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The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. [1] It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. [1]
In physiology, [B: 2] a refractory period is a period of time during which an organ or cell is incapable of repeating a particular action, or (more precisely) the amount of time it takes for an excitable membrane to be ready for a second stimulus once it returns to its resting state following an excitation. It most commonly refers to ...
A Wiggers diagram modified from [1]. A Wiggers diagram, named after its developer, Carl Wiggers, is a unique diagram that has been used in teaching cardiac physiology for more than a century.
The first 2.5 seconds show a normal cardiac cycle. This is followed by a period of delayed sinus activity which initiates a takeover response by the ventricular pacemaker cells resulting in a ventricular escape beat. Two escape beats are shown between 5-8 seconds.
Afterload is the mean tension produced by a chamber of the heart in order to contract. It can also be considered as the ‘load’ that the heart must eject blood against. Afterload is, therefore, a consequence of aortic large vessel compliance, wave reflection, and small vessel resistance (LV afterload) or similar pulmonary artery parameters (RV afterload
The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle. The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole.
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This period is approximately equal to the absolute refractory period (ARP), it occurs because the fast sodium channels remain closed until the cell fully repolarizes. [1] During this period, depolarization on adjacent cardiac muscles does not produce a new depolarization in the current cell as it has to refract back to phase 4 of the action ...