Distinct and Separable Constructs

Study objectives: We tested the hypothesis that descriptors of breathlessness represent distinct and separable cognitive constructs, and predicted that the use of descriptors of breathlessness by healthy individuals is the same as their use by patients with cardiopulmonary disease. Design: Cluster analyses obtained in healthy individuals were compared with those obtained previously in patients who complained of breathing discomfort. In addition, we used multidimensional scaling (MDS) techniques to analyze relationships among descriptors in healthy individuals. Setting: Public university. Participants: The participants were 100 healthy individuals (48 men and 52 women) ranging in age between 18 and 65 years (mean, 27.9 6 11.7 years). Measurements and results: Participants judged the dissimilarity among pairs of 15 descriptors of breathlessness that were used previously to examine the experience of dyspnea in patients who complained of breathing discomfort. Cluster analysis solutions obtained in the healthy individuals were virtually identical to those obtained previously in patients. Three dimensions (attributes) of breathing discomfort were uncovered with MDS: “Depth and frequency of breathing,” “Perceived need, or urge, to breathe,” and “Difficulty breathing and phase of respiration.” The results did not depend on age, sex, levels of education, or the presence of uncomfortable awareness of breathing with activities. Conclusions: The relations among descriptors of breathlessness obtained in healthy individuals support the contention that the association of different clusters with different disease states reflects distinct and separable cognitive constructs that are not simply dependent on the presence of an underlying pathophysiology or on a specific disease condition. Our results in healthy individuals also suggest that distinct qualities of breathlessness relate to different physiologic mechanisms underlying respiratory discomfort. (CHEST 2000; 118:679–690)