The single-breath transfer factor for carbon monoxide and respiratory symptoms in a Norwegian community sample

Reduced single-breath transfer factors of the lung for carbon monoxide are seen in a number of conditions. The hypothesis of the present study was tha t self-reported respiratory symptoms differ in their prediction of TL,CO le vel in a general population in Norway. A cross-sectional survey of a general population sample in Norway, made up of 1,275 subjects aged 18-73 yrs, was conducted in 1987-1988. The attendees (84% response rate) filled in a questionnaire on respiratory symptoms and underwent standardized spirometric and TL,CO measurements and clinical exam ination. Associations between TL,CO and respiratory symptoms were assessed using multiple regression models. Tests for interaction were used to examin e whether these associations varied with sex, age and smoking habits. Data from 1,221 subjects were analysed. Both males and females who reported respiratory symptoms had significantly lower TL,CO after adjusting for age and height. In a multiple linear regres sion analysis of rr,co, adjusting for sex, age, height and smoking habits, the symptoms for which statistical significance was attained, were morning cough, chronic cough and breathlessness. However, only the breathlessness s core was independently associated with the TL,CO (-0.42 mmol.min(-1).kPa(-1 ) per breathlessness score unit) after adjusting for other respiratory symp toms, and the relationship was stronger in males than in females. In this study, the strongest predictor for a decreased single-breath transf er factor of the lung for carbon monoxide was the presence of self-reported breathlessness, regardless of age, smoking habits and height.