Pulmonary function and the risk of functional limitation in chronic obstructive pulmonary disease

Abstract

The authors' objective was to analyze the impact of respiratory impairment on the risk of physical functional limitations among adults with chronic obstructive pulmonary disease (COPD). They hypothesized that greater pulmonary function decrement would result in a broad array of physical functional limitations involving organ systems remote from the lung, a key step in the pathway leading to overall disability. The authors used baseline data from the Function, Living, Outcomes, and Work (FLOW) study, a prospective cohort study of adults with COPD recruited from northern California in 2005-2007. They studied the impact of pulmonary function impairment on the risk of functional limitations using validated measures: lower extremity function (Short Physical Performance Battery), submaximal exercise performance (6-Minute Walk Test), standing balance (Functional Reach Test), skeletal muscle strength (manual muscle testing with dynamometry), and self-reported functional limitation (standardized item battery). Multiple variable analysis was used to control for confounding by age, sex, race, height, educational attainment, and cigarette smoking. Greater pulmonary function impairment, as evidenced by lower forced expiratory volume in 1 second (FEV(1)), was associated with poorer Short Physical Performance Battery scores and less distance walked during the 6-Minute Walk Test. Lower forced expiratory volume in 1 second was also associated with weaker muscle strength and with a greater risk of self-reported functional limitation (p < 0.05). In conclusion, pulmonary function impairment is associated with multiple manifestations of physical functional limitation among COPD patients. Longitudinal follow-up can delineate the impact of these functional limitations on the prospective risk of disability, guiding preventive strategies that could attenuate the disablement process.

FIGURE 1

Impact of pulmonary function impairment on functional limitation (lower extremity functioning, exercise performance, and balance), California, 2005-2007. The figure shows scatterplots and the fitted regression lines. Part A shows the relation between the log odds (logit) of poor lower extremity function (i.e., the lowest quartile of the Short Physical Performance Battery (SPPB) score) and forced expiratory volume in 1 second (FEV₁). Part B depicts the association between distance walked in 6 minutes (6-Minute Walk Test) and FEV₁. Part C displays the association between the Functional Reach Test of standing balance and FEV₁. One foot = 0.3048 m.

FIGURE 2

Impact of pulmonary function impairment on functional limitation (skeletal muscle strength), California, 2005-2007. The figure depicts scatterplots of the relation with the fitted regression line. Part A shows the relation between quadriceps strength and forced expiratory volume in 1 second (FEV₁). The remaining parts depict the association between the following muscle groups and FEV₁: part B, hip flexor strength; part C, hip abductor strength; part D, elbow flexor strength; and part E, grip strength. One pound = 453.5924 g.

FIGURE 3

Impact of pulmonary function impairment on self-reported functional limitation, California, 2005-2007. The figure shows the association between the log odds (logit) of each self-reported functional limitation and forced expiratory volume in 1 second (FEV₁) fitted by the LOWESS procedure. Part A shows self-reported functional limitation (“unable to do” or “severe limitation” in a battery of basic physical activities (refer to Materials and Methods)). Part B shows limitation of moderate activities (health limits “a lot” in performing moderate activities, such as moving a table, pushing a vacuum cleaner, bowling, or playing golf). Part C depicts limitation in climbing several flights of stairs. In each case, the relation was curvilinear, and a quadratic term was statistically significant in the logistic regression analysis. LOWESS, locally weighted regression scatterplot smoother.