Regulation of heart rate: effect of inflation of lungs.

The effect of respiration on heart rate has been described as sinus arrhythmia in anaesthetized animals by Heymans (6). Each inspiration is accompanied by an acceleration and slowing accompanies every expiration. A sustained inflation of the lungs in dog has been shown to cause bradycardia (l ) i. e. the opposite of the classical sinus arrhythmia. The above results have been obtained on animals under the artificialy produced conditions in the laboratory. The aim of the present study was to test the validity of the above observation on concious human subjects where the inflation of lungs is produced entirely by the voluntary effort of the inspiratory muscles instead of the respiratory pump and the responsiveness of the regulating centres is unhampered by anaesthetics. The results obtained in this way are presented below and an attempt has been made to explain the underlying physiology.