CVS 217 Theoretical PDF

5. Protodiastole phase, 0.04 second. 6. Isometric relaxation phase, 0.06 second. 7. Maximum filling phase, 0.1 second. 8. Reduced filling phase, 0.2 second. Another way of Classification (important): 1. Ventricular systole includes phases No. 2, 3, 4. 2. Early dia...

5. Protodiastole phase, 0.04 second. 6. Isometric relaxation phase, 0.06 second. 7. Maximum filling phase, 0.1 second. 8. Reduced filling phase, 0.2 second. Another way of Classification (important): 1. Ventricular systole includes phases No. 2, 3, 4. 2. Early diastole includes phases No. 5, 6, 7. 3. Mid diastole includes phase No. 8. 4. Late diastole includes phase NO. 1. NOTES: Lt. V Rt. V Aorta Pulmonary a. Systolic pressure 120 25 120 25 Diastolic pressure 0 0 80 10 b. 70% of blood passes from A. to V. by pressure difference (i.e., passively). 30% of blood only passes with help of atrial contraction, so the main function of atria is RESERVOIR OF BLOOD. c. Atrial systole 0.1 second, atrial diastole 0.7 second. Ventricular systole 0.3 second, ventricular diastole 0.5 second. 82 83  PHASES OF CARDIAC CYCLE The cardiac cycle can be divided into the following phases: 1. Atrial Systole (Late Diastole): Duration 0.1 sec. When S.A.N. discharges its impulse to spread over both atria, P- wave of E.C.G. is produced and begins before mechanical systole of atria by 0.02 sec. Atria will contract, intra-arterial pressure increases and about 30% of blood will be pumped into the ventricles while A.V. valves are opened. Ventricular volume increases, while intraventricular pressure slightly increases (still lower than atrial pressure) and then decreases due to relaxation of the ventricles to accommodate blood. The volume of the ventricle at the end of ventricular diastole is called End-Diastolic volume and is about 135 ml. Aortic and pulmonary pressure decrease gradually because blood escapes from them to the periphery while aortic and pulmonary valves are still closed. N.B. After atrial systole, ventricular systole begins (0.3 sec.), and is divided into 3 phases, (isometric, maximal and reduced ejection). 2. Isometric contraction phase: Duration: 0.05 sec. When excitation wave spreads over both ventricles, it will produce QRS complex of E.C.G. which will precede the mechanical systole of the ventricles by 0.02 sec. Contraction of the ventricles will increase intraventricular pressure rapidly (from 0 to about 80 mmHg in the left ventricle and from 0 to about 10 mmHg in the right ventricle). The intraventricular pressure will exceed the intra-atrial pressure and then blood tends to regurgitate back in the atria, but this is prevented by sudden closure of A.V. valves. The aortic and pulmonary valves are still closed, the pressure in the aorta and pulmonary artery is decreasing due to escape of blood to the periphery. 84  The ventricles are now closed chambers (A.V. valves and aortic valves are closed), thus they will contact isometrically i.e. without change in their volume (isovolumetric cont.). The intra-atrial pressure shows a slight rise in pressure due to bulging of the cusps of A.V. valves in the cavity of the atria. 3. Maximal Ejection Phase: Duration 0.15 sec. ·At the beginning of this phase, the intraventricular pressure still increases due to ventricular systole and exceeds the aortic and pulmonary pressure. Aortic and pulmonary valves will open and the blood is rapidly ejected in the aorta and pulmonary artery. ·Ventricular volume markedly decreases. ·The aortic and pulmonary pressures increase and reach a maximum at the end of this phase (120 mmHg in aorta and 25 mmHg in pulmonary artery), because blood coming to them is more than blood leaving them. ·Ventricles, aorta and are considered now as one chamber. ·Intra-atrial pressure curve shows a sharp drop at the beginning of this phase due to descend of A.V. ring down-ward. Then intra- atrial pressure starts to increase gradually due to accumulation of venous return while A-V. valves are closed. 4. Reduced Ejection Phase: Duration 0.1 sec. ·During this phase less blood will be ejected from the ventricles. The volume of the ventricles and their pressure decrease gradually. ·Aortic and pulmonary pressure start to decrease because blood coming to them is less than blood leaving them. ·Intra-arterial pressure is still increasing due to venous return while A-V. valves are still closed. ·During period of ventricular systole (isometric, maximal and reduced ejection) about 70 ml of blood are ejected by each ventricle per beat during rest and this is called stroke volume. About 65 ml of blood will be left in each ventricle & is called End-systolic volume. 5. Protodiastolic Phase: Duration 0.04 sec. It is very short period between the end of ventricular systole and beginning of closure of aortic and pulmonary valves. The ventricle stops to contract. 85 ·Ventricular pressure decreases, while its volume is not changed. Blood passes by its momentum increasing aortic pressure. ·At the end of this phase, the pressure in the ventricles will be lower than aortic and pulmonary pressure, blood would like to return back into the ventricles, but this is prevented by sudden closure of aortic and pulmonary valves, (in the next phase). ·Atrial pressure is still increasing. 6. Isometric Relaxation Phase: Duration 0.06 sec. ·When ventricles start to relax, the intraventricular pressure decreases rapidly below aortic and pulmonary pressures. ·Volume of ventricles is not changed because both semilunar and A.V. valves are closed and ventricles act as closed chambers. Sudden closure of semilunar valves will produce sharp fall in aortic pressure called incisura or dicrotic notch. This is followed by rise in aortic pressure (dicrotic wave) due to elastic recoil of aorta. ·Atrial pressure is still increasing, due to accumulation of venous return. The T-wave of E.C.G. ends during this phase. 7. Rapid Filling Phase: Duration 0.1 sec. ·At the beginning of this phase the intra-atrial pressure is increasing above the ventricular pressure, this will open A-V. valves. Blood will pass passively from atria to ventricles, the pressure in atria slightly decreases, but is still higher than the ventricular pressure. ·Volume of ventricles increase rapidly. ·Aortic and pulmonary pressure start to decrease due to escape of blood to the periphery while their valves are closed. 8. Reduced Filling Phase (Mid diastole): Duration 0.2 sec. ·A.V. valves are still opened and blood continues to flow from atria to ventricles but at a slower rate. ·Volume of ventricles increase gradually, but the ventricular pressure does not increase because they relax to accommodate the extra-amount of blood reaching them. ·Aortic and pulmonary pressure are still decreasing because blood is leaving them while their valves are still closed. 86  CHANGES WHICH OCCUR DURING CARDIAC CYCLE I.LEFT VENTRICULAR PRESSURE CHANGES DURING CARDIAC CYCLE: 1.Atrial systole phase:. When the atria contracts, blood passes to ventricle causing an increase in V. pressure.. Then, the V. relaxes to accommodate the pumped blood. This, in turn, decreases V. pressure. 2.Isometric contraction phase: ·The mitral valve closes and so does the aortic valve. Thus the ventricle is no more than a closed chamber filled with blood. As blood is not compressible, the V. contracts without change in volume (isometric contraction). ·The contraction causes the Lt. V. pressure to increase to 80 mmHg. ·At this pressure, aortic valve is opened. 3.Maximal (rapid) ejection phase: ·The amount of blood ejected through the aortic valve exceeds the amount of blood which leaves the aorta. Thus, aortic pressure increases. ·The pressure in Lt. V. increases to 120 mmHg. This is because. forms continuous chamber with aorta. 4.Reduced ejection phase: ·The amount of blood ejected through the aortic valve is less than the amount of blood which leaves the aorta. Thus, aortic pressure and hence ventricular pressure decreases. 5.Protodiastolic phase: ·This is a very short phase between the end of ventricular contraction and the closure of aortic valve. When the ventricle stops to contract, the ventricular pressure decreases below the aortic pressure. However, the aortic valve does not close due to momentum of the ejected blood. Once the momentum of ejected blood is overcomed, the aortic valve closes. 87  6.Isometric relaxation phase: ·When the V. tends to relax, the blood tends to regurge but this is prevented by sudden closure of aortic valve. This is because the regurgitating blood fills the pockets of the aortic valve allowing its edges to come in close contact with each other and the valve is closed. ·The aortic valve is closed and so does the mitral valve, thus, the ventricle is no more than a closed chamber filled with blood. Thus, the ventricle relaxes without change in volume. However, the ventricular pressure decreases to 0 mmHg. ·At this pressure, the mitral valve opens. 7.Maximal (rapid) filling phase: ·The V. relaxes. This decreases the V. pressure; thus blood is sucked from A to V. The filling increases the pressure. ·In other word, the drop in V. pressure caused by V. relaxation overhangs the increase in pressure caused by V. filling. Thus, V. pressure decreases. 8.Reduced filling phase: ·During this phase, the drop in V. pressure caused by V. relaxation is less than the increase caused by V. filling. Thus, V. pressure increases. NOTES: Ventricular filling occurs in three phases in that order (sequence). (7,8 & 1). Maximal filling, reduce filling then atrial systole. 70% of blood passes from V. to A. in the 1st two phases of V. relaxation and only 30% of blood passes during atrial systole. II.VENTRICULAR VOLUME CHANGES DURING CARDIAC CYCLE: Phase Ventricular volume 1.Atrial systole phase Increases 2.Isometric contraction phase Constant 3.Maximal ejection phase Decreases 4.Reduced ejection phase Decreases 5.Protodiastolic phase Constant 6.Isometric relaxation phase Constant 88