Relation of ventilatory impairment and of chronic mucus hypersecretion to mortality from obstructive lung disease and from all causes.
The relation of ventilatory impairment and chronic mucus hypersecretion to death from all causes and death from obstructive lung disease (chronic bronchitis, emphysema and asthma) was studied in 13,756 men and women randomly selected from the general population of the City of Copenhagen. During the 10 year follow up 2288 subjects died. In 164 subjects obstructive lung disease was considered to be an underlying or a contributory cause of death (obstructive lung disease related death); in 73 subjects it was considered to be the underlying cause of death (obstructive lung disease death). Forced expiratory volume in one second, expressed as a percentage of the predicted value (FEV1% pred), and the presence of chronic phlegm were used to characterise ventilatory function and chronic mucus hypersecretion respectively. For mortality analysis the proportional hazards regression model of Cox was used; it included age, sex, pack years, inhalation habit, body mass index, alcohol consumption, and the presence or absence of asthma, heart disease, and diabetes mellitus as confounding factors. By comparison with subjects with an FEV1 of 80% pred or more, subjects with an FEV1 below 40% pred had increased risk of dying from all causes (relative risk (RR) = 5.0 for women, 2.7 for men), a higher risk of obstructive lung disease related death (RR = 57 for women, 34 for men), and a higher risk of obstructive lung disease death (RR = 101 for women, 77 for men). Chronic mucus hypersecretion was associated with only a slightly higher risk of death from all causes (RR = 1.1 for women, 1.3 for men). The association between chronic mucus hypersecretion and obstructive lung disease death varied with the level of ventilatory function, being weak in subjects with normal ventilatory function (for an FEV1 of 80% pred the RR was 1.2), but more pronounced in subjects with reduced ventilatory function (for an FEV1 of 40% pred the RR was 4.2). A similar though statistically non-significant trend was observed with regard to obstructive lung disease related death. This study shows that impaired lung function is very strongly related to total mortality, obstructive lung disease related mortality, and obstructive lung disease mortality and suggests that chronic mucus hypersecretion, in those with impaired ventilatory function, is also a significant risk factor for death from obstructive lung disease.