Factors Influencing Respiration During Heavy Exercise1

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Abstract
Studies on the control of respiration during heavy exercise (at maximal O2 intake level) show that arterial O2 tension does not decline and is not responsible for the hyperpnea observed. Arterial CO2 tension does not rise under these circumstances and is also thought to play no role in the production of hyperpnea. Changes in arterial pH do not correlate with changes in ventilation, particularly during recovery from exercise. CO2 tension in femoral and brachial venous blood rises during heavy exercise, and continues to rise for a short while after cessation of exercise, at a time when ventilatory volume is decreasing rapidly. There is very little change in jugular venous CO2 and O2 tension during exercise and recovery from it. Some aspect of central blood volume seems to parallel changes in ventilatory volume during exercise and recovery. It is concluded that the latter may be a factor in the control of ventilation during exercise. The possibility that mixed venous CO2 tension may also be related has not been ruled out; this would require the presence of CO2 receptors in the right heart or in the lungs themselves.