Cardiac dynamics during upright cycle exercise in boys

Insight into the cardiac responses to exercise necessitates an understandin g of both physiological data and cardiac dimensional changes. This study wa s designed to assess cardiovascular alterations during progressive uptight cycle exercise in ten healthy 10-12-year-old boys. Doppler echocardiography was used to estimate stroke volume, and 2-dimensional echocardiography was used to evaluate changes in left ventricular systolic and diastolic dimens ions. Test-retest reproducibility was high for both techniques. Mean peak s troke index and cardiac index values were 62 +/- 12 ml m(-2) and 11.79 +/- 2.62 L min(-1) m(-2), respectively. Stroke volume rose by 40% over resting values with early exercise (50 watt work load), but beyond moderate intensi ties (approximately 50% VO(2)max) little change was seen. The left ventricu lar diastolic dimension rose slightly at the onset of exercise and then dec lined slowly. A progressive and more precipitous decline was observed in sy stolic dimension, resulting in an increase in shortening fraction from 29% to 47%. This was accompanied by a dramatic fall in peripheral vascular resi stance from 13.9 to 8.0 units at the onset of exercise. These findings sugg est a close matching of increases in heart rate and systemic venous return and imply a significant role of peripheral pump function in the circulatory responses to exercise in children. The cardiac dynamics observed in this s tudy mimic those previously described in adult subjects. (C) 2000 Wiley-Lis s, Inc.