Ability of healthy men to discriminate between added inspiratory resistive and elastic loads.

Previous studies of the latencies for the detection of inspiratory resistive (R) and elastic (E) loads revealed that R loads were detected earlier in the loaded breath than E loads (Respir. Physiol. 34: 267--77, 1978). These results suggested that the load information generated by R and E loads have different temporal patterns. We hypothesized that these differences might provide a mechanism for subjects to accurately discriminate between R and E loads and secondly, that the R and E load sensations perceived by subjects should have different temporal characteristics. To test these hypotheses we studied six healthy subjects in a two-part study. In this first, two levels of R and E loads (near threshold and 4--5 times threshold) were randomly presented for single inspirations separated by 3--6 unloaded breaths for a total of 10 presentations each. Subjects indicated detection and type of load perceived by pressing R or E marker buttons. In the second part, using the same loading protocol, subjects squeezed a hand grip dynamometer to express the pattern of perceived load sensation. Results indicate that subjects cannot discriminate between near-threshold R and E load but can discriminate between R and E loads 4--5 times threshold with considerable accuracy. Mean grip responses show that perceived load sensations arise earlier and reach maximum values sooner during R loaded breaths. Grip responses are consistent with the previously reported differences in R and E detection latencies and support the hypothesis that load discrimination is mediated by differences in the temporal pattern of load information generated during R and E loaded breaths.