Gluteal Muscle Atrophy and Increased Intramuscular Lipid Concentration Are Not Mitigated by Daily Artificial Gravity Following 60-Day Head-Down Tilt Bed Rest.

Exposure to spaceflight and head-down tilt (HDT) bed rest leads to decreases in the mass of the gluteal muscle. Preliminary results have suggested that interventions, such as artificial gravity (AG), can partially mitigate some of the physiological adaptations induced by HDT bed rest. However, its effect on the gluteal muscles is currently unknown. This study investigated the effects of daily AG on the gluteal muscles during 60-day HDT bed rest. Twenty-four healthy individuals participated in the study: eight received 30 min of continuous AG; eight received 6 × 5 min of AG, interspersed with rest periods; eight belonged to a control group. T1-weighted Dixon magnetic resonance imaging of the hip region was conducted at baseline and day 59 of HDT bed rest to establish changes in volumes and intramuscular lipid concentration (ILC). Results showed that, across groups, muscle volumes decreased by 9.2% for gluteus maximus (GMAX), 8.0% for gluteus medius (GMED), and 10.5% for gluteus minimus after 59-day HDT bed rest (all p < 0.005). The ILC increased by 1.3% for GMAX and 0.5% for GMED (both p < 0.05). Neither of the AG protocols mitigated deconditioning of the gluteal muscles. Whereas all gluteal muscles atrophied, the ratio of lipids to intramuscular water increased only in GMAX and GMED muscles. These changes could impair the function of the hip joint and increased the risk of falls. The deconditioning of the gluteal muscles in space may negatively impact the hip joint stability of astronauts when reexpose to terrestrial gravity.

Subdural Hemorrhage in a Military Aviator.

BACKGROUND: The occurrence of any intracranial bleeding is highly significant from an aeromedical risk perspective and potentially career-ending for a military aviator. Where it arises from head trauma, there is always concern regarding ongoing risk of post-traumatic epilepsy. CASE REPORT: A 26-yr-old male military aviator with persistent headache was found to have small right frontal and parietal subacute subdural hematomas, most likely precipitated by minor head trauma and possibly exacerbated by other concurrent physiological stressors. The hematomas resolved with conservative management and the aviator made a full recovery. DISCUSSION: The association between traumatic subdural hematomas and the occurrence of post-traumatic epilepsy is well documented, and this, together with the possibility of recurrent bleeding, must be considered the significant aeromedical risks. However, this case presents an unusual situation of small subdural hematomas in isolation with no other features suggestive of significant traumatic brain injury. Relevant medical literature was found to be substantially lacking, and no other similar case reports of aviators could be found. An aeromedical decision-making process is discussed in relation to returning the aviator to flying duties in a restricted capacity.

Hypoxia awareness training for aircrew: a comparison of two techniques.

INTRODUCTION: Major hazards associated with hypoxia awareness training are the risks of decompression sickness, barotrauma, and loss of consciousness. An alternate method has been developed which combines exposure to a simulated altitude of 10,000 ft (3048 m) with breathing of a gas mixture containing 10% oxygen and 90% nitrogen. The paradigm, called Combined Altitude and Depleted Oxygen (CADO), places the subjects at a physiological altitude of 25,000 ft (7620 m) and provides demonstration of symptoms of hypoxia and the effects of pressure change. CADO is theoretically safer than traditional training at a simulated altitude of 25,000 ft (7620 m) due to a much lower risk of decompression sickness (DCS) and has greater fidelity of training for fast jet aircrew (mask-on hypoxia). This study was conducted to validate CADO by comparing it with hypobaric hypoxia. METHODS: There were 43 subjects who were exposed to two regimens of hypoxia training: hypobaric hypoxia (HH) at a simulated altitude of 25,000 ft (7620 m) and CADO. Subjective, physiological, and performance data of the subjects were collected, analyzed, and compared. RESULTS: There were no significant differences in the frequency and severity of the 24 commonly reported symptoms, or in the physiological response, between the two types of hypoxia exposure. CONCLUSIONS: CADO is similar to HH in terms of the type and severity of symptoms experienced by subjects, and appears to be an effective, useful, and safe tool for hypoxia training.

In-flight hypoxia incidents in military aircraft: causes and implications for training.

BACKGROUND: Hypoxia has long been recognized as a significant physiological threat at altitude. Aircrew have traditionally been trained to recognize the symptoms of hypoxia using hypobaric chamber training at simulated altitudes of 25,000 ft or more. The aim of this study was to analyze incidents of hypoxia reported to the Directorate of Flying Safety of the Australian Defence Force (DFS-ADF) for the period 1990-2001, as no previous analysis of these incidents has been undertaken. The data will be useful in planning future training strategies for aircrew in aviation physiology. METHOD: A search was requested of the DFS-ADF database, for all Aircraft Safety Occurrence Reports (ASOR) listing hypoxia as a factor. These cases were reviewed and the following data analyzed: aircraft type, number of persons on board (POB), number of hypoxic POB, any fatalities, whether the victims were trained or untrained as aircrew, if the symptoms were recognized as hypoxia, symptoms experienced, the altitude at which the incident occurred, and the likely cause. RESULTS: During the period studied. 27 reports of hypoxia were filed, involving 29 aircrew. In only two cases was consciousness lost, and one of these resulted in a fatality. Most incidents (85.1%) occurred in fighter or training aircraft with aircrew who use oxygen equipment routinely. The majority of symptoms occurred between 10,000 and 19,000 ft. The most common cause of hypoxia (63%) in these aircraft was the failure of the mask or regulator, or a mask leak. Rapid accidental decompression did not feature as a cause of hypoxia. Symptoms were subtle and often involved cognitive impairment or light-headedness. The vast majority (75.8%) of these episodes were recognized by the aircrew themselves, reinforcing the importance and benefit of hypoxia training. CONCLUSION: This study confirms the importance and effectiveness of hypoxia training for aircrew. Hypoxia incidents occur most commonly at altitudes less than 19,000 ft. This should be emphasized to aircrew, whose expectation may be that it is only a problem of high altitude. Proper fitting of masks, leak checks, and equipment checks should be taught to all aircrew and reinforced regularly. Current hypobaric chamber training methods should be reviewed for relevance to the most at-risk aircrew population. Methods that can simulate subtle incapacitation while wearing oxygen equipment should be explored. Hypoxia in flight still remains a serious threat to aviators, and can result in fatalities.