THE DARLINGTON AND NORTHALLERTON PROSPECTIVE ASTHMA STUDY - BEST FUNCTION PREDICTS MORTALITY DURING THE FIRST 10 YEARS

The Darlington/Northallerton prospective study of asthmatics referred to secondary care started in 1983, with review and new entry at 5-yr i ntervals. The principal outcome measures are: mortality (presented her e), best function and therapeutic step. All adult asthmatics with grea ter than or equal to 15% peak flow (PEF) reversibility to greater than or equal to 200 l min(-1) were included. Socio-demographic variables. PEF and spirometry were recorded prospectively. Best vital capacity ( FVC) and PEF were assessed according to protocol. The mortality of the original cohort after 10 yr was expressed as standardized mortality r atio (SMR) against the local population, with history and pulmonary fu nction at entry as explanatory variables. Ninety-live per cent follow- up was achieved in 628 subjects, with 173 deaths (29.1% of those trace d). The excess death rate was nearly 50% (SMR 1.47, 95% CI 1.26-1.71), with 56% of deaths due to respiratory disease (expected 10%). After a llowance for age and sex, there was a consistent inverse relationship between mortality and entry best FVC. increased risk of death 1.51 (95 % CI 1.33-1.72) per 10% deficit of best FVC predicted. The risk of res piratory death was eight times greater, and of non-respiratory death t hree times greater, in the lowest compared with the highest quartile o f best FVC. There were no interactions with smoking, but possible enha ncement of the effect in the socially deprived. Best FVC was a particu larly powerful predictor of mortality in subjects <65 years at entry, in whom 64% of the excess deaths occurred. Most of the excess in respi ratory deaths was not due to acute severe asthma but to the developmen t of chronic obstructive pulmonary disease (COPD), as defined function ally, irrespective of smoking habit which made no further contribution to mortality.