Comparison of Cardiac Diastolic Time During Graded Exercise in Relation to Age and Fitness Level

Abstract

Cardiac cycle is divided to two phases, systolic and diastolic phase. Diastolic time (DT) correlates with the degree of coronary circulation. We have reported that Systolic time (ST) and DT fit well to a cubic regression equation in relation to RR interval that converged to the origin of the coordinates. Using this equation, we are able to calculate easily the ratio of DT for RR interval (%DT) at any heart rate (HR). PURPOSE: The purpose of this study is to compare %DT at the same HR during graded exercise among persons of different age and fitness. METHODS: Subjects were 7 male university students, 10 middle aged male persons (46-63yr), and 8 middle and high aged female persons (55-67yr). The Research Ethics Board of the University of Tokushima gave approval for this study. The exercise test was performed on an electrically braked cycle ergometer with two incremental loading methods that were different between male and female. ECG and phonocardiogram were recorded during exercise. The exercise test was quit when the subjects indicated score of 15 or 16 in RPE. The aerobic capacity of the subject was determined according to heart sounds breaking point (HSBP). ST was determined as interval of first heart sound (S1) and second heart sound (S2), DT was determined from the equation of [RR interval-ST]. The regression equation was determined in each subject. %DTs at 90, 100, 110, 120, 130, and 140 bpm of HR were calculated from the equations. RESULTS: The mean of HSBPs of male students, middle aged male persons, and middle and high aged female persons were 1.96 (SD: 0.25), 1.30 (0.22), and 0.77 (0.19) watts/wt, respectively. %[email protected] of three groups were 61.0 (1.3), 57.3 (2.7), and 55.2 (2.5) %, respectively. And [email protected] of three groups were 54.6 (1.8), 52.1 (2.7), and 45.5 (3.0) %, respectively. %DT showed tendency of decrease according to increase in age. The relationship between %DT and HSBP/wt showed positive significant correlation at the phases of 90-140bpm of HR. %[email protected] were under 50% in 7 aged subjects. CONCLUSIONS: %DT may be a useful indicator in exercise prescription for middle and high aged persons.