Prestretched airway smooth muscle response to length oscillation.

Airway smooth muscle (ASM) hyperconstriction is the cause of many respiratory diseases including asthma. In vitro testing has demonstrated that the active forces of ASM are reduced by length oscillation (LO) mimicking tidal breathing. In a previous study, we demonstrated that this force reduction can be further enhanced when superimposing oscillations (with certain frequencies and amplitudes) on this LO. In contrast, it has been reported that pressurizing the lung may help in relieving asthmatic airway constrictions. Ultimately, this pressurizing stretches the ASM and may disturb the acto-myosin cross-bridges in a manner similar to LO; however, it is of a static rather than dynamic nature. This research investigates the effect of combining both prestretch- and LO-applications on contracted porcine ASM. Isolated porcine ASM relaxation was tested with a 0.56%, 2%, or 4% stretch of its reference length (Lref) in addition to LO. These oscillations are composed of a main wave mimicking the normal breathing (frequency of 0.33 Hz and amplitude of 4% Lref) and superimposed oscillations (frequencies of 20, 30, 40, 60 and 80 Hz and amplitude of 1% Lref). The oscillations were maintained for 10 min. The results demonstrate that a prestretch of 0.56% and 2% Lref does enhance the contracted ASM relaxation at certain superimposed length oscillations frequencies while of 4% Lref does not. [ABSTRACT FROM AUTHOR]