Cardiac Performance During Exercise in Dogs with Constricted Pulmonary Artery

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Abstract
In dogs, the pulmonary artery was constricted by banding; the cross-sectional area of the pulmonary artery after banding averaged 16% of the prebanded area. The right ventricular pressure in six unanesthetized dogs at rest averaged 89 mm Hg two and one-half to three months following constriction and 106 mm Hg in three of these when studied nine months following constriction. All animals were studied during exercise on a treadmill. A doubling of the cardiac output during exercise was achieved by increasing the heart rate, while the stroke volume remained unchanged. The duration of systole decreased. Right ventricular systolic pressure increased markedly during exercise. The highest right ventricular pressure in dogs free of pulsus alternans was 158 mm Hg. A regular pulsus alternans usually supervened at heart rates in excess of 180 beats/min. Under these circumstances the maximal pressure generated was 228 mm Hg. Average right atrial pressure increased from 3.5 to 24 mm Hg. The right ventricular stroke work was somewhat less than that of the left ventricle at rest but exceeded it during exercise in these experiments. The compensation for chronic obstruction to right ventricular outflow was fully operative two and one-half months after banding, and no significant change in performance was observed later.