The quantification of respiratory sensations by normal subjects.

The technique of open magnitude scaling was used in normal subjects to define the exponent (n) of Stevens; psychophysical power law for four respiratory variables: tidal volume (VT), inspiratory flow (V), ventilation (Ve), and frequency (f). Stevens' psychophysical law states that the perceived magnitude (psi) of a stimulus is related to the physical magnitude (phi) by a constant (k) and an exponent (n): psi = kappaphin. The mean value of n was for VT 1.14 plus or minus 0.08 (SEM), V 1.13 plus or minus 0.15, for Ve 1.28 plus or minus 0.11 and for f 1.04 plus or minus 0.15. These results show that these respiratory variables are judged with an expanded sensory scale. The similarity of exponents for VT and V leaves open the possibility tht both are sensed by the same neurophysiological mechanism. Further experiments on VT showed that both passive ventilation and chest vibration impaired the ability of subjects to accurately judge tidal volumes. Our results indicate that the sensation of volume is mediated by afferent information generated by receptors affected by respiratory muscle concentration.