oa Cardiovascular Journal of Africa - The influence of calcium concentration on the performance of the hypothermic working rat heart
Cooling of the working rat heart to 30ï¿½C caused an increase in stroke volume and peak systolic pressure while the heart rate decreased. The mean aortic flow decreased at 30ï¿½C, in the presence of 2,5 and 1,25 mM CaCI2, but increased by 29% at 0,63 mM CaCI2. Power output increased by 48% at 0,63 mM CaCI2, but decreased at 2,5 and 1,25 mM CaCI2. At constant preload, isotonic contraction of isolated papillary muscle and Langendorff perfused hearts increased, respectively, by 37% and 43% at 0,63 mM CaCI2. It can therefore be concluded that preload-independent increase in power output is a major determinant of the working heart's higher aortic output at 30ï¿½C, 0,63 mM CaCI2; and also that at a Ca2+ concentration of less than 1 mM the product of stroke volume and heart rate is such that cardiac output of the isolated working rat heart is higher at 30ï¿½C than at 37ï¿½C.
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