Immature airways are compliant structures. In isolated tracheal segments, trachealis muscle stimulation has been shown to decrease airway compliance(C). We hypothesized that changes in airway stiffness resulting from trachealis stimulation could be quantitated bronchoscopically from airway pressure-area (P-A) relationships. We obtained pressure-volume (P-V) and P-A curves in preterm and newborn lamb tracheae (n=4) before and after stimulation of the trachealis with methacholine (MCh). Tracheal segments were suspended over hollow mounts in a lucite plethysmograph (PG) filled with warmed, oxygenated Krebs buffer solution (KBS) at 37±2° C at pH 7.40±0.05. A 3.6 mm flexible bronchoscope (FB) was placed in one hollow mount, and the luminal image was recorded on a video recorder. A bronchoscopy brush was advanced a known amount to determine distance of the image from the FB tip. With the PG sealed, KBS was injected to increase PG pressure incrementally to 40 cmH2O. Images were recorded at each pressure, then KBS was withdrawn in a similar fashion. A micropipette was attached to the PG to determine pressure-related volume changes. The segment was then sealed at both ends, and air withdrawn from it to lower intraluminal pressure in the same increments. Changes in volume in the micropipette were recorded at each interval, after which air was injected stepwise into the airway until atmospheric pressure was reached. MCh was injected into the PG (final concentration 10-3M), and all measurements were repeated. Recorded images were corrected for distortion and quantitated by an image analysis system. For each segment, volume and area changes were normalized to the resting volume and area. The deflation C±SD before and after MCh were 3.1±0.9 and 1.6±0.7 ml/cmH2O, respectively (p=0.02). Corresponding P-A values were 5.41±1.6 and 2.2±1.1 mm2/cmH2O (p<0.002). The P-A and P-V measurements reflected changes in airway stiffness comparably. We conclude that quantitative FB detects changes in airway C. We speculate that this technique can be used clinically in the intact airway to assess wall stiffness.

Supported by Allegheny Singer Research Institute.