Cardiovascular Physiology Lecture 2 PDF

Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ Lecture 2 Objectives: -Demonstration of cardiac cycle and its mechanical events -Normal heart sounds and abnormal added sounds. The heart as a pump The electrical activity of the heart is designed to serve the pumping action of the hear...

Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ Lecture 2 Objectives: -Demonstration of cardiac cycle and its mechanical events -Normal heart sounds and abnormal added sounds. The heart as a pump The electrical activity of the heart is designed to serve the pumping action of the heart. This is accomplished when depolarization process triggers a wave of contraction that spreads through the myocardium. In single muscle fibers, contraction starts just after depolarization and lasts until about 50 ms after repolarization is completed. The cardiac cycle : the cardiac events that occur from the beginning of one heart beat to the beginning of the next.the cardiac cycle consists of period of relaxation called diastole during which the heart fills with blood followed by a period of contraction called systole. The term systolic pressure refers to the peak pressure reached during systole; similarly, the diastolic pressure refers to the lowest pressure during diastole. Mechanical events of the cardiac cycle Mechanical events of left ventricle: the different mechanical events of left ventricle during cardiac cycle: It is divided into four phases: 1-phase I: Period of filling. 2- Phase II: period of isovolumic Contraction. 3- Phase III: period of ejection. 4-Phase IV: Period of isovolumic relaxation. PHASE I during ventricular systole large amounts of blood accumulate in the atria because of the closed atrioventricular valves ( A-V) valves. therefore as soon as systole is over and ventricular pressures is fall , the moderately increased pressures in the atria push the A-V valves open and allow blood to flow rapidly in to the ventricles. this is called period of rapid filling of the ventricles which last for the first third of diastole. during the middle third of diastole only small amount of blood flows into ventricles. About 70% of the ventricular filling occurs passively during diastole. During the last third of diastole , Contraction of the atria propels some additional blood into the ventricles. This account for about 25% of the filling. yet the ventricle can continue to operate satisfactory without this extra 25%.Therefore when the atria fail to function the difference is 1 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ unlikely to noticed unless a person exercises , here sign of heart failure occasionally develop ,especially shortness of breath. -phase II Isovolumetric (isovolumic) ventricular contraction: At the start of ventricular systole, the A-V valves close. Ventricular muscle initially shortens relatively little, but intra-ventricular pressure rises sharply as the myocardium presses on the blood in the ventricle. This will last for about 0.05 seconds, until the pressures in the left and right ventricles exceed the pressures in the aorta (80 mm Hg) and pulmonary artery (10 mm Hg) and the aortic and pulmonary valves open. PHASE III- Ventricular ejection: During this phase, aortic and pulmonary valves open. Ejection is rapid at first, slowing down as systole progresses. The intra-ventricular pressure rises to a maximum and then declines somewhat before ventricular systole ends. Peak pressures in the left and right ventricles are about 120 and 25 mm Hg, respectively. Late in systole, pressure in the aorta actually exceeds that in the left ventricle, but for a short period momentum keeps the blood moving forward. This momentum decreases during the latter part of systole. 70% of the emptying occurring during first third of ejection and the remaining 30% during the next two thirds.so the first third called the period of rapid ejection and the last two thirds called the period of slow ejection. - A so called incisura occurs in aortic pressure curve when aortic valve closes. This is caused by short period of backward flow of blood immediately before closure of the valve, followed by sudden cessation of the backflow. Phase IV- Isovolumetric ventricular relaxation: at the end of systole , ventricular relaxation begins suddenly allowing the intraventricular pressure to fall rapidly. The period at which ventricular pressure continues to drop rapidly after the closure of the valves. This period ends when the ventricular pressure falls below the atrial pressure and the A-V valves open, permitting the ventricles to fill. Pressure changes in the atria include : three major pressure elevation called a , c and v atrial pressure waves. The a wave caused by atrial contraction, right atrial pressure rises 4-6 mmHg , left atrial pressure rises about 7-8mmHg. C wave occurs when the ventricles begin to contract causing bulging of the atrioventricular valves backward toward the atria and due to slight backflow of blood to the atria. the v wave is due to atrial filling. 2 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ Figure2 Events of cardiac cycle showing changes in left atrial pressure, left ventricular pressure and aortic pressure Length of systole and diastole The normal duration of the cardiac cycle in a resting adult heart with a heart rate of 75 beats per minute is about 0.8 seconds, 0.3 seconds for the systole and 0.5 seconds for the diastole. Cardiac muscle has the property of contracting faster when the heart rate is high, and the duration of systole decreases from 0.27 seconds at a heart rate of 65 to 0.16 seconds at a rate of 200 BPM. when the heart rate is increased, diastole is shortened to a much greater degree. For example, at a heart rate of 65, the duration of diastole is 0.62 seconds, whereas at a heart rate of 200, it is only 0.14 seconds. This fact has important physiologic and clinical implications, because during diastole the heart muscle rests, and most of the ventricular filling occurs here. At very high heart rates, filling may be compromised to such a degree that cardiac output per minute falls. 3 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ End diastolic volume , end systolic volume, stroke volume and Ejection fraction : during diastole , normal filling of the ventricles increases the volume of each ventricle to about 110-120 ml. This volume is called end diastolic volume. Stroke volume :The amount of blood ejected by a ventricle per each contraction, at rest is about 70-90 ml/beat.Stroke volume differs depending on age and size of body. Stroke volume= end diastolic volume – end systolic volume The remaining volume (50-60 ml) is called end systolic volume. The fraction of the end-diastolic volume that is ejected is called ejection fraction. Ejection fraction = Stroke volume/ end diastolic volume %. Normal ejection fraction of left ventricle is about 65% , right ventricle is (45%). Heart sounds When the stethoscope is placed on the chest wall over the heart, two sounds are normally heard during each cardiac cycle (1st & 2nd heart sounds). Opening of the valve does not hear because this is slowly developing process that normally makes no noise. When the valve close, the vanes of the valves and the surrounding fluid vibrate under the influence of the sudden pressure. 1-First heart sound: When the ventricles contract, first heart sound is heard by closure of the A-V valves. Vibration is soft low in pitch (lub) and relatively long. The valves bulge backward toward the atrium until the chordae tendineae abruptly stops the back bulging. 2-Second heart sound: When the aortic and pulmonary valves close at end of systole, they close rapidly and vibrate for short period of higher pitch (dub). The duration of the 1st. heart sound (0.15 second), is longer than the second heart sound (0.12 second); this is because the semilunar valves are tauter than AV valves, so they vibrate for short period than do AV valves. The first heart sound has a lower frequency (pitch) which is 25-45 Hz than second heart sound (50 Hz) this is because of tautness and greater elasticity coefficient of the arteries. 2nd heart sound is loud and sharp when the diastolic pressure in aorta or pulmonary artery is elevated causing the valves to shut briskly at end of systole. Second heart sound is single during expiration, while the interval between aortic and pulmonary valve closure during inspiration is 4 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ frequently long enough for the second sound to be re-duplicated (physiological splitting) because during inspiration, the venous return increases, so there will be a delay in filling the right ventricle and delay in the closure of the pulmonary valve. Third heart sound: Soft low pitch sound heard about one third of the way through diastole in many normal young individuals. It coincide with the period of rapid ventricular filling is probably due to vibration set up by the in- rush of blood. Fourth heart sound : can sometimes be heard immediately before 1st heart sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hypertrophy. Both sounds (third and fourth) are best heard with the bell of the stethoscope at the cardiac apex. Murmurs and bruits : abnormal sound heard in various parts of CVS. Normal blood flow is laminar and non-turbulent (silent) up to critical velocity. Above this velocity and beyond an obstruction, blood flow is turbulent (creates sound). The major cause of cardiac murmur is the disease of the heart valves. When the orifice of a valve is narrowed (stenosis), blood flow through it is accelerated and turbulent. When a valve is incompetent, blood flow backward through it (regurgitating) that accelerates flow (figure3). Murmur due to disease of a particular valve can generally be heard well when the stethoscope is over that valve. Example of vascular sounds outside the heart is the bruit over the carotid artery when its lumen is narrowed by atherosclerosis. Valve abnormality Timing of murmur Aortic or pulmonary Stenosis Systolic insufficiency diastolic Mitral or tricuspid Stenosis Diastolic insufficiency Systolic Figure3 Heart murmurs References -Ganong and Guyton textbooks -principle of human physiology 5th edition 5 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ Case scenario 60 yr-old male with history of arterial hypertension, complains of palpitation and shortness of breath , admitted to EU, by examination the patients with heart rate about 125 beat/ minute, Answer the following 1. with this heart rate, Which part of cardiac cycle is affected more , systolic or diastolic? 2. what is the effect of this heart rate on LV end diastolic volume and stroke volume? 3.is there probability of development of 4th HS ? why? 6 Cardiovascular physiology --------- ‫ احالم كاظم‬.‫د‬ Case scenario 60 yr-old male with history of arterial hypertension, complains of palpitation and shortness of breath , admitted to EU, by examination the patients with heart rate about 125 beat/ minute, Answer the following 1. with this heart rate, Which part of cardiac cycle is affected more , systolic or diastolic? 2. what is the effect of this heart rate on LV end diastolic volume and stroke volume? 3.is there probability of development of 4th HS ? why? 6