Hypercapnic and hypoxic ventilatory responses.

Abstract

The developmental pattern of ventilatory responses, through childhood and puberty into adulthood, is not known. Therefore we studied hypercapnic (HCVR) and hypoxic ventilatory responses (HOVR) in 59 subjects (29 males and 30 females) 4-49 yr of age, of whom 35 were children (<18 yr old). There was a significant correlation between HCVR and weight (r=0.33, P<0.02), vital capacity (r=0.30, P<0.05), and body surface area (r=0.30, P<0.05) but not height (r=0.22, NS). There was no correlation between HOVR and any of the correction factors. To account for disparities in body size, volume-related results were scaled for body weight. Thee HCVR corrected for weight (HCVR/WT) decreased with age (r=-0.57, P<0.001). HCVR/WT was significantly higher in children than in adults (0.056±0.024 vs. 0.032±0.015 l.kg -1 .min -1 .Torr end-tidal PCO 2 -1 , P<0.001). The (tidal volume/inspiratory duration/weight, respiratory rate, and heart rate responses to hypercapnia were increased in the children, and the CO 2 threshold was lower (36±5 vs. 40±6 Torr, P<0.05). Similarly, the HOVR corrected for weight (HOVR/WT) decreased with age (r=0.34, P<0.05), and HOVR/WT was significantly higher in children than in adults (-0.035±0.017 vs. -0.024±0.016 l.kg -1 .min -1 .%arterial O 2 saturation -1 , P<0.02). The respiratory rate and heart rate responses to hypoxia were increased in the children. We conclude that rebreathing HCVR and HOVR are higher during childhood than during adulthood.