Airway anesthesia and respiratory adaptations to dead space loading and exercise

In exercising humans, added external dead space (VD) increases minute ventilation (VI) and causes a slower and deeper breathing pattern (J. Appl. Physiol. 1991; 70:55-62). Recent studies suggest that airway receptors sensitive to topical anesthesia influence VI and breathing pattern responses to exercise and to added VD. We tested these hypotheses with a technique of airway anesthesia (Anesthesia) that has been shown to reliably attenuate airway reflexes. Anesthesia was administered by local laryngopharyngeal application and aerosolized lidocaine inhalation, and was confirmed by citric acid aerosol inhalation challenges. Twelve normal males performed maximal incremental cycle ergometer exercise on 4 d (randomized) after Anesthesia with (Anesthesia VD) and without added VD (Anesthesia Control) and after normal saline inhalation (Saline) with (Saline VD) and without added VD (Saline Control). There were no differences in the VI and breathing pattern responses during exercise between the Saline Control and the Anesthesia Control tests. After both Saline and Anesthesia inhalation, added VD resulted in an increase in VI both at rest and during exercise. At matched VI (98 L/min), the differences in tidal volume (VT) between the Saline Control and Saline VD tests (delta = 0.23 +/- 0.24 L, mean +/- SD) and the Anesthesia Control and Anesthesia VD tests (delta = 0.20 +/- 0.28 L) were not significantly different. Our study had a power of greater than 95% to detect significant differences in VI or breathing pattern due to Anesthesia. We conclude that in normal humans, airway receptors do not play a major role in ventilation and breathing pattern control during exercise, and that the respiratory adaptations to added VD during exercise are not mediated by airway afferent reflexes.