The Influence of Heart Rate on Left Ventricular Volume in Dogs*

Abstract

The effects of changes in heart rate must be understood before ventricular performance can be evaluated in studies of the response to drugs, injury, or abnormal circulatory states. This report describes the effects of sudden changes in heart rate on the stroke, end-systolic, and enddiastolic volume of the canine left ventricle. The ventricular volumes were measured by thermodilution, an indicator dilution method in which injected cold blood serves as the indicator (1). METHODSThere were 160 experimental periods in 11 mongrel dogs that were anesthetized with a chloralose-urethane mixture. Aortic thermodilution curves were obtained after rapid injection of cooled autologous blood into the left ventricle. A 4F catheter with an ultrasmall bead thermistor secured to its end 1 was used to record blood temperature. It was introduced into a carotid artery and advanced so that its tip was just above the aortic valve. The time constant of this assembly was 0.12 second when tested in slowly flowing water. A 7F catheter with multiple side holes and a closed end was manipulated into the left ventricle from a femoral artery for injection purposes and to record left ventricular pressure with a strain gauge. A bead thermistor was secured within its lumen near the tip to monitor the temperature of the injected blood immediately before it entered the left ventricle. This assembly had a time constant of 0.05 second in flowing water. Inj ections were made with a metal syringe driven by compressed air that introduced a known amount, usually 3 to 5 ml, of cooled, heparinized, autologous blood into the left ventricle in less than 0.5 second. The mean temperature of the inj ected blood was determined by planimetry of the recorded temperature curve during injection. Stroke volume (SV), end-systolic volume (ESV), and end-diastolic volume (ED V) were calculated from the resultant aortic thermodilution curve sensed by the aortic thermistor catheter. The formulas used to calculate these volumes were:where Vi = volume of injected cooled blood in ml, Tb = left ventricular blood temperature before injection, T1 = mean temperature of injected blood, just before it entered the left ventricle, and 2;(ATb) = the sum of the differences between base-line aortic temperature and that resulting in the aorta from each systole, as measured at end-diastole;2) ES V/ED V = AT,+, ATn' where AT,, and AT,,+, are differences between base-line aortic temperature and that at beats n and n + 1, respectively, measured at end-diastole from the exponential step-function of the aortic thermodilution curve;3) SV ED V(ml) = ES V; EDV ESV(ml) = EDV -SV; 4) and 5) Cardiac output (L/min) = (heart rate) (S V)The details of this method have been published previously (1) -One to five determinations of left ventricular volumes, left ventricular pressure, and heart rate were made during each control and experimental period. Various heart rates faster than control were produced with a 6F electrode catheter passed up a femoral vein and placed fluoroscopically against the right...

Left Ventricular Volume Measurements in Man by Thermodilution*

“…The ratio of each pair of downslope deflections (T4/T3, and so forth) was compared with the average of such ratios for that curve. The difference was (9). The fraction of the EDV ejected as the FSV ranged from 27 to 54%o in the five patients with "normal" ventricular function (miscellaneous group).…”

Left Ventricular Volume in Man Measured by Thermodilution*

“…The single study of paroxysmal tachycardia illustrates the reduction in ventricular end-diastolic volume with cardiac rate described by Bristow, Mintz, Ferguson, and Rapaport (20) in dogs. A similar trend was seen in the over-all data (Figure 3).…”

Experimental myocardial infarction

“…In the isolated ventricle (1, 2), isolated mammalian cardiac muscle (3,4), and canine bypass preparations (5), increase in force of contraction occurs with increasing frequency of contraction up to a certain range. In intact animals (6)(7)(8)(9) and in man (10) with normal cardiac function, this increase in inotropy is not readily appreciated by routine hemodynamic measurements. Increases in cardiac output or marked decreases in left ventricular filling pressures are seldom noted over a wide range of cardiac rates.…”

“…was placed in the aorta under fluoroscopic control, and Cournand catheters Nos. [7][8][9] (100 cm in length) were placed in the pulmonary artery and left ventricle. In nine animals an additional catheter was placed retrogradely in the left atrium.…”

“…After completion of the study, the arteriotomy was repaired. The animals were restudied in similar fashion [6][7][8] Instrumentation. Atrial pacing was carried out using a Grass model S4G stimulator (Grass Instrument Co., Quincy, Mass.).…”