Comparison of subjects' perception of inspiratory and expiratory resistance

Six healthy male adults were studied at five levels of suprathreshold added resistance (delta R) applied thrice to either inspiration (I) or expiration (E) in a random sequence. Subjects squeezed on isometric handgrip dynamometer to express the perceived magnitude of the load. Peak mouth pressure (Pm), flow, grip (G), and delta R were analyzed to derive the exponent for Steven's power law. We observed that the slope for log G vs. log delta R was significantly greater for I loads than for E loads (P less than 0.05), but the intercepts for E loads were significantly elevated. However, the slopes and intercepts for log G vs. log Pm during the same I and E loads were not significantly different. When subjects were instructed to target I or E flow to a preset level, we observed no difference between the slopes and intercepts for log G vs. log delta R during I and E loading. These results suggest that 1) the sensory information utilized in judging the magnitude of added resistance is more likely related to the force generated by the respiratory muscles (Pm) rather than delta R per se; and 2) similar muscle receptors and neural processing systems are utilized in the estimation of added loads involving either inspiratory or expiratory muscle groups.