Key result
In an experimental canine model, the magnitude of the gradient of systolic flow (ratio of deep to shallow flow) was 0.54 ± 0.12, consistent with extravascular compression across the left ventricular wall.
Why the study?
Does provision of perfusion pressure only during systole alter the transmural distribution of blood flow compared to perfusion throughout the cardiac cycle in unloaded canine hearts?
Does provision of perfusion pressure only during systole alter the transmural distribution of blood flow compared to perfusion throughout the cardiac cycle in unloaded canine hearts?
Systolic perfusion in unloaded canine hearts demonstrates a gradient of extravascular compression across the left ventricular wall, reducing deep myocardial blood flow relative to shallow flow.
Answers are grounded in this paper and cite their sources.
Supports extravascular compression in canine LV; leaves open relevance to clinical systolic perfusion strategies.
The left coronary arteries of dogs were cannulated and perfused with blood from support dogs. The experimental hearts were unloaded by severing the aortas to maximize strains and minimize fiber stress. In each heart we compared the transmural distribution of blood flow in two states: (1) provision of perfusion pressure (40 mm Hg) only during systole and then (2) provision of perfusion pressure throughout the cardiac cycle. The distribution of flow in each of these perfusion states was labeled with a diffusible radioisotope (42K or 86Rb, one labeling the first state; the other labeling the second). Quantitative, paired autoradiography was used to visualize the two flow distributions. The differences between the two distributions after standardization was plotted as differences between activity vs. depth in the myocardium (r = 0.91). This was fitted with a line by least squares, the slope of which was significantly different from zero at the 0.005 level. The magnitude of the gradient of the systolic flow was represented by the ratio of deep to shallow flow. The mean of these ratios was 0.54 +/- 0.12 (95% confidence interval). A graphical analysis shows that the data are consistent with a gradient of extravascular compression across the left ventricular wall.
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Williams et al. (1981) studied this question. Perfusion pressure only during systole vs. Perfusion pressure throughout the cardiac cycle was evaluated on Transmural distribution of blood flow (p=<0.005). In an experimental canine model, the magnitude of the gradient of systolic flow (ratio of deep to shallow flow) was 0.54 ± 0.12, consistent with extravascular compression across the left ventricular wall.
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