Hypoxic and hypercapnic response in asthmatic subjects with previous respiratory failure.

Three children and two young adults with severe asthma who had frequent episodes of respiratory failure were studied. Isocapnic hypoxia and hyperoxic hypercapnia were produced separately using a rebreathing apparatus. Alveolar carbon dioxide tension and oxygen tension were estimated by continuously sampling expired gases. The three young children had a diminished response to hypoxia but a normal response to hypercapnia when compared to control asthmatic children (p less than 0.05) or healthy children (p less than 0.05). The two young adult patients had a normal response to hypoxia but one had a low response to hypercapnia. Studies of parents of these patients suggested that the chance combination of a possibly familial, inappropriate response to hypoxia with severe asthma would lead to a risk of respiratory failure.