Hemodynamic responses to exercise in normal children

Ten normal children and 13 with mild pulmonary stenosis (aged 5 to 16 years, mean 11) underwent supine isotonic exercise testing during diagnostic cardiac catheterization. Oxygen consumption (VO₂), intracardiac pressures, pulmonary and systemic arterial oxygen (O₂) saturations, hemoglobin levels and respiratory quotients were measured. Cardiac index, stroke index, systemic and pulmonary vascular resistances and exercise factor were determined. No differences were found between the two groups, and the circulatory response to exercise was defined for these 23 "normal" children. Children have a response to supine exercise that is similar to, but more variable than, that reported for adults. Children under age 12 years with lower hemoglobin levels (13.2 versus 13.9 g/100 ml) manifested increased O₂ extraction with exercise (pulmonary arterial O₂ saturation = 45versus 54 percent in children over 12 years) (P < 0.05), although the exercise stress was the same for both groups. No other variables were age-related. Although stroke index rose 8 percent (P < 0.02) and pulmonary vascular resistance decreased 19 percent (P < 0.001) with exercise, the normal ranges for the group were wide. Similarly, the mean exercise factor was 718, but ranged from 341 to 1,056. The variability of the exercise response in normal children somewhat limits the clinical use of exercise in children with heart disease. None-theless, a normal exercise response in children may be defined as follows: (1) a close relation between cardiac index (CI) and VO₂ (Cl = 0.065 VO₂ + 3.48; r = 0.88); (2) a cardiac index 6.0 liters/min per m² or more when VO₂ is 600 ml/min per m²; (3) no increase in pulmonary vascular resistance; (4) a decrease in right atrial pressure (4.1 to 3.1 mm Hg, P < 0.001); and (5) a decrease in systemic vascular resistance (more than 20 percent, P < 0.001) with exercise.