Isovolumetric contraction

Filling Isovolumetric contraction Ejection Isovolumetric relaxation... 

It will be recalled that the Frank mechanism [68] deals with isovolumetric contraction, while Patterson and Starling s observations [69] focus on the ejecting ventricle. Both phenomena can be integrated into a single analytical expression describing ventricular pressure, pv, as a function of ventricular volume, Vy, and time, t, formally written as py(Vy, t). From experiments on isolated dog hearts, it was found... 

This model can also be used to predict the isovolumetric pressure Pisoit)- Thus during an isovolumetric contraction the flow is zero, the volume remains constant at its end-diastolic value (EDV), and the model reduces to the following form ... 

The accuracy of the model was tested using a servocontrolled isolated heart preparation (Janicki et aL, 1974) whereby it was possible to have controlled ejecting and isovolumetric contractions. The model parameters (i.e., AI-A6 and yj were calculated from the ejecting pressure-volume data and the model was then used to predict the peak isovolumetric pressure. When the predicted and measured peak isovolumetric pressure from 10 experiments were compared a correlation coefficient of 0.97 was found (Figure 3). Similar results have been obtained in open chest experiments with the heart intact. 

The "rowing model" is generally accepted, but other quite different processes have been proposed to account for the elementary cycle of muscle contraction. Muscle contracts nearly isovolumetrically thus, anything that expands the sarcomere will cause a contraction. 

Isolated Hearts Similarly, an entire heart can be removed from an animal donor (e.g., rabbit) and studied in isolation via Langendorff perfusion using different modes of contraction such as isovolumetric (Qu et al., 2013) or working heart under various conditions of preload and afterload (Werchan and McDonough, 1987). This approach shares many of the characteristics of the isolated tissue approach, including the need for technical expertise to run... 

Figure 11. Top plot shows the type of liner relationships that is observed when active oxygen consumption per beat is plotted against PVA in ejecting or isovolumetric whole heart contractions. The bottom plot shows the relationship between active oxygen consumption and PVA when the basal and activation metabolisms are subtracted out. Experimentally it is found that all the data cluster around the 40% isoefficiency line (dotted line). The contribution of stroke work (stippled area) and potential energy terms (clear area) to PVA are shown. If the efficiency values were different for different types of contractions the data would have been widely scattered. The solid lines show various other isoefficiency values.

Once ventricular pressure exceeds the pressure in the aorta, the aortic valve opens and systolic ejection commences (C to D). Blood flows out from the ventricle into the aorta based on the pressure gradient, the inertances, and the resistances of the outlet. The muscle continues to contract until the cardiac action potentials have run their course. As the muscle begins to relax, pressure will drop until it falls below the aortic pressure. At this time, the aortic valve closes, and again blood flow ceases. Meanwhile, the ventricle continues to relax, decreasing the ventricular pressure. This period (D to A) is termed isovolumetric relaxation. Here, muscle relaxation can be thought of as increasing the compliance of the... 

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