Changes in cardiac contractility during graded exercise are greater in subjects with smaller body mass index, and greater in men than women: analyses using wave intensity and force-frequency relations.

Introduction And Purpose: Estimation of the contractility of the left ventricle during exercise is an important part of the rehabilitation protocol. It is known that cardiac contractility increases with an increase in heart rate. This phenomenon is called the force-frequency relation (FFR). Using wave intensity, we aimed to evaluate FFR noninvasively during graded exercise.

Methods: We enrolled 83 healthy subjects. Using ultrasonic diagnostic equipment, we measured wave intensity (WD), which was defined in terms of blood velocity and arterial diameter, in the carotid artery and heart rate (HR) before and during bicycle ergometer exercise. FFRs were constructed by plotting the maximum value of WD (WD) against HR. We analyzed the variation among FFR responses of individual subjects.

Results: WD increased linearly with an increase in HR during exercise. The average slope of the FFR was 1.0 ± 0.5 m/s bpm. The slope of FFR decreased with an increase in body mass index (BMI). The slopes of FFRs were steeper in men than women, although there were no differences in BMI between men and women.

Conclusions: The FFR was obtained noninvasively by carotid arterial wave intensity (WD) and graded exercise. The slope of the FFR decreased with an increase in BMI, and was steeper in men than women.