Cardiac Cycle PDF

Cardiac Cycle Dr. Sovan Bagchi, PhD Professor of Physiology www.gmu.ac.ae COLLEGE OF MEDICINE  Learning Objectives Describe pressure volume loop of a cardiac cycle Define stroke volume, end-diastolic ventricular...

Cardiac Cycle Dr. Sovan Bagchi, PhD Professor of Physiology www.gmu.ac.ae COLLEGE OF MEDICINE  Learning Objectives Describe pressure volume loop of a cardiac cycle Define stroke volume, end-diastolic ventricular volume, end-systolic ventricular volume, ejection fraction, and give the normal values under resting conditions Describe heart sounds Describe cardiac murmurs Events of the Cardiac Cycle Left ventricular pressure- volume loop  End diastolic ventricular volume is the volume of blood in each ventricle at the end of diastole. (End diastolic volume= 130 ml ) End systolic ventricular volume is the volume of blood that remains in each ventricle at the end of systole. (End systolic volume= 50 ml) Stroke Volume is the amount of blood ejected by each ventricle per stroke( or contraction). (Stroke volume = 70 - 90 ml) Ejection fraction is the percentage of the ventricular volume ejected with each stroke. (Ejection fraction = 55 to 65%) A relatively good index of ventricular function  Heart Sounds The heart sounds are produced by vibrations caused by the sudden closure of valves or due to myocardial contraction or due to vibration caused by rushing of blood into the chambers of the heart. Four heart sounds can be recorded via phonocardiography, but normally only two, the first and the second heart sounds, are audible through a stethoscope.  First Heart Sound Caused by the vibrations set up by the sudden closure of AV valves. Occurs at the beginning of ventricular systole. Low pitched( 25 – 45 Hz) Longer duration( 0.14 Sec) Can be heard in the mitral and tricuspid area, but better heard in mitral area.  Second Heart Sound Caused by the closure of Semilunar valves (Aortic and pulmonary valves) Occurs at the end of ventricular systole. High pitched( 50 Hz) Shorter duration( 0.11 sec) Auscultated in aortic and pulmonary areas.  Third and fourth Heart Sounds Third Heart Sound is caused by rushing of blood from atria into ventricle during rapid filling phase of diastole. Normally heard in most children and young adults. It may also be pathological. Fourth Heart Sound is caused by the atrial contraction, which occurs at the end of ventricular diastole Normally inaudible It indicates some resistance to ventricular filling, e.g. stiff ventricle in heart failure  Cardiac Murmurs - abnormal heart sound - occur in valvular diseases and septal defects  Two Basic Types of Valvular Diseases 1) valvular stenosis, a narrowing of the valve 2) valvular insufficiency (incompetence). A valve is unable to close fully Thus, there is some backflow (regurgitation) of blood.  Systolic Murmur of Aortic stenosis ▪ Blood is ejected from the left ventricle through a small fibrous opening of aortic valve. ▪ Blood pressure can be as high as 300 mmHg because of the resistance to ejection ▪ Systolic murmur ▪ Ventricle shows concentric hypertrophy Diastolic Murmur of Aortic Regurgitation Retrograde flow from aorta into ventricle Diastolic murmur Increase in EDV( preload) Increase in left ventricular and aortic systolic pressures Eccentric hypertrophy  Diastolic Murmur of Mitral stenosis Blood passes with difficulty through the stenosed mitral valve Emptying of left atrium into left ventricle is impaired Diastolic murmur Pressure and volume of left atrium is increased Systolic Murmur of Mitral Regurgitation Regurgitation of blood from LV to LA throughout the ventricular systole Atrial volume and pressures are increased Systolic murmur Ventricular volume and pressures are increased during diastole No pressure gradient between atrium and ventricle Altered states and changes in pressure and volume Exercise: Rise in ventricular pressure preload is increased only in heavy exercise Fall in ESV due to increased ejection fraction Heart failure: Fall in Ventricular systolic pressure, increased preload, loop shifts to right Aortic stenosis: Iincreased left ventricular systolic pressure Aortic insufficiency: Increased preload, increased left ventricular pressure  Learning Resources Text Book: Hall, John E. Guyton and Hall textbook of medical physiology 14th edition. 2021. Chapter 9, Page no. 113-126, https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3- s2.0-B9780323597128000096?scrollTo=%23hl0000271 Power-point presentation in the moodle www.gmu.ac.ae COLLEGE OF MEDICINE