[The effect of heart rate on the time constant of isovolumic relaxation of the left ventricle].
A time constant (T) of the left ventricular isovolumic relaxation, which expresses the relaxation rate of the left ventricle, may be affected by change of the heart rate. There are few clinical reports concerning the relationship between T and heart rate. We studied the relationship between T and heart rate in 10 patients with normal coronary arteries and left ventricular function. Left ventricular pressure was measured using a catheter-tip manometer during right atrial pacing, which was performed at the rate of 10, 20, 40 beats/min in addition to the baseline rate, and finished at 140 or 150 beats/min. Two measurements were made for T.1) Tw from the slope of In (pressure) against time, and 2) Tb by exponential analysis which also estimated the asymptote. As the heart rate increased, both Tw and Tb gradually shortened (Tw: from 38.5 +/- 4.9 msec at the control heart rate to 28.9 +/- 5.6 msec at 140 or 150 beats/min; Tb: from 54.7 +/- 11.4 msec at the control heart rate to 34.9 +/- 5.7 msec at 140 or 150 beats/min). These findings suggest that left ventricular isovolumic relaxation is strongly affected by change of the heart rate in man.
Mori
S
S
First Department of Internal Medicine, Mie University School of Medicine, Tsu.
Yamakado
T
T
Ohkubo
S
S
Hayashi
T
T
Teramura
S
S
Fukui
A
A
Murayama
S
S
Kato
N
N
Ueda
K
K
Nakano
T
T
D000328:Adult; D003971:Diastole; D005260:Female; D006339:Heart Rate; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D013997:Time Factors; D016277:Ventricular Function, Left; D017725:Ventricular Pressure