CONTINUOUS MEASUREMENT OF CANINE CORONARY BLOOD-VOLUME CHANGE WITH ALTERATIONS OF HEART-RATE

Objective: The aim was to examine the effects of heart rate on total c oronary blood volume with pressure-type plethysmography in isolated an d vasodilated canine hearts. Methods: Nine hearts were excised from an aesthetised mongrel dogs (13.1-15.2 kg) and perfused with arterial blo od of other dogs (17.0-29.0 kg). The venous blood returning to the rig ht atrium and both ventricles was drained under constant negative pres sure (-10 mm Hg). A thin latex balloon filled with water was inserted into the left ventricle to keep the intraventricular volume constant. The pressure difference between the cylinder into which the heart was placed and a compensation chamber was measured as a change in coronary blood volume while heart rate was altered from 120 beats.min-1 (contr ol heart rate) to a target level (60, 90, 150, or 180 beats.min-1). Re sults: The mean coronary blood volume change compared with that at con trol heart rate was 1.65(SEM 0.32) ml.100 g-1 at 60 beats.min-1 (p<0.0 05) and -0.74(0.20) ml.100 g-1 at 180 beats.min-1 (p<0.005) under the perfusion pressure of 70 mm Hg. The mean volume decreased with the inc rease in heart rate. Diastolic-systolic variations in coronary blood v olume also decreased with an increase in heart rate, from 0.61(0.06) m l.100 g-1 (60 beats.min-1) (p<0.005) to 0.12 ml.100 g-1 (180 beats.min -1). Both mean change and variation were almost linear functions of R- R interval (r=0.88 and r=0.83). Lowering the perfusion pressure from 7 0 to 40 mm Hg diminished the changes in both mean and variation of the coronary blood volume. Conclusions: Tachycardia reduces the mean coro nary blood volume and the diastolic-systolic variations in isolated va sodilated canine hearts.