The continuous method also permits calculation of an absolute threshold corresponding to the onset of breathlessness in a manner similar to standard procedures followed throughout other areas of sensory psychophysics. In other words, there are no statistical assumptions required in determining the threshold for a single subject because the value is inherent in the rating method. We have defined the threshold as the physiologic value corresponding to the “first dyspnea rating that surpasses the No. 0.5 (just noticeable)” on the Borg scale. As with all such measures of threshold obtained by classical psychophysical methods, this particular criterion is arbitrary in that other cutoff values could have been selected. What is important here is that the same statistical criterion be applied for all comparisons among conditions. www.mycanadianfamilypharmacy.net
Comparison Between Patients With COPD and Healthy Subjects
Although peak exercise physiologic values were all lower in the COPD population than in the healthy control subjects, the peak ratings of breathlessness were comparable. Similar results have been observed previously, and the lower physiologic values are likely due to the impaired exercise capacity in patients with respiratory disease.
The slopes of the linear function were significantly higher for patients with COPD compared to healthy, age-matched subjects for both the discrete and continuous methods. These results are consistent with previous studies that also showed a higher slope for work (or Vo2) and dyspnea in patients with respiratory disease compared to healthy individuals. These collective findings indicate that the linear regression slope relating breathlessness to a physiologic exercise variable has discriminative properties.
As expected, the x-intercepts for power production and V02 were lower in the patients with COPD compared to the elderly healthy subjects. These findings are generally similar to the x-intercepts reported by Killian. Moreover, the reduced x-intercepts are consistent with the lower absolute threshold, and indicate that patients with COPD experience the onset of breathlessness at lower levels of exercise intensity compared with healthy individuals.