Abstract:
The performance of mechanical work by isolated cardiac muscle samples has typically been studied by subjecting their tissues to an isotonic shortening protocol, which results in "flat-topped" work-loop profiles. In order to better replicate the forces experienced by these tissues in vivo, we have developed a system for imposing a model-based, time-varying, load on isolated cardiac tissue preparations. A model of systemic afterload was developed from the combination of a Windkessel-type model of vascular fluid impedance, and the Laplace law of the heart, and encoded into a hardware-based control system. The model-predicted length change was then imposed on an isolated cardiac trabecula in a work-loop calorimeter, giving rise to force-length work-loops that more closely resemble those experienced by these tissues in vivo.