Effects of altering ventricular rate on blood flow distribution in conscious dogs.

WHITE, SAXON, THOMAS PATRICK, CHARLES B. HIGGINS, STEPHEN F. VATNER,DEAN FRANKLIN, AND EUGENE BRAUNWALD. Effects of altering ventricular rate on blood Jlow distribution in conscious dogs. Am. J. Physiol. 221(5): 1402-1407. 1971.-The peripheral vascular response to stepwise changes in ventricular rate was studied in eight conscious dogs with chronic atrioventricular block. Systemic arterial pressure, cardiac output, and flows in the left circumflex coronary, mesenteric, renal, and external iliac arteries were measured using chronically implanted pressure gauges and Doppler ultrasonic or electromagnetic flow transducers. Between 110 and 180 beats/min, arterial pressure and cardiac output were independent of ventricular rate, but fell as rate was further raised or lowered. Total systemic vascular resistance rose at the lowest rates. In the peripheral circulation, coronary flow rose continuously and renal flow remained unchanged as rate was elevated from 40 to 220 beats/min, while mesenteric and hindlimb flows fell at lower rates. Sudden cessation of pacing at 100 beats/min was followed by asystole from 6 to 12 set, a fall in arterial pressure to 20 mm Hg, and flow in all beds ceased. On resumption of ventricular contraction, to spontaneous rates averaging 52 beats/min, the hemodynamic pattern resembled that seen at the lowest pacing rates with flow resistance rising to the greatest extent in the hindlimb (132 =t 4.7 y0 of control) and less so in the coronary circulation (119 rt 7.5 y0 of control). There was little change in the mesenteric circulation, and renal resistance decreased (81 =t 5.4% of control).