Ventilatory response and drive of asthmatic children to alveolar hypoxia.

Hypoxic ventilatory responses and 100-msec inspiratory occlusion pressures (P100s) were measured at constant alveolar PCO2 (normocapnia) in 13 asthmatic [12.5 +/- 1.0 (S.E.) years] and in 12 normal children (13.3 +/- 0.6 years) to determine the appropriateness of the asthmatics' minute ventilation and ventilatory (inspiratory) drive, respectively. Most asthmatics were well controlled with continuous drug therapy and exhibited only mild pulmonary abnormalities at the time of testing. Hypoxia-induced increases in minute ventilation were quantitated in terms of A-values per m2 body surface area. An A-value describes, in numerical terms, the slope of the hyperbolic ventilatory response to progressive alveolar hypoxia. Larger A-values denote greater increases in ventilation. The A-values were not significantly different between the asthmatic (105 +/- 14) and normal children (123 +/- 24). The occlusion pressures were significantly different, however, and were 2.3 +/- 0.2 cm H2O (sub-atmospheric) for the asthmatics and 1.5 +/- 0.1 cm H2O for the normal children at an alveolar PO2 = 80 mm Hg, and 7.7 +/- 0.9 and 5.2 +/- 0.8 cm H2O for the respective groups at an alveolar PO2 = 40 mm Hg (P less than 0.05). These findings indicate that asthmatic children with minimal pulmonary abnormalities maintain a normal ventilatory response to alveolar hypoxia by increasing their ventilatory drive, whereas adult asthmatics have been reported to have less than normal increase in ventilatory drive and hence a diminished ventilatory response during hypoxic exposure.