Upper airway resistance during progressive hypercapnia and progressive hypoxia in normal awake subjects

Ventilatory motor output is known to influence the upper airway. Although i nspiratory upper airway resistance decreases during progressive hypoxia or hypercapnia, the effects of hypoxia and hypercapnia on expiratory upper air way resistance remain unknown. In the present study, we attempted to examin e whether the expiratory and the inspiratory upper airway resistances were modified in the same way by progressive hyperoxic hypercapnia or by progres sive normocapnic hypoxia. Nine healthy subjects (five males, four females, 33 +/- 9 years) participated in the study. Inspiratory upper airway (iUAR) and expiratory upper airway resistances (eUAR) were calculated at flow 300 mi s(-1). Both resistances were obtained during a baseline period and durin g progressive hyperoxic hypercapnia or progressive normocapnic hypoxia. In all subjects, iUAR and eUAR decreased significantly during hypercapnic or h ypoxic challenge (P < 0.05). eUAR was always lower than iUAR during hyperca pnic challenge (P < 0.0001) and during hypoxic challenge (P<0.0001). The au thors conclude that expiratory upper airway resistance, as with inspiratory resistance, decreases during progressive hypercapnia or during progressive hypoxia. Pharyngeal dilator or constrictor muscle activities may be implic ated. (C) 2000 Elsevier Science B.V. All rights reserved.