Detection of added respiratory loads in patients with restrictive lung disease

In patients with airways obstruction, inspiratory resistive load detection conforms to Weber's law: the higher the background or intrinsic pulmonary resistance, the greater the threshold resistance (the resistance detected 50% of the time, delta R50). In patients with restrictive lung disease, the pulmonary elastance is increased, and the present study was undertaken to assess whether Weber's law applies to elastic load detection in these patients. In 7 patients with restrictive lung disease caused by interstitial fibrosis, there was a significantly decreased total lung capacity compared with that in 6 normal subjects (mean, 63.1 and 101% predicted, respectively; p less than 0.01) and significantly increased total pulmonary elastance (means +/- SD, 14.4 +/- 4.7 and 9.6 +/- 1.8 cmH2O/L, respectively; p less than 0.05). There was no significant difference (p greater than 0.1) between the 2 groups in delta R50; however, the elastic load detection threshold, delta E50, was significantly greater (p less than 0.05) in the patients than in the normal subjects (mean +/- SD, 2.8 +/- 1.3 and 1.4 +/- 0.4 cmH2O/L, respectively). When the detection threshold was adjusted for the background elastance, however, there was no significant difference between the 2 groups (mean +/- SD, 0.21 +/- 0.1 and 0.15 +/- 0.04, respectively; p greater than 0.05). These results confirm that Weber's law is also applicable to the detection of added elastic loads in patients with restrictive lung disease.(ABSTRACT TRUNCATED AT 250 WORDS)