Comparison of continuous and discrete measurements of dyspnea during exercise in patients with COPD and normal subjects

STUDY OBJECTIVES: The objectives of this study were as follows: (1) to compare results of the discrete and the continuous methods for measuring breathlessness; (2) to examine test-retest reliability; (3) and to test the hypothesis that patients with COPD have higher slopes and lower x-intercepts and absolute thresholds for power production, oxygen consumption (O(2)), and minute ventilation as independent variables and breathlessness ratings as the dependent variable, as compared with healthy subjects. DESIGN: Visit 1 (familiarization) and visit 2 and visit 3 (2 days apart) with randomized assignment of the discrete and continuous methods for subjects rating breathlessness during cycle ergometry. SETTING: Cardiopulmonary exercise laboratory in a university medical center. PARTICIPANTS: Twenty-four patients with COPD (mean age, 66 +/- 8 years [+/- SD]) and 24 healthy subjects (mean age, 66 +/- 10 years). INTERVENTIONS: None. Measurements and results: Ratings of breathlessness on the Borg scale on cue with subjects moving and pressing the computer mouse button to indicate a rating (discrete method) or by moving the position of the mouse to adjust a vertical bar to indicate a change in breathlessness (continuous method). There were no significant differences in results between visit 2 and visit 3. Although peak exercise variables were similar with the discrete and continuous methods, both groups provided significantly more ratings of breathlessness with the continuous method. Patients with COPD exhibited higher slopes, lower x-intercepts, and lower absolute thresholds (breathlessness rating >/==" BORDER="0"> 0.5 ["just noticeable"] on the Borg scale) for power production and O(2)-breathlessness compared with healthy subjects (p < 0.05). CONCLUSIONS: Elderly patients with COPD and healthy subjects are able to use the continuous method successfully. Reliability is excellent for both methods. The continuous method provides a greater number of breathlessness ratings over the course of exercise, and allows the clinician to calculate an absolute threshold and just-noticeable differences. Regression parameters and absolute thresholds discriminate between patients with COPD and healthy subjects.