Reporting peak expiratory flow in older persons.

Abstract

Peak expiratory flow ("peak flow") predicts important outcomes in older persons. Nevertheless, its clinical application is uncertain because prior strategies for reporting peak flow may not be valid. We thus determined the frequency distribution of peak flow by the conventional strategy of percent predicted (%predicted) and by an alternative method termed standardized residual (SR) percentile, and evaluated how these two metrics relate to health status in older persons. Participants included 754 community-dwelling persons aged >/= 70 years. Data included chronic conditions, frailty indicators, and peak flow. Mean age was 78.4 years, with 63.7% reporting a smoking history, 17.4% chronic lung disease, and 77.1% having one or more frailty indicators. Peak flow >/= 80 %predicted was recorded in 67.5% of participants, whereas peak flow >/= 80th SR percentile was only noted in 15.9%. A graded relationship was observed between peak flow and health status, but %predicted yielded health risk at peak flows currently considered normal (80-100 %predicted), whereas SR percentile conferred health risk only at severely reduced peak flows (< 50th SR percentile). Peak flow expressed as SR percentile attains a frequency distribution more consistent with the characteristics of our elderly cohort, and establishes health risk at more appropriate levels of reduced peak flow. These findings establish the need for longitudinal studies based on SR percentile to further evaluate the use of peak flow as a risk assessment tool in older persons and to determine if pulmonary function, in general, is better reported in older persons as SR percentile, rather than as %predicted.