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

The effect of the first cigarette in the morning on the airway resistance (Raw) which can be measured by body-plethysmography was investigated in 70 inhaling cigarette smokers. The test population showed a significant (P less than 0.0005) fall in Raw 8 min after smoking. A further study (n = 16) showed that the fall in Raw 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 less than 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 less than 0.01 and P less than 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 (QN2O) before, and 18-22 min after, smoking the first cigarette in the morning. After smoking, there was a significant (P less than 0.0005) fall in the QN2O by an average of 11.3%. The decrease in the Raw, the fall in the PaO2 with compensatory overventilation, the increase in P(A-a)O2 and P(A-a)CO2 and the decrease in the QN2O are interpreted as manifestations of pronounced acute ventilation-perfusion mismatching induced by smoking.