Logarithmic superposition in airway smooth muscle dynamics

Airway smooth muscle contraction is the main driving mechanism in asthma. However, in the dynamic environment of the ASM passive dynamics play an important role. The main aim of this research is to investigate the relative contribution of passive dynamics to ASM tissue dynamics and to characterize this behavior. The major finding of this study is the ability of the principle of logarithmic superposition to describe a wide range of dynamic behavior in relaxed (unstimulated) ASM and to a lesser extend in contracted ASM. The ability of this model to describe the force response to length oscillations in contracted muscle shows that cross-bridge cycling in ASM when fully contracted is not affected by oscillations. We hypothesize that this could be caused either by a very slow cross-bridge cycling rate, or by a large degree of non-contractile cross-linking which results in a greatly increased passive force.