Dyspnea in chronic obstructive pulmonary disease (COPD) has been viewed as breathing effort due to increased ventilatory demand, alterations in pulmonary mechanics, and breathing patterning. Human responses, including distress and emotional arousal are not addressed in this model, although the distressing quality of dyspnea in clinical groups is well known. The purpose of this quasi-experimental design was to describe and compare breathing effort perceptual sensitivity (sensory dimension) and breathing discomfort perceptual sensitivity (affective dimension) during conditions of inspiratory threshold loading and incremental exercise and to determine relationships between dyspnea dimensions and ventilatory function, exercise and dyspnea tolerance, functional level, and affective states.

A convenience sample of 27 outpatients with COPD and function limited by dyspnea underwent inspiratory threshold loading; sixteen subjects also exercised to maximal tolerance on a cycle ergometer. Perceptual sensitivity to breathing effort and discomfort were measured on separate visual analogue scales (VAS) under both conditions. Other variables included ventilatory function (level of obstructive disease, maximal inspiratory pressure), exercise tolerance (oxygen consumption, ventilatory equivalent for carbon dioxide), dyspnea tolerance (VAS and Mahler Baseline Dyspnea Index, MBDI), functional level (MBDI, Chronic Respiratory Disease Questionnaire) and affective state (Beck Hopelessness Scale, Spielberger State-Trait Anxiety Inventory, Profile of Mood States).

A repeated measures ANOVA on the threshold loading data revealed that magnitude of effort was greater than discomfort across all loads (p =.05) and greater perceptual sensitivity to breathing discomfort than breathing effort (p =.053). Visual inspection of the exercise data revealed two subjects reporting breathing discomfort greater than effort, five reporting effort greater than discomfort, and nine noting no difference. Greater levels of obstructive disease were associated with a higher relative perceptual sensitivity to breathing effort than discomfort under both conditions. Functional level (MBDI) was greater in subjects reporting greater relative perceptual sensitivity to breathing effort than discomfort during threshold loading. Correlations with other variables were not significant.

This study suggests that dyspnea, like pain, may include separate affective and sensory dimensions with implications for functional adaptation to progressive disease in COPD. Measurement of both dimensions may provide more accurate quantification of dyspnea and enhance the evaluation of dyspnea-related therapeutics.