RELATIONSHIP BETWEEN STRENGTH OF SHORT-TERM SYSTEMIC AUTOREGULATION AND INITIAL RESISTANCE

The relationship between strength of short-term whole body autoregulat ion and peripheral resistance in the reference state (initial resistan ce) was investigated in 9 anesthetized closed-chest dogs and 18 anesth etized open-chest cats. Baroreflex regulation was abolished in one of three ways: barodenervation, ganglionic blockade, or setting pressure constant in the isolated carotid sinuses after vagotomy. Ascending aor tic pressure and flow and venous pressure were measured in the referen ce state and 1-3 min after partial occlusions of the inferior vena cav a. Cardiac output and peripheral resistance (ratio between arterioveno us pressure difference and cardiac output) were normalized for body we ight. Strength of autoregulation was quantified by a resistance gain ( G(ra)), defined as the ratio between change in normalized peripheral r esistance and corresponding change in normalized cardiac output. A bro ad range of values for peripheral resistance in the reference state (R (o)) was obtained as a result of the different interventions used to a bolish baroreflex regulation. Arteriovenous pressure difference and no rmalized cardiac output during multiple vena cava occlusions in the 9 dogs and in 8 of the cats were fitted with a parabola convex to the fl ow axis. From the best fit, G(ra) was estimated. In the remaining 10 c ats G(ra) was estimated from a single occlusion of vena cava. When dat a of all dogs and cats were taken together, we found a linear relation ship between G(ra) and R(o): G(ra) = K-1.R(o) + K-2. The constants K-1 and K-2 were 17.9 x 10(-3) min.kg.ml(-1) and -14.5 x 10(-3) mmHg.min( 2).kg(2).ml(-2), respectively. The correlation coefficient was 0.9.