1. The detection of added inspiratory airflow resistances was studied in normal individuals under two circumstances: first, while breathing unhindered, and secondly, while breathing against continuously applied (‘basal’) inspiratory elastic loads. The addition of basal elastic loads resulted in impaired detection of flow-resistive loads whether expressed as added flow resistance or as a proportion of the basal flow resistance.
2. When loads were plotted on a logarithmic scale, load-detection relationships were linear, permitting both threshold and slope of the detection response (‘sensitivity’) to be assessed. Impaired detection associated with basal elastic loads was shown to be due to a raised threshold without change in ‘sensitivity’.
3. When the flow resistances submitted for detection were expressed as a proportion of the sum of the basal flow resistance and added elastance, the probability of detection was independent of the magnitude of the added elastance.
4. The interaction between basal elastic and added flow-resistive loads suggests that at the time of detection the basal elastance acts in a manner similar to that of an added flow resistance.
5. Added basal flow resistances had no significant effect on the detection of threshold elastic loads.