Summer - United States Special Operations Command

Loss of Consciousness and Seizure During Normobaric Hypoxia TrainingMoniaga, Natalie C.; Griswold, Cheryl A.Aviation, Space, and Environmental Medicine, Volume 80, Number 5, May 2009 , pp. 485-488(4)ABSTRACTLoss of consciousness is a symptom with a broad differential diagnosis. Distinguishing between syncopeand seizure in a patient with a history of loss of consciousness can be equally difficult as their presentationcan be very similar. We present the case of a naval electronic countermeasures officer who experienced a lossof consciousness while undergoing hypoxia training with the reduced oxygen breathing device (ROBD). Duringthe episode the patient experienced tonic-clonic contractions with subsequent vertebral fractures, resultingin a prolonged grounding period. The patient's work-up focused on ruling out inherent cardiac and neurologicetiologies. After extensive examination and consultation with neurology, the patient was diagnosed with hypoxiainducedseizure, but was not felt to have an underlying seizure disorder. After reviewing his case, the Naval AerospaceMedical Institute felt that this incident represented a physiologic event and not a medical condition inherentto the aviator. It was, therefore, determined that this episode was not considered disqualifying and did not requirea waiver for return to duties involving flight. Our discussion details the appropriate work-up for loss ofconsciousness, examines possible physiologic explanations for this event, and describes aeromedical considerations.The authors include the patient's physiology instructor, one of the primary witnesses for the event, andthe patient's flight surgeon, who was extensively involved in his care.Ventilated Vest and Tolerance for Intermittent Exercise in Hot, Dry ConditionsWith Military ClothingBarwood, Martin J.; Newton, Phillip S.; Tipton, Michael J.Aviation, Space, and Environmental Medicine, Volume 80, Number 4, April 2009 , pp. 353-359(7)ABSTRACTIntroduction: Recent research has focused on developing air-ventilated garments to improve evaporative coolingin military settings. This study assessed a ventilated vest (Vest) in hot (45°C), dry (10% RH) ambient conditionsover 6h of rest and exercise. It was hypothesized that the Vest would lower the thermal strain and increasethe amount of exercise done by subjects. Methods: Eight healthy heat-acclimated men, wearing combat clothing,body armor, and a 19-kg load in webbing walked on a treadmill at 5 km • h−1 at a 2% incline until rectaltemperature (Trec) reached 38.5°C. They then rested until Trec reached 38°C, at which point they recommencedwalking. On one occasion the subjects wore a Vest, blowing ambient air around the torso. On the second occasionsubjects did not wear the vest (NoVest). Exercise/rest ratio, Trec, skin temperature (Tsk), sweat responses,rating of perceived exertion (RPE), and thermal comfort (TC) were measured. Results: Subjects wearing theVest exercised for significantly longer (18%; 11 min/h) as a percentage of total exposure time, stopped exercisesignificantly less often [Mean (SD); NoVest: 3 (2) stops; Vest: 1 (2) stops], and maintained significantly lowerskin temperature under the body armor [Tchest: NoVest 37.55 (0.51)°C; Vest: 35.33 (1.00)°C; Tback: NoVest:36.85 (0.83)°C; Vest: 35.84 (0.88)°C]. The Vest provided 28 W of cooling during exercise and 73 W when atrest as estimated by thermometry. Conclusion: A ventilated vest can provide cooling, and thereby reduce thermalstrain and increase exercise done in dry environmental temperatures up to 45°C, without causing skin irritationand discomfort.58Journal of Special Operations Medicine Volume 9, Edition 3 / Summer 09