The measurement of breathlessness induced in normal subjects: individual differences.

Normal subjects show wide variability in their sensory scaling of breathlessness for equivalent degrees of ventilatory stimulation and behave "characteristically' irrespective of stimulus type. Observed differences are not explained by physical characteristics, ventilatory sensitivity or pattern of breathing although there is a weak association with the degree of physical fitness. Differences are seen when scaling is performed with reference to both rigidly defined extremes of breathlessness (visual analogue scaling) and a subject's own relative changes in the intensity of this sensation (magnitude estimation). These findings may explain the common observation, in patients with respiratory disease, of dyspnoea out of proportion to the pathophysiological state.