Hamilton DR, Murray JD, Kapoor D, Kirkpatrick AW. Cardiac health for astronauts: current selection standards and their limitations. Aviat Space Environ Med 2005; 76:615–626. Introduction: The screening tests for coronary artery disease (CAD) for applicants and the active astronaut corps are similar to those performed in the 1960s. Due to the limited treatment and return capabilities of most space vehicles, an in-flight cardiac event would result in mission failure. Improved CAD screening of astronauts is, therefore, paramount to long-duration mission success. Methods: Literature review was performed to compare active and retired astronaut populations to other asymptomatic low-risk cohorts. All populations were examined to determine the incidence and prevalence of CAD. Framingham risk scores were calculated in NASA’s active and retired astronaut corps and compared with age- and gender-matched controls. Results: The current standards used for astronaut selection have been successful in creating a cohort that has less risk than their age- and gender-matched counterparts from the general population. However, the existing astronaut cardiovascular screening and selection tests do not adequately rule out CAD for long-duration missions, and, therefore, a “significant” risk of cardiac event remains, especially as we look toward Exploration Class missions. Conclusions: The current astronaut selection and retention standards may not adequately prevent cardiac events from occurring with the longer duration flights. Future research should be directed toward increasing the primary and secondary prevention of CAD in the astronaut cohort. In the meantime, the space program should evaluate the use of more aggressive terrestrial screening tools. It is important not to remove all older, experienced pilots from spaceflight crews unless overt or predictable pathology has been clearly identified.
Cymerman A, Muza SR, Friedlander AL, Fulco CS, Rock PB. Saccadic velocity and pupillary reflexes during acclimatization to altitude (4300 m). Aviat Space Environ Med 2005; 76:627–634. Introduction: Oculometrics have been shown to be responsive to acute hypoxemia. We investigated whether oculometrics could be used as an objective index of a hypoxic effect on the central nervous system (CNS) during altitude acclimatization. We hypothesized that oculomotor reflexes [pupil diameter (PD), constriction amplitude (CA), constriction latency (CL), and saccadic velocity (SV)] changed in concert with a select number of accepted acclimatization variables and that these changes correlated with the severity of acute mountain sickness (AMS). Methods: After sea-level, baseline (SLB) measurements were obtained, 18 men (19–33 yr) were transported to Pikes Peak, CO (4300 m), where they remained for 14 d. Periodic measurements (days 1–4, 6, 7, 9, 10, and 12) were made of PD, CA, CL, and SV in addition to heart rate (HR), pulse oximetry (SpO2), end-tidal PO2 and PCO2, 24-h urinary catecholamine concentrations, and AMS severity (environmental symptoms questionnaire, ESQ). Results: PD and CL decreased from SLB on days 1–4 and subsequently returned toward SLB; these changes paralleled changes in ventilatory and circulatory variables. CA decreased on days 1 and 2 and remained decreased for 12 d. SV increased over days 1–6 then returned toward SLB with continued exposure, similar to changes in urinary catecholamines. With acclimatization, CL correlated with HR and SpO2; SV correlated with PCO2, HR, and SpO2. AMS severity peaked during days 2–4, returned toward SLB over the next 10 d, and correlated only with CL (p = 0.045). Conclusions: Oculometrics can be used as an indicator of CNS hypoxia and altitude acclimatization, although there was no strong correlation with AMS severity.
Pilmanis AA, Webb JT, Balldin UI. Partial pressure of nitrogen in breathing mixtures and risk of altitude decompression sickness. Aviat Space Environ Med 2005; 76:635–641. Background: Many aircraft oxygen systems do not deliver 100% O2. Inert gases can be present at various levels. The purpose of this study was to determine the effect of these inert gas levels on decompression sickness (DCS). Methods: Subjects were exposed for 4 h to 5486 m (18,000 ft) with zero prebreathe, using either mild (Test A) or strenuous exercise (Test B), and breathing 60%N2/40%O2. Test C used a breathing mixture of 40%N2/60%O2 at 6858 m (22,500 ft) with zero prebreathe and mild exercise. Test D investigated a breathing mixture of 2.8%N2/4.2%argon/93%O2 with 4 h exposures to 7620 m (25,000 ft), mild exercise, and 90 min of preoxygenation. The controls were from previous studies using similar conditions and 100% O2. Results: The DCS risk for Tests A and B and the Control for B was 7%; the Control for Test A was 0% (n.s.). Breathing the 40%N2/60%O2 mixture (Test C) resulted in 43% DCS compared with 53% DCS with 100% O2 (n.s.). When the 2.8%N2/4.2%argon/93%O2 mixture was used, the results showed 25% DCS compared with 31% DCS with 100% O2 (n.s.). Conclusions: The increased nitrogen and argon levels in the breathing gas while at altitudes of 5486 m to 7620 m did not increase DCS risk. These results support the concept of using the partial pressure gradient of inert gases instead of the percentage of N2 or argon in a breathing gas mixture to determine the risk of DCS during altitude exposure.
Flanagan MB, May JG, Dobie TG. Sex differences in tolerance to visually-induced motion sickness. Aviat Space Environ Med 2005; 76:642–646. Background: Women report a history of motion sickness (MS) about twice as frequently as men, but the results of experimental studies are equivocal. In the present investigation, we sought to replicate previous findings that women report a greater history of MS than men when interrogated with MS history questionnaires. We examined the hypothesis that those reporting that they are prone to MS are less likely to volunteer for MS provocative experiments than those who are MS resistant. Finally, using a subset of these participants, we exposed men and women, during two separate sessions, to visually elicited apparent motion, with and without voluntary head motion (pseudo-Coriolis stimulation), to examine any differences in MS elicited between these two groups on exposure to such motion stimulation. Method: Experiment 1 used a MS History Questionnaire, which included an opportunity for male and female participants to volunteer for “psychology experiments” in the coming semester. This instrument was used to determine effects of sex and volunteer status on motion sickness susceptibility (MSS). Experiment 2 involved exposing a subset of these participants to rotation of a vertically striped rotating drum under static and head movement conditions. Measures of vection and MS were recorded. Results: We found higher MSS scores in women vs. men, particularly when looking at participants who elected to volunteer. Women in the second experiment reported significantly more MS, but they exhibited less tolerance with head movement. No significant differences in vection were observed. Conclusions: The results indicate that laboratory manipulations that are more provocative of MS reveal reliable sex differences.
McLellan TM, Kamimori GH, Voss DM, Bell DG, Cole KG, Johnson D. Caffeine maintains vigilance and improves run times during night operations for Special Forces. Aviat Space Environ Med 2005; 76:647–654. Purpose: This study examined the effects of caffeine (CAF) on vigilance, marksmanship, and run performance during 27 h of sustained wakefulness in Special Forces personnel. Methods: There were 31 soldiers (29.8 ± 5.4 yr, 86.4 ± 8.6 kg) who were divided into placebo (PLAC, n = 15) and CAF (n = 16) groups. A 6.3-km control run was completed on the morning of Day 1. In the evening of Day 2, soldiers performed a control observation and reconnaissance vigilance task (ORVT) in the field. This 90-min task was repeated twice more between 02:00 and 06:00 on Day 3 during an overnight period of sleep deprivation. Marksmanship was assessed before and after the ORVT. PLAC or 200 mg of CAF gum was administered at 01:45, 03:45, and approximately 06:30 on Day 3. A final 6.3-km run commenced within 30 min of receiving the final dose. Results: ORVT was maintained in CAF at control levels of 77 ± 13% during the overnight testing. However, values decreased significantly for PLAC from 77 ± 15% to 54 ± 29% and 51 ± 31% during the first and second overnight testing periods, respectively. CAF had no effect on marksmanship but improved 6.3-km run times by 1.2 ± 1.8 min. Run times slowed for PLAC by 0.9 ± 0.8 min from approximately 35 min during the control run; the changes in performance were significant between groups. Conclusions: It was concluded that CAF maintained vigilance and improved running performance during an overnight field operation for Special Forces personnel.
Hope A, Hjelle J, Aanderud L, Aakvaag A. Time and temperature effects on body fluid loss during dives with the open hot-water suit. Aviat Space Environ Med 2005; 76:655–660. Background: Bodyweight (BW) losses up to 5 kg have been observed during diving with the open hot-water suit (HWS). The objective of these dives was to study the hormonal, hematological, and renal effects of dehydration during shallow HWS diving. Methods: In series 1, four divers dove for 3.5 h each day for 7 d. In series 2, 12 divers dove to 6–8 msw for 1, 2, and 4 h. Blood and urine samples, BW measurements, oral temperature, and thermal stress indices were collected. Results: Average ΔBW (± SD) for the 28 dives in series 1 was 1.5 ± 0.8 kg, and the largest BW reductions were 3.2 and 3.0 kg, corresponding to 3.7 and 4.7% of BW. Changes in thermal stress, hemoglobin, hematocrit, aldosterone, and electrolyte excretion correlated with BW reduction. In series 2, average BW reductions were 0.46 ± 0.27, 0.96 ± 0.38, and 1.55 ± 0.59 kg during 1-, 2-, and 4-h dives. BW reduction correlated significantly with thermal stress (p < 0.01). Aldosterone increased after 1 and 2 h and plasma renin activity was unchanged. Atrial natriuretic peptide increased in all dives (p < 0.01) and arginine vasopressin increased in the 4-h dives (p < 0.05). The 7.2% decrease in plasma volume, the increases in hemoglobin, hematocrit and serum proteins, and an unchanged plasma osmolality indicate an isotonic dehydration after the 4-h dives. Conclusions: BW loss during HWS diving is mainly caused by sweating. Dives of 4 h produce an isotonic dehydration and a break for fluid intake is, therefore, recommended.
Partner AM, Scott RAH, Shaw P, Coker WJ. Contact lenses and corrective flying spectacles in military aircrew—implications for flight safety. Aviat Space Environ Med 2005; 76:661–665. Background: Refractive devices used by aviators need to suit the aerospace environment or their failure can have serious implications. A relatively minor visual disability can result in loss of life and aircraft. We surveyed commonly occurring problems with the different types of refractive correction worn by Royal Air Force (RAF) aircrew over the previous 12 mo. We also asked if they had experienced any flight safety incidents (FSI) relating to their refractive correction. Methods: A retrospective anonymous questionnaire survey was given to 700 active aircrew occupationally graded as requiring corrective flying spectacles (CFS) or contact lenses (CL) for flying. Results: 63% (443) of the questionnaires were completed. CL were worn by 53% of aircrew; 71% of them used daily disposable CL. CFS were worn by the remaining 47% of aircrew, 14% of whom used multifocal lenses. Of CFS wearers, 83% reported problems including misting, moving, discomfort, and conflict with helmet-mounted devices (HMD). CL-related ocular symptoms were reported in 67% of wearers including cloudy vision, dry eye, photophobia, red eyes, excessive mucus formation, CL movement, itching, and grittiness. No CL-related FSI were reported over the previous 12 mo compared with 5% CFS-related FSI (p < 0.001). The graded performance of CL for vision, comfort, handling, convenience, and overall satisfaction was significantly higher than for CFS. Conclusion: CFS are associated with problems in terms of comfort and safety. CL are well tolerated by aircrew, and deliver improved visual performance.
Blatteau J-É, Gempp E, Galland F-M, Pontier J-M, Sainty J-M, Robinet C. Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med 2005; 76:666–669. Background: A single bout of aerobic exercise 24 h before a dive significantly reduces the formation of circulating venous gas emboli (VGE) on decompression. The purpose of this investigation was to determine the effect of aerobic exercise 2 h before a dive. Methods: There were 16 trained military divers who were compressed to 30 msw (400 kPa) for 30 min breathing air in a dry hyperbaric chamber at rest, then decompressed at a rate of 10 m · min−1 with a 9-min stop at 3 msw. Each diver performed two dives 3 d apart, one with and one without exercise that consisted of running for 45 min at 60–80% of maximum heart rate (estimated as 220 − age). VGE were graded according to the Spencer scale using a pulsed Doppler detector on the precordium at 30 min (T30) and 60 min (T60) after surfacing. Results: Mean bubble grades at T60 were 1.25 for control dives and 0.44 for dives preceded by exercise, the difference being highly significant. None of the divers showed an increase in venous bubble grade after exercise. Conclusion: Like exercise 24 h ahead, 45 min of running 2 h before a dive decreases bubble formation after diving, suggesting a protective effect of aerobic exercise against DCS. The threshold of exercise intensity and duration necessary to change venous circulating bubbles is unknown. Mechanisms underlying the protective effect of exercise remain unclear. Rather than altering the nitrogen elimination rate, exercise may affect the population of gaseous nuclei from which bubbles form.
Taneja N, Pinto LJ, Dogra M. Aircrew ejection experience: questionnaire responses from 20 survivors. Aviat Space Environ Med 2005; 76:670–674. Background: Published studies on ejection have focused predominantly on the injuries sustained by aircrew and discussed their preventive measures from an aeromedical perspective. However, studies have not discussed aircrew experiences related to ejection or how they would like to advise other aircrew to successfully handle ejection as an event. Such information can assist in designing realistic indoctrination and training programs. This study was conducted to fill gaps in our understanding of aircrew perspectives of successful ejections. Methods : Aircrew reporting to the Institute of Aerospace Medicine (IAM), Indian Air Force, for post-ejection evaluation during the period of May 2003 to January 2005 completed a questionnaire that was designed for the study. Results : A total of 20 aircrew completed this questionnaire. The mean age of the aircrew was 30.25 ± 4.45 yr. Most of them had logged more than 500 flying hours. Some aircrew described their initial moments of ejection as “blacked out,” “dazed, yet conscious,” or as “a shock that gradually decreased.” Practicing ejection drills on the ground, being prepared at all times, making a timely decision to eject, and assuming correct posture were identified as the most important factors for success. Descriptions of ejection as an event suggest intense emotional arousal could occur following ejection. Discussion : This study provides first hand inputs into the psychological processes accompanying ejections. Such information could be very useful in understanding the critical factors that influence successful ejection.
Ludwig DA. Use and misuse of p-values in designed and observational studies: guide for researchers and reviewers. Aviat Space Environ Med 2005; 76:675–680.Analysis of scientific data involves many components, one of which is often statistical testing with the calculation of p-values. However, researchers too often pepper their papers with p-values in the absence of critical thinking about their results. In fact, statistical tests in their various forms address just one question: does an observed difference exceed that which might reasonably be expected solely as a result of sampling error and/or random allocation of experimental material? Such tests are best applied to the results of designed studies with reasonable control of experimental error and sampling error, as well as acquisition of a sufficient sample size. Nevertheless, attributing an observed difference to a specific treatment effect requires critical thinking on the part of the scientist. Observational studies involve data sets whose size is usually a matter of convenience with results that reflect a number of potentially confounding factors. In this situation, statistical testing is not appropriate and p-values may be misleading; other more modern statistical tools should be used instead, including graphic analysis, computer-intensive methods, regression trees, and other procedures broadly classified as bioinformatics, data mining, and exploratory data analysis. In this review, the utility of p-values calculated from designed experiments and observational studies are discussed, leading to the formation of a decision tree to aid researchers and reviewers in understanding both the benefits and limitations of statistical testing.
Grossman CM, White JC, Dunn PM. Pulmonary embolism aggravated by two short flights 3 days apart. Aviat Space Environ Med 2005; 76:681–683.An elderly internist experienced aggravation of preexisting pulmonary emboli following each of two short flights of 75 min apiece 3 d apart. A brief discussion of risk factors is included. It is suggested that pertinent reports should separate venous thromboembolic disease (VTE) from uncomplicated deep venous thrombosis (DVT).
Sulit DJ, Clarke JE. Psoriatic arthritis in a military aviator. Aviat Space Environ Med 2005; 76:684–688.Psoriatic arthritis is a chronic spondyloarthropathy whose pathogenesis is unknown. We present a case of a naval flight officer who presented with chronic psoriatic arthritis, which ultimately became well controlled with etanercept treatment. The naval flight officer was granted military aeromedical waivers for psoriatic arthritis, cutaneous psoriasis, and chronic medication use. We also review the medical literature on psoriatic arthritis disease and etanercept and discuss their aeromedical implications in military aviation.
Gibson TM, Harrison MH. Aviation medicine in the United Kingdom: from the end of World War I to the end of World War II, 1919–1945. Aviat Space Environ Med 2005; 76:689–691.This is the second of three brief papers that summarize the history of Aviation Medicine in the Royal Air Force. British aviation medicine research was rescued from the doldrums of retrenchment after the end of the First World War by the need to support attempts on world records for height and speed. Despite this, the outbreak of the Second World War still found the British inadequately prepared. This part of the account of British aviation medicine research charts its transition from an organization with three full-time workers into a thriving research institute.
Gontcharov IB, Kovachevich IV, Pool SL, Navinkov OL, Barratt MR, Bogomolov VV, House N. In-flight medical incidents in the NASA-Mir program. Aviat Space Environ Med 2005; 76:692–696.This paper summarizes medical experience during the six NASA-Mir flights from March 14, 1995, to June 4, 1998. There were 7 U.S. astronauts who were part of 6 Mir space crews and worked jointly with 12 Russian cosmonauts. Advances in space medicine have created a safer environment; however, experience shows that crewmembers experience traumatic injuries and illnesses of diverse etiologies during spaceflight. During these joint flights both Russian and U.S. medical kits were available to crewmembers who could access either medical kit as appropriate. The Russian medical team had primary responsibility for monitoring and care of all crewmembers and analyzing medical results. When medical incidents occurred, the appropriate Russian or U.S. medical team determined the plan for diagnosis and treatment. Each team kept the other informed regarding medical situations during the flights and strictly observed the principles of medical confidentiality. A summary of medical incidents by programmatic element is described as experienced by the crewmembers and the ground support medical teams. The most frequent medical cases were small traumatic injuries to the skin and mucous membranes and fluctuations in the cardiovascular system, manifesting primarily in the form of cardiac dysrhythmias. The ability to use both the Russian medical aids and the U.S. medical kit significantly increased the effectiveness and reliability of therapeutic and prophylactic care. The degree of medical care and cooperation established precedents for integrating these systems for the medical support of expeditions on the International Space Station.