Clinical Studies on Reversibility of Pulmonary Airway Dysfunctions in Asymptomatic Smokers: Role of Nervous Mechanism in Small Airway Disease

Pulmonary function tests were performed on twenty eight males, among whom eight were healthy nonsmokers and twenty were asymptomatic smokers. Pulmonary function tests such as spirometry, respiratory impedance (Z3Hz), single breath nitrogen washout (SBN2) and volume of isoflow (VisoV) were done before and after inhalation of orciprenaline sulphate and atropine sulphate in all nonsmokers and smokers. Subdivisions of lung volume, diffusing capacity (DLco) and arterial blood gas analysis were conducted only before inhalation of drugs. Acute effects were studied after smoking a cigarette and effects of orciprenaline inhalation after smoking were also observed. Furthermore, effects of smoking on prior inhalation of orciprenaline, atropine or lidocaine were evaluated.
The results obtained were as follows:
1) There were no differences in the results of routine pulmonary function tests, between nonsmokers and smokers except Z3Hz, which was significantly higher in smokers (p<0.01) and there was a tendency to decrease in flow especially at low lung volumes in smokers. Smokers could be well differentiated from nonsmokers by VisoV/FVC (p<0.001) and the difference in distribution of ventilation was greater (p<0.05).
2) In nonsmokers, Z3Hz decreased and V50 increased significantly after inhalation of orciprenaline and atropine. FEV1.o increased significantly with atropine inhalation only. There were no changes in VisoV/FVC with inhalation of orciprenaline or atropine.
In smokers, Z3Hz and VisoV/FVC decreased significantly after inhalation of orciprenaline or atropine (p<0.001). FEV1.o and flow rates improved significantly with both drugs.
3) After smoking a cigarette, Z3Hz and VisoV/FVC significantly increased (p < 0.01), but inhalation of orciprenaline or atropine prior to smoking significantly inhibited the acute effects of smoking and lidocaine completely inhibited the acute effects of smoking.
These results indicate that several parameters such as Z3Hz, flow at low lung volume, VisoV/FVC could detect the airway dysfunctions in asymptomatic cigarette smokers. These airway dysfunctions might be due to increased vagal tone, leading to narrowing of the airways and these airway dysfunctions were reversible by bronchodilator drugs.