Intraventricular Pressure Changes During Cardiac Cycle
Intraventricular pressure is the pressure developed inside the ventricles of the heart. It is essential for m7e circulation of blood, because the flow of blood through systemic and pulmonary circulation depends. upon the pressure at which the blood is pumped out of ventricles. Thus, intraventricular pressure is essential for the circulation of blood.
Methods Of Study
Intraventricular pressure is measured by cardiac catheterization.
Maximum And Minimum Pressure In Ventricles
There is some difference in the pressure in right Ventricle and left ventricle. The pressure is always more in left ventricle than in the right ventricle.
Intraventricular Pressure Curve
Intraventricular pressure curve has seven segments.
‘A-B’ segment is a positive wave and appears during atrial systole. Rise in pressure during this period is due to the entry of a small amount of blood into the ventricles because of atrial systole. the pressure rises to about 6 to 7 mm Hg in the right ventricle and to about 7 to 8 mm Hg in the left ventricle. ‘B’ indicates the closure Of atrioventricular valves.
‘B-C’ segment appears during isometric contraction. During isometric contraction period, there is a sharp rise in the intraventricular pressure. ‘C’ denotes the opening of semilunar valves.
‘C-D’ segment appears- during ejection period. During ejection period, the pressure in the ventricles rises to the peak and then falls down. First part of the curve indicates the maximum ejection and the pressure increases to the maximum. Second part of the curve represents the slow ejection phase when the pressure decreases.
Maximum pressure rise in right ventricle is about 25 mm Hg and the maximum pressure rise in left ventricle is about 120 mm Hg, during the peak of this wave. Maximum pressure in the left ventricle is 4 to 5 times more than that in the right ventricle, because of the thick wall of the left ventricle.
‘D-E’ segment appears during protodiastole. Pressure decreases slightly due to the starting of ventricular relaxation. ‘E’ indicates the closure of semilunar valves.
‘E-F’ segment’ is obtained during isometric relaxation. There is a sharp fall in the intraventricular pressure during this phase. Pressure in the ventricle falls below the pressure in the atria and this causes the opening of atrioventricular valves. ‘F’ represents the opening of atrioventricular valves.
‘F-G’ segment appears during rapid filling phase. In spite of filling of blood, pressure decreases in the ventricles. It is because of the relaxation of the ventricles.
‘G-A’ segment is the last part of intraventricular pressure curve. It is obtained during slow filling phase. Because of continuous relaxation of ventricles during slow filling period, the ventricular pressure decreases further.
Aortic Pressure Changes During Cardiac Cycle
Aortic pressure is the pressure developed in the aorta. It is necessary to maintain the blood flow through the circulatory system.
Method Of Study
Changes in aortic pressure during the cardiac cycle recorded by using catheter.
Maximum And Minimum Pressure In Aorta
Pressure in systemic aorta is always higher than that of pulmonary artery. It is because of the higher pressure in left ventricle than in the right ventricle. Minimum pressure in systemic aorta is much greater than the minimum pressure in the left ventricle. It is due to the presence of elastic tissues in the aorta, which enable the aorta to recoil and maintain the minimum pressure at a higher level.
Aortic Pressure Curve
During the ejection period of the cardiac cycle, the pressure in the aorta increases and reaches the peak. During diastole, it reduces gradually and reaches the minimum level. At the time of closure of semilunar valves, an incisura occurs due to back flow of some blood towards the ventricles.
Ventricular Volume Changes During Cardiac Cycle
Volume of blood in the ventricles is an important factor to maintain cardiac output and blood circulation.
Methods Of Study
1- By Using Henderson Cardiometer
This study is done only in animals. Cardiometer is a cupshaped device with an outlet. At the top, it is closed by means of a rubber diaphragm. A small hole is made in the diaphragm, through which the ventricles of the anime! are pushed. Cardiometer is connected to a recording device like Marey tambour (a small stainless steel capsule covered by rubber membrane).
2- By Angiography
Angiography is the radiographic study of heart and blood vessels using a radiopaque contrast medium. During angiography, it is possible to measure the ventricular dimensional area and thickness of ventricular wall. From the values obtained. the ventricular volume is calculated.
Volume Of Blood In Right And Left Ventricles
End-Diastolic Volume and End-Systolic Volume
Amount of blood is the same in both right and left ventricles. Maximum volume of blood in each ventricle after filling (end-diastolic volume) is 130 to 150 mL. Minimum volume of blood left in the ventricles at the end of ejection period (end of systolic volume) is 60 to 80 mL.
Ejection fraction (E) is the stroke volume divided by end-diastolic volume, expressed in percentage.
Ventricular Volume Curve
Ventricular volume curve recorded by using Henderson cardiometer has seven segments.
‘A-B’ segment wave is because of atrial systole or last filling phase of ventricles, during which a small amount of blood enters the ventricles from the atria. It increases the ventricular volume slightly. ‘B’ indicates the Closure of atrioventricular valves.
‘B-C’ segment is a positive wave, which is obtained during isometric contraction. Actually, the ventricular volume is not altered during isometric contraction. However, the slight upward deflection of this wave is an artifact. It is because the heart thrusts itself into the cardiometer during isometric contraction. ‘C’ represents the opening of semilunar valves.
‘C-D’ segment occurs during ejection period. Initially, there is a sharp fall in the ventricular volume. This occurs during rapid ejection. Later, during slow ejection period, the blood leaves the ventricles slowly. So the ventricular volume decreases slowly.
‘D-E’ segment part of the ventricular volume curve is recorded during protodiastole. There is no change in the ventricular volume during protodiastole. ‘E’ denotes the closure of semilunar valves.
‘E-F’ segment appears during isometric relaxation period of the cardiac cycle. Actually, the ventricular volume c is not altered during isometric relaxation. However, there is a slight upward deflection in the curve due to artifact. It is because of the entrance of blood into coronary artery from aorta during this period. It increases the pressure within the cardiometer. ‘F’ indicates the opening of atrioventriculat valves.
‘F-G’ segment appears during rapid filling phase. Rapid rise in ventricular volume is due to sudden rush of blood after the opening of atrioventricular valves.
‘G-A’ segment is recorded during slow filling phase. Ventricular volume increases slowly because of slow filling.