Experimental comparison of dyspnea and pain.

Dyspnea and pain are similarly unpleasant, alarming physical sensations, but studies examining both sensations in combination are lacking. In the present study, dyspnea was induced in 7 healthy volunteers by breathing through inspiratory resistive loads and the effects were compared with those of a heat pain stimulus. End-tidal partial pressures of carbon dioxide (PET(CO2)), inspiratory time (Ti), breathing frequency (f), experienced unpleasantness, and intensity were measured. No difference was observed between dyspnea and pain in experienced intensity and unpleasantness (p > .05). During dyspneic stimulation, slightly higher Ti was found than for pain (p < .08). PET(CO2) showed slight increases during the dyspneic versus the baseline and painful conditions (deltaPET(CO2) = 1.5 and 1.3 mmHg, respectively; p < .01 andp < .05). This study shows that the effects of dyspnea and heat pain can be compared within one experiment; both stimuli can be presented with similar intensity and unpleasantness, which is a prerequisite for comparing responses to them. The changes in PET(CO2) between our conditions were minimal, allowing an application of the present design to future fMRI studies.