Predictors of survival in subjects with chronic airflow limitation

In a study of chronic airflow limitation, we followed 140 subjects living in Utah at altitudes of 1,300 to 1,500 meters for seven to 13 years. Twelve-year survival probabilities were determined and compared with an age- and sex-matched Utah population. The lowest 12-year survival probability was 0.40 for those patients with a forced expiratory volume in one second/forced vital capacity ($\text{FEV}{}_1\text{FVC}$) of less than or equal to 0.40, indicating that there is much variability in survival. Other indicators of a lower survival probability (and increased death risk ratio) were an FEV₁ percent predicted less than or equal to 50, an FEV₁ less than or equal to 1.5 liters, male gender, partial pressure of oxygen (P_O2) [exercise] less than or equal to 50 mm Hg, partial pressure of carbon dioxide (P_CO2) [rest] greater than 39 mm Hg, P_CO2 (exercise) greater than 39 mm Hg, FVC percent predicted less than or equal to 80, P_O2 (rest) less than or equal to 55 mm Hg, and a carbon monoxide diffusing capacity (DL_CO) percent predicted less than or equal to 80. Current smokers had a poorer survival probability than the reference population and an increased death risk when compared with the nonsmokers in the study. Pack/years of smoking also affected survival. Other variables associated with reduced survival were a diagnosis of chronic bronchitis combined with emphysema, more rapid annual declines in the FEV₁ and/or FVC, low alpha₁-antitrypsin levels, a 20 percent improvement in FEV₁ following the use of a bronchodilator aerosol, and a lower socioeconomic class. Differences between these findings and those noted in other studies are in the main due to differences in the characteristics (such as age, diagnosis, and extent of disease) of the patients in the study populations. The findings have relevance in estimating a patient's prognosis and for developing guidelines for disability determination purposes.