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Comparison of Continuous and Discrete Measurements of Dyspnea During Exercise in Patients With COPD and Normal Subjects: Test-Retest Reliability

The best-fitting linear equation is shown for each relationship. For each group, there were high Pearson correlation coefficients for power production (r = 0.96 to 0.98), Vo2 (r = 0.95 to 0.96), and Ve (r = 0.95 to 0.97) and breathlessness ratings. There were no differences in the magnitude of the correlations between the discrete and continuous methods. A power function was also fit to the same data sets, but in all but one case there was no significant difference between the correlation coefficients (as an indicator of goodness of fit) obtained from the two models. The only exception was that linear function for VE-breathlessness fit the data significantly better (p < 0.05) than did the power function. Based on the above results, and because various authors’ have previously reported linear regression analyses to describe similar data, we present our current results as linear functions. Moreover, the differences between the continuous and discrete methods, and the differences between patients with COPD and healthy control subjects, were the same whether the data were fit by a linear or power function.
There were no significant differences for pulmonary function test data and exercise data (linear regression parameters, peak values, absolute thresholds, as well as Ekman fractions) between visit 2 and visit 3 in patients with COPD, in healthy subjects, or when the groups were combined. Based on the observed consistency, data from visit 2 and visit 3 were combined for all subsequent analyses. cheap-asthma-inhalers.com

Comparison Between Discrete and Continuous Methods
Table 2 presents the measures for breathlessness ratings for discrete and continuous methods. There were no significant differences for peak ratings of breathlessness between the two methods in either group. However, subjects in each group provided a significantly greater number of breathlessness ratings with the continuous method compared with the discrete method (Table 2).
Table 2—Selected Measures of Breathlessness Ratings During Exercise

Variables COPD Healthy
Discrete Method Continuous Method Discrete Method Continuous Method
Ratings, No. 4.8 ± 1.4|J 11 ± 3.5 j 6.5 ± 2.9 13.8 ± 8.3
Time to reach threshold, min 3.6 ± 0.9j 5.5 ± 1.8
Peak breathlessness 6.8 ± 2.2 6.3 ± 1.7 6.2 ± 2.2 6.0 ± 1.8
Ekman fraction 0.33 ± 0.14 0.29 ± 0.13