The Cardiac Cycle
Left ventricular pressure
Left atrial pressure
Figure 1. Cardiac bicycle of the left next of the heart. The EKG below the diagram reflects the matching waves through each step of the cardiac cycle. The bottom line represents the an initial and second heart sounds.
You are watching: When atrial pressure is greater than ventricular pressure, the ____________ valves open.
The cardiac cycle represents the hemodynamic and also electric transforms that take place in systole and also diastole. That has plenty of phases.
Phases that the Cardiac Cycle:Isovolumetric ventricular contraction (a-b): This step marks the start of systole and also starts v the illustration of the QRS facility on the EKG and also the closure of the AV valves at point (a). V all valves closed, the ventricle generates optimistic pressure there is no any adjust in that volume (isovolumetric) to get rid of the semilunar valves resistance that open at allude b. This phase typically lasts for 6% the the cardiac cycle.Rapid ejection (b-c): as the semilunar valves open at suggest (b), there is a quick ejection of blood as result of increased ventricular contractility. The arterial pressure rises until getting to it best at suggest (c). This phase typically lasts for 13% the the cardiac cycle.Reduced ejection (c-d): This step marks the start of ventricular repolarization as illustrated by the start of the T tide on the EKG. Repolarization leader to a rapid decrease in ventricular pressures and also hence the lessened rate that ejection. However, some forward circulation of blood continues an additional to remnant kinetic energy from the vault phase. This phase typically lasts for 15% that the cardiac cycle.Isovolumetric relaxation (d-e): as soon as the ventricular pressure drop below the diastolic aortic and pulmonary pressures (80 mmHg and also 10 mmHg respectively), the aortic and pulmonary valves close developing the 2nd heart sound (point d). This clues the beginning of diastole. The ventricles generate an adverse pressure without changing their volume (isovolumetric) so the the ventricular pressure becomes lower than the atrial pressure. This phase commonly lasts because that 8% the the cardiac cycle.Ventricular filling (e-a): together the AV valves open up at point (e), ventricular pour it until it is full starts. The initial fast filling is greatly augmented by ventricular suction which results from ventricular untwisting and also the return of each ventricular muscle fiber come its slack length. The ventricular pressure progressively increases till it equals the atrial pressure and the AV valves close (point a). This phase usually lasts for 44% the the cardiac cycle.Atrial contraction: Finally, close to the end of ventricular diastole, the atrial contraction contributes around 10% of the ventricular pour it until it is full volume. This is stood for by the P tide on the EKG of the following cycle. This phase usually lasts because that 14% the the cardiac cycle.
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Content ©2017. Some legal rights Reserved.Date last modified: July 7, 2017.Ashraf Aly and Soham DusguptaDept. The PediatricsUniversity the Texas clinical Branch.