The two groups were age matched, and in both, pulmonary function was within the normal range, but FEVi o% and maximum expiratory flow at 25% and 50% vital capacity were significantly lower in smokers than in nonsmokers. In nonsmokers, the concentration of exhaled NO increased after breath-holding in a time-dependent manner (Fig 1). However, the concentration of exhaled NO was not affected by breath-holding in smokers. The level of exhaled NO was higher in nonsmokers than in smokers, and this difference became larger as breath-holding time increased. To evaluate the correlation between endogenous NO level in exhaled air and the degree of airflow obstruction in smokers, we used a new parameter.
NO concentration difference (ANO), which we determined as follows: ANO=NO -N0; where NO is the concentration of NO in exhaled air after 15 s breath-holding, and NO is the concentration of NO in exhaled air during normal breathing. We found a positive correlation between ANO and airflow obstruction (FEVi o%) (Fig 2).
Figure 1. Top: NO in exhaled air measured by the sequential breath-holding method. Bars indicate breath-holding. A, Nonsmoker (33 years old); B, smoker (35 years old). Bottom: Comparison of NO concentrations in exhaled air by nonsmokers and smokers.
Figure 2. Correlation between NO concentration difference (ANO) and airflow obstruction (FEVi.o%).