008; 79:495–9. Introduction: Many cold-water scenarios cause the head to be partially or fully immersed (e.g., ship wreck survival, scuba diving, cold-water adventure swim racing, cold-water drowning, etc.). However, the specific effects of head cold exposure are minimally understood. This study isolated the effect of whole-head submersion in cold water on surface heat loss and body core cooling when the protective shivering mechanism was intact. Methods: Eight healthy men were studied in 17°C water under four conditions: the body was either insulated or exposed, with the head either out of the water or completely submersed under the water within each insulated/exposed subcondition. Results: Submersion of the head (7% of the body surface area) in the body-exposed condition increased total heat loss by 11% (P < 0.05). After 45 min, head-submersion increased core cooling by 343% in the body-insulated subcondition (head-out: 0.13 ± 0.2°C, head-in: 0.47 ± 0.3°C; P < 0.05) and by 56% in the body-exposed subcondition (head-out: 0.40 ± 0.3°C and head-in: 0.73 ± 0.6°C; P < 0.05). Discussion: In both body-exposed and body-insulated subconditions, head submersion increased the rate of core cooling disproportionally more than the relative increase in total heat loss. This exaggerated core-cooling effect is consistent with a head cooling induced reduction of the thermal core, which could be stimulated by cooling of thermosensitive and/or trigeminal receptors in the scalp, neck, and face. These cooling effects of head submersion are not prevented by shivering heat production.

McLellan TM. Chemical-biological protective clothing: effects of design and initial state on physiological strain. Aviat Space Environ Med 2008; 79:500–8. Purpose: This study examined whether heat strain during low states of chemical and biological protection (CB_low) impacted tolerance time (TT) after transition to a high state of protection (CB_high) and whether vents in the uniform reduced heat strain during CB_low and increased TT. Methods: There were eight men who walked at 35°C in CB_low and then transitioned to CB_high. Subjects wore fatigues in CB_low with an overgarment during CB_high (F+OG) or a new 1-piece (1PC) or 2PC uniform throughout CB_low and CB_high. One condition also tested opened vents in the torso, arms, and legs of the 2PC uniform (2PC_vent) during CB_low; these vents were closed during CB_high. Also worn were fragmentation and tactical vests and helmet. Results: Heart rates were reduced significantly during CB_low for F+OG and 2PC_vent (114 ± 13) vs. 1PC and 2PC (122 ± 18). Rectal temperature (T_re) increased least in CB_low for F+OG (0.86 ± 0.23°C) and was significantly lower for 2PC_vent (1.02 ± 0.25°C) vs. 2PC (1.11 ± 0.27°C). T_re increased rapidly during CB_high for F+OG, which had the shortest TT (40 ± 9 min). Increased thermal strain during CB_low for 1PC negated its advantage in CB_high and TT (46 ± 21 min) was similar to F+OG. Differences in T_re between 2PC and 2PC_vent remained during CB_high where TT was increased during 2PC_vent (74 ± 17 min) vs. 2PC (62 ± 19 min). Conclusions: It was concluded that heat strain during CB_low impacted TT during CB_high, and use of vents reduced heat strain during CB_low, thereby increasing TT.

Cole BL, Lian K-Y, Lakkis C. Color vision assessment by Farnsworth lantern: results using alternative pass-fail criteria. Aviat Space Environ Med 2008; 79:509–13. Introduction: The Farnsworth lantern is used in the United States and Australia to assess pilot applicants who have deficient color vision (DCV). Its efficacy was questioned following a crash in July 2002 because the DCV pilot confused the red and white approach path signals, despite having passed the Farnsworth test. The Farnsworth lights are larger and brighter than many aviation signals and it has a higher pass rate than the lantern tests used in other countries. Moreover, applicants can pass by making no errors on 1 run of 18 lights, which is too small a sample. Methods: There were 3 runs of the Farnsworth lantern given to 100 male subjects with DCV. The effect on pass rate of changing the number of runs and the pass criterion was assessed. Results: There were 20 subjects who passed the Farnsworth lantern test. Their average error rate over three runs was 3.9%; two had an error rate of 13% and five confused red and white signals, the colors used in approach path signals. One subject passed by having zero errors on run 1 but made 13% errors on the next two runs. If all subjects are given two runs after a practice run, 15% pass if the pass criterion is ≤ 1 error and 11% pass if it is zero errors. No subject made red-white color confusions with the zero error pass criterion. Conclusions: A practice run and two test runs should always be given. The pass criterion should be ≤ 1 error in total on the two test runs.

Strader JR, Harrell TW, Adair A, Kruyer WB. Efficacy of echocardiographic screening of pilot applicants. Aviat Space Environ Med 2008; 79:514–7. Background: The efficacy of cardiac screening programs for individuals in competitive athletics and high-risk occupations such as commercial and military aviation continues to be highly debated. For the past 12 yr, all United States Air Force (USAF) pilot applicants have undergone screening echocardiography. Methods: All available studies were reviewed for disqualifying (DQ) diagnoses. Findings were analyzed and compared to current USAF waiver policy. Results: Between inception in March 1994 and 01 September 2006, there were 20,208 screening echocardiograms performed. Of these, 294 (1.45%) were initially read as disqualifying. The most common diagnoses were bicuspid aortic valves with mild or less aortic insufficiency (N = 154, 0.76%), mitral valve prolapse with mild or less mitral regurgitation (N = 51, 0.25%), and trileaflet aortic valve with mild aortic insufficiency (N = 58, 0.29%). Evolution of USAF waiver policy has now rendered these diagnoses waiverable for entry into pilot training. Under current policy, 285/294 would be eligible for an unrestricted waiver, leaving only 9 individuals “DQ/no-waiver” (0.0445%). There were no cases of hypertrophic cardiomyopathy. Although the number of USAF pilot applicants has increased in recent years, the DQ/no-waiver rate has actually decreased, with only a single DQ/no-waiver finding since 2004 (N = 5802 studies; 0.0172%). Discussion: The infrequency of positive findings in this large cohort of screening echocardiography raises questions about the appropriateness of such programs. Under current USAF policy, it is not efficacious to perform screening echocardiography on all pilot applicants.

Akerø A, Christensen CC, Edvardsen A, Ryg M, Skjønsberg OH. Pulse oximetry in the preflight evaluation of patients with chronic obstructive pulmonary disease. Aviat Space Environ Med 2008; 79:518–24. Introduction: In a British Thoracic Society (BTS) statement on preflight evaluation of patients with respiratory disease, sea level pulse oximetry (Spo_2sl) is recommended as an initial assessment. The present study aimed to evaluate if the BTS algorithm can be used to identify chronic obstructive pulmonary disease (COPD) patients in need of supplemental oxygen during air travel, i.e. patients with an in-flight P_ao₂ < 6.6 kPa (50 mmHg). Methods: There were 100 COPD patients allocated to groups according to the BTS algorithm: Spo_2sl > 95%, Spo_2sl 92–95% without additional risk factors; Spo_2sl 92–95% with additional risk factors; Spo_2sl < 92%; and patients using domiciliary oxygen. Pulse oximetry, arterial blood gases, and an hypoxia-altitude simulation test (HAST) to simulate a cabin altitude of 2438 m (8000 ft), were performed. Results: The percentage of patients in the various groups dropping below 6.6 kPa during HAST were: Spo_2sl > 95%: 30%; Spo_2sl 92–95% without additional risk factors: 67%; Spo_2sl 92–95% with additional risk factors: 70%; Spo_2sl < 92%: 83%; and patients using domiciliary oxygen: 81%. In patients dropping below P_ao₂ 6.6 kPa, supplemental oxygen of median 1 L · min^{− 1} was needed to exceed this limit. Discussion: If in-flight P_ao₂ ≥ 6.6 kPa is regarded as a strict requirement, the use of pulse oximetry as an initial assessment in the preflight evaluation of COPD patients, as suggested by the BTS, might not discriminate adequately between patients who fulfill the indications for supplemental oxygen during air travel, and patients who can travel without such treatment.

Tvaryanas AP, Thompson WT. Recurrent error pathways in HFACS data: analysis of 95 mishaps with remotely piloted aircraft. Aviat Space Environ Med 2008; 79:525–32. Background: According to Reason's model of accident causation, mishaps tend to fall into recurrent patterns. This model is the foundation for the Human Factors Analysis and Classification System (HFACS), which is now widely used in aviation accident analysis. The purpose of this study was to determine if it was possible to use HFACS to identify recurrent error pathways within an existing mishap database. Methods: All MQ-1 Predator remotely piloted aircraft (RPA) mishaps and safety incidents reported to the Air Force Safety Center during fiscal years 1997–2005 were evaluated and entered into a mishap database (N = 95). An exploratory principal component analysis (PCA) was used to assess the factorial structure within the set of crewmember-related mishaps (N = 48). The results of the PCA were used to define recurrent pathways from latent to active failure and hence mishaps. A tree diagram was subsequently created to quantitatively assess the associations identified in the PCA. Results: Four factors were identified, each consisting of one of the HFACS categories of active failure and one or more categories of latent failure. Two additional factors were identified, consisting of fatigue and motivational latent failures. Based on analysis of the tree diagram, the majority of mishaps were caused by latent failures involving organizational factors and the technological environment. Conclusions: It was possible to identify four recurrent error pathways associated with the four types of HFACS active failures within this sample of RPA mishaps. Two of these error pathways, accounting for 57% of crewmember-related mishaps, were consistent with situation awareness errors associated with perception of the environment.

Gutovitz S, Weber K, Kaciuban S, Colern R, Papa L, Giordano P. Middle ear pressure and symptoms after skydiving. Aviat Space Environ Med 2008; 79:533–6. Objectives: Altitude-related otic barotrauma and its symptoms have been identified from air-travel, scuba diving, and hyperbaric chambers, but not in skydiving. It is not known whether skydiving-related otic barotrauma could cause symptoms severe enough for medical attention or be implicated in skydiving-related accidents. This study assessed the effect of altitude change on middle ear pressures in skydivers by comparing changes in pressure before and after a skydive, pressure changes in those who developed middle ear symptoms vs. those who did not, and pressures in those who attempted equalization vs. not. Methods: This prospective observational cohort enrolled skydivers on random days in Deland, FL. A tympanometer was used to measure middle ear pressures in decapascals (daPa) on the ground before and after skydiving. Results: Average middle ear pressures in 69 subjects were significantly different before (−23.5 daPa) and after (−70.5 daPa) the skydive. There were 13 subjects (18.8%) who had middle ear symptoms after descent, but there were no statistically significant differences in ear pressure changes in those with (−57.5 daPa) and without (−44.2 daPa) symptoms after their jump. There was, however, a significant difference in pressure in those jumpers who did (−32.7 daPa) and did not (−75.7 daPa) equalize successfully after their jump. Conclusions: Rapid skydiving descent from high altitudes causes negative middle ear pressure changes. The ability to equalize ear pressures after a jump had a large impact on the change in ear pressure. However, the change in middle ear pressure was not associated with the presence of middle ear symptoms.

Harris D, Li W-C. Cockpit design and cross-cultural issues underlying failures in crew resource management. Aviat Space Environ Med 2008; 79:537–8. High power-distance has been implicated in many aircraft accidents involving Southeast Asian carriers where crew resource management (CRM) has been identified as a root cause. However, this commentary argues that the design of modern flight decks and their standard operating procedures have an inherent Western (low power-distance) bias within them which exacerbates these CRM issues.