Steinbach GC, Macias BR, Tanaka K, Yost WT, Hargens AR. Intracranial pressure dynamics assessed by noninvasive ultrasound during 30 days of bed rest. Aviat Space Environ Med 2005; 76:8590. Introduction: Intracranial pressure (ICP) may be an important contributor to symptoms of space adaptation syndrome during the initial days of microgravity exposure. The temporary nature of these symptoms suggests that some physiologic adaptation or compensation occurs. Fluid shifts similar to those in microgravity can be simulated on Earth using head-down tilt (HDT) bed rest. This study was performed to calibrate a new noninvasive ICP instrument and to investigate ICP adaptation during 30 d of HDT bed rest. Methods: A noninvasive ultrasound technique that measures small skull expansions with fluctuations in ICP was used to measure cranial oscillations before and near the end of 30-d HDT bed rest in eight healthy, male volunteers. Pulse phase-locked loop (PPLL) output voltage and arterial BP were continuously monitored and correlated. Results: The amplitude of intracranial distance pulsation decreased during 30-d bed rest. Prior to bed rest, the PPLL amplitude was 25 ± 9 mV and this amplitude was reduced by 60% to 9 ± 4 mV (a value consistent with that of upright posture) at the end of HDT bed rest (p = 0.01). Discussion: PPLL measurements of skull pulsations are acutely posture dependent, being significantly higher in supine and HDT as compared with upright posture. A cephalad fluid shift is probably the responsible mechanism. Our results indicate that there are adaptations to intracranial pooling of blood and tissue fluid during bed rest that reduce skull pulsation amplitudes to values similar to those obtained in normal upright posture. Detailed studies of the time course of cranial vessel and bone adaptations may provide insights into the potential adaptative mechanisms.

Serrador JM, Schlegel TT, Black FO, Wood SJ. Cerebral hypoperfusion precedes nausea during centrifugation. Aviat Space Environ Med 2005; 76:91–96. Introduction: Nausea and motion sickness are important operational concerns for aviators and astronauts. Understanding the underlying mechanisms associated with motion sickness may lead to new treatments. The goal of this work was to determine if changes in cerebral blood flow precede the development of nausea in subjects susceptible to motion sickness. Methods: Cerebral flow velocity in the middle cerebral artery (transcranial Doppler), BP, and end-tidal CO₂ were measured while subjects were rotated on a centrifuge (250° · s⁻¹). Following 5 min of rotation, subjects were translated 51.5 cm off-center, creating a +1 Gx centripetal acceleration in the nasal-occipital plane. Results: There were 10 subjects who completed the protocol without symptoms while 5 developed nausea (4 while off-center and 1 while rotating on-center). Prior to nausea, subjects had significant increases in BP (+13 ± 3 mmHg, p < 0.05) and cerebrovascular resistance (+46 ± 17%, p < 0.05) and decreases in cerebral flow velocity both in the second (−13 ± 4%) and last minute (−22 ± 5%) before symptoms (p < 0.05). In comparison, subjects resistant to motion sickness demonstrated no change in BP or cerebrovascular resistance in the last minute of off-center rotation and only a 7 ± 2% decrease in cerebral flow velocity. All subjects had significant hypocapnia (−3.8 ± 0.4 mmHg, p < 0.05); however, this hypocapnia could not fully explain the cerebral hypoperfusion associated with the development of nausea. Conculsions: These data indicate that reductions in cerebral blood flow precede the development of nausea. Further work is necessary to determine what role cerebral hypoperfusion plays in motion sickness and whether cerebral hypoperfusion can be used to predict the development of nausea in susceptible individuals.

Nelson JW, Werner JK, Burge JR. Isoproterenol accelerates decompression sickness and death after saturation dives in swine. Aviat Space Environ Med 2005; 76:97–102. Background: Disabled submarine (DISSUB) survivors are expected to achieve inert gas tissue saturation that would likely cause severe decompression sickness (DCS). Rescue procedures in a DISSUB scenario cannot accommodate a staged decompression and the availability of recompression treatment chambers is limited. Alternatives to the standard recompression procedures for treating DCS are needed. Experimentally, isoproterenol has successfully addressed many underlying physiological concerns expected to result in cardiopulmonary DCS in this group. Hypothesis: We hypothesized that isoproterenol would reduce the incidence of cardiopulmonary DCS in a saturation dropout model. Methods: Yorkshire swine (21.8 ± 1.68 kg) were fitted with an external jugular catheter and compressed to 4.33 ATA in a dry chamber for 22 h. They were infused with isoproterenol (0.002 mg · kg⁻¹) while still at depth and returned to the surface without decompression stops. They received additional infusions every 10 min throughout a 2-h observation period. Signs of DCS were recorded to the nearest minute. Results: Isoproterenol administration resulted in a significant increase in the incidence of severe cardiopulmonary DCS (13/34 control vs. 12/18 isoproterenol) and death from DCS (10/34 control vs. 11/18 isoproterenol). There was no difference in the incidence of severe neurological DCS. Conclusions: Administering isoproterenol as an intervention/treatment for DCS significantly increases the risk of cardiopulmonary DCS and death following saturation dropout in 20-kg swine. As an adjunctive therapy or alternative to staged decompression, isoproterenol in the dose regimen delivered here is not expected to improve outcome in a DISSUB mass casualty scenario.

Sandor PMB, McAnally KI, Pellieux L, Martin RL. Localization of virtual sound at 4 Gz. Aviat Space Environ Med 2005; 76:103–107. Introduction: Acceleration directed along the body’s z-axis (Gz) leads to misperception of the elevation of visual objects (the “elevator illusion”), most probably as a result of errors in the transformation from eye-centered to head-centered coordinates. We have investigated whether the location of sound sources is misperceived under increased Gz. Method: Visually guided localization responses were made, using a remotely controlled laser pointer, to virtual auditory targets under conditions of 1 and 4 Gz induced in a human centrifuge. As these responses would be expected to be affected by the elevator illusion, we also measured the effect of Gz on the accuracy with which subjects could point to the horizon. Results: Horizon judgments were lower at 4 Gz than at 1 Gz, so sound localization responses at 4 Gz were corrected for this error in the transformation from eye-centered to head-centered coordinates. We found that the accuracy and bias of sound localization are not significantly affected by increased Gz. Conclusion: The auditory modality is likely to provide a reliable means of conveying spatial information to operators in dynamic environments in which Gz can vary.

LaJambe CM, Kamimori GH, Belenky G, Balkin TJ. Caffeine effects on recovery sleep following 27 h total sleep deprivation. Aviat Space Environ Med 2005; 76:108–113. Introduction: Caffeine is widely used to reverse alertness and performance decrements. However, caffeine’s effects on subsequent recovery sleep and post-recovery performance are not well documented and, therefore, were evaluated. Methods: Six habitually low (LC: ≤ 100 mg · d⁻¹) and three habitually high (HC: ≥ 400 mg · d⁻¹) caffeine users completed a randomized crossover design. After 20 h of wakefulness, repeated doses of caffeine gum [0 (placebo) mg, 100 (low dose) mg, or 300 (high dose) mg] were administered at 03:00, 05:00, and 07:00. At 10:00 (27 h sleep deprivation) subjects slept for 8 h, followed by Psychomotor Vigilance Task (PVT) administration at 33 and 65 min post-awakening. Results: Low dose caffeine increased stage 1 minutes only. However, high dose caffeine impaired sleep maintenance (reduced total sleep time/increased wake) and reduced sleep depth (increased stage 1 minutes/percentage and slow-wave sleep (SWS) latency, and reduced SWS minutes during the first third of the sleep period). With high dose caffeine, LC users had less SWS percentage as compared with HC users. The HC users had reduced stage 2 percentage with high dose caffeine as compared with placebo and low dose caffeine. Caffeine dose and habitual caffeine use did not influence post-recovery sleep PVT performance. Discussion: Caffeine exerts mild deleterious dose-response effects on recovery sleep following total sleep deprivation, primarily early in the sleep period, with potential recovery from these effects after sufficient sleep as suggested by lack of post-recovery sleep performance deficits. Habitual caffeine use appears to minimally reduce caffeine effects.

Gempp E, Blatteau J-E, Louge P, Drouillard I, Galland F-M. N-terminal pro brain natriuretic peptide increases after 1-h scuba dives at 10 m depth. Aviat Space Environ Med 2005; 76:114–116. Objectives: The N-terminal pro brain natriuretic peptide (N-BNP) is a promising cardiac natriuretic peptide used as a clinical hormonal marker in cardiac dysfunction. The main stimulus for N-BNP synthesis and secretion is cardiac wall stress, which is recognized as a common denominator of many cardiac diseases. Diving is associated with environmental factors leading to variations in thoracic blood volume and hemodynamic changes. The purpose of the present study was to examine the changes in the concentration of N-BNP in healthy men during and after scuba diving. Method: There were 10 healthy military divers (mean age 33 yr) who performed a dive in the sea for 1 h at 10 m depth. Venous blood samples were taken at timed intervals to allow evaluation of plasma levels of N-BNP at different steps, namely at T0 (before immersion), at T30 min (during the dive, after a short surfacing), at T60 min (right after surfacing), at T300 min (post-dive), and finally at T24 h. Peptide blood concentrations were determined by electrochemoluminiscence immunoassay. Data were analyzed using parametric statistics. Results: When compared with T0, the results show a significant increase of N-BNP levels (in % of baseline levels) at T60 (128 ± 5%, p < 0.043) and at T300 (149 ± 8%, p < 0.001). Conclusion: This preliminary study reveals that N-BNP rises with scuba diving. Our findings suggest that diving involves a mechanical strain on the heart with a persistent endocrine myocardial activity post-dive.

Kaur C, Singh J. Fos expression in the suprachiasmatic nucleus in rats following high altitude exposure. Aviat Space Environ Med 2005; 76:117–120. Introduction: Disturbances of circadian rhythms occur at high altitude. We examined the suprachiasmatic nucleus (SCN), considered to be the biological clock in mammals that regulates circadian rhythmicity, in adult rats following an exposure to simulated high altitude. Methods: Male adult Wistar rats weighing 250 g were exposed to an altitude of 8000 m in an altitude chamber, following which they were sacrificed at various time intervals ranging from 45 min to 3 d. Normal rats of similar weight kept outside the chamber were used as controls. Sections of hypothalamus containing the suprachiasmatic nucleus were processed immunohistochemically for expression of Fos, neuronal nitric oxide synthase (nNOS), and endothelial nitric oxide synthase (eNOS). Results: At 45 min, 4 h, and 24 h following the altitude exposure, a large number of Fos-positive neurons were detected as compared with the control rats in which occasional Fos-positive neurons were observed. Increased expression of nNOS and eNOS was also observed at 45 min and 4 h following the altitude exposure. Conclusions: It is suggested that the neuronal activation indicated by upregulated expression of Fos and nitric oxide (NO) generated by nNOS may be involved in the disturbed circadian rhythms of the cardiovascular system (e.g., heart rate and BP), hormone secretion, and sleep-wake cycle which occur frequently during sojourns to high altitude. Increased eNOS expression also indicates excess production of NO, which may be involved in vasodialation and increased blood flow to the SCN following the exposure and may also be involved in modulating the circadian rhythms at high altitude.

Florence G, Riondet L, Serra A, Etienne X, Huart B, Van Beers P, Bonneau D, Gomez-Merino D, Drogou C, Pradeau P. Psychostimulants and G tolerance in rhesus monkeys: effects of oral modafinil and injected caffeine. Aviat Space Environ Med 2005; 76:121–126. Introduction: Caffeine and modafinil are psychostimulants that may be taken by fighter aircraft pilots to reduce fatigue. Fighter pilots are subjected to high positive G loads that reduce cerebral blood flow and consequently may induce G-LOC. The aim of the experiment was to determine whether these drugs may reduce tolerance to G stress. Methods: Seven adult male rhesus monkeys participated in the experiment. Five were equipped with ECoG and ECG wires and underwent two G tests (A and B). Each experiment consisted of five centrifuge runs. Before the runs, the monkeys received no drug (control) or were given either 7.5 mg · kg⁻¹ caffeine IM or 64 mg · kg⁻¹ modafinil PO or the corresponding vehicles. The runs were performed up to +13 Gz with an onset rate of 0.1 G · s⁻¹ (test A) or 3 G · s⁻¹ (test B). The run was ended when the electrical activity of one ECoG channel had disappeared (i.e., G-LOC). Results: In experiment A, drug administration had no significant effect. In experiment B, the injection of the caffeine-free solvent caused a delay in G-LOC compared with the control condition (no administration). Caffeine solvent also induced an increase in plasma osmolality. Discussion: Modafinil administration has no significant effect on the G tolerance of rhesus monkeys. Regarding caffeine, the drug seems to have caused the reverse effect compared with the solvent. Conclusions: Caffeine and modafinil administration had no significant effect on the G-tolerance of rhesus monkeys when compared with controls. This result needs to be confirmed in humans.

Delpero WT, O’Neill H, Casson E, Hovis J. Aviation-relevent epidemiology of color vision deficiency. Aviat Space Environ Med 2005; 76:127–133. Introduction: The Colour Vision Study Group of Transport Canada undertook a prevalence review to ascertain the degree and type of color vision deficiency (CVD) common in different populations. This was performed as a first step toward establishing whether a bone fide occupational requirement for color vision in aviation can be determined. Literature Search: Peer-reviewed articles with large populations and appropriate methodology for measuring CVD were assessed. Those pertaining to congenital CVD were cross-sectional prevalence studies with greater than 100 subjects assessed with a combination of pseudoisochromatic plates (PIPs) and Farnsworth D15 and/or an anomaloscope. Of 162 papers reviewed, 36 met these criteria for inclusion in the congenital CVD section. Acquired CVD papers were included based on the quality of color vision tests employed. Congenital CVD: Data on congenital and acquired CVD are presented separately in parts 1 and 2. Part 1 demonstrates that although the prevalence numbers for North American and European populations are consistent with those reported in reference texts, congenital CVD is actually less prevalent in Asian, African, and Native populations. Therefore, the reported overall 8% prevalence of CVD in men applies only to Euro-Caucasians and is significantly lower in other racial groups. Possible evolutionary implications of dichromatism in humans are explored. Acquired CVD: In this section the current understanding of acquired color vision deficiency, with an estimated prevalence ranging from 5 to 15% (51,95), is reviewed. Acquired CVD is frequently associated with significant impairment of visual acuity and/or visual field. However, many ocular diseases and drugs do primarily affect color vision, independent of other visual function, and one must remain vigilant to their presence. Conclusion: Congenital CVD is present in a consequential percentage of men, but considerable variability exists in different populations (2–8%). Acquired CVD may elude detection, but if severe is also associated with loss of visual acuity and/or visual field. Senescence remains the most common and increasingly prevalent cause for acquired CVD.

Leach J. Cognitive paralysis in an emergency: the role of the supervisory attentional system. Aviat Space Environ Med 2005; 76:134–136.Many witnesses attest that victims of a disaster often perish because they ‘freeze’ in the face of danger. It has been proposed that this cognitive paralysis occurs due to temporal and cognitive constraints on survival response times while leaving open the question of which cognitive component is implicated in this behavior. This paper proposes, firstly, that the temporal constraints which occur during an emergency inhibit the functioning of the supervisory attentional system (SAS), which leads to the victim showing: 1) an appropriate response, if trained; 2) stereotypical or otherwise irrational behavior, if untrained; or 3) cognitive paralysis. Secondly, that the main role of the SAS is to operate as a temporal buffer, enabling a survival response to be prepared prior to facing a life-threatening event and not as a real-time immediate responder. It is argued that the initial cognitive paralysis differs at the cognitive and neurological levels from the more prolonged hypoactive behavior commonly seen in victims rescued from disasters and which is considered to be a form of disassociative reaction.

Syburra T, Sütsch G, Huber S, Schnüriger H, Lachat M, Suter J. Isolated dextrocardia in a commercial pilot candidate. Aviat Space Environ Med 2005; 76:137–140.Positional anomalies of the heart are rare and are seldom found during routine physical examinations. We describe the case of a 25-yr-old Swiss airline pilot candidate whose aeromedical examination was normal except that an unusual ECG raised suspicion, leading to a diagnosis of dextrocardia with a normal arrangement of atria and abdominal viscera. This diagnosis in a pilot candidate should raise concern because a high percentage of such individuals have congenital heart defects. Further tests were conducted to rule out associated cardiac malformations, conduction anomalies, or rhythm disturbances. Testing also excluded other associated diseases such as primary ciliary dyskinesia and Kartagener’s syndrome. Dextrocardia is not listed as a disqualifying condition in the applicable aeromedical regulations (Joint Aviation Authorities Medical Manual, Joint Aviation Requirements-Flight Crew Licensing guidelines). Therefore, after demonstrating that there were no physical, hemodynamic, or electrophysiological abnormalities, the candidate was allowed to enroll in civilian pilot training without restrictions.

Grossman A, Barenboim E, Azaria B, Sherer Y, Goldstein L, Korianski J. Laparoscopic inguinal hernioplasty in aviators. Aviat Space Environ Med 2005; 76:141–143.Repair of inguinal hernias may be performed using either open surgery or laparoscopic techniques. Following surgery, a 6-wk waiting period is generally recommended before a pilot returns to active duty, including flight in high-performance aircraft. A shorter waiting period would be operationally useful and may be possible following either a trans-abdominal preperitoneal (TAPP) laparoscopic technique or a totally extra-peritoneal (TEP) approach. In this manuscript we present the cases of four aviators who underwent inguinal hernia repair via the TEP approach and were returned to the cockpit 21 d later with no evident complications. Although this sample is small, it emphasizes the potential benefit of the TEP approach in aviators.

Torgovicky R, Azaria B, Grossman A, Eliyahu U, Goldstein L. Sinus vein thrombosis following exposure to simulated high altitude. Aviat Space Environ Med 2005; 76:144–146.A relation exists between high altitude exposure and a hypercoagulable state, the nature of which is not entirely clear. This has been mostly reported in mountain climbers. We report a 19-yr-old female, working as a high-altitude chamber instructor, who presented with severe frontal headaches which persisted for a month following routine high altitude chamber training. The patient was in generally good health and was using oral contraceptives for 3 yr prior to the event. Due to the unremitting nature of the symptoms, the patient was admitted to a neurology department, and computerized tomography (CT) and magnetic resonance imaging (MRI) were performed. Sagittal and transverse sinus vein thrombosis were diagnosed and anticoagulant therapy was initiated (low molecular weight heparin followed by warfarin). Following treatment, a slow symptomatic improvement was observed, and the patient was discharged. On discharge, it was recommended she continue oral anti-coagulant therapy (warfarin). A complete coagulation screening panel was performed, which was negative. Although the relation between high altitude exposure and a hypercoagulable state is well known, this is the first time a case of sinus vein thrombosis has been reported after high altitude chamber training. Careful history and closely monitored medical follow-up should be performed on all designated staff exposed to simulated altitude. Even though there is no conclusive evidence regarding it, we suggest, as a matter of caution, that women using oral contraceptives should consider their risks before deciding to undertake exposure to simulated altitude in chambers. Literature review and detailed recommendations for prevention are provided.