Genc KO, Humphreys BT, Cavanagh PR. Enhanced daily load stimulus to bone in spaceflight and on Earth. Aviat Space Environ Med 2009; 80:919–26.Introduction: It has been hypothesized that bone loss arising from long-duration space travel is caused by a reduction in mechanical stimuli to the skeleton. The daily load stimulus (DLS) theory was first proposed to relate daily time histories of mechanical loading from ground reaction forces to bone homeostasis. In this methods paper, an enhanced daily load stimulus (EDLS) is proposed to account for recently developed theories on saturation and recovery of the osteogenic potential of bone with repeated cyclic loading and the potential benefits of standing. Model Development: To determine periods of continuous activity (sitting, standing, walking, running, and other activity), an activity determination algorithm based on entire days of in-shoe forces was developed. The rainflow peak counting method was used to analyze the in-shoe force data from entire working days in preparation for the calculation of the EDLS. Parameters characterizing saturation and recovery with cyclical loading from running and walking as well as the effects of standing were estimated based on data in the literature. Discussion: The activity algorithm proved to be accurate and robust when applied to in-shoe force data from entire waking days. The EDLS may be useful in prescribing “dose-based” exercise prescriptions to crewmembers during long-duration spaceflights and missions to the Moon and Mars. Validation of the proposed EDLS model will be possible with data from an ongoing human bed rest study examining changes in bone mineral density with controlled skeletal loading.

Gennser M, Blogg SL. Venous gas emboli in goats after simulated submarine escape from 290 msw breathing air or hyperoxic gas. Aviat Space Environ Med 2009; 80:927–32.Introduction: Escape from a disabled submarine has many inherent risks including the development of venous gas emboli (VGE). Breathing hyperoxic gas during rapid ascent from 2500 kPa (240 msw) reduces VGE; we investigated whether it would also be beneficial during an escape from 3000 kPa (290 msw), thought to be at the limit of human escape from a sunk sub. Methods: Adult castrated male or female goats (45-85 kg; N = 35) underwent dry chamber compression to 3000 kPa in 28 s, then decompressed at a rate of 2.75 m · s⁻¹ while breathing either air or hyperoxic gas (60/40% O₂/N₂). Postsurfacing, precordial Doppler measurements were made using the Kisman Masurel (KM) scoring system; the animals were observed for signs of decompression illness (DCI) and/or oxygen toxicity. Results: Six animals in the air group (N = 19) and two in the hyperoxic group (N = 10) suffered from severe pulmonary barotrauma on surfacing and were euthanized. No cases of DCI arose later than 5 min postsurfacing. Oxygen toxicity was not observed. Although initial bubble scores (median KM score 4) were the same in both groups, the time taken for the median KM score to reach 3 or less was significantly faster in the hyperoxic group (20 min vs. 120 min). Disappearance of VGE was faster in the hyperoxic group. Conclusion: Breathing hyperoxic gas during escape from 3000 kPa reduces the overall time with circulating VGE and, despite exposure to a maximum inspired partial pressure of oxygen of 1.8 MPa, symptoms of oxygen toxicity were not observed.

Connolly DM, Barbur JL. Low contrast acuity at photopic and mesopic luminance under mild hypoxia, normoxia, and hyperoxia. Aviat Space Environ Med 2009; 80:933–40.Introduction: Visual acuity is compromised under low luminance, low contrast viewing conditions that occur in contemporary night flying, but the effect of hypoxia on low contrast acuity in dim light remains poorly defined. This study examined the effects of oxygenation state on the contrast thresholds required to maintain visual acuity in 12 subjects at low photopic (12 cd · m⁻²), upper mesopic (1 cd · m⁻²), and mid-mesopic (0.1 cd · m⁻²) luminance. Methods: The Contrast Acuity Assessment test (City University, London) was used to measure the contrast thresholds needed for gap orientation discrimination using a Landolt C stimulus. The thresholds were measured at the fovea and at eccentricities up to ± 5° from fixation under mild hypoxia (breathing 14.1% oxygen), hyperoxia (100% oxygen), and normoxia (air). The diameter of the pupil was measured using infrared imaging and the influence of oxygenation state on pupil size assessed. Subsequently, normoxic thresholds were measured in detail under conditions of constant retinal illuminance to enable prediction of the effects of oxygenation state in the mesopic range. Results: Relative to normoxia, hypoxia caused the contrast thresholds to increase at all light levels, but particularly at mesopic luminance. Hyperoxia decreased contrast thresholds, but only at the lowest light level. In general, hypoxia caused a reduction in mean pupil size while hyperoxia caused the pupil to dilate. Subjects with naturally smaller pupils tended to exhibit greater hypoxic impairment. Conclusions: Mild hypoxia degrades low contrast acuity progressively with decreasing mesopic luminance. At 0.1 cd · m⁻², supplementary oxygen enhances low contrast acuity, implying that visual performance is oxygen-dependent in the mid-mesopic range. Relative to performance under mild hypoxia at 3048 m (10,000 ft), supplementary oxygen can extend functionally useful vision to lower light levels. The findings are relevant to contemporary military night flying, viewing the external scene directly or through night vision devices, or viewing dimly illuminated flight deck instruments.

Bonato F, Bubka A, Palmisano S. Combined pitch and roll and cybersickness in a virtual environment. Aviat Space Environ Med 2009; 80:941–5.Background: Stationary subjects who perceive visually induced illusions of self-motion, or vection, in virtual reality (VR) often experience cybersickness, the symptoms of which are similar to those experienced during motion sickness. An experiment was conducted to test the effects of single and dual-axis rotation of a virtual environment on cybersickness. It was predicted that VR displays which induced illusory dual-axis (as opposed to single-axis) self-rotations in stationary subjects would generate more sensory conflict and subsequently more cybersickness. Methods: There were 19 individuals (5 men, 14 women, mean age = 19.8 yr) who viewed the interior of a virtual cube that steadily rotated (at 60° · s⁻¹) about either the pitch axis or both the pitch and roll axes simultaneously. Subjects completed the Simulator Sickness Questionnaire (SSQ) before a trial and after 5 min of stimulus viewing. Results: Post-treatment total SSQ scores and subscores for nausea, oculomotor, and disorientation were significantly higher in the dual-axis condition. Conclusions: These results support the hypothesis that a vection-inducing VR stimulus that rotates about two axes generates more cybersickness compared to a VR stimulus that rotates about only one. In the single-axis condition, sensory conflict and pseudo-Coriolis effects may have led to symptoms. However, in the dual-axis condition, not only was perceived self-motion more complex (two axes compared to one), the inducing stimulus was consistent with twice as much self-motion. Hence, the increased likelihood/magnitude of sensory conflict and pseudo-Coriolis effects may have subsequently resulted in a higher degree of cybersickness in the dual-axis condition.

Butler C, Griffin MJ. Motion sickness with combined fore-aft and pitch oscillation: effect of phase and the visual scene. Aviat Space Environ Med 2009; 80:946–54.Background: The view ahead influences the motion sickness of car passengers but has been found to have little influence on the sickness caused by low frequency fore-and-aft oscillation. Acceleration and deceleration of vehicles is accompanied by pitch motions that may influence sickness. Hypotheses: It was hypothesized that: 1) a visual scene would influence sickness caused by combined fore-and-aft and pitch oscillation; and 2) sickness would be dependent on the phase between the fore-and-aft oscillation and the pitch oscillation. Method: While viewing one of three visual scenes (internal view, blindfold, or external view), 6 groups of 20 subjects were exposed for 30 min to 1 of 2 motions (in-phase or out-of-phase combinations of 0.1 Hz fore-and-aft and pitch oscillation). The 0.1-Hz fore-and-aft oscillation at ± 1.26 ms⁻² rms (displacement of ± 3.18 m) was combined with ± 3.69° pitch oscillation either in phase (so the pitch increased acceleration in the plane of the seat to ± 1.89 ms⁻²) or out of phase (to reduce acceleration to ± 0.63 ms⁻²). Results: With both types of motion (in-phase and out-of-phase oscillation) there was significantly less sickness with an external view than with an internal view or a blindfold. There was evidence of an interaction between the effects of viewing condition and the effect of the phase between the fore-and-aft and the pitch oscillation consistent with blindfolded subjects experiencing less sickness when they experienced greater forces. Conclusions: Motion sickness caused by combined fore-and-aft and pitch oscillation depends on both the visual scene and the phase between the fore-and-aft and pitch motions. The minimization of sickness arising from such motions should involve the optimization of both the visual environment and the phase.

Fulco CS, Muza SR, Beidleman B, Jones J, Staab J, Rock PB, Cymerman A. Exercise performance of sea-level residents at 4300 m after 6 days at 2200 m. Aviat Space Environ Med 2009; 80:955–61.Partial acclimatization resulting from staging at moderate altitude reduces acute mountain sickness during rapid exposure to higher altitudes (e.g., 4300 m). Whether staging also benefits endurance performance has not yet been scientifically evaluated. Purpose: Determine the effectiveness of staging at 2200 m on time trial (TT) performance of unacclimatized sea-level residents (SLR) during rapid exposure to 4300 m. There were 10 healthy men (mean ± SE: 21 ± 1 yrs) who performed 720 kJ cycle TT at SL and following ~2 h of exposure to 4300 m (459 Torr) before (ALT-1) and after (ALT-2) living for 6 d at 2200 m (601 Torr). Methods: Hemoglobin concentration ([Hb]), hematocrit (Hct), arterial oxygen saturation (S_ao₂), ratings of perceived exertion (RPE), and heart rate (HR) were measured before and during exercise. Results: Compared to SL (73 ± 6 min), TT performance was impaired (P < 0.01) by 38.1 ± 6 min at ALT-1, but only by 18.7 ± 3 min at ALT-2. The 44 ± 8% TT improvement at 4300 m was directly correlated with increases in exercise S_ao₂ (R = 0.88, P < 0.03), but not to changes in [Hb] or Hct. In addition, RPE was lower (13 ± 1 vs.16 ± 1, P < 0.01) and HR remained at ~148 ± 5 bpm despite performing the TT at a higher power output during ALT-2 than ALT-1 (120 ± 7 vs.100 ± 10 W, P < 0.01). Conclusion: Partial acclimatization resulting from staging attenuated the impairment in TT performance of SLR rapidly exposed to 4300 m. The close association between improved TT performance and changes in exercise S_ao₂, compared to a lack of association with changes in [Hb] or Hct, suggest ventilatory acclimatization may have been the major factor contributing to the performance improvement.

Taylor MK, Mujica-Parodi LR, Potterat EG, Momen N, Dial Ward MD, Padilla GA, Markham AE, Evans KE. Anger expression and stress responses in military men. Aviat Space Environ Med 2009; 80:962–7.Introduction: A better understanding of individual differences in the human stress response may enhance prevention and treatment of operational stress reactions. In this study, we examined the relationships of anger experience and expression to stress indices during daily living and in response to military survival training in 45 men. Methods: Prior to participation in survival training, subjects completed self-report measures of perceived stress and anger. The revised Impact of Event Scale was then administered 24 h after the conclusion of training. Results: As expected, outward anger expression was positively associated with perceived stress during free living (P < 0.0125). Outward anger expression, inward anger expression, and angry temperament then combined to account for 25% of the variance in psychological impact of a stressful mock-captivity challenge. Conclusion: Anger characteristics are associated with human stress endpoints, both during daily living and in response to an ecologically valid stressor. These findings may assist in the prevention and treatment of operational stress reactions.

Rayman RB. Essential thrombocythemia: aeromedical considerations. Aviat Space Environ Med 2009; 80:968–70.Essential thrombocythemia is a chronic myeloproliferative disease with possible thrombotic and hemorrhagic complications due to an abnormal increase in platelets. It is diagnosed by platelet count and the presence of increased numbers of megakaryocytes in the bone marrow. Most patients remain asymptomatic, although thrombotic events can occur in most systems of the body. A number of treatment medications are available, including hydroxyurea, anagrelide, interferon alpha, and sodium salicylate. Aeromedical disposition of aircrew engaged in civil and military aviation would depend upon the nature of operations, tolerance to the medications prescribed, and the occurrence of complications. For spaceflight, disqualification would be most prudent.

Powell-Dunford N, Cuda AS, Moore JL, Crago MS, Deuster PA. Menstrual suppression using oral contraceptives: survey of deployed female aviation personnel. Aviat Space Environ Med 2009; 80:971–5.Introduction: Increasing numbers of women perform aviation duties in the combat flight environment. Oral contraceptive pills (OCPs) afford numerous health and operational benefits, including prevention of anemia and suddenly incapacitating conditions, as well as menstrual suppression when taken continuously. Until now, the use of OCPs in the combat flight environment has not been examined. Methods: An anonymous, voluntary questionnaire was distributed to 62 female U.S. Army aviation personnel who had recently deployed in support of combat flight operations to characterize continuous OCP use and perceived barriers to this practice, as well as to determine associations with menstrual burden. Results: There were 81% (N = 50) of the women who had personal experiences using OCPs and 93% (N = 58) were aware that continuous use can suppress menstruation. For deployment, 66% (N = 41) desired menstrual suppression, yet only 33% (N = 20) reported any OCP use. Even fewer (15%; N = 10) reported using continuously. Of the women who did not use OCPs continuously, 35% had insufficient knowledge about OCPs and 44% of women reported difficulty in remembering to take a daily pill. Continuous OCP users were more compliant (P = 0.019), reported less spotting (P = 0.007) and fewer unexpected menstrual cycles (P = 0.03) than conventional OCP users. A trend toward reduced cramping was noted (P = 0.064). Most women (60%) desired standardized entry-level education about menstrual suppression through OCPs. Conclusions: The use of continuous OCPs is low in deployed women with aviation-related duties, yet a majority desires menstrual suppression. Continuous OCP use in this setting is associated with significantly improved compliance and significant reductions in specific menstrual burdens. Entry-level education is desirable and may reduce barriers to continuous OCP use by addressing risks, side effects, and daily pill adherence strategies. Flight surgeons should provide further education and consider continuous OCP dosing in the austere environment of combat flight.

Hynynen E, Konttinen N, Rusko H. Heart rate variability and stress hormones in novice and experienced parachutists anticipating a jump. Aviat Space Environ Med 2009; 80:976–80.Introduction: Chronic work stress and overtraining are known to influence heart rate (HR) and heart rate variability (HRV) at rest and decreased nocturnal HRV is associated with cardiovascular health and disease. The purpose of this study was to examine whether anticipation of an acute highly stressful event influences HR and HRV during the night and morning. Methods: Nocturnal HR and HRV and urinary stress hormones (cortisol, adrenaline, noradrenaline) as well as HR and HRV responses to an orthostatic test on the morning of a parachute jump day or control day were analyzed from 14 novice and 7 experienced parachute jumpers. Results: There were no differences in any HRV indices during the night or the orthostatic test between the jump and control situations. The novices had higher HR than experienced jumpers in the orthostatic test in the morning and also during the jump, but no differences were found between the groups in nocturnal HR and HRV indices or HRV indices during the orthostatic test. There were no differences in nocturnal stress hormone secretions except slightly elevated adrenaline secretion during the jump night compared to the control night (P = 0.014). Conclusions: The parachute jump did not substantially influence HR, HRV, or stress hormones during the night or the orthostatic test in the morning preceding the jump. The results suggest that the parachute jump as an acute highly stressful event had no anticipatory effect on autonomic modulation of the heart even though both the novices and experienced jumpers had markedly accentuated sympathetic activation during the parachuting.

Deviri E, Caine Y, Henig-Hadar A, Saute M, Ish Tov E. Aeromedical transport of a patient with massive chylothorax following pneumonectomy for mesothelioma. Aviat Space Environ Med 2009; 80:981–3.Introduction: Long-distance transportation of a patient in an unstable condition is a challenging operation. When circumstances require using a commercial flight it is even more so. Case Report: A 57-yr-old man in Israel underwent extrapleural pneumonectomy for mesothelioma, following which he developed a massive chylothorax of more than 6 L · d⁻¹. Due to the failure of medical treatment and the high operative risk under such conditions, it was decided to transfer him to the United States by commercial flight for a percutaneous, fluoroscopy-guided closure of the thoracic duct. The patient was accompanied by a physician and a non-medical assistant and occupied a first-class seat enclosed by curtains. He arrived at the departure airport in a hypovolemic state with low cardiac output and blood pressure of 78/60 Torr. During the flight he was treated with intravenous fluids, chest physiotherapy, and oxygen. In addition, fibrin clots blocked the drainage system on two occasions, requiring corrective action. On arrival in the United States the patient's condition had improved: his blood pressure was 123/91 Torr with a capillary oxygen saturation of 95% without supplementary oxygen. During the 18 h in transit (11 h in flight) he had lost more than 5 L of lymph. Conclusion: Under carefully controlled circumstances it is possible to use commercial flights to transport patients whose condition is unstable and complicated. Safety can be increased by focusing on the specific problems associated with the clinical condition and anticipating possible adverse events during the flight.

Wagner EB, Charles JB, Cuttino CM. Opportunities for research in space life sciences aboard commercial suborbital flights. Aviat Space Environ Med 2009; 80:984–6.The emergence of commercial suborbital spaceflight offers a wide range of new research and development opportunities for those in the space life sciences. Large numbers of diverse flyers, frequent re-flights, and flexible operations provide a fertile ground for both basic and applied science, as well as technology demonstrations. This commentary explores some of the unique features available to the space life science community and encourages engagement with commercial developers and operators during the design phase to help optimize platform designs and operations for future research.

Waldroup AW. You're the flight surgeon: malaria. Aviat Space Environ Med 2009; 80:991–2.

Graveline DE, McCally M. Body fluid distribution: implications for zero gravity. Aerosp. Med. 1962; 33:1281.