elhilt.blogg.se - Normal heartbeat sound

This phase usually lasts for 8% of the cardiac cycle. The ventricles generate negative pressure without changing their volume (isovolumetric) so that the ventricular pressure becomes lower than the atrial pressure.

Isovolumetric relaxation (d-e): When the ventricular pressures drop below the diastolic aortic and pulmonary pressures (80 mmHg and 10 mmHg respectively), the aortic and pulmonary valves close producing the second heart sound (point d).

This phase usually lasts for 15% of the cardiac cycle. However, some forward flow of blood continues secondary to remnant kinetic energy from the previous phase. Repolarization leads to a rapid decline in ventricular pressures and hence the reduced rate of ejection.

Reduced ejection (c-d): This phase marks the beginning of ventricular repolarization as depicted by the onset of the T wave on the EKG.

This phase usually lasts for 13% of the cardiac cycle. The arterial pressure increases until reaching its maximum at point (c).

Rapid ejection (b-c): As the semilunar valves open at point (b), there is a rapid ejection of blood due to increased ventricular contractility.

This phase usually lasts for 6% of the cardiac cycle. With all valves closed, the ventricle generates positive pressure without any change in its volume (isovolumetric) to overcome the semilunar valves resistance that open at point (b).

Isovolumetric ventricular contraction (a-b): This phase marks the beginning of systole and starts with the appearance of the QRS complex on the EKG and the closure of the AV valves at point (a).

The cardiac cycle represents the hemodynamic and electric changes that occur in systole and diastole. The bottom line represents the first and second heart sounds.

The electrocardiogram (EKG) below the diagram shows the corresponding waves with each phase of the cardiac cycle. Cardiac cycle of the left side of the heart.