Relationship between smoking and the single breath nitrogen washout

In 1974, a collaborative study was carried out in three North American cities; Portland, Oregon, Montreal, Quebec, and Winnipeg, Manitoba. The objectives of this study were to determine the distribution of closure volume (CV) by age, sex and smoking habits in a defined population and to analyze the relationships between CV and smoking in each sex, having standardized for age. We found that nonsmokers in different cities appear to be very similar in terms of closing volume/vital capacity (CV/VC), closing capacity/total lung capacity (CC/TLC) and the slope of alveolar plateau ΔN₂/L and that smokers are different from nonsmokers in terms of these variables. We also found that age has a far greater effect on the variables tested than smoking. From this we conclude that some factor or factors interact with smoking in the development of irreversible airway obstruction.