Ventilatory response to exercise in children with congenital central hypoventilation syndrome

Abstract

The role of the central and peripheral chemoreceptors in the hyperpnea of exercise has been controversial. We studied five children, age 6 to 11 yr, with absent hypercapneic and hypoxic ventilatory responses during wakefulness (congenital central hypoventilation syndrome, CCHS). Each child performed an incremental treadmill exercise test. Maximal oxygen consumption (V_O2) and minute ventilation (V_E) at maximal exercise were lower than but not significantly different from these values in a group of nine normal control children of similar age, height, and weight (V_O2/kg, 33.7 ± 5.0 versus 45.4 ± 2.9 ml/kg/min, mean ± SEM, NS; V_E 28.3 ± 7.3 versus 43.8 ± 3.9 L/min, NS). Oxygen tension and saturation fell and CO₂ tension rose significantly at maximal exercise in CCHS but not in control subjects. In contrast to control subjects, CCHS subjects increased V_E largely by increasing respiratory frequency (f) rather than tidal volume (V_T). In the oldest child, submaximal exercise tests at 50% V_O2, with varying pacing rate, showed a significant positive relation between pacing rate and f, but not V_T. Thus, V_E was higher at the faster pacing rate. Further incremental testing in the two oldest subjects with recording of the pacing rate showed positive linear relations between pacing frequency and breathing frequency and between pacing frequency and V_E up to a maximum pacing rate of 48 to 50 paces per 15 s. V_E beyond this level varied randomly around the maximum level. We conclude that exercise-induced hyperpnea can occur in the absence of chemoreceptor function. In the CCHS children, limb movement is an important determinant of the ventilatory response to exercise. We speculate that movement may be an important influence on ventilation under all circumstances and in all states of arousal in CCHS children.