Validity and Reliability of D-PPAC and C-PPAC Instruments Across COPD Populations

Use of the Daily-PROactive and Clinical visit-PROactive Physical Activity (D-PPAC and C-PPAC) instruments in patients with chronic obstructive pulmonary disease (COPD) has demonstrated validity, reliability, and responsiveness. Results of the study were published in the journal Thorax.

Data were retrospectively pooled from 7 prospective randomized controlled trials (RCTs) that examined the effect of pharmacologic and nonpharmacologic interventions in patients with COPD from 17 countries in Europe and North America.

The investigators sought to confirm the reliability and validity of the PPAC instruments in multiple independent patient samples, to test their responsiveness, and to define their minimal important differences (MIDs) in a large population of patients with varying COPD severity from different settings and countries. The D-PPAC and C-PPAC tools combine questionnaires with activity monitor data, in order to measure patients’ experiences of physical activity. Their amount, difficulty, and total scores range from 0 (ie, the worse score) to 100 (ie, the best score) but require additional psychometric assessment.

Data from the 7 RCTs were utilized to evaluate the internal consistency of the D-PPAC and the C-PPAC, and to construct their validity according to age groups, sex, COPD severity, country, and language, along with responsiveness to interventions, the ability to detect change, and MIDs. A total of 1324 patients had available data on activity monitor, as well as D-PPAC and/or C-PPAC questionnaires. Of these individuals, 950 and 651 were included in the D-PPAC-related and C-PPAC-related analyses, respectively. The mean participant age was 66 years.

Both the D-PPAC and C-PPAC scores demonstrated strong internal consistency in all participants and following stratification. Both overall and after stratification, D-PPAC and C-PPAC amount scores exhibited weak associations with health-related quality of life (HRQoL) measures, moderate correlations with exercise capacity, and strong associations with objective physical activity. Difficulty scores demonstrated moderate to strong correlations with dyspnea, HRQoL, and exercise capacity, as well as low correlations with objective physical activity level other than in The Netherlands. Since all of the D-PPAC and C-PPAC scores differentiated statistically across moderate to very severe COPD stages, dyspnea grades, and tertiles of 6-minute walking distance, this implies good known-group validity.

Difficulty scores demonstrated improvement following pharmacologic treatment and pulmonary rehabilitation, whereas amount scores showed improvement after behavioral physical activity interventions. All of the scores were responsive to changes in self-reported physical activity experience (both worsening and improving), as well as to the occurrence of COPD exacerbations during follow-up. MIDs were estimated to 6 for amount and difficulty scores, and to 4 for total score.

Limitations of the study includes is the lack of inclusion of exacerbating or recently exacerbated patients, which prevented the team from testing the validity of the PPAC instruments in patients experiencing the most difficulty with physical activity as well as testing the responsiveness of PPAC scores to interventions during exacerbations.

The researchers concluded that the D-PPAC and C-PPAC tools, which combine questionnaire with activity monitor data, are valid and reliable across diverse COPD populations, as well as responsive to both pharmacologic and nonpharmacologic interventions.

Reference

Garcia-Aymerich J, Puhan MA, Corriol-Rohou S, et al; PROactive consortium. Validity and responsiveness of the Daily- and Clinical visit-PROactive Physical Activity in COPD (D-PPAC and C-PPAC) instruments. Thorax. Published online January 21, 2021. doi:10.1136/thoraxjnl-2020-214554