Ventricular volume changes can be assessed in real time using echocardiography or radionuclide imaging, or by using a special volume conductance catheter placed within the ventricle.
To analyze systole and diastole in more detail, the cardiac cycle is usually divided into seven phases. The first phase begins with the P wave of the electrocardiogram , which represents atrial depolarization, and is the last phase of diastole. Phases represent systole, and phases represent early and mid-diastole.
The last phase of the cardiac cycle ends with the appearance of the next P wave, which begins a new cycle. Detailed descriptions of each phase can be obtained by clicking on each of the seven phases listed below.
Cardiovascular Physiology Concepts Richard E. Klabunde, PhD. The T wave represents the repolarization of the ventricles and marks the beginning of ventricular relaxation. In a normal, healthy heart, there are only two audible heart sounds : S 1 and S 2.
In both cases, as the valves close, the openings within the atrioventricular septum guarded by the valves will become reduced, and blood flow through the opening will become more turbulent until the valves are fully closed. There is a third heart sound, S 3 , but it is rarely heard in healthy individuals.
It may be the sound of blood flowing into the atria, or blood sloshing back and forth in the ventricle, or even tensing of the chordae tendineae. S 3 may be heard in youth, some athletes, and pregnant women.
If the sound is heard later in life, it may indicate congestive heart failure, warranting further tests. The fourth heart sound, S 4 , results from the contraction of the atria pushing blood into a stiff or hypertrophic ventricle, indicating failure of the left ventricle.
A few individuals may have both S 3 and S 4 , and this combined sound is referred to as S 7. Figure 3. In this illustration, the x-axis reflects time with a recording of the heart sounds. The y-axis represents pressure. The term murmur is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood.
Murmurs are graded on a scale of 1 to 6, with 1 being the most common, the most difficult sound to detect, and the least serious. The most severe is a 6. Phonocardiograms or auscultograms can be used to record both normal and abnormal sounds using specialized electronic stethoscopes. During auscultation, it is common practice for the clinician to ask the patient to breathe deeply. This procedure not only allows for listening to airflow, but it may also amplify heart murmurs.
Inhalation increases blood flow into the right side of the heart and may increase the amplitude of right-sided heart murmurs. Expiration partially restricts blood flow into the left side of the heart and may amplify left-sided heart murmurs. Figure 4 indicates proper placement of the bell of the stethoscope to facilitate auscultation.
Figure 4. Proper placement of the bell of the stethoscope facilitates auscultation. At each of the four locations on the chest, a different valve can be heard. The cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0. Beginning with all chambers in diastole, blood flows passively from the veins into the atria and past the atrioventricular valves into the ventricles.
The atria begin to contract atrial systole , following depolarization of the atria, and pump blood into the ventricles. The ventricles begin to contract ventricular systole , raising pressure within the ventricles. When ventricular pressure rises above the pressure in the atria, blood flows toward the atria, producing the first heart sound, S 1 or lub. As pressure in the ventricles rises above two major arteries, blood pushes open the two semilunar valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase.
Following ventricular repolarization, the ventricles begin to relax ventricular diastole , and pressure within the ventricles drops. As ventricular pressure drops, there is a tendency for blood to flow back into the atria from the major arteries, producing the dicrotic notch in the ECG and closing the two semilunar valves.
The second heart sound, S 2 or dub, occurs when the semilunar valves close. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle. The valves prevent backflow of blood. Cardiac cycle of the left side of the heart. The electrocardiogram EKG below the diagram shows the corresponding waves with each phase of the cardiac cycle.
The bottom line represents the first and second heart sounds. T he cardiac cycle represents the hemodynamic and electric changes that occur in systole and diastole. It has many phases.
Normal pressures in various chambers of the heart. The first heart sound S1 represents closure of the atrioventricular mitral and tricuspid valves as the ventricular pressures exceed atrial pressures at the beginning of systole point a. S1 is normally a single sound because mitral and tricuspid valve closure occurs almost simultaneously.
Clinically, S1 corresponds to the pulse. The second heart sound S2 represents closure of the semilunar aortic and pulmonary valves point d. S2 is normally split because the aortic valve A2 closes before the pulmonary valve P2. The closing pressure the diastolic arterial pressure on the left is 80 mmHg as compared to only 10 mmHg on the right. This higher closing pressure leads to earlier closure of the aortic valve. In addition, the more muscular and stiff "less compliant" left ventricle LV empties earlier than the right ventricle.
The venous return to the right ventricle RV increases during inspiration due to negative intrathoracic pressure and P2 is even more delayed, so it is normal for the split of the second heart sound to widen during inspiration and to narrow during expiration. Clinically, this is more remarkable with slow heart rates.
The third heart sound S3 represents a transition from rapid to slow ventricular filling in early diastole.
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