Influence of voluntary hyperventilation on cardiac output

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Abstract
The influence of voluntary hyperventilation on cardiac output was studied in six sitting and four supine subjects by the dye dilution method, using an ear oximeter. All studies were made during the performance of a steady work load of 150 kg-m/min. on a bicycle. There was a positive correlation between increase in ventilation and increase in cardiac output, the average ratio being 41 ml blood/liter ventilation increase. This was not affected by the duration of hyperventilation for periods up to 75 sec and was of the same order in the supine or sitting position. When the thoracic pressure changes of hyperventilation were simulated by raising airway resistance without increase in ventilation there was no correlation between changes in pressure and cardiac output. Thus, it could not be shown that the influence of hyperventilation on circulation was due to the mechanical effect of intrathoracic pressure on venous return, though the increased work of breathing may have been partly responsible for the change in cardiac output observed. Submitted on August 21, 1961