Initial Ventricular Impulse

Abstract

During the early stages of ventricular systole, myocardial tension develops very rapidly, ventricular pressure rises steeply to exceed arterial pressure, and momentum is then rapidly imparted to the blood flowing out of the ventricles. The acceleration of blood out of the ventricles is an expression of the force being applied by the contracting myocardium, and the peak flow velocity can be regarded as the product of the net force applied over the time from the onset of ejection to the peak. The product of force and time is designated by a well-established physical term: impulse (I=Ft). Thus, "initial ventricular impulse" appears to be an appropriately descriptive term for the dynamic properties of ventricular ejection. Direct and continuous records of acceleration, the outflow rate of blood, and the rates of change of ventricular and arterial pressure demonstrate that ejection of blood from both ventricles (particularly the left) is more like striking a piston with a mallet than like squeezing blood out of a chamber. These dynamic characteristics of ventricular ejection are greatly altered by autonomic control and by simulated disease conditions. Initial ventricular impulse is greatly augmented during exercise, by stimulation of sympathetic nerves to the heart, and following long diastolic intervals. On the contrary, initial ventricular impulse is markedly depressed during premature ventricular contractions, acute coronary occlusion, exsanguination hypotension, general anesthesia, etc. Thus, signs of changing ventricular impulse may have significant value in assessing the performance capability of the heart. For this purpose, certain clinical tests of cardiac performance (e.g., arterial pressure pulses, electrokymograms, precordial displacements, ballistocardiograms) may have unsuspected importance. Experiments on animals have considerable value in suggesting measurements that might be appropriately employed on human subjects and patients, but because of species differences, the validation of initial ventricular impulse as clinical test of value must ultimately be accomplished by appropriate measurements conducted on human subjects. For this reason, a specific experimental design is suggested for the evaluation of certain indirect indicators that may have potential value in routine assessment of the cardiac status. By means of modern high-speed computers, cross correlations, and factor analysis could bring to light the aspects of peripheral arterial pulse waves, kinetocardiograms, electrokymograms, and ballistocardiograms of reliable predictive value in assessing initial ventricular impulse in man.