A negative pressure ventilation (NPV) by unilateral or bilateral diaphragm pacing (DP) was prepared for canine experiments. A shift from positive pressure ventilation (PPV) to NPV resulted in elevation of mean aortic pressure, increase in stroke volume and depression of mean pulmonary arterial pressure. Examination of the interaction between respiratory cycle and cardiac function during PPV, disclosed a reduction of right ventricular stroke volume and elevation of mean aortic and right ventricular end-diastolic pressure at end inspiration, compared to those at end expiration. During NPV with DP, left ventricular stroke volume, heart rate and mean aortic pressure were increased immediately after DP (immediately after inspiration) compared to those at end expiration. The experimental model of DP, in which respiratory condition could be easily altered, was considered to be useful to evaluate the effect of NPV on cardiac function.
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