Donna Goff

Cardiac responses to progressive exercise in normal children: a synthesis.

UNLABELLED The cardiac responses to exercise are influenced by a complex interplay of changes in diastolic filling, intrinsic myocardial contractility, heart rate, and ventricular afterload. PURPOSE To characterize these responses in children, findings are reported from two studies utilizing Doppler echocardiographic assessment of stroke volume and cardiac output during maximal upright and semisupine cycle exercise. METHODS In study 1, stroke volume, heart rate, and peak aortic velocity were assessed during upright cycle exercise to exhaustion in 39 sixth-grade boys. In study 2, similar methods were used to examine cardiac responses to semisupine exercise with measurement of left ventricular dimensions by two-dimensional echocardiography. RESULTS The 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 also suggest 1) peripheral vasodilatation plays an important role in the early rise in stroke volume, 2) increasing heart rate acts to maintain a stable stroke volume and left ventricular diastolic dimension at high workloads, and 3) improvements in contractility serve to maintain stroke volume as the systolic ejection period shortens.

Normalization of Maximal Cardiovascular Variables for Body Size in Premenarcheal Girls

Abstract. Previous studies have indicated the importance of allometric scaling of VO2max for body size. However, no information is available on adjusting maximal cardiac output (Qmax) and stroke volume (SVmax) for body dimensions. The allometric exponent b was determined for the equation Y=aXb (where Y is the physiological outcome and X is the anthropometric variable) for VO2max, Qmax, and SVmax relative to mass, height, and body surface area (BSA) in 24 premenarcheal girls (mean age 12.2 years) during cycle testing. Values for b were 1.08 and 1.05 for BSA relative to Qmax and SVmax, approximating that of 1.0 using the traditional ratio standard (cardiac index and stroke index). Exponents of body mass relative to VO2max, Qmax, and SVmax (0.55, 0.55, and 0.59, respectively) eliminated the effects of body size, but the ratio standard (M1.0) did not. In this group of subjects, use of the ratio standard BSA was an appropriate means of adjusting maximal values of Q and SV for body size.