Echocardiographic evaluation of left ventricular reserve in normal children during supine bicycle exercise

To evaluate left ventricular reserve in normal children 127 healthy boys and girls (71 males, 56 females) were investigated with echocardiography during supine bicycle exercise at levels of 6, 9, 12 and 15 kpm/min/kg body weight. Left ventricular function parameters were obtained from the M-mode echocardiogram, electrocardiogram and phonocardiogram. The children were separated into three groups according to body surface area: group I less than 1.1 m2, group II 1.1-1.4 m2, and group III greater than 1.4 m2. Fractional shortening (FS) of the left ventricle rose during exercise from 37 +/- 4 to 46 +/- 4% with no significant differences between the three groups. Velocity of circumferential fiber shortening (Vcf) in group I augmented from 1.3 to 2.25 circ./sec, in group II from 1.29 to 2.60 circ./sec, and in group III from 1.17 to 2.74 circ./sec (P = 0.01). In the recovery period heart rate (HR) and blood pressure normalized earlier than did fractional shortening and velocity of circumferential fiber shortening. This could be expressed best by the ratios FS/HR and Vcf/HR. There were no significant differences between sexes, although there was a tendency to higher blood pressure and heart rate, a greater increase in velocity of circumferential fiber shortening and a smaller increase in fractional shortening in girls. These data indicate that girls increased cardiac output during exercise more by increasing their heart rate than did boys.