We used data from an ongoing population-based, longitudinal cohort study of U.S. adults with various airways diseases followed by telephone interview. During the initial recruitment in 2001, subjects aged 55–75 years were asked if they had ever been diagnosed by a physician with chronic bronchitis, emphysema, chronic obstructive pulmonary disease (COPD) or asthma; if so, they were included in the OLD cohort (n=517 at baseline). The initial recruitment also included individuals with allergic rhinitis or sleep apnea, who are not included in this analysis. Annual retention among the original sample averaged approximately 80% over 5 annual followup telephone interviews through 2006. In 2006, another 375 individuals were added from northern California using the same recruitment protocol, for a total sample size of 675 at that point. Of this total, 243 reported either COPD or emphysema, 209 reported chronic bronchitis without concomitant COPD or emphysema, and 139 reported asthma only. In 2007, 86% (583 individuals) were reinterviewed. The analyses reported here are limited to individuals who reported COPD, emphysema, chronic bronchitis, or asthma; completed a home visit with a corresponding telephone interview in either 2006 or 2007, as described below (n=206); and completed at least 1 followup telephone interview in the year after the home visit (n=176). The study was approved by the University Committee on Human Research.
At the end of both the 2006 and 2007 telephone interviews, participants who lived in Northern California were asked to participate in a home visit. Among the assessments made during the home visit were spirometry and a physical activity questionnaire. Home visits were conducted an average of 45 days following the telephone interview. Home visit personnel received extensive training in all procedures and were required to demonstrate correct performance of all procedures, including spirometry, prior to going out into the field. Of 327 individuals who were geographically eligible, 251 (77%) received a home visit; 240 of these had self-reported physician diagnose of COPD, emphysema, chronic bronchitis, or asthma. Of the 240, 34 individuals did not complete spirometry and/or the physical activity measure, leaving 206 with complete data from the home visit.
Physical activity was measured with the Community Healthy Activities Model Program for Seniors (CHAMPS) Physical Activity Questionnaire for Older Adults.4
The CHAMPS is a self-report questionnaire designed specifically for use with older populations, and has been found to be valid, reliable, and sensitive to change.4,5
Respondents report the total time spent in activities for a typical week. Each activity is linked to a metabolic equivalent (MET) value. Two measures of estimated caloric expenditure per week can be derived from questionnaire responses: expenditure in all activities including light intensity activities, and expenditure only in activities of moderate or vigorous intensity (MET value ≥3.0). We defined physical inactivity as no expenditure reported in moderate or vigorous intensity activities.
Disability was measured using the Valued Life Activities (VLA) scale, which assesses difficulty in functioning in 28 activity domains, ranging from self-care to household chores to social and recreational activities.6,7
Respondents rate difficulty caused by their condition in each life activity (0=no difficulty, 1=a little difficulty, 2=a lot of difficulty, and 3=unable to perform). Activities that respondents do not perform for reasons unrelated to their respiratory condition or that are not applicable to them are not rated or included in scoring. The summary score used for this study was the proportion of activities affected (unable to perform or able to perform but with some level of difficulty; % affected). An increase in disability was defined as an increase ≥10% in the proportion of VLAs affected between the baseline and 1-year follow-up telephone interviews, a cut-point that we have used in previous analysis.8
Age, sex, race, education, and smoking history were collected in the telephone interview. Smoking history was classified as current, former, or never. Participants were asked whether a physician had diagnosed any of the following comorbid conditions: high blood pressure, heart disease, diabetes, arthritis, cancer, stroke, or kidney disease. For analysis, individuals were categorized as having 0, 1, or ≥2 of these comorbid conditions.
Pulmonary function testing
was conducted using the EasyOne™ Frontline spirometer (NDD Medical Technologies, Chelmsford, MA), which meets American Thoracic Society (ATS) criteria. Spirometry was performed according to ATS guidelines.9
Predictive equations derived from NHANESIII were used to calculate percent predicted pulmonary function values.10
Differences between individuals who were available for the 1-year follow-up and those who were lost to followup were tested with t-tests and χ2 analyses. Bivariate differences between individuals stratified by baseline physical inactivity and between individuals stratified by an increase in VLA disability were also tested with t-tests and χ2 analyses. Logistic regression tested the risk of mortality conferred by physical inactivity, with and without adjustment for FEV1% predicted. Multivariate logistic regression tested the relationship between baseline physical inactivity and a prospective increase in disability, with adjustment for sex, comorbidities, smoking status, education, forced expiratory volume in 1 second, % of predicted (FEV1% predicted), and baseline VLA disability.