Cardiopulmonary response to acute altitude exposure: water loading and denitrogenation

In order to determine if a positive water balance would impair cardiovascular and ventilatory adjustments during acute altitude exposure, six healthy male subjects were exposed to 4570 m for 2 h with and without water loading. No significant differences in any of the measured variables were observed between normal and overhydrated subjects. In order to determine if rapid ascent to altitude involves the formation of nitrogen bubbles which could impair gas exchange, 11 subjects were exposed to 4570 m with and without denitrogenation (by breathing 100% O2 prior to ascent) and 6 subjects were exposed to normobaric hypoxia (14% O2). Prior O2 breathing reduced the hyperventilatory and alkalotic responses to altitude, tachycardia did not develop, and systemic blood pressure fell, despite the fact that arterial desaturation was similar to that during the untreated altitude exposure. Reduced urine flow and increased urine osmolality were observed in two subjects at 4570 m, but these changes were not observed in the same subjects after O2 breathing. Breathing 14% O2 also produced the same degree of arterial desaturation but the hyperventilatory response was significantly greater than in the prior altitude exposures. Heart rate, blood pressure, and urine flow and osmolality were not altered and symptoms of altitude illness were minimal. Thus, neither of our hypotheses proved to be correct; however, we did observe a prolonged effect of O2 breathing on the hypoxic ventilatory response, and a potential effect of hypobaria on ventilation.