| Human beings are able to have conscious awareness of some aspects of their breathing. The perception of respiratory mechanical events, including load detection and magnitude estimation, has been studied extensively by using psychophysical methods. Recently, the respiratory-related evoked potential (RREP) has been used to provide a unique way to investigate the neural activities associated with breathing against mechanical loads. However, the afferent pathways mediating load perception and RREP are still largely unknown. The major goal of this study was to investigate the role of lung vagal afferents in perceptual and RREP response to inspiratory loads.; Using human double-lung transplantation as a model of pulmonary denervation, we studied breathing pattern, load detection and magnitude estimation during breathing against inspiratory resistive loads and RREP in response to inspiratory occlusions. Two groups of subjects, double lung transplant recipients (DLT, n = 10) and matched normal subjects (NOR, n = 12), completed this experiment. Results demonstrated that the breathing patterns during unloaded and loaded breathing were similar in both groups. Handgrip responses, as well as the slope of logHG%-logPm and logHG%-logR were also comparable in the two groups during the magnitude estimation experiment. However, the detection threshold and Weber Fraction were significantly elevated in the DLT group as compared with the NOR group (2.91 +/- 0.5 cmH2O/L/s vs 1.55 +/- 0.3 cmH2O/L/s, and 0.50 +/- 0.1 vs 0.30 +/- 0.1, respectively). Moreover, despite a similar early-latency RREP response, DLT had significantly delayed and attenuated P3 response. These results suggest that lung vagal afferents are involved in cognitive processing of respiratory stimuli during breathing against mechanical loads, but are not essential to load perception and RREP response. Respiratory sensation related to loaded breathing may be due to multiple and simultaneous sensory input. |
