Left Ventricular Ejection in Conscious Dogs:

The maximum acceleration of blood from the left ventricle was studied in conscious dogs in which ascending aortic blood flow was measured with an electromagnetic flowmeter; normal values at rest ranged between 5 and 11 g . The left ventricular myocardium was stimulated with intracoronary injections of calcium gluconate and isopropylnorepinephrine; maximum acceleration, peak flow, and the rate of rise of left ventricular pressure were the only parameters, measured or derived, that showed a consistent increase. The largest increase always occurred in maximum acceleration. Changes of posture, with the presumed associated changes in end diastolic dimensions, did not alter the maximum acceleration. The results suggested that maximum acceleration was closely related to the maximum force exerted by the heart in initial systole, and to the maximum initial velocity of shortening of left ventricular muscle. Temporary regional myocardial ischaemia produced larger and earlier decreases in maximum acceleration than in other parameters measured suggesting that it was a sensitive index of myocardial contractile function.