Peripheral chemoreceptor function in children with myelomeningocele and Arnold-Chiari malformation type 2

Blunted rebreathing hyperoxic hypercapnic ventilatory and arousal responses are frequent in older children with myelomeningocele (MMC) and Arnold-Chiari malformation type 2 (ACM). In contrast, isocapnic hypoxic rebreathing ventilatory responses are only occasionally affected. Thus, regions mediating the hypoxic ventilatory response appear usually preserved in children with MMC and ACM. Peripheral chemoreceptor function (PCR), however, has not been critically assessed in these children. To study this, PCR was measured in ten children and adolescents with MMC and ACM with normal alveolar ventilation during wakefulness, and in ten sex- and age-matched controls by measuring the ventilatory responses induced by 100% O₂ breathing, five tidal breaths of 100% N₂, and vital capacity breaths of 15% CO₂ in O₂. In general, tidal breathing of 100% O₂ resulted in smaller decreases in minute ventilation (V̇E) responses in patients with MMC, although absent V̇E responses to hyperoxia were found in four patients. Vital capacity breaths of 15% CO₂ elicited similar increases in V̇E in five patients and in ten controls, but no changes in V̇E were found in the remaining five patients (p<0.02). Acute hypoxia induced by N₂ tidal breathing resulted in significant linear regression correlations between V̇E and SpO₂ in five patients with MMC, while absent responses were measured in those same five patients with absent hypercapnic responses. We conclude that PCR, when assessed by acute hypoxia, hyperoxia, or hypercapnia is abnormal in some children with MMC and ACM, particularly in those demonstrating abnormal ventilation during sleep. We postulate that the large interindividual variability of PCR is dependent on the severity of brainstem involvement of PCR afferents or central respiratory integration sites.