RESPIRATORY DRIVE IN NONSMOKERS AND SMOKERS ASSESSED BY PASSIVE TILT AND MOUTH OCCLUSION PRESSURE - RESPONSE TO REBREATHING CARBON-DIOXIDE

Respiratory center function was assessed in smokers using measurement of mouth occlusion pressure during CO2 rebreathing and 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 min in the supine position and then after 90.degree. head-up passive tilt to the standing position. In nonsmokers, significant increases from supine to standing positions occurred in minute ventilation from 6.22 .+-. 1.47 to 7.32 .+-. 1.16 l/min (P < 0.05); tidal volume from 368 .+-. 93 to 462 .+-. 108 ml (P < 0.01) and mean inspiratory flow from 263 .+-. 61 to 320 .+-. 43 ml/s (P < 0.01). Responses of smokers to tilt were variable; 14 showed changes similar to nonsmokers, but 6 showed no increase of ventilation and respiratory drive upon tilting. The latter also showed blunted response to rebreathing CO2 in the supine position as estimated by plotting mouth occlusion pressures against end-tidal CO2 tension. Disturbances of respiratory center control are common in smokers without major obstruction of the airways.