Am. J. Respir. Crit. Care Med., Volume 162, Number 5, November 2000, 1690-1696

The Perception of Respiratory Work and Effort Can Be Independent of the Perception of Air Hunger

ROBERT W. LANSING, BRIAN S.-H. IM, JULIE I. THWING, ANNA T. R. LEGEDZA, and ROBERT B. BANZETT

Physiology Program and Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts; Department of Psychology, University of Arizona, Tucson, Arizona; and Department of Medicine, Harvard Medical School, Boston, Massachusetts

Dyspnea in patients could arise from both an urge to breathe and increased effort of breathing. Two qualitatively different sensations, "air hunger" and "respiratory work and effort," arising from different afferent sources are hypothesized. In the laboratory, breathing below the spontaneous level may produce an uncomfortable sensation of air hunger, and breathing above it a sensation of work or effort. Measurement of a single sensory dimension cannot distinguish these as separate sensations; we therefore measured two sensory dimensions and attempted to vary them independently. In five normal subjects we obtained simultaneous ratings of air hunger and of work and effort while independently varying PCO₂ or the level of targeted voluntary breathing. We found a difference in response to the two stimulus dimensions: air hunger ratings changed more steeply when PCO₂ was altered and ventilation was constant; work or effort ratings changed more steeply when ventilation was altered and PCO₂ was constant. We conclude that "air hunger" is qualitatively different from "work and effort" and arises from different afferent sources.

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