Objective: Elderly people with chronic obstructive pulmonary disease (COPD) experience a gradual deterioration in functional status that leads to premature disability and eventually to loss of independence. The decline in functional status negatively affects most aspects of life and leads to a decline in quality of life. An important goal of nursing care is to optimize functioning through pulmonary rehabilitation. Little is known about the specific factors that contribute to decline in functional performance for people with COPD, but from a theoretical perspective functional performance will be affected by a combination of factors including disease related variables, functional capacity (aerobic capacity, muscle strength) and symptoms. The objective of this research was to determine the extent to which these variables influence functional performance of usual activities. Design: A cross sectional descriptive research design was used. Sample, Setting, Years: The sample was 71 men and 37 women with moderate to severe COPD and no other major health problems that would affect functioning. The mean age was 65 (SD=7). The forced expiratory volume in 1 second (FEV1) was 51 (SD=18) % predicted. Arterial partial pressure of oxygen and carbon dioxide were 78 (SD=10) and 40 (SD=4) mmHg. Body mass index and body weight were 27 (SD=5) and 79 (SD=19) Kg. Body composition measured by dual energy x-ray absorptiometry was a mean of 30 (SD=7) percent body fat and 53 (SD=11) Kg of nonosseous lean mass. Data were collected in a clinical laboratory from 1998 to 2000. Variables Studied: Functional performance was the dependent variable. Independent variables were: severity of disease as reflected by airflow obstruction, hyperinflation of the chest and gas exchange; functional capacity as reflected by walking capacity, inspiratory muscle strength and peripheral muscle strength; symptoms of dyspnea and fatigue. Methods: Functional performance was measured with the Functional Performance Inventory (FPI) (Leidy, 1995). Independent variables were measured as follows: airflow obstruction (FEV1 % predicted), hyperinflation (residual volume/total lung capacity), gas exchange (diffusion capacity, DLco % predicted), walking capacity (6 minute walk test), inspiratory muscle strength (maximal inspiratory pressure (PImax)), peripheral muscle strength (isokinetic strength of knee flexors and extensors and handgrip strength), dyspnea and fatigue (Chronic Respiratory Disease Questionnaire (CRQ) (Guyatt et al., 1987)). A composite score for peripheral muscle strength was calculated by averaging knee extensor and flexor strength and handgrip strength, using percent of predicted normal values for each. The potential range for the modified CRQ Dyspnea, CRQ fatigue and total FPI was 6-42, 4-28 and 0-3 respectively. Higher scores reflect fewer symptoms and a higher level of functioning. Findings: The means (SD) were as follows: total FPI 2.2 (.4), RV/TLC .56 (.08), DLco 60 (21) % predicted, 6-minute walk distance 1,304 (295) feet, PImax 84 (25) % predicted, peripheral muscle strength 82 (15) percent predicted, CRQ dyspnea 25 (7), CRQ fatigue 17 (4). Total functional performance scores on the FPI were correlated with the following: FEV1 % predicted (r=0.27), DLco (r=0.42), 6 minute walk distance (r=0.50), PImax (r=0.24), peripheral muscle strength (r=0.38), CRQ dyspnea (r=0.33), and CRQ fatigue (r=0.28). With stepwise regression DLco, peripheral muscle strength and fatigue accounted for 28% of the variance in total FPI. Six-minute walk distance entered the equation in the first step, but was removed in the fourth step of the process. Relationships were explored further with path analysis and DLco, peripheral muscle strength, CRQ dyspnea and CRQ fatigue accounted for 31% of the variance in total FPI. The path model revealed a direct path from DLco (beta weight=.34), peripheral muscle strength (beta weight=.30) and CRQ fatigue (beta weight=.20) to functional performance. The CRQ Dyspnea had a direct effect on fatigue (beta weight=.45) and an indirect effect on total FPI, mediated by fatigue. Conclusions: Diffusion capacity, peripheral muscle strength and symptoms of dyspnea and fatigue contribute to functional performance in people with COPD. These results suggest that fatigue and peripheral muscle strength are more important than previously thought. Dyspnea and fatigue are known to be the most common symptoms of COPD, but most attention has been given to dyspnea and these findings highlight the importance of fatigue. Traditionally pulmonary rehabilitation includes strength training and aerobic training, but most of the focus is on improving aerobic capacity. These findings emphasize the importance of peripheral muscle strength training in conjunction with aerobic exercise training. Implications: Diffusion capacity cannot be modified, but the remaining three variables can be modified through a combination of pulmonary rehabilitation and nursing interventions. More emphasis should be placed on interventions to minimize fatigue and to improve peripheral muscle strength.
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