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

Background: Evaluation of the contractile state 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. Objectives: We assessed the feasibility of measuring carotid arterial wave intensity and determining force-frequency (contractility-heart rate) relationships (FFR´s) during exercise totally noninvasively. Methods: We measured carotid arterial wave intensity with a combined color Doppler and echo tracking system in 15 healthy young male volunteers (age 20.8 ± 1.3 years) at rest and during exercise. FFR´s were constructed by plotting the maximum value of wave intensity (WD₁) against heart rate (HR). Results: WD₁ increased linearly with an increase in HR. The goodness-of-fit of the regression line of WD₁ on HR in each subject was very high (r² 0.67 ~ 0.91, p <; 0.0001 respectively). The slope of the WD₁-HR relation ranged from 0.31 to 1.52 [m/s³(beat/min)]. Conclusions: A global LV FFR 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 FFR in the context of cardiac rehabilitation.