The absolute threshold for breathlessness was taken as the X variables accompanying the first time the black bar on the screen matched or surpassed the No. 0.5 (“just noticeable”) on the Borg scale. Starting with values beyond the absolute threshold, we computed a series of “change” thresholds considered as justnoticeable differences (JNDs) in breathlessness with the continuous method. A change in breathlessness was indicated whenever the bar was moved to a higher position on the scale and was stationary for at least 1 s. The scale value present after such change was treated as a single rating obtained by the continuous method. This definition of a rating was more conservative than the one used in our previous study, and resulted in a much smaller number of total ratings over the duration of exercise. An Ekman fraction was calculated as the ratio of the breathlessness JND on the Borg scale to the previous breathlessness rating. When multiplied by 100, this measure indicates the percentage of change in breathlessness associated with each physiologic or work JND starting from the absolute threshold to the rating just prior to peak breathlessness. http://cfm-online-shop.com/
The peak values for breathlessness and the physiologic variables were selected when exercise stopped because of exhaustion or symptom limitation. All data are reported as mean ± SD; p < 0.05 was considered statistically significant.
A total of 49 subjects were enrolled in the study. One patient was withdrawn from the study after visit 2 because she was unable to use the computer system consistently. Table 1 gives the characteristics of the 24 patients with COPD and 24 age-matched healthy subjects who completed the study. The age and gender distribution of the two groups were similar.
Figure 2 represents exercise data for an individual patient with COPD to illustrate the relationships between the physiologic variables and breathlessness ratings. The different graphs show the relation between the independent variables of power production (Fig 2, top), V02 (center), and Ve (bottom) and the corresponding ratings of breathlessness.
Figure 2. Illustrative data (continuous method) obtained from a 51-year-old male patient with COPD, showing breathlessness ratings as a function of power production (top), V o2 (center), and Ve (bottom).
Table 1—Selected Characteristics for Patients With COPD and Healthy Subjects at Visit 2
|Age, yr||66 ± 10||66 ± 8|
|Female/male gender, No.||11/13||11/13|
|FEVb % predicted||51 ± 14||112 ± 24|
|At peak exercise|
|Power production, W||84.2 ± 21.7t||142.2 ± 38.2|
|V/O2, mL/kg/min||16.5 ± 3.7t||26.8 ± 6.0|
|V/e, L/min||44.3 ± 12.2t||72.0 ± 21.3|