Determinants of Duration and Mean Rate of Ventricular Ejection

Abstract

The independent influences of stroke volume, heart rate, aortic pressure, hypothermia, sympathoniiiuetic amines, metered mitral and aortic valvular regurgitation, and alterations in myocardial contractility on the duration and mean rate of ventricular ejection and filling were studied. These observations were made in a metabolically supported, isolated heart preparation with performance characteristics comparable to the nouisolated heart. I T HAS long been recognized that the duration of mechanical ventricular systole is inconstant and is modified by a variety of hemodynamic, physical and humoral influences. It is generally held that mechanical systole is abbreviated by tachycardia 1 " 3 and the administration of sympathomimetic amines, 8 ' 4 and prolonged by an increase in stroke volume 1 ' 8i 4 and by hypothermia. 5 " 7 The effects of an increase in aortic pressure have been inconstant. s> 4> 8 However, in previous studies on the duration of ventricular ejection, the effect of independently altering each pertinent variable while holding the others constant has not been accomplished. The objectives of this investigation were to ascertain the effect on the duration and mean rate of left ventricular ejection of the independent alteration of stroke volume, heart rate, aortic pressure, temperature, cardioactive sympathomimetic amines, and mitral and aortic valvular regurgitation. METHODThe isolated supported heart preparation, the performance characteristics and stability of which have been described in detail elsewhere," was employed. This preparation consists of an isolated dog heart from which all coronary venous blood flows into the venous system of an intact, anesthetized dog which in turn continuously replaces biochemically normal arterial blood into the reservoir of the isolated heart system. The independent augmentation of stroke volume while heart rate WJIH held constant by right atrial stimulation was From the laboratory of Cardiovascular Physiology, achieved by increasing left atrial inflow and adjusting the aortic resistance so as to keep mean aortic pressure constant. Similarly, the independent effect of changes in aortic pressure while maintaining stroke volume and heart rate constant was studied by appropi-iate adjustment of left atrial inflow and of the aortic resistance. The effects of heart rate changes were observed by varying the atrial stimulation rate while maintaining mean aortic pressure and cardiac output constant. The effects of hypothermia were studied by cooling the blood in the reservoir of the isolated, supported heart system while maintaining mean aortic pressure, cardiac output and heart rate constant.The duration of left ventricular ejection was measured from aortic pressure pulses obtained through a catheter in the aortic arch with a Statham P-23D strain gage and generally recorded at 100 mm./sec. paper speeds on a direct-writing oscillograph. Speeds of 50 mm./sec. were occasionally used. The interval between the onset of the rise in aortic pressure and the incisura was taken as the...

Pressure-flow studies in man. An evaluation of the duration of the phases of systole

“…Differences in the slope of this relationship noted by these workers can be explained by the extent to which the interventions used to alter heart rate changed stroke volume as well. Although experimental work in the dog (7,8) has indicated that stroke volume was a major determinant of the duration of ejection, several authors have examined the multiple correlation of duration of ejection, stroke volume, and heart rate in man with incongruous results. From such studies it has been concluded that stroke volume is of no importance in determining duration of ejection (16), that stroke volume has a significant but relatively minor effect (13), and that stroke volume is an important determinant of duration of ejection (20).…”

Acute Effects of Passive Smoking on Peripheral Vascular Function

“…The aortic pressure waveform depends on the ventricular ejection time, which is proportionally associated with cardiac cycle duration. 12 Consequently, the change in AIx may be masked or overestimated when there are concomitant alterations in HR. This is why all of the AIx presented in the article are corrected for HR according to the linear relationship established by Wilkinson et al, 13 namely, that for every 10-bpm increase in HR, AIx decreases by 4%.…”

Shortening of Electromechanical Systole as a Manifestation of Excessive Adrenergic Stimulation in Acute Myocardial Infarction

“…[9][10][11][12][13][14] Patients with acute myocardial infarction frequently exhibit excessive adrenergic activity as evidenced by an elevation of plasma and 24-hour urinary catecholamines. [15][16][17][18][19][20][21][22][23] It was therefore hypothesized that the abbreviated electromechanical systole characteristic of patients with myocardial infarction is a direct reflection of increased sympathetic nervous system activity.…”