Study objective: Dyspnea is the uncomfortable sensation of breathing and is an impairing symptom in a variety of diseases. Like pain, it motivates adaptive behavior to regain homeostasis, and both sensations share various characteristics. Whereas the realization of the multidimensionality of pain was a key contribution to pain research, little is known about a similar multidimensionality in the perception of dyspnea. The present study examined whether sensory and affective aspects of induced dyspnea can be differentiated.
Design: A controlled laboratory study.
Setting: Psychophysiologic laboratory of the Psychological Institute III, University of Hamburg, Germany.
Participants: Ten healthy volunteers aged 24 to 52 years (mean, 35 years).
Interventions: Dyspnea was induced by breathing through inspiratory resistive loads of increasing magnitude (0.99 to 2.33 kPa/L/s), alternating with episodes of unloaded breathing. Inspiratory time (Ti) and breathing frequency (f) were continuously monitored. The experienced intensity and unpleasantness of dyspnea were rated after each episode on separate visual analog scales (VASs), which were presented in permuted order. Intraindividual linear regression slopes were calculated separately for both dimensions and compared.
Measurements and results: Breathing through inspiratory resistive loads resulted in increases of VAS ratings for intensity and unpleasantness paralleled by increases in Ti and decreases in f (p = 0.012 and p = 0.003, respectively). The mean regression slope for perceived unpleasantness was higher than for perceived intensity (mean ± SD, 2.83 ± 1.28 and 2.11 ± 1.74, respectively; p = 0.032), indicating stronger increases of unpleasantness with increasing magnitude of resistive loads.
Conclusions: The results show that the sensory and affective dimension of experimentally induced dyspnea can be differentiated in healthy volunteers. The obtained multidimensionality of dyspnea converges with previous reports on similarities between dyspnea and pain. Implications for future studies on the perception of dyspnea are provided.