Adv Exp Med Biol
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The technique of galvanic vestibular stimulation (GVS) has been used for a long time. The stimulus produces stereotyped automatic postural and ocular responses. The mechanisms underlying these responses are not understood although they are commonly attributed to altered otolith output. ⋯ Bilateral bipolar GVS should also produce an otolith signal consistent with tilt towards the cathodal side or a translational acceleration towards the anodal side. The expected responses for other configurations of GVS are also described. The model appears consistent with published data on the ocular and postural responses to GVS, and suggests other testable hypotheses concerning postural, ocular and perceptual responses to GVS.
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The mechanisms of sensory transduction in the fine nerve terminals of free nerve endings supplied by Adelta and C sensory axons are largely a matter of speculation. This is because the nerve terminals are small and inaccessible, particularly in intact tissues like skin. However, some of the difficulties associated with investigating the physiology of fine nerve terminals have recently been overcome using an in vitro preparation of the guinea-pig cornea that allows nerve terminal impulses (NTIs) to be recorded extracellularly from single polymodal and cold receptor nerve terminals. ⋯ At the same temperature, NTIs are larger in amplitude and faster in time course during heating than those during cooling. The differential effect of heating and cooling on NTI shape is not considered to result simply from the temperature dependence of voltage-activated conductance kinetics or activity dependent changes in membrane excitability. Instead, changes in NTI shape may reflect changes in nerve terminal membrane potential that underlie the process of thermal transduction.
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An 8000-m peak bring challenges of extremes of hypoxia and weather as well as the normal hazards of climbing itself. These challenges have taken a severe toll: 604 mountaineers have died on those great peaks since 1950. Little is known about whether mountain height, use of supplemental oxygen, or team size might influence rates of death or of success. ⋯ We present several examples from a research program that is attempting to analyze factors that potentially influence success or death rates on the 8K peaks. (1) Apparent risk of death in the notorious Khumbu Icefall on Mt. Everest has declined dramatically in recent years. This decline could reflect improved route finding and technique, but might also reflect climate warming, which has caused the Khumbu glacier to shrink and slow in recent decades. (2) Risk of death during descent from an 8000-m peak increases with the height of the peak. (3) Risk of death during descent from the summit of Everest or of K2 is elevated for climbers not using supplemental oxygen. (4) We outline some new studies that are exploring how convective heat loss, which influences wind chill, changes with altitude as well as the incidence of storms: both factors will impact the probability success and death of Himalayan mountaineers.
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Chronic mountain sickness (CMS) is a poorly understood syndrome, characterized by hypoxemia and polycythemia and occurring in persons residing at high altitude. To better characterize the disorder, we have reviewed measurements in more than 750 men and 200 women living at altitude as published and as submitted by colleagues. In men, blood hemoglobin concentration (Hb) and arterial oxygen saturation (SaO2) related to altitude (r=0.72). ⋯ Pulmonary hypertension was related to chronic hypoxia, with an uncertain contribution from polycythemia. In CMS there were profound hypoxemia at night, decrease in cerebral blood flow, and loss of cerebral blood flow regulation, possibly causing the cerebral symptoms. We speculate that the relationship of Hb to SaO2 is more useful than of hemoglobin to altitude, that hypoventilation awake and asleep are the primary causes accentuating altitude-hypoxia, and that the brain is the primary target organ in the disorder.