The mechanical characteristics of the central segment of isolated cat papillary muscle were determined with recently developed equipment. Two small sharpened stainless steel pins, inserted transversely through the muscle, were used to mark the ends of a segment not damaged by attachments. Installation of the pins did not affect the performance of the muscle. The distance between the pins was measured and controlled to produce isometric and afterloaded isotonic contractions of the segment of the muscle between the pins. Data from such contractions were compared with traditional whole muscle measurements made on the same preparation. The isometric length-tension curve of the central segment was significantly higher than that of the whole muscle, and there was no plateau of developed force at long lengths in five of six muscles studied. In the resting state, the segment was more compliant than the whole muscle for physiologic lengths and much stiffer for longer lengths. Segment velocity and shortening were significantly higher than whole muscle velocity and shortening at comparable loads.
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Articles you may be interested inA long-range-corrected density functional that performs well for both ground-state properties and timedependent density functional theory excitation energies, including charge-transfer excited states Development of a sum-over-states density functional theory for both electric and magnetic static response properties Not only for the the heart, but also for papillary muscle a contraction variable K can be defined (in analogy with the deformation variable A ) in a phenomenological approach that makes use of the finding that two of the three constants (c 2 and c 3 ) in the isochronics of such a muscle can be considered functions of the third one (K). This fact provides four constants (k i' k2' k~, and k 4 ) of an energy density function. A tentative bridge to the heart (for clinical application) is laid; four analogous constants of the same order of magnitude can be measured there.
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