The purpose of this study was to investigate the prognostic value of change in heart rate (HR) response to oxygen uptake (VO₂) during exercise in patients with coronary heart disease (CHD).We retrospectively studied 204 patients with CHD who were sent to our exercise testing laboratory between August 1983 and February 1985. The following equation was used to determine the relation between VO₂ and HR during a graded treadmill exercise test: HR= A・exp ^B･VO2, where the constant b was defined as the inclination of the exponential curve-fitting model for oxygen uptake and heart rate during graded treadmill exercise (I-ECOH). Data on mortality were determined in May 2006 by examining medical records from the outpatient clinic and/or conducting telephone interviews with the patients or their families. Among the 204 study subjects, there were 54 cardiac deaths during the entire 20-year follow-up period. Kaplan-Meier survival curves for 20 years of follow-up demonstrated a survival rate of 81.3% for patients with a lower I-ECOH (＜35) and 56.0% for those with a higher I-ECOH (≧35), showing a significant difference in survival (p＜0.001). Multivariate Cox proportional hazards analysis revealed left ventricular ejection fraction (LVEF), peak oxygen uptake (VO₂ peak) and I-ECOH as independent predictors of survival. In this analysis, the prognostic power of minutes ventilation/carbon dioxide output (VE/VCO₂)slope was insignificant. The patients were divided into two groups with (＜45%) and without (≧60%) LV dysfunction using LVEF for more detailed analysis. The VO₂ peak and VE/VCO₂ slope were significant independent predictors of survival in patients with LV dysfunction. However, the I-ECOH was a significant independent predictor of survival in patients with and without LV dysfunction. Our data indicate that I-ECOH provides independent prognostic information on CHD patients with and without LV dysfunction.

This study was conducted to clarify the validity and availability of inclination of exponential curve-fitting model for oxygen uptake (VO₂) and heart rate (HR) during incremental exercise (I-ECOH) as an index of cardio-pulmonary functional reserve in patients with ischemic heart disease (IHD). A treadmill exercise test was used to measure the VO₂(L/kg/min) and HR (beat/min) during incremental exercise of all subjects. I-ECOH was derived from the following equation : HR=A·exp^B·VO2. The constant "B" represents I-ECOH. The following two identifications were made : 1) the relation between peak oxygen uptake (VO₂peak) and I-ECOH in IHD patients with normal left ventricular function and with chronic heart failure (CHF); 2) the relation between I-ECOH and the New York Heart Association (NYHA) functional classification of IHD patients with CHF.There were significant differences among IHD patients with normal left ventricular function, CHF patients, normal controls and long distance runners in I-ECOH and VO2peak, respectively (p<0.001). There were inverse correlations between I-ECOH and VO2peak in IHD patients with normal left ventricular function (r=-0.64, p<0.001) and CHF (r=-0.63, p<0.001). I-ECOH could be used to discriminate effectively between NYHA functional classes (p<0.001).In conclusion, these results suggest that I-ECOH is adequate and useful as an index of cardio-pulmonary functional reserve in patients with ischemic heart disease.

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