RT Journal Article
SR Electronic
T1 Airway wall responses to tidal breathing and deep inspiration
JF European Respiratory Journal
JO Eur Respir J
FD European Respiratory Society
SP P818
VO 40
IS Suppl 56
A1 Thomas K Ansell
A1 Peter B. Noble
A1 Howard W. Mitchell
A1 Peter McFawn
YR 2012
UL http://erj.ersjournals.com/content/40/Suppl_56/P818.abstract
AB IntroductionMechanical stretch attenuates airway smooth muscle (ASM) force production, which may explain the reversal of bronchoconstriction (i.e. bronchodilation) following a deep inspiration (DI) in vivo. We measured the effect of simulated DI on both narrowing and ASM force in isolated bronchi.MethodsBronchial segments were dissected from pig lungs and maintained in organ bath chambers. Airway narrowing (% volume) to acetylcholine (ACh, 10-7M - 3x10-3M) was measured under static transmural pressure (Ptm) conditions and during fixed Ptm oscillations simulating tidal breathing (Δ5cmH2O) with intermittent DI (Δ25cmH2O). In a separate group of experiments, the above protocols were repeated using fixed volume oscillations to simulate tidal and DI breathing whilst measuring the increase in Ptm produced by ASM contraction. Under each condition, airway wall stiffness was measured from the change in Ptm and volume during tidal oscillations.ResultsUnder static conditions, maximal response to ACh was 92.3±4.3% narrowing (n=6) and 73.5±9.2cmH2O Ptm (n=4). DI to Δ25cmH2O reversed ∼60% narrowing at low doses of ACh but had no affect at moderate or high doses, whereas fixed volume DI attenuated ASM force to 12.7±5.6cmH2O (t-test, p<0.01) even at high doses. At maximal contraction to ACh, stiffness increased ∼10 fold in both groups of which DI had no affect under fixed Ptm conditions but reversed 60.9±4.4% (p<0.001) under fixed volume oscillation conditions.ConclusionsThe mechanical loading conditions present during tidal breathing and DI influence the airway response to mechanical stretch. Inhibition of bronchoconstriction to mechanical stretch is minimal during fixed Ptm oscillations particularly at high levels of ASM activation.