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Comparison of Continuous and Discrete Measurements of Dyspnea During Exercise in Patients With COPD and Normal Subjects

Comparison of Continuous and Discrete Measurements of Dyspnea During Exercise in Patients With COPD and Normal SubjectsExercise testing provides a direct approach to examine an individual’s perception of breathlessness based on the principles of psychophysics. The traditional approach has been to ask the patient at specific time intervals (eg, each minute of an incremental or ramp exercise test) to select a rating on the Borg scale or on a visual analog scale that matches severity of breathlessness. However, there are at least two major limitations of this methodology. First, if the patient can only exercise for 3 to 4 min because of severe respiratory disease, only a few ratings of dyspnea are obtained. Second, the subject is asked “on cue” each minute to provide a rating. Although this discrete method for measuring breathlessness is convenient from the physician’s perspective, it is completely arbitrary for the patient because the experience of breathlessness can change continuously during the exercise test. Due to these limitations, valuable information may be lost about the progressive nature of dyspnea throughout exercise. this

In 1993, Harty et al reported that six healthy individuals were able to continuously report ratings of breathlessness using a potentiometer to indicate a score on a visual analog scale during cycle ergometry, In 2001, we described the validity, reliability, and responsiveness of a continuous method for recording changes in dyspnea. With this method, subjects moved a computer mouse forward or backward during cycle ergometry in order to adjust a vertical bar on a monitor that was positioned adjacent to the Borg scale to indicate changes in the severity of breathlessness. Our initial testing included 28 healthy, college-age subjects (14 women and 14 men) along with preliminary evaluation of 6 patients with COPD.
The present study had three objectives. First, we sought to establish that elderly individuals could successfully use the computer system and provide comparable results (slope and intercept) with the continuous method, as obtained with the standard discrete approach. Second, we examined test-retest reliability of the continuous method in patients with COPD and in healthy individuals of similar age and gender. Third, we wanted to determine whether the parameters obtained from the continuous method (slope, intercept, and absolute threshold) differentiated symptomatic patients with COPD from healthy control subjects of comparable age.