Weber's law and resistive load detection.

The threshold of detection for added resistive loads to breathing (delta R50) was measured in 4 normal subjects at 4 different background resistances (Ro). Under normal conditions (Ro = 2.26 +/- 0.16 (SEM) cm H2O/L/s), the mean delta R50 was 0.53 +/- 0.17 cm H2O/L/s and the Weber fraction (delta R50/Ro) was 0.24 +/- 0.07. When the background resistance was increased, the threshold of detection increased proportionately, so that the Weber fraction did not change significantly. The background resistance was also decreased by having the subject breathe heliox. Although this did not result in a change in delta R50 (0.68 +/- 0.1 cm H2O/L/s), the Weber fraction increased to 0.49 +/- 0.08. These results show that although the Weber fraction is relatively constant over a wide range of background resistances, it rises sharply at low levels of background resistance, a finding that is similar to other sensory modalities.