Cardiovascular Physiology Lecture Notes - Fall 2024

CARDIOVASCULAR PHYSIOLOGY 2. The cardiac cycle Andre Azevedo, DVM, MSc Assistant Professor of Veterinary Physiology [email protected] Learning objectives for this lecture Describe all phases of the cardiac cycle Describe...

CARDIOVASCULAR PHYSIOLOGY 2. The cardiac cycle Andre Azevedo, DVM, MSc Assistant Professor of Veterinary Physiology [email protected] Learning objectives for this lecture Describe all phases of the cardiac cycle Describe the functioning of heart valves during cardiac cycle Blood flow Terminology SYSTOLE Contraction and emptying DIASTOLE Relaxation and filling CARDIAC OUTPUT Is the total volume of blood ejected by the heart per minute STROKE VOLUME The volume of blood ejected by the ventricle on each beat Contract Relax  The cardiac cycle All the events that occur from the beginning of one heartbeat to the beginning of the next one Each cardiac cycle is initiated by spontaneous generation of an action potential in the sinus node (SA) The action potential travels from the SA node, through the atria and then through the AV node into the ventricles There is a delay during the passage of the cardiac impulse from the atria into the ventricle The cardiac cycle The cardiac cycle consists of a period of relaxation called DIASTOLE during which the heart fills with blood This is followed by a period of contraction called SYSTOLE The total duration of a cardiac cycle, including systole and diastole, is the reciprocal of the heart rate If the HR is 80 beats per minute, the duration is 1/80 (0.0125 minutes per beat)  The cardiac cycle PHASES OF THE CARDIAC CYCLE: ATRIAL SYSTOLE ISOVOLUMETRIC CONTRACTION VENTRICULAR SYSTOLE VENTRICULAR EJECTION ISOVOLUMETRIC RELAXATION RAPID VENTRICULAR FILLING VENTRICULAR DIASTASIS (Reduced ventricular filling) DIASTOLE (Including atrial systole) The atrial diastole occurs during ATRIAL SYSTOLE ventricular systole and 2/3 of the ventricular diastole ISOVOLUMETRIC CONTRACTION The diastole represents most of... (and so on) the cardiac cycle  Cardiac cycle - Rapid ventricular filling The atria function as a primer pump for the ventricles Blood flows continually from the great veins into the atria - AV valves are open 80% of the blood flows directly through the atria into the ventricles BEFORE THE ATRIA CONTRACT PIT into ventricle SA Node fine Systole Atrium  The ventricles are able to Cardiac cycle - Atrial systole pump more blood than is required by the resting body. If atria fail to function, the Atrial systole forces blood into the ventricles ventricles continue to work (with the 80% filling from the ventricular filling Atrial contraction causes additional 20% filling of the ventricles phase). Clinical signs can be noticed usually after exercise.  0 0 Cardiac cycle - Isovolumetric contraction FEW In a fraction of a second the pressure then will be high The outflow of blood from the ventricles during SYSTOLE begins enough to open semilunar with the ISOVOLUMETRIC (ISOMETRIC) CONTRACTION valves (against the pressure in the aorta and pulmonary artery) As ventricular contraction begins, the ventricular pressure rises No emptying is occurring during abruptly need blood to this phase - No change in CAUSES A-V VALVES TO CLOSE (pressure > 80 mmHg) volume (ISOVOLUMETRIC) flow in passively Cardiac muscle tension is increasing with little or no Fressure shortening of the muscle fibers FIRST PART of ventricular systole (1/2) values prevent backflow due to  bytafaitycethyes.ae A-V Valves The A-V VALVES prevent backflow of blood from the ventricles to the atria during SYSTOLE Valves open and close passively OPEN when a forward pressure gradient forces blood in the forward direction CLOSE when a backward pressure gradient pushes blood backward vk.ie intt.Yren A-V Valves WHEN A-V VALVES CLOSE, WE HEAR THE FIRST HEART SOUND (S1) (Long lasting: Lubb)  A-V Valves A-V VALVES are attached to the PAPILLARY MUSCLES by the CHORDA TENDINEA They DO NOT help the valves to close! They pull the vanes of the valves inward toward the ventricles during systole To prevent their bulging too far backward toward the atria CHORDA TENDINEA RUPTURE OR PAPILLARY MUSCLE PARALYSIS CAUSES SEVERE OR LETHAL CARDIAC INCAPACITY  Cardiac cycle – Ventricular ejection When the pressure is high enough, the semilunar valves open and blood begin to be ejected out of the ventricles 4090 Only 60% of the total volume is ejected – EJECTION FRACTION stolen 70% of the ejected blood flows during the first third of ejection – RAPID EJECTION the 30% is ejected during the next two-thirds – SLOW EJECTION SECOND PART of ventricular systole (2/2)  Cardiac cycle – Isovolumetric relaxation At the end of the systole, ventricular relaxation (DIASTOLE) begins suddenly Allowing both right and left intraventricular pressures to decrease rapidly This causes the closing of the semilunar valves AV valves remain closed prey flow Phebaft sound The volume does not change: ISOVOLUMETRIC First part of VENTRICULAR DIASTOLE (1/4)  more rigid SEMILUNAR valves no chordae ten or pap muscles The SEMILUNAR VALVES prevent backflow of blood from the aorta and pulmonary arteries into the ventricles during DIASTOLE Function quite different from the A-V valves Specially constructed to resist a lot of physical stress support No support by the chordae tendineae more Smaller openings – rapid ejection pressure Higher pressures in the arteries during systole – snap closed SEMILUNAR valves WHEN SEMILUNARS CLOSE, WE HEAR THE SECOND HEART SOUND (S2) (Rapid snap: Dub)  Cardiac cycle - Rapid ventricular filling As soon as systole is over and ventricular pressure falls, the pressure inside of the atria forces the A-V valves to open Blood flows rapidly into the ventricles Second part of VENTRICULAR PHASE OF RAPID FILLING OF THE VENTRICLES (80%) DIASTOLE (2/4) lasts for about 1/3 of all the ventricular diastole  Cardiac cycle - Diastasis Entering the last third of the DIASTOLE only a small amount of blood flows into the ventricles – Diastasis, or slow ventricular filling Blood that continues to empty into the atria from the veins and passes through the atria directly into the ventricles Persists until the SA node initiates an AP leading to atrial contraction again Third part of VENTRICULAR DIASTOLE (3/4)  Cardiac cycle - Atrial systole Atrial systole forces blood into the ventricles Atrial contraction causes additional 20% filling of the ventricles Fourth part of VENTRICULAR DIASTOLE (4/4)  occursalastatrick The cardiac cycle Ei CARDIAC CYCLE VIDEO: https://www.youtube.com/watch?v=qmpd82mpVO4 1 ain valuessed 60 ted mess The cardiac cycle During diastole, normal filling of the ventricles increases the volume of each ventricle This volume is called END DIASTOLIC VOLUME The fraction of this volume that is ejected is the EJECTION FRACTION (60%) 4090 of blood stays During systole, the ventricles eject and the volume decrease The total volume of blood ejected by the ventricle on each beat is called STROKE VOLUME ML ejection fraction 60mL The remaining volume in each ventricle is called END SYSTOLIC VOLUME CARDIAC OUTPUT is the total volume ejected by the heart per minute stroke volume X hr min  I The cardiac cycle ejected  The cardiac cycle faster When the heart rate increases, the duration of each cardiac cycle decreases Including the contraction and relaxation phases The great percentage of decreasing occurs during diastole The heart beating at a very fast rate does not remain relaxed long enough to allow complete filling of the cardiac chambers before next contraction Stroke volume amoiitmuh Wcontract most cardiac hardstone if draftheart beforefilled time of receives blood The Wiggers’ Diagram Carl J. Wiggers (1883-1963) American Physiologist Interactive cardiac cycle https://www.humanbiomedia.org/cardiac-cycle-simulation/ Questions? Review questions Why are the ventricles partially filled with blood at the beginning of the cardiac cycle? A. Because the blood flows passively and immediately from the atria to the ventricles B. Because the ventricles receive blood directly from aorta and pulmonary vein C. Because the ventricles receive blood directly from vena cava and pulmonary artery Which valves will allow the flow of blood during ventricular filling? A. Mitral and Aortic B. Mitral and tricuspid C. Tricuspid and Aortic D. Tricuspid and Pulmonic The first heart sound is a consequence of: A. Opening of the A-V valves B. Closing of the A-V valves C. Opening of the semilunar valves D. Closing of the semilunar valves Which phase of the cardiac cycle occurs immediately after the opening of the semilunar valves? A. Diastasis B. Atrial systole C. Rapid ventricular filling D. Ventricular ejection E. Isovolumic relaxation F. Isovolumic contraction What is the accurate formula of stroke volume? A. EDV+ESV B. EDV*ESV C. ESV-EDV D. none of the above About the cardiac cycle: A. During joint diastole, the atria contract B. During atrial systole, the bicuspid and tricuspid valves are open C. During ventricular systole, the atria contract D. During atrial diastole, the semilunar valves are closed Happy studying!