For all sensory modalities, Weber’s law states that the physical change in the size of a JND must be increased by a constant fraction of its original or background value to produce a perceived change in sensory experience. Whereas the Weber fraction relates to a physical or physiologic variable, the Ekman fraction refers to a sensory sensation such as breathlessness. With the continuous, but not the discrete, method for measuring breathlessness, the change in breathlessness can be determined over the course of exercise (ie, Ekman fraction). Our results showed similar mean Ekman fractions between patients with COPD (33%) and healthy, age-matched subjects (29%). Of interest, these values are higher than the 23% that we observed in 14 healthy, female college subjects, and the 18% observed in 14 healthy, male college students. Whether the observed differences in the Ekman fractions are real and, if so, are related to the age of the subjects will require future testing in a larger population. Here
The current study extends our previous report that elderly individuals, both healthy subjects as well as patients with COPD, can successfully use a computer system to provide spontaneous and continuous ratings of breathlessness during exercise. Furthermore, these results highlight several advantages of the continuous method. The continuous method illustrates clearly how the perception of breathlessness changes throughout the entire course of an exercise test rather than only at arbitrary 1-min time intervals. Thus, the standard discrete approach of obtaining ratings each minute may not accurately reflect the individual’s perceptual changes in dyspnea.
A major advantage of the continuous method is that substantially greater numbers of breathlessness ratings can be obtained compared with the discrete method. This can be important because many patients with severe cardiopulmonary disease are only able to exercise for a few minutes. Consequently, only four or five data points for dyspnea ratings may be obtained using the discrete method. This outcome occurred in many of the patients with COPD in our study. From a statistical standpoint, it can be problematic fitting a reliable quantitative function using a small number of data points.
Additional benefits of the continuous method are that an absolute threshold and an Ekman fraction can be determined directly as part of the measurement process. It is possible, though unproven, that these metrics may have clinical utility in examining the efficacy of various treatments being evaluated during the stimulus of exercise.