The effects of airway anesthesia on detection of added inspiratory elastic loads.

We studied the effects of airway anesthesia on the ability to detect added inspiratory elastic loads in 5 healthy conscious human subjects. The ability to detect inspiratory elastic loads (range, 0.933 to 2.125 cmH2O/l) was determined by repeated single-breath presentation of different elastic loads by connecting the inspiratory side of a mouthpiece to rigid boxes of adjustable volume. In addition, measurements of total respiratory elastance, body plethysmography and pattern of ventilation were made. In each subject, the study was repeated after a local application of 4% lidocaine solution to the upper airways and, on a separate occasion, to both upper and lower airways. The mean values for respiratory elastance, the threshold elastic load, and the Weber fraction during the control periods were not statistically different from the mean values after upper airway anesthesia or combined upper and lower airway anesthesia. These results suggest that the site of elastic load detection in normal subjects does not reside in the upper or lower airways.