title: Frequency-force relationships of mammalian ventricular muscle in vivo and in vitro.
abstract: The change in contractility with increasing heart rate was studied in the left ventricle of dogs and in isolated trabeculae carneae of cats. For some of the studies in situ a transient isovolumic state was created by aortic occlusion. At physiological temperatures the frequency-force relationship is flatter than at room temperature and at the same temperature it is flatter in vivo than in vitro. The frequency-(dF/dt)max relationship is steeper than the frequency-force relationship at both temperatures in vivo and in vitro. The frequency-(dF/dt)max relationship is steeper in vitro than it is in situ, although the discrepancy is less marked than in the case of the frequency-force relationship. It is concluded that "staircase" plays less of a physiological role in adjustment of contractile state in situ than might be inferred from studies of isolated tissue.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002415:Cats; D003864:Depression, Chemical; D004285:Dogs; D004558:Electric Stimulation; D004594:Electrophysiology; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D013268:Stimulation, Chemical; D014439:Tyramine / Q000494:pharmacology; D016276:Ventricular Function
chemical_list: D002118:Calcium; D014439:Tyramine