Background: The Lambda-Mu-Sigma (LMS) method calculates the lower limit of normal for spirometric measures of pulmonary function as the fifth percentile of the distribution of z scores, suitably accounting for age-related changes in pulmonary function. Extending prior work, and to assess whether the LMS method is clinically valid when evaluating respiratory impairment in the elderly, our current objective was to evaluate the association of LMS-defined respiratory impairment (airflow limitation and restrictive pattern) with all-cause mortality and respiratory symptoms (chronic bronchitis, dyspnea, or wheezing) in older persons.
Methods: Spirometric data and outcome data on white participants aged 65 to 80 years were obtained from the Third National Health and Nutrition Examination Survey (NHANES-III, n = 1497) and the Cardiovascular Health Study (CHS, n = 3583). Multivariable analyses determined the corresponding associations, adjusting for important covariates.
Results: In the NHANES-III and CHS populations, respectively, LMS-defined airflow limitation had adjusted hazard ratios (95% confidence interval) of 1.64 (1.28-2.11) and 1.69 (1.48-1.92) for mortality; adjusted odds ratios for respiratory symptoms were 2.71 (1.92-3.83) and 2.63 (2.11-3.27). The LMS-defined restrictive pattern was also significantly associated with mortality (adjusted hazard ratios of 1.98 [1.54-2.53] and 1.68 [1.44-1.95]), as well as with respiratory symptoms (adjusted odds ratios of 1.55 [1.03-2.34] and 1.37 [1.07-1.75]) in NHANES-III and CHS, respectively.
Conclusions: The LMS-defined airflow limitation and restrictive pattern confers a significantly increased risk of death and likelihood of having respiratory symptoms. These results support the use of LMS-derived spirometric z scores as a basis for evaluating respiratory impairment in older persons.