Control of segment length or force in isolated papillary muscle: an adaptive approach.

Mechanical studies of isolated cardiac muscle are complicated as a result of damage inflicted on the ends of the muscle during excision and mounting procedures. Inhomogeneities between the healthy central and weakened end portions of the muscle make it difficult to interpret studies where only total muscle length is controlled. Measurement and control of central segment length is clearly desirable but fraught with technical difficulties. We present a novel application of adaptive control methods that minimizes the difficulties encountered with current control techniques. This method, which allows control of either segment length or force, takes advantage of the repetitive, periodic nature of contractions. Here deviations of measured segment length or force signals from a desired response during one twitch are used to modify the muscle length command signal for use on the next twitch. This process continues for successive twitches until either segment length or force is within desired limits. The adaptive method allows greater stability and immunity to noise than classical feedback strategies.