Respiratory sensation related to resistive loads in lung transplant recipients

In order to assess the contribution of pulmonary afferent nerves to the processing of respiratory sensation, we compared sensation related to inspiratory resistive loaded breathing in 14 lung transplant recipients with normal lung function with that in 14 matched healthy control subjects. Respiratory sensation was characterized for each subject by the correlation coefficient and slope of the linear relationship between the intensity of sensation (expressed as Borg scores [BSc]) and peak inspiratory mouth pressure (peak Pm), which was considered the main physical stimulus of the sensation. Individual correlation coefficients were very high and did not differ between lung transplant recipients and controls. In contrast, individual slopes of BSc as a function of peak Pm (BSc/peak Pm slopes) were significantly lower in lung transplant recipients than in controls (0.63 versus 1.26; p < 0.01). Furthermore, ventilatory responses to external loads differed significantly between lung transplant recipients and controls in terms of higher values and ranges of generated peak Pm and peak inspiratory flow in lung transplant recipients than in controls (all p < 0.05). These results suggest that pulmonary afferent nerves may contribute to ventilatory and sensory responses to external loads. However, as suggested by the inverse relation between BSc/peak Pm slopes and peak Pm ranges, higher stimulus ranges in lung transplant recipients may also have contributed to intergroup differences in respiratory sensation related to loaded breathing.