The purpose of this study was to track changes in stroke volume during exercise by impedance cardiography in order to validate the method, and to obtain such data in a large number of healthy children for reference purposes. One hundred and fifteen healthy children (aged 7-19 years) performed progressive exercise to voluntary exhaustion with work increments every minute on a cycle ergometer. Oxygen uptake (̇ VO2) was measured on a breath-by-breath system. Cardiac output was measured with an ICG-M501 impedance cardiograph. Stroke volume was normalized for body surface area and expressed as stroke volume index. Cardiac output was regressed against ̇ VO2, and differences between stroke volume index at rest and exercise were assessed by repeated measures analysis of variance. Cardiac output increased linearly with ̇ VO2 in all subjects: individual slopes and intercepts averaged 5.16 (1.56) 1·min-1 per 1·min-1̇ VO2, and 4.25 (1.92) 1·min-1, respectively [mean(SD)]. Stroke volume index rose by an average of 29% from rest to exercise, reaching a maximum of 52 m1·m-2 in boys and girls. Most subjects demonstrated a continuous, gentle rise in stroke volume index with increasing work rate, though a minority demonstrated a falling index as work increased above the anaerobic threshold, despite rising cardiac output. Impedance cardiography accurately tracks cardiac output and can be a useful clinical and research tool in pediatric cardiology and exercise physiology.
Bibliographical noteFunding Information:
Acknowledgements Funded by a grant from the Heart and Stroke Foundation of Nova Scotia.
- Anaerobic threshold
- Bio-impedance cardiography
- Stroke volume