Functional Status And Its Correlates In Patients With Chronic Obstructive Pulmonary Disease At Stable Phase

BackgroundChronic obstructive pulmonary disease (COPD) is a chronic and slowly progressive disorder characterized by airflow restriction which is not fully reversible, and higher morbidity, mortality and social burden, and so has become one of important public health issues globally. According to a population-based investigation in 2007, overall prevalence of COPD in China was 8.2 percent. Both dyspnea and activity limitation are typical symptoms of COPD, and so sedentary lifestyle or inactivity is most likely chosen by the patients for coping with dyspnea in exertion, which leads to their deconditioning and muscular degeneration, and further increases their dyspnea and affects their activities of daily living in turn. Capacity of daily activities in patients with COPD and factors correlated to their functional status were studied by different methods in varied dimensions. However, no consensus has been achieved on functional status of the patients yet, and discrepancies in physiological, psychological and social factors correlated to it and their interaction still existed. No such studies in patients with COPD have ever been conducted in China. Evaluation for their daily functional performance among patients with COPD is of great significance in correct and comprehensive assessment of efficacy of the treatment and exploration of correlates to COPD.Objectives1. To describe functional performance in Chinese patients with moderate and severe COPD at stable phase;2. To explore physiological, pathological and psychosocial factors related to functional performance and their interaction in patients with moderate and severe COPD at stable phase; and3. To verify validity and reliability of functional performance inventory-short form in Chinese version (FPI-SF-C). Materials and MethodsA descriptive, cross-sectional design was used for the study. One hundred and twenty-nine patients with stable COPD with established diagnosis were recruited by convenience sampling during March 2009 to January 2010 from pulmonary outpatient clinics of three tertiary-care hospitals in Beijing, China. Their functions in six dimensions, such as body care, household maintenance, physical exercise, recreation, spiritual and social activities were evaluated by face-to-face interview with FPI-SF-C, which included 32 items scoring from zero to three for each of them, with more scores, better function. Demographic data were collected with a general questionnaire from each of the patients studied, and modified pulmonary functional status and dyspnea questionnaire (PFSDQ-M), hospital anxiety and depression scale (HAD), social support rating scale (SSRS) were finished by the patients themselves with informed consents and collected on the spot. FPI-SF-C and PFSDQ-M were verified for their validity and reliability before use. Six-minute walking distance (6MWD) was measured using procedures recommended by the American Thoracic Society (ATS) after interview. Spirometry and bronchodilator test were performed on the same day prior to interview or one week before interview. Scores of the scale measurements between the patients with varied characteristics were compared with non-parametric tests using SAS version 9.1 software. Path analysis was used to explore physiological, pathological, and psychosocial factors related to functional performance and their interaction in patients with moderate and severe COPD at stable phase using LISREL version 8.7 software.Results1. Demographic and clinical characteristicsOne hundred and twenty-nine patients with COPD were recruited,91 men and 17 women, for the study, with an average age of 67 years,89.9 percent of them living in urban areas and 53.5 percent with junior high school education or below. One hundred and seventeen patients were current smokers or ex-smokers, with a mean duration of smoking of 37.8 years and a mean smoking index of about 40 pack-years. Their forced expiratory volume in first second (FEV1) averaged 1.12 liters and 6MWD averaged 465.2 meters.2. Functional performanceTotal score for FPI-SF averaged 2.07 plus and minus a standard deviation of 0.40, highest in that of body care subscale (2.78±0.31) and lowest in household maintenance (2.10±0.61). Total score of FPI-SF correlated significantly with 6MWD (r=0.51), score of modified Medical Research Council dyspnea scale (MMRC) (r=-0.54), body mass index, air-flow obstruction, functional dyspnea and exercise capacity (BODE) index (r=-0.35), respectively (all P<0.01), and weaker association between FPI-SF score and forced expiratory volume at the first second (FEV1) (r=0.33) and FEV1% predicted (r=0.20), respectively, (both P<0.05) was found. Based on the criteria of the global initiative for chronic obstructive lung disease (GOLD), total score of FPI-SF differed significantly among patients with COPD in varied severity (Kruskal-Wallis x2=10.46, P=0.005).3. Symptoms and psychosocial statusOne hundred and nineteen (92.2%) and seventy-four (57.4%) of the 129 patients experienced dyspnea and fatigue, respectively. Total scores of FPI-SF differed significantly between patients with mild dyspnea and moderate and severe one (Z=3.97, P<0.001) and with mild fatigue and moderate and severe one (Z=-2.93, P=0.003). A score of eight or more in HAD scale was used as cut-off value for discrimination of clinical depression or anxiety, and 24 (24.0%) were predisposed to depression and 19 (18.6%) to anxiety. Total scores of FPI-SF differed significantly between the patients with and without depression predisposition (Z=-2.91, P=0.004), and scores of anxiety correlated significantly with scores of depression (Pearson's r=0.63, P<0.001). The patients got both good subjective and objective support with SSRS, and total score of FPI-SF differed significantly between patients with higher and lower social support (Z=-2.22, P=0.03).4. Testing for presumed functional status modelPath analysis showed a better goodness-of-fit between the presumed functional status model and real functional measurements (x2=19.38,?=18, P=0.37, RMSEA=0.026, IFI=0.99, CN=211.48), with statistical significance for path coefficients for all variables in the model (P<0.05). Score of MMRC dyspnea, scores for fatigue and depression, and 6MWD all could influence total score of FPI-SF directly, with oath coefficients of -0.31,-0.30,0.28 and -0.15, respectively. But no direct influence of exogenous variable, such as age, FEV1% predicted and score of social support on total score of FPI-SF was found, and 6MWD, score of MMRC dyspnea and score of depression could influence it indirectly via mediators, with the highest overall effect in score of MMRC dyspnea (coefficient of effect 0.50).5. Reliability and validity of the Chinese version of the FPI-SFCronbach's alpha was 0.89 for the total FPI-SF, ranging from 0.70 to 0.89 for varied subscales, and intraclass coefficient of correlation was 0.97 in 30 patients with repeated tests within two weeks. Total score of FPI-SF correlated significantly to 6MWD (r=0.56), MMRC dyspnea score (r=-0.55), BODE index (r=-0.47), FEV1 (r=0.41), and FEV1% predicted (r=0.26), respectively (all P<0.05), suggesting its good construct validity.Conclusions1. Functional performance of patients with COPD at stable phase was affected mildly or moderately, least in their body care and moderately in household maintenance.2. Dyspnea and fatigue were major symptoms in patients with COPD at stable phase, and they would experience mild or moderate dyspnea and fatigue with exertion in activities of daily living. These patients could predispose to depression and anxiety, and their functional performance would be more affected in those with disposition to depression. However, they all had good subjective and objective supports, but without sufficient utilization of them. Functional performance differed significantly between the patients with varied social support.3. Exercise capacity, dyspnea, fatigue and depression directly influenced their functional performance, with dyspnea showing the strongest effect on it, followed by fatigue. Age, severity of illness and social support had indirect influence on their functional performance with exercise capacity, dyspnea and depression as mediators, other than direct effects.