Reflex regulation of ventricular work performance.

Previous investigators have concluded that the contractility of the ventricle is reflexly modified by alterations of pressure within the carotid sinuses.1" Others were unable to confirm these findings and concluded that intrinsic adaptation of the myocardium to altered hemodynamic conditions was sufficient to explain the changes of cardiac performance.! The carotid sinus reflex is known to be capable of strongly influencing peripheral vascular resistance and systemic arterial pressure."' It is also well known that this reflex possesses the capability of exerting chronotropic influences on the hearte which at times may be so pronounced as to cause circulatory collapse!6 The work performance of the ventricle has been shown to be a function of arterial pressure.7 In previous work' systemic arterial pressure was permitted to change while studying the influences of altering carotid sinus pressure upon left ventricular function. Furthermore the carotid sinuses were not separately perfused, so that reducing the carotid arterial pressure presumably also diminshed cerebral blood flow. This maneuver has been shown to elicit very pronounced sympathtic responses.8'9 The objectives of the present investigation were to assess the influences of brachiocephalic hypotension and of isolated carotid sinus hypotension upon ventricular work performance under conditions of controlled aortic pressure and to compare these changes with those observed when aortic pressure was permitted to rise reflexly. METHODS Cats were anesthetized with pentobarbitol (30 mg/kg). Following placement of an endotracheal tube, the chest was opened and ventilation was maintained with a Harvard constant volume respiratory pump. The descending thoracic aorta was can-nulated, and left ventricular output (minus coronary flow) was measured with a * Associate Professor of Pathology.