Noninvasive evaluation of left ventricular force−frequency relationships by measuring carotid arterial wave intensity during exercise stress

BACKGROUND AND PURPOSE: Estimation of the contractility of the left ventricle during exercise is important in drawing up a protocol of cardiac rehabilitation. It has been demonstrated that color Doppler- and echo tracking-derived carotid arterial wave intensity is a sensitive index of global left ventricular (LV) contractility. We assessed the feasibility of measuring carotid arterial wave intensity and determining force−frequency (contractility−heart rate) relations (FFRs) during exercise totally noninvasively. METHODS: We measured carotid arterial wave intensity with a combined color Doppler and echo tracking system in 25 healthy young male volunteers (age 20.8 ± 1.2 years) at rest and during exercise. FFRs were constructed by plotting the maximum value of wave intensity (WD(1)) against heart rate (HR). RESULTS: We first confirmed that HR increased linearly with an increase in work load in each subject (r(2) = 0.95 ± 0.04). WD(1) increased linearly with an increase in HR. The goodness-of-fit of the regression line of WD(1) on HR in each subject was very high (r(2) = 0.48−0.94, p < 0.0001, respectively). The slope of the WD(1)-HR relation ranged 0.30−2.20 [m/s(3) (beat/min)]. CONCLUSIONS: Global LV FFRs can be generated in healthy young volunteers with an entirely noninvasive combination of exercise and wave intensity. These data should show the potential usefulness of the FFR in the context of cardiac rehabilitation.