BACKGROUND: Seven astronauts after 6-mo missions to the International Space Station showed unexpected vision problems. Lumbar punctures performed in the four astronauts with optic disc edema showed moderate elevations of cerebral spinal fluid pressure after returning to Earth. We hypothesized that lower body negative pressure (LBNP) imposed during head-down tilt (HDT) would reduce intraocular pressure (IOP) and transcranial ultrasound pulse amplitude, a noninvasive intracranial pressure (ICP) surrogate.METHODS: Participating in this study were 25 normal healthy nonsmoking volunteers (mean age: 36 yr). Subjects were positioned supine (5 min), sitting (5 min), 15° whole body HDT (5 min), and 10 min of HDT with LBNP (25 mmHg). The order of HDT and HDT+LBNP tests was balanced. Right and left IOP, transcranial ultrasound pulse amplitude, arm blood pressure, and heart rate were measured during the last minute (steady state) of each testing condition.RESULTS: IOP significantly decreased from supine to sitting posture by 3.2 ± 1.4 mmHg (mean ± SD: N = 25), and increased by 0.9 ± 1.3 mmHg from supine to the HDT position. LBNP during HDT significantly lowered IOP to supine levels. In addition, LBNP significantly reduced transcranial ultrasound pulse amplitudes by 38% as compared to the HDT condition (N = 9). Sitting mean blood pressure (BP) was significantly higher (+5 mmHg) than BP values after 10 min of LBNP during HDT. However, heart rate was not significantly different across all conditions.DISCUSSION: These data suggest that short duration exposures to LBNP attenuate HDT-induced increases in IOP and ICP.Macias BR, Liu JHK, Grande-Gutierrez N, Hargens AR. Intraocular and intracranial pressures during head-down tilt with lower body negative pressure. Aerosp Med Hum Perform. 2015; 86(1):3–7.

BACKGROUND: Weightlessness results in negative physiological changes. Excessive iron in organisms likewise leads to numerous damages. In this study, we investigated the effect of a combination of iron overload and weightlessness simulated by tail-suspending on rats.METHODS: Male Wistar rats were randomly divided into four groups: control (CON), iron overload (IO), simulated weightlessness (SW), and iron overload plus simulated weightlessness (IO+SW). After the experiment, the rats were evaluated through routine blood, serum ferritin, histology, and micro-computed tomography analyses.RESULTS: As compared to CON, a combination of IO and SW resulted in a 15.9% loss of rat bodyweight versus treatment with each alone (3.3% in IO, 11.7% in SW group). Although iron overload is mainly responsible for an increase in hemoglobin (4.7% in IO the group) and serum ferritin (71.7% in IO group) concentration, simulated weightlessness facilitates such increase (5.3% and 118.4% in IO + SW group, respectively). Similarly, iron overload resulted in severe iron deposition on the liver and spleen, and the deposition became more serious in the combined model. In contrast, the simulated weightlessness is mainly responsible for the damage to the femur.DISCUSSION: All the results demonstrated that the combined conditions exhibited a significantly different effect on rats from those with either simulated weightlessness or iron overload alone, and that these different effects are organ-dependent.Wang A, Zang J, Wang J, Nie G, Zhao G, Chen B. Excessive iron and weightlessness effects on the femurs and livers of rats. Aerosp Med Hum Perform. 2015; 86(1):8–14.

INTRODUCTION: Positive pressure breathing (PPB) can cause circulatory dysfunction due to peripheral pooling of blood. This study explored a better way at ground level to simulate pure oxygen PPB at 59,055 ft (18,000 m) by comparing the physiological changes during PPB with pure oxygen and low oxygen at ground level.METHODS: Six subjects were exposed to 3 min of 69-mmHg PPB and 3 min of 59-mmHg PPB with pure oxygen and low oxygen while wearing the thoracic counterpressure jerkin inflated to 1× breathing pressure and G-suit inflated to 3 and 4× breathing pressure. Stroke volume (SV), cardiac output (CO), heart rate (HR), and peripheral oxygen saturation (S_po₂) were measured. Subjects completed a simulating flying task (SFT) during 3-min PPB and scores were recorded.RESULTS: HR and SV responses differed significantly between breathing pure oxygen and low oxygen. CO response was not significantly different for pure oxygen and low oxygen, the two levels of PPB, and the two levels of G-suit pressure. S_po₂ declined as a linear function of time during low-oxygen PPB and there was a significant difference in S_po₂ response for the two levels of PPB. The average score of SFT during pure oxygen PPB was 3970.5 ± 1050.4, which was significantly higher than 2708.0 ± 702.7 with low oxygen PPB.CONCLUSIONS: Hypoxia and PPB have a synergistic negative effect on both the cardiovascular system and SFT performance. PPB with low oxygen was more appropriate at ground level to investigate physiological responses during PPB and evaluate the protective performance of garments.Liu X, Xiao H, Shi W, Wen D, Yu L, Chen J. Physiological effects of positive pressure breathing with pure oxygen and a low oxygen gas mixture. Aerosp Med Hum Perform. 2015; 86(1):15–20.

INTRODUCTION: Perfluorocarbon (PFC) formulations can be a useful adjunct treatment for decompression sickness (DCS) when staged decompression procedures cannot be followed due to time constraints or lack of equipment. The benefit of PFC treatment is believed to result from its ability to transport more dissolved gas than can be transported by blood alone. Dodecylfluoropentane (DDFPe) is a unique nanodroplet compound that expands into a gaseous state when exposed to physiological temperatures, resulting in a higher dissolved gas-carrying capacity than standard PFC formulations.METHODS: We investigated the efficacy of DDFPe in reducing morbidity and mortality in a rat model of severe DCS. Male Sprague-Dawley rats (250-280 g) were compressed to 210 fsw for 60 min before rapid decompression. Animals were immediately injected with 2% DDFPe (0.07 ml · kg⁻¹, 0.5 ml · kg⁻¹, 1.0 ml · kg⁻¹) or saline, and were transferred to a 100% O₂ environment for 30 min.RESULTS: Of the animals in the saline group, 47% (18/38) did not survive the decompression event, while ∼98% (46/47) of the animals in the DDFPe group did not survive. Of the animals that died during the observation period, the saline group survived on average 89% longer than DDFPe treated animals. Seizures occurred in 42% of the DDFPe group vs. 16% in the saline group. Histological analysis revealed the presence of large, multifocal gas emboli in the liver and heart of DDFPe treated animals.CONCLUSIONS: We conclude that DDFPe is not an effective nonrecompressive treatment for DCS in rodents.Sheppard RL, Regis DP, Mahon RT. Dodecafluoropentane (DDFPe) and decompression sickness-related mortality in rats. Aerosp Med Hum Perform. 2015; 86(1):21–26.

BACKGROUND: Habitual exposure to carbon dioxide (CO₂) is expected, but it is not proven, to dull ventilatory sensitivity to co₂ by reducing hypercapnic ventilatory response (HCVR) as it is expressed by the slope of the derived response curve (CO₂ sensitivity: V_E/P_etco₂). It was hypothesized that HCVR is decreased by repeated breath hold maximal efforts (RBHE) before and after apnea training in comparison with no training and the control condition.METHODS: Two groups of breath holders, a control (CBH) group and novices to breath hold activities (NBH), visited the laboratory on four different occasions. In the first visit, subjects performed a HCVR test, whereas in the second visit they completed five successive RBHE separated by 2-min intervals. Another HCVR test was performed 2 min after cessation of the last apnea. For the next 14 d, only the NBH group trained by performing daily five RBHE separated by 2-min intervals. Subsequently, in a third and a fourth condition, subjects repeated the experimental protocol of the second and first visit.RESULTS: Although breath hold time (BHT) increased after apnea training in the NBH group by 46%, CO₂ sensitivity slopes were not different among experimental conditions and groups (2.8 0.3, 2.9 0.4 L min¹ mmHg¹ in the CBH and 2.7 0.5, 2.7 0.3 L min¹ mmHg¹ in the NBH during the second and third visit, respectively).CONCLUSION: HCVR after five RBHE or 14 d of apnea training was not decreased despite the achieved BHT enhancement. Hypercapnic dullness of ventilation is a complex biological process which takes more than 14 d of training to develop.Bourdas DI, Tsakiris TS, Pavlakis KI, Triantafillou DV, Geladas ND. Repeated apneas and hypercapnic ventilatory response before and after apnea training. Aerosp Med Hum Perform. 2015; 86(1):2733.

INTRODUCTION: Deep dives using rebreather devices result in oxygen exposures that carry a risk of cerebral oxygen toxicity. Elevation of arterial CO₂ levels increases this risk. CO₂ retention may occur during the deep working phases of dives, but it has not been investigated in ‘real world’ dives at the end of resting decompression when oxygen exposures are peaking, often to levels higher than recommended maxima.METHODS: We conducted an observational field study to measure end tidal CO₂ (P_etco₂) in divers surfacing after decompression. Sixteen rebreather divers conducted two dives and two completed one dive (a total of 34 dives) to depths ranging from 44–55 msw. Bottom times ranged from 35 to 56 min and time spent on decompression ranged from 40 to 92 min. The first breaths on reaching the surface after removing the rebreather mouthpiece were taken through a portable capnograph. The P_etco₂ was recorded for the first breath that produced a clean capnography trace. P_etco₂ measurement was repeated for each subject 2–3 h after diving to give paired observations.RESULTS: There were no differences between mean surfacing P_etco₂ [36.8 mmHg (SD 3.0)] and the mean P_etco₂ made later after diving [36.9 mmHg (SD 4.0)]. One subject on one dive returned a surfacing P_etco₂ higher than a nominal upper limit of 45 mmHg.DISCUSSION: We found no general tendency to CO₂ retention during decompression. It is plausible that breaching oxygen exposure limits during resting decompression is less hazardous than equivalent breaches when exercising at deep depths.Mitchell SJ, Mesley P, Hannam JA. End tidal CO₂ in recreational rebreather divers on surfacing after decompression dives. Aerosp Med Hum Perform. 2015; 86(1):41–45.

Neck pain occurs at a significant rate in the military helicopter community. It is often attributed to the use of night vision goggles (NVG) and to a number of additional factors such as anthropometrics, posture, vibration, mission length, physical fitness, and helmet fit or load. A number of research studies have addressed many aspects of this epidemic, but an up-to-date and comprehensive review of the literature is not currently available. This paper reviews the spinal anatomy in general and then summarizes what is known about the incidence and prevalence of neck injuries, how the operational environments and equipment may contribute to these injuries, and what can be done to address them from a prevention and/or rehabilitation perspective.Harrison MF, Coffey B, Albert WJ, Fischer SL. Night vision goggle-induced neck pain in military helicopter aircrew: a literature review. Aerosp Med Hum Perform. 2015; 86(1):46–55

BACKGROUND: Accurate color vision is essential for optimal performance in aviation and space environments using nonredundant color coding to convey critical information. Most color tests detect color vision deficiency (CVD) but fail to diagnose type or severity of CVD, which are important to link performance to occupational demands. The computer-based Cone Contrast Test (CCT) diagnoses type and severity of CVD. It is displayed on a netbook computer for clinical application, but a more portable version may prove useful for deployments, space and aviation cockpits, as well as accident and sports medicine settings. Our purpose was to determine if the CCT can be conducted on a tablet display (Windows 8, Microsoft, Seattle, WA) using touch-screen response input.METHODS: The CCT presents colored letters visible only to red (R), green (G), and blue (B) sensitive retinal cones to determine the lowest R, G, and B cone contrast visible to the observer. The CCT was measured in 16 color vision normals (CVN) and 16 CVDs using the standard netbook computer and a Windows 8 tablet display calibrated to produce equal color contrasts.RESULTS: Both displays showed 100% specificity for confirming CVN and 100% sensitivity for detecting CVD. In CVNs there was no difference between scores on netbook vs. tablet displays. G cone CVDs showed slightly lower G cone CCT scores on the tablet.CONCLUSIONS: CVD can be diagnosed with a tablet display. Ease-of-use, portability, and complete computer capabilities make tablets ideal for multiple settings, including aviation, space, military deployments, accidents and rescue missions, and sports vision.Chacon A, Rabin J, Yu D, Johnston S, Bradshaw T. Quantification of color vision using a tablet display. Aerosp Med Hum Perform. 2015; 86(1):56–58.

BACKGROUND: Pneumocephalus secondary to trauma or tumors can have varied symptom severity. It is important to recognize and quantify pneumocephalus for medical evacuation and treatment. This case presents current recommendations for travel in the literature and how they are applicable in returning to flying duties after neurosurgical interventions.CASE REPORT: This is the case of a Naval aircrew member who developed an osteoma and subsequently periorbital emphysema and pneumocephalus. This required medical evacuation from a remote territory, a team surgical approach, and later testing to allow him to return to flight duties in rotary aircraft.DISCUSSION: A search of the literature did not reveal any previous cases of civilian or military flight crew having returned to flying duties after pneumocephalus or neurosurgery. Barometric chamber testing was performed post-operatively to provide clearance. Literature review revealed mixed advice on when one can safely fly commercially after neurosurgery and may be applicable in a case series of medical evacuation or future clearance in returning to flight duties.Ruddick B, Tomlin J. Pneumocephalus and neurosurgery in rotary aircrew. Aerosp Med Hum Perform. 2015; 86(1):59–61.

Andrus DE. You’re the flight surgeon: sarcoidosis. Aerosp Med Hum Perform. 2015; 86(1):67–69.

Govil N. You’re the flight surgeon: aviator with brief psychotic episode. Aerosp Med Hum Perform. 2015; 86(1):69–72.