Timing points, cardiac cycle

The key point of the cardiac cycle diagram is to be able to use it to explain the flow of blood through the left side of the heart and into the aorta. An appreciation of the timing of the various components is, therefore, essential if you are to draw an accurate diagram with which you hope to explain the principle. 

Blood flow to the coronary arteries arises from orifices located immediately distal to the aorta valve. Perfusion pressure is equal to the difference between the aortic pressure at an instantaneous point in time minus the intramyocardial pressure. Coronary vascular resistance is influenced by phasic systolic compression of the vascular bed. The driving force for perfusion therefore is not constant throughout the cardiac cycle. Opening of the aortic valve also may lead to a Venturi effect, which can slightly decrease perfusion pressure. If perfusion pressure is elevated for a period of time, coronary vascular resistance declines, and blood flow increases however, continued perfusion pressure increases lead, within limits, to a return of coronary blood flow back toward baseline levels through autoregulation. 

Although flie interpretation of the amplitude of the ICG is obscured by many complicating factors, a more relevant aspect of the ICG signal may be found in the time relationships, especially when the timing of specific marker points in the ICG signal is compared with that of marker points in the ECG. Regardless of the multiple sources of the signal, the ICG reflects the mechanical/hydrodynamical aspects of the cardiac cycle, as described by... 

Fig. 15.5. Retrospectively gated image acquisition by CT does not only contain information about the coronary arteries but also about the function of the myocardium. Newer postprocessing is under development, and tries to determine the axial CT slices reconstructed at different time points of the cardiac cycle. These workstations may provide data about the global functional parameter, as well as regional wall motion abnormalities...

I want to make one other comment regarding the difference between Dr. Sagawa s model and Dr. Welkowitz s model. Both are lumped models. Dr. Sagawa s model, however, is appropriate for only one point in time, namely end systole. Dr. Sagawa has extended the model to represent the ventricular system in the normal state. The lumped model that Dr. Welkowitz presented represents the full cardiac cycle. 

The timing of a cardioversion shock. point in time of the cardiac cycle. 

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