24 Following rapid ascent to high altitude, periodic breathing during sleep is almost universal and contributes to the disturbing dreams, frequent arousals, awakenings, and subjective sense of poor-quality sleep often experienced at altitude.25,26 The underlying pattern of periodic breathing is exacerbated by hypoxia and

amplified by Inhibitors,research,lifescience,medical an increased hypoxic ventilatory response. The resulting hyperventilation leads to a hypocapnic alkalosis which can depress ventilation even to the point of apnea. Hypoventilation leads to hypoxia and a further reduction in oxygen saturation which, in turn, stimulates hyperventilation and generates a self-sustaining cycle.26 Via its effect on the carotid body, acetazolamide leads to a significant reduction in

periodic breathing, improves arterial saturation during sleep at high altitude, and helps to prevent or diminish the symptoms of AMS.26 Because of the risk of respiratory depression, sedative hypnotic drugs should be Inhibitors,research,lifescience,medical avoided. MENTAL PERFORMANCE AND CEREBRAL ATROPHY The brain normally accounts for 20% of total oxygen consumption. Under the high-altitude conditions of moderate to severe hypoxia, mental performance is impaired.14 Inhibitors,research,lifescience,medical Impairment in codification and short-term memory is especially noticeable above 6,000 m, and alterations in accuracy and motor speed occur at lower altitudes.27 Of greater concern are studies that indicate both amateur and professional climbers ascending to very high and extreme altitudes are at risk for subcortical lesions and cortical atrophy.28,29 selleck inhibitor weight LOSS AT ALTITUDE Altitude exposure may lead to considerable weight loss, which appears to be Inhibitors,research,lifescience,medical a function of both absolute altitude and the duration Inhibitors,research,lifescience,medical of exposure. Physical activity, nausea due to AMS, and lack of palatable food all contribute to weight loss at altitude, and

this weight loss can be further exacerbated by gastro-enteritis, upper respiratory infections, and low temperatures. Initial weight losses of approximately 3% occur at elevations below 4,000 m, and weight Tryptophan synthase losses up to 15% may occur during extended stays from 5,000 to 8,000 m.30 The initial weight loss likely reflects a diuresis and loss of water. Beyond this initial diuresis, weight loss appears to be preventable by maintaining physical activity and an adequate dietary intake; unfortunately, some trekking companies skimp on the quality and variety of food and contribute to weight loss by failing to provide an adequate diet. Above 5,000 m weight loss is probably unavoidable and is mainly a result of muscle fiber atrophy independent of activity level, possibly related to the direct effects of hypoxia on protein metabolism.30,31 PHYSICAL CONDITION AND EXERCISE Exercise capacity diminishes with altitude.