Peripheral airways resistance in smokers

To determine peripheral airways resistance (R(p)) in asymptomatic smokers, we used a wedged bronchoscope technique to study 19 volunteers (18 to 44 yr of age) who actively smoked for 2 to 28 pack-years. A fiberoptic bronchoscope was wedged in a subsegmental bronchus of the right upper lobe. Using a double lumen catheter inserted through the working channel of the bronchoscope, we infused 5% CO₂ in air through one lumen and measured pressure through the second lumen. R(p) was determined as the average of the peripheral resistance measured at three or more flow rates. This resistance ranged from 0.003 to 0.075 cm H₂O/ml/min in the 19 subjects. We have previously shown normal subjects to have an average R(p) of 0.009 ± 0.002 cm H₂O/ml/min (mean ± SE) and asthmatic subjects an average of 0.069 ± 0.017 cm H₂O/ml/min. Thus, despite normal pulmonary function as assessed by spirometry, these asymptomatic smokers demonstrated a wide range of R(p) values from normal to that observed in asthmatic subjects. These findings are consistent with a mechanism that considers the high resistance to result from inflammatory changes in the small airways.