Cardiac responses to progressive exercise in normal children: a synthesis

The cardiac responses to exercise are influenced by a complex interplay of changes in diastolic filling, intrinsic myocardial contractility, heart rat e, and ventricular afterload. Purpose: To characterize these responses in c hildren, findings are reported from two studies utilizing Doppler echocardi ographic assessment of stroke volume and cardiac output during maximal upri ght and semisupine cycle exercise. Methods: In study 1, stroke volume, hear t rate, and peak aortic velocity were assessed during upright cycle exercis e to exhaustion in 39 sixth-grade boys. In study 2, similar methods were us ed to examine cardiac responses to semisupine exercise with measurement of left ventricular dimensions by two-dimensional echocardiography. Results: T he findings support patterns similar to that previously described in adults , with an initial rise in stroke volume reaching a plateau at mild-moderate exercise intensities. Conclusions: The observations in these two studies a lso suggest 1) peripheral vasodilatation plays an important role in the ear ly rise in stroke volume, 2) increasing heart rate acts to maintain a stabl e stroke volume and left ventricular diastolic dimension at high workloads, and 3) improvements in contractility serve to-maintain stroke volume as th e systolic ejection period shortens.