Predictive value of the single-breath nitrogen test for hospitalization due to respiratory disease

The relationship between indices of the single-breath nitrogen test (SBNT) measured in 1974 and hospitalization in the 9 year period 1977-1986 was examined in a random population sample of 876 men aged 46-69 years. Men who could not perform acceptable SBNT tracings had an increased risk of hospitalization due to respiratory disease in general. When age and smoking habits were controlled for, slope of phase III was significantly related to hospitalization due to respiratory disease in general and chronic obstructive pulmonary disease (COPD), whereas closing volume and closing capacity were marginally related to hospitalization due to respiratory disease in general but not to hospitalization due to COPD. The relationship between slope of phase III and hospitalization due to COPD remained significant after the forced expiratory volume in 1 sec (FEV1) was controlled for: odds ratio 1.4 per % N2/L (95% confidence interval 1.1-1.7). The effect of the slope of phase III was considered to be clinically insignificant, and we conclude that in a random population sample indices from only 1 SBNT do not provide prognostic information concerning hospitalization in addition to that provided by FEV1.