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The shape of the Ventricular function Curve. A Ventricular function Curve was created by plotting Left Ventricular End-diastolic pressure against stroke work. The curve In Figure 1, displays that increase as increase LVEDP increase SW also increased as expected by starling Law of the heart. The ventricular function curve appears to only display the part of the ascendingly limb when compared to traditional curves as there is no sign of plateauing of high Pressure the sharp line of the ascendingly limb seen during low pressure. Most importantly, relative to baseline, with similar Left ventricular end diastolic pressure, the stroke Work was reduced.
Contrary these findings, the initial increase in blood volume (represented as the
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The pressure surrounding the LV more than inside the ventricle LVEDP may not be correctly found, requiring the subtraction of external pressure from LVEDP in order to provide an accurate transmural LVEDP, thus since the LVEDP is decreased the left ventricle end diastolic Volume would also be reduced explaining the resultant reduction In Stroke Work. In other words, it is possible that the reduction in Stroke work from the initial volume loading is a consequence of the readable LVEVP being modified by the imbalance of external LV pressure. Implying that the change in real LVEDP may be more in line with starling law, However, without readings of the surrounding pressure, there is no way to justify this claim.
Another explanation for this phenomenon, enhanced Heart rate derived from baroreflex activity . This would indicate that the increased load causes a rise in initial End-systolic volume, and therefore a decrease in Stroke volume . This explanation is plausible as there was a reduction in the MAP and total peripheral resistance relative to baseline after expansion. Interestingly, whether the cause or not, this initial rise in HR does help to explain why HR remained higher throughout a majority of the volume reductions as explain by the Positive staircase