Contraction–relaxation coupling is unaltered by exercise training and infarction in isolated canine myocardium

Figures

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  Figure 1.. Schematic of how calculations of dF/dt, −dF/dt, TTP, and RT50 were made in the analysis of twitch data. Data shown were recorded from canine right ventricular trabecula, plotting Fdev (normalized to cross-sectional area assuming ellipsoid shape of muscle, in millinewtons per square millimeter) versus time (in milliseconds). Example tangent lines used to calculate dF/dt and −dF/dt are shown. The length of time from the initiation of the twitch contraction to the maximal Fdev is the TTP. The length of time from the peak Fdev to 50% of the peak Fdev is the RT50.

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  Figure 2.. Data presented were from one dog in the CS group. (A) The results from the length-dependent activation experiment show strong linear correlation between CR rates, with a Pearson coefficient of R2 = 0.981. (B) The results from the frequency-dependent activation experiment show a strong linear correlation for CR, R2 = 0.993. (C) These data show that the results of the isoproterenol dose–response experiment have a strong linearity, with R2 = 0.997. (D) Combination of all three experiments into one plot showing a tight linear correlation for all cardiac output regulatory mechanisms at R2 = 0.965. Linear regression and Pearson correlation coefficient are calculated as shown.

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  Figure 3.. Weighted average of data across all animals within each experimental group for length-dependent activation, frequency-dependent activation, and β-adrenergic stimulation measurements, testing all three cardiac output regulatory mechanisms. (A) Data from the CS group show strong correlation across all three cardiac output regulatory mechanism tests at R2 = 0.997. (B) Data from the CT group show tight correlation at R2 = 0.996. (C) Data from the MIS group show tight correlation, with R2 = 0.997. (D) Data from the MIT group show tight linear correlation, with R2 = 0.997. Linear regression and Pearson correlation coefficient are calculated as shown.

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  Figure 4.. Plot of TTP versus RT50. Values were calculated as the weighted averages from all three experimental protocols (length, frequency, and β-adrenergic stimulation). Regardless of the experimental group to which the animals belong, TTP (as a surrogate for contraction) and RT50 (as a surrogate for relaxation) remain tightly correlated, with an overall Pearson coefficient of 0.943. These results demonstrate that CR coupling persists when contraction and relaxation kinetics are determined from contraction and relaxation times and not a scaling of relaxation with peak force.