Cardiac cycle aorta

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. 

Typical pressure and velocity fluctuations throughout the cardiac cycle in man are shown in Figure 56.3 Although mean pressure decreases slightly toward the periphery due to viscous effects, peak pressure shows small increases in the distal aorta due to wave reflection and vessel taper. A rough estimate of mean... 

Shear stress Shear stress is exerted on the valve by blood flowing across the face of the valve tissue. In basic terms, shear stress is defined as the component of the stress parallel to the surface of interest. The aortic valve experiences completely different shear profiles on each side of the leaflet, tightly correlating with the preferential calcification of the fibrosa [16, 53]. Shear stress at the leaflet surface is experienced in a cyclical manner—due to the blood flow during the typical cardiac cycle. The ventricularis is subjected to unidirectional shear stress as blood is ejected from the ventricle to the aorta whereas the fibrosa experiences oscillatory shear stress. Oscillatory shear stress at the fibrosa has been directly associated with valve dysfunction and CAVD [16, 53, 54]. Aboelkassem et al [55] derived a ma-... 

There is continuous pressure in arteries to propel blood through them. The level of blood pressure fluctuates during each cardiac cycle. Pressure is highest during systole (contraction) when blood is ejected from the left ventricle into the aorta this pressure is labeled SBP. Pressure is lowest during diastole (relaxation) and labeled... 

Fig. 1 Ensemble-averaged original signals (ECG, Plv, Pao, AZ) and the calculated (dPLv/dt, d PAc/dP, d Z/dP) signals. The pressure in the LV and aorta was recorded with the same catheter-tip manometer during different cardiac cycles with similar durations. For convenient presentation of the related blood volume changes, AZ curves and their derivatives, are inverted, i.e., the positive deflections of the curves correspond to the decrease in impedance.

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