RESUMEN
The present study was undertaken to examine cardiovascular function before and after either intravenous or intra-arterial infusion of hypertonic saline (7.5% NaCl) in halothane-anesthetized dogs. A high-fidelity micromanometer and ultrasonic dimension transducers were implanted to measure pressure and wall motion of the left ventricle (LV). Cardiac output (CO) was measured using an elelctromagnetic flowmeter and thermodidlution. The slop (Ees) of the linear regression of the LV pressure-diameter relationship was used as an index of cardiac contractility. Intravenous infusion of hypertonic saline (3 ml/Kg) increased mean arterial pressure (MAP, 104 ñ 6 to 116 ñ 6 mmHg), heart rate (HR, 124 ñ 21 to 140 ñ 13 bpm), CO(3.2 ñ 0.9 to 4.2 ñ 0.5 l/,) and Ees (11.6 ñ 2.1 to 14.8 ñ 1.9 mmHg/mm). Systemic vascular resistance (SVR) fell by 18%. The above responses were similar whether infusion was intravenous or intra-arterial into innervated or denervated hind limbs. While nerve blockade at T-4 (xylocaine) attenuated the changes in CO and SVR and completely prevented the tachicardia, the inotropic response remained intact. These studies suggest tht the cardiac effect of hypertonic saline infusion are not mediated by pulmonary or peripheral osmoreceptors and the increased contractility may results form a direct myocardial effect of increased osmolatity