Effect of tracheal smooth muscle tone on collapsibility of immature airways.
To test the influence of smooth muscle tone on extremely immature airways, tracheal segments (n = 19) were excised from premature lambs at 114-121 days gestation and mounted in a chamber filled with Krebs solution. Inflation (Si) and collapsing (Sc) compliance were determined by altering transmural pressure from 30 to 0 Torr and -30 to 0 Torr, respectively, both during control (C) and after acetylcholine (ACh) administration (experimental, E). Flow (V = 2-15 l/min) was then introduced through the tracheal lumen while chamber pressure (Pc) was increased from 0 to 30 Torr and driving pressure (Pd) was recorded for both C and E conditions. Tracheae were found to be extremely compliant; both Si and Sc were significantly (P less than 0.005) lower after ACh administration. Resistance to airflow (R = Pd/V) was also significantly (P less than 0.05) lower after ACh administration at each compressive pressure and each flow value. These results suggest that the highly compliant preterm trachea exhibits pressure-flow characteristics similar to a Starling resistor, and the effects of compressive pressures may be attenuated by ACh-induced smooth muscle contraction. Comparison of these results with data from adult and newborn animals suggests a developmental difference in tracheal mechanics and pressure-flow relationships, as well as in the way airway function is altered by smooth muscle stimulation.
Penn
R B
RB
Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
Wolfson
M R
MR
Shaffer
T H
TH
D000109:Acetylcholine / Q000494:pharmacology; D000403:Airway Resistance; D000818:Animals; D008170:Lung Compliance; D009129:Muscle Tonus; D009130:Muscle, Smooth / Q000502:physiology*; D011312:Pressure; D012756:Sheep / Q000502:physiology*; D014132:Trachea / Q000502:physiology*
D000109:Acetylcholine