Springer 2005
Quality of Life Research (2005) 14: 1835–1843 DOI 10.1007/s11136-005-5693-3
Functioning and psychological status among individuals with COPD Patricia P. Katz, Mark D. Eisner, Edward H. Yelin, Laura Trupin, Gillian Earnest, John Balmes & Paul D. Blanc Department of Medicine, University of California, San Francisco, 3333 California Street, Suite 270 San Francisco, CA, USA (E-mail:
[email protected]) Accepted in revised form 12 April 2005
Abstract Background: We examined the link between functioning and psychological status among persons with chronic obstructive pulmonary disease (COPD), using measures of both general functional status and performance of life activities. Methods: 334 persons with COPD were interviewed by telephone. Functioning was assessed with two measures of difficulty with specific types of activities (self-care, recreational activities/hobbies) and a general measure of functional status (SF-12 Physical Component Score (PCS)). Results: About 16.2% of the sample had SF-12 Mental Component Score (MCS) scores indicative of psychological distress (MCS < 35). In separate regression models, difficulty with self-care and recreational activities was associated with an increased likelihood of distress (self-care: OR ¼ 2.9, 95%CI 1.3, 6.6; recreation: OR ¼ 7.5 [2.4, 23.7]), while PCS scores were not. In a model including all three predictors, difficulty with recreation was strongly associated with distress (OR ¼ 7.7 [2.1, 29.2]), difficulty with self-care was less strongly associated with distress (OR ¼ 2.1 [0.8, 5.5]), and PCS did not contribute significantly to the predictive ability of the model. However, low functioning as measured by the PCS was a significant risk factor for difficulty performing activities. Conclusions: Measures of activity difficulty were independent predictors of psychological distress, while general physical function was not. Poor general physical function was a risk factor for activity difficulties, suggesting an indirect relationship between low PCS and psychological distress, with activity difficulties as the intermediate variable. Key words: COPD, Disability, Function, Psychological function Introduction Individuals with chronic obstructive pulmonary disease (COPD) have greater levels of functional limitation and disability than persons of comparable age in the general population [1–4]. These functional decrements can be observed whether function is defined as generic functional status (e.g., difficulty in the performance of specific actions such as walking one block), or as difficulty performing specific activities of daily living (e.g., difficulty in caring for one’s self or one’s home). For example, McSweeny reported dysfunction in a broad range of areas, particularly home management, sleep and rest, recreation and pastimes, and employment, in a group of COPD patients [4].
A high prevalence of psychological distress has been noted among individuals with COPD [5–9]. Although depression and/or depressive symptoms are noted more commonly in chronic disease in general, the prevalence among persons with COPD seems to be particularly high [8]. Some studies have reported links between poor functioning and psychological distress among persons with COPD [4, 6, 8]. Similar associations have been found in other chronic health conditions and the general elderly population [10–12]. For example, among individuals with rheumatoid arthritis, declines in the ability to perform a wide range of life activities were associated with the subsequent onset of new depressive symptoms [13, 14]. In these same studies, declines in generic function were not significantly predictive of
1836 new depression when declines in performance of life activities were also considered. Among adults with asthma, performance of life activities is more closely linked to disease-specific quality of life than are measures of general functioning [15]. In this cross-sectional study, we examined the link between functioning and psychological status among persons with COPD. To ascertain the roles of different types of functioning, we used measures of both generic function and performance of life activities as predictors of psychological status. Our hypothesis was that performance of life activities would be more strongly linked to psychological status than would general function.
Methods Data source Subjects Subjects were drawn from a larger, populationbased study of adults in the US with obstructive lung disease. Details of study recruitment have been previously published [16]. Briefly, the 379 individuals in this analysis were a subset of a cohort of adults aged 55–75 recruited through random digit dial telephone interviews. During the recruitment, subjects were asked if they had ever been diagnosed by a medical doctor with chronic bronchitis, emphysema, or COPD. Individuals responding affirmatively to any of these three conditions, a subset of the larger study group, were included in this analysis. The study was approved by the University of California, San Francisco, Committee on Human Research. Variables The telephone survey addressed demographic and socioeconomic background, respiratory symptoms, medications, co-morbid conditions, employment history, smoking history, psychological distress, and function. Three measures of functioning were examined. Two assessed difficulty with specific types of activities (self-care and recreational activities/hobbies), chosen to represent the low and high ends of a ‘‘difficulty’’ spectrum of activities. The third measure of functioning was a measure of generic functional status.
Performance of self-care activities Self-care activities such as dressing and showering, were measured using items from the Functional Performance Inventory (FPI; body care subscale [17, 18]). Subjects rated the amount of difficulty experienced with each activity on a four-point scale (‘‘no difficulty,’’ ‘‘some difficulty,’’ ‘‘much difficulty,’’ or ‘‘unable to do’’). Although subjects could also respond that they did not perform activities for reasons other than health, none responded in this way for the self-care items. For analysis, responses were collapsed into any difficulty with any self-care activity vs. no difficulty in any activity. Performance of recreational activities and hobbies The second measure of functioning assessed the ability to perform recreational activities or hobbies. This single item was also taken from the FPI, and difficulty was rated with the same scale used for the self-care items. For analysis, responses were collapsed into any difficulty vs. no difficulty. Generic functional status The third measure of functioning was a standard measure of generic physical function, the Physical Component Summary (PCS) score of the SF-12 [19], a shortened version of the widely used SF-36 [20]. The PCS scores derived from the SF-12 appear to be comparable to those derived from the SF-36 [19, 21, 22]. Scores on the PCS range from 0 to 100, with a population mean of 50; higher scores reflect better functioning. Physical functioning is assessed on the SF-12 with items such as ‘‘Does your health limit you in climbing several flights of stairs?’’, ‘‘Have you accomplished less than you would like as a result of your physical health?’’, and ‘‘Were you limited in the kind of work or other regular daily activities you do as a result of your physical health?’’. Because PCS scores were not normally distributed in this cohort, they were recoded to form categories based on quartiles. Individuals whose scores were in the highest quartile (i.e., had the best functioning) were the referent group for regression analyses. Quartiles were formed using age-based PCS norms for the general US population [19]. Psychological status Psychological status was assessed with the Mental Component Summary (MCS) score of the SF-12 [19]. Scores on the MCS range from 0 to 100, with a
1837 population mean of 50 and higher scores reflecting better functioning. The MCS scores derived from the SF-36 have been shown to be associated with the likelihood of depression, life stress, and life satisfaction [20]; MCS scores derived from the SF12 appear to be comparable to those derived from the SF-36 [19, 21, 22]. Like PCS scores, MCS scores were not normally distributed. Therefore, rather than use the continuous MCS score in analyses, we created a dichotomous ‘‘distress’’ category, defined by an MCS score $20,000). The presence of each of the following comorbid conditions was assessed from a condition checklist in the interview: diabetes, arthritis, congestive heart failure, coronary artery disease or heart attack (CAD), and lung cancer. Because there was no significant difference between those classified as distressed vs. not distressed in the proportion of subjects with CAD and lung cancer, these two conditions were not included as covariates in regression analyses, while the other conditions were included. The COPD Severity Score, a newly developed and validated measure, was included to account for severity of disease [23, in press]. The COPD Severity Score has a range of 0–30, and takes into account medications, symptoms, hospitalizations, intubation, antibiotic use, and oxygen use. Smoking status (ex-smoker or current smoker vs. never smoked) was also included. Statistical analysis Of the 379 subjects with COPD, 40 responded that they did not perform recreational activities for reasons other than health, and were excluded from all analyses. The MCS scores of the excluded subjects were slightly lower than those of the
remainder of the group (44.9 vs. 49.6, p < 0.05). An additional five subjects had missing data on critical variables and were also excluded, leaving an analysis sample of 334 subjects. The association of functional measures with psychological status was assessed using multiple logistic regression analyses in which psychological distress (MCS score < 35) was the dependent variable and measures of function were the primary independent variables. All regression analyses controlled for the covariates listed above. Analyses were conducted in three steps: Step 1. The association of the three measures of function (any self-care difficulty, any difficulty in recreational activities, and PCS score quartiles) with psychological distress was examined in three separate regression models. (Each model included only one measure of functioning.) Step 2. The two measures of activity difficulty were included in the same regression model. Step 3. PCS-12 scores were added to the regression model. Both the independent contribution of PCS-12 to the predictive power of the model and the increase in predictive power from the Step 2 model were assessed.
Results Subject characteristics Subject characteristics are shown in Table 1. The sample was predominantly female and white, and the average age was 64 years. Consistent with other published estimates, about 80% of the sample were current or former smokers [24, 25]. Individuals who were distressed were more likely to have low family incomes, less likely to be married, more likely to be current smokers, and were more likely to report having concurrent asthma, diabetes, congestive heart failure, and arthritis. Those who were distressed also had higher COPD Severity Scale scores, reflective of more severe disease. More severe disease among the distressed group is also reflected by greater likelihood of use of corticosteroids, metered dose inhalers, nebulizers, and antibiotics, and greater likelihood of hospitalization for lung problems in the past year, as shown in Table 1. The mean MCS score was 49.6, similar to the population mean of 50 (Table 2). Approximately
1838 Table 1. Subject characteristics (n = 334) Total sample
Age, years (mean ± SD) Female, % (n) High school education or less, % (n) Race: White, non-Hispanic, % (n) Family income ‡$20,000 per year, % (n) Married/with partner, % (n) Smoking status, % (n) Current smoker Former smoker Never smoked Other health conditions, % (n) No other health conditions Asthma Diabetes Congestive heart failure Heart disease Arthritis Lung cancer COPD severity scorey Home oxygen use, current, % (n) Systemic corticosteroid use, 3 months or more during past 2 years, % (n) Use metered dose inhaler in past year, % (n) Use nebulizer in past year, % (n) Antibiotics for lung problem in past year, % (n) Hospitalized for lung problem in past year, % (n) Ever intubated, % (n)
64.1 63.2 51.2 84.7 35.3 48.2
(±6.2) (211) (171) (283) (118) (161)
Psychological distress No (n = 280)
Yes (n = 54)
64.3 61.1 51.1 86.4 32.1 51.1
63.1 74.1 51.9 75.9 51.9 33.3
(±6.3) (171) (143) (242) (90) (143)
(±5.3) (40) (28) (41) (28) (18)
32.3 (108) 49.1 (164) 18.6 (62)
24.2 (55) 54.2 (123) 21.6 (49)
49.5 (53) 38.3 (41) 12.2 (13)
24.9 36.5 20.7 13.6 19.0 65.1 2.4 7.2 9.3 30.8
(83) (122) (69) (45) (63) (216) (8) (±6.5) (31) (103)
28.2 32.9 17.5 10.5 18.0 61.9 2.5 6.6 9.3 28.2
(92) (49) (29) (50)) (172) (7)) (±6.2) (26) (79)
17.8 55.6 37.0 29.6 24.5 81.5 1.9 10.8 9.3 44.4
(30) (20) (16) (13) (44) (1) (±7.1) (5) (24)
44.0 13.5 31.1 12.9 4.5
(147) (45) (104) (43) (15)
41.1 10.7 29.2 10.4 4.3
(115) (30) (79) (29) (12)
59.3 27.8 46.3 25.9 5.6
(32) (15) (25) (14) (3)
p* 0.21 0.09 0.99 0.06 0.008 0.02
