The effects of high altitude ascent on splenic contraction and the diving response during voluntary apnoea.

New Findings: What is the central question of this study? What is the relative contribution of a putative tonic splenic contraction to the haematological acclimatization process during high altitude ascent in native lowlanders? What is the main finding and its importance? Spleen volume decreased by -14.3% (-15.2 ml) per 1000 m ascent, with an attenuated apnoea-induced [Hb] increase, attesting to a tonic splenic contraction during high altitude ascent.

Pulmonary gas exchange is reduced by the cardiovascular diving response in resting humans.

The diving response reduces the pulmonary O(2) uptake in exercising humans, but it has been debated whether this effect is present at rest. Therefore, respiratory and cardiovascular responses were recorded in 16 resting subjects, performing apnea in air and apnea with face immersion in cold water (10 degrees C). Duration of apneas were predetermined to be identical in both conditions (average: 145 s) and based on individual maximal capacity (average: 184 s).

Cardiovascular and respiratory responses to apneas with and without face immersion in exercising humans.

The effect of the diving response on alveolar gas exchange was investigated in 15 subjects. During steady-state exercise (80 W) on a cycle ergometer, the subjects performed 40-s apneas in air and 40-s apneas with face immersion in cold (10 degrees C) water. Heart rate decreased and blood pressure increased during apneas, and the responses were augmented by face immersion.

Diving response and arterial oxygen saturation during apnea and exercise in breath-hold divers.

This study addressed the effects of apnea in air and apnea with face immersion in cold water (10 degrees C) on the diving response and arterial oxygen saturation during dynamic exercise. Eight trained breath-hold divers performed steady-state exercise on a cycle ergometer at 100 W. During exercise, each subject performed 30-s apneas in air and 30-s apneas with face immersion.