[Primary effect of carotid body stimulation on left ventricular inotropism in swine]

The cardiovascular response to carotid body stimulation has been a interesting and simultaneously controversial subject. In fact, several authors described different responses depending on the animal species used (cat, dog, rabbit, monkey), time of stimulation (short-term v. long-term) and experimental conditions and procedures. According to our experience, the response to carotid body stimulation with cyanide, in normal breathing dogs, consists in hyperpnoea, bradycardia with arterial blood pressure fall (by means of longer diastolic periods), followed by a marked rise in arterial blood pressure and heart rate, after curarization. Concerning the inotropic response to carotid chemoreceptors stimulation, there exists some controversial and even antagonic opinions. In fact, some authors describe a positive inotropic effect, others a negative inotropic effect, and others still defend no inotropic response at all. In the present work, the authors try to contribute to the solution of this problem, studying a group of animals (pig) anaesthetised with chloralose, in which the major modulators of the inotropic response to carotid body stimulation (ventilation; heart rate; and ventricular load conditions) were controlled. To the evaluation of cardiac contractile state, indexes derived from the systolic isovolumic phase were used (maximum left ventricular pressure, dP/dtmax; dP/dtmin) in all the animals. In some animals, other indexes were also used (Vmax, Vpm, (dP/dt)/DP40, Tau and PB). The authors concluded that, in the present experimental conditions, the primary response to carotid body stimulation, in the pig, includes a positive inotropic effect.