CHEMOSENSITIVITY AND PERCEPTION OF DYSPNEA IN PATIENTS WITH A HISTORYOF NEAR-FATAL ASTHMA

Background. Many deaths from attacks of asthma may be preventable. How ever, the difficulty in preventing fatal attacks is that not all the p athophysiologic risk factors have been identified. Methods. To examine whether dyspnea and chemosensitivity to hypoxia and hypercapnia are f actors in fatal asthma attacks, we studied 11 patients with asthma who had had near-fatal attacks, 11 patients with asthma who had not had n ear-fatal attacks, and 16 normal subjects. Their respiratory responses to hypoxia and hypercapnia, determined by the standard rebreathing te chnique while the patients were in remission, were assessed in terms o f the slopes of ventilation and airway occlusion pressure as a functio n of the percentage of arterial oxygen saturation and end-tidal carbon dioxide tension, respectively. The perception of dyspnea was scored o n the Borg scale during breathing through inspiratory resistances rang ing from 0 to 30.9 cm of water per liter per second. Results. The mean (+/-SD) hypoxic ventilatory response (0.14+/-0.12 liter per minute pe r percent of arterial oxygen saturation) and airway occlusion pressure (0.05+/-0.05 cm of water per percent of arterial oxygen saturation) w ere significantly lower in the patients with near-fatal asthma than in the normal subjects (0.60+/-0.35, P<0.001, and 0.16+/-0.08, P<0.001, respectively) and the patients with asthma who had not had near-fatal attacks (0.46+/-0.29, P = 0.003, and 0.15+/-0.09, P = 0.004). The Borg score was also significantly lower in the patients with near-fatal as thma than in the normal subjects, and their lower hypoxic response was coupled with a blunted perception of dyspnea. Conclusions. Reduced ch emosensitivity to hypoxia and blunted perception of dyspnea may predis pose patients to fatal asthma attacks.