Respiratory drive in nonsmokers and smokers assessed by passive tilt and mouth occlusion pressure. Response to rebreathing carbon dioxide.

The purpose of the present investigation was to assess respiratory center function in smokers using (1) measurement of mouth occlusion pressure during carbon dioxide rebreathing and (2) noninvasive measurement of breathing pattern during passive upright tilt. The breathing patterns of 20 normal nonsmokers and 20 smokers without major obstruction of the airways were monitored noninvasively with respiratory inductive plethysmography for 15 minutes in the supine position and then after 90 degrees head-up passive tilt to the standing position. In nonsmokers, significant increases from supine to standing positions included the following: (1) minute ventilation from 6.22 +/- 1.47 to 7.32 +/- 1.16 L/min (p less than 0.05); (2) tidal volume from 368 +/- 93 to 462 +/- 108 ml (p less than 0.01); and (3) mean inspiratory flow from 263 +/- 61 to 320 +/- 43 ml/sec (p less than 0.01). Responses of smokers to tilt were variable; 14 showed changes similar to nonsmokers, but six showed no increase of ventilation and respiratory drive upon tilting. The latter also showed blunted response to rebreathing carbon dioxide in the supine position as estimated by plotting mouth occlusion pressures against end-tidal carbon dioxide tension. These data suggest that disturbances of respiratory center control are common in smokers without major obstruction of the airways.