Effects of length oscillation on the subsequent force development in swine tracheal smooth muscle

Abstract

It has been shown that deep inspiration (DI) taken before application of bronchoconstricting stimuli causes a reduction in the subsequent bronchoconstriction; a fast DI has a greater inhibitory effect than a slow DI. We hypothesize that periodic length changes imposed on a relaxed airway smooth muscle (ASM) would attenuate subsequent bronchoconstriction by disrupting the organization of the contractile apparatus, and this could be an important mechanism for the observed bronchoprotective effect of DI and tidal breathing. Length oscillations of different amplitude, frequency, and duration were applied to a relaxed muscle. The effects of such perturbations on force development were then assessed. Results show that oscillations reduce the subsequent force generation and that the magnitude of force reduction is proportional to amplitude and duration of the length oscillation. After the oscillation, isometric force recovered to the preoscillation level in a series of isometric contractions, and the rate of recovery was facilitated by frequent stimulation. The in vitro behavior of ASM found in this study could account for the observed temporary reduction in bronchoconstriction subsequent to a DI.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

“…Response of resting ASM to mechanical perturbation It was mentioned briefly previously that length oscillation applied to ASM in the relaxed state has been found to have an inhibitory effect on the muscle's ability to generate force in the subsequent contractions [69]. The same study also revealed that the inhibitory effect was linearly correlated to the amplitude and duration of oscillation, but was relatively independent of oscillation frequency.…”

“…observed to diminish the muscle's ability to generate force in the subsequent contractions [69]. It was postulated by KING et al [26] that this post-oscillation refractoriness of resting ASM was responsible for the bronchoprotective effect of deep inspiration taken before bronchoprovocation seen in nonasthmatics, and that in asthmatics, this refractoriness might be absent.…”

“…WANG et al [69] found that periodic stretching of isolated porcine ASM in the relaxed state resulted in a decrease of force production with subsequent contractions. However, pressure oscillation in isolated airway segments that periodically strained the ASM embedded within the segment led to a slight increase of the pressure generated in the subsequent isovolumic ''constriction'' [295,296].…”

Airway Smooth Muscle in Asthma Symptoms: Culprit but Maybe Innocent

“…Importantly, the maximal force-generating capacity of ASM during or immediately following these oscillations is also reduced (66,84,85,128,186,198,242). The decline in isometric force that ensues length oscillations has been shown to be proportional to the amplitude and the duration of the stretch, but not to the frequency (242). These results demonstrated that the force produced by ASM in response to a given stimulus is greater in a static environment than a dynamic environment.…”

“…Nevertheless, these length oscillations are known to decrease ASM stiffness, even during supra-maximal activation with ACh (66,84,128,198). Importantly, the maximal force-generating capacity of ASM during or immediately following these oscillations is also reduced (66,84,85,128,186,198,242). The decline in isometric force that ensues length oscillations has been shown to be proportional to the amplitude and the duration of the stretch, but not to the frequency (242).…”