Acute ventilation-perfusion mismatching resulting from inhalative smoking of the first cigarette in the morning

Summary The effect of the first cigarette in the morning on the airway resistance (R_aw) which can be measured by body-plethysmography was investigated in 70 inhaling cigarette smokers. The test population showed a significant (P<0.0005) fall in R_aw 8 min after smoking. A further study (n = 16) showed that the fall in R_aw was most likely to be attributable to a decrease in the trapped air. The effect of the first cigarette in the morning on the arterial blood gases and on the alveolar-arterial oxygen difference P(A-a)O₂ and carbon dioxide difference P(A-a)CO₂ was investigated in 12 inhaling cigarette smokers. Smoking gave rise to a significant (P < 0.0005) fall in the partial pressure of oxygen (PaO₂) with compensatory overventilation. At the same time, the P(A-a)O₂ and the P(A-a)CO₂ increased significantly (P<0.01 and P<0.05, respectively). This effect could be observed for up to 24 min after smoking. In addition, the flow of blood in the pulmonary capillaries was measured in 28 test subjects with the nitrous oxide method (_N2O) before, and 18–22 min after, smoking the first cigarette in the morning. After smoking, there was a significant (P<0.0005) fall in the _N2O by an average of 11.3%. The decrease in the R_w the fall in the PaO₂ with compensatory overventilation, the increase in P(A-a)O₂ and P(A-a)O₂ and the decrease in the _N2O are interpreted as manifestations of pronounced acute ventilation-perfusion mismatching induced by smoking.Abbreviations Cdyn dynamic compliance - Cdyn 40a dynamic compliance at 40 breaths/min - _N2O pulmonary capillary blood flow measured by the N₂O method - P(A-a)a alveolararterial pressure difference - Pa arterial partial pressure - P_AOa alveolar pressure difference measured in the pressure-flow curve at zero flow - R_awa airway resistance - sGaw specific airway conductance - SVI stroke volume index - TGV thoracic gas volume - BSA body surface area