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1 Physiology, School of Biomedical and Chemical Sciences, University of Western Australia, Perth, WA, Australia
* To whom correspondence should be addressed. E-mail: leppitch{at}cyllene.uwa.edu.au.
A period of deep inspiration (DI) in man has been shown to attenuate subsequent bronchoconstriction a phenomenon termed bronchoprotection. The bronchoprotective effect of DI may be caused though a depression in the force production of airway smooth muscle (ASM). We determined the response of whole airway segments and isolated ASM to a period of cyclic stretches. Isovolumetric contraction to electrical field stimulation (EFS) was assessed in porcine bronchial segments before and after intraluminal pressure oscillation from 5 to 25 cmH2O for 10 minutes at 0.5 Hz. Morphometry showed that this pressure oscillation stretched ASM length by 21%. Following pressure oscillation the response to EFS was not reduced but instead was modestly enhanced (P < 0.01). Airway responses to EFS returned to pre-oscillation levels 10 minutes after the end of oscillation. The increase in EFS response following pressure oscillation was not altered by the addition of indomethacin. In a separate experiment we assessed isometric force in isolated ASM strips before and after length oscillation. The amplitude, frequency and duration of length oscillation were similar to that induced in bronchial segments. In contrast to bronchial segments, length oscillation of ASM produced a significant depression in isometric force induced by EFS (P < 0.01). These results suggest that the response of ASM to length oscillation is modified by the airway wall. They also suggest that the phenomenon of bronchoprotection reported in some in vivo studies may not be an intrinsic property of the airway.
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