Cardiovascular+Physiology+L02+%28cardiac+cycle%29+-+Summer+2024.pdf

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 cy...

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 wr 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  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 was 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 g Last yell  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 Atrial contraction causes additional 20% filling of the ventricles the ventricular filling phase). Clinical signs can be noticed usually after exercise.  Cardiac cycle - Isovolumetric contraction 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 abruptly No emptying is occurring during this phase - No change in tyke CAUSES A-V VALVES TO CLOSE (pressure > 80 mmHg) volume (ISOVOLUMETRIC) Cardiac muscle tension is increasing with little or no shortening of the muscle fibers  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 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 CE 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 Only 60% of the total volume is ejected – EJECTION FRACTION 70% of the ejected blood flows during the first third of ejection – RAPID EJECTION 30% is ejected during the next two-thirds – SLOW EJECTION is Whatever thepressure te make willopen high the othersite to  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 The volume does not change: ISOVOLUMETRIC First part of VENTRICULAR DIASTOLE  SEMILUNAR valves 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 No support by the chordae tendineae Smaller openings – rapid ejection 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 lasts for about 1/3 of the ventricular diastole  Cardiac cycle - Diastasis In the MID PORTION OF DIASTOLE only a small ammount of blood flows into the ventricles 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  Cardiac cycle - Atrial systole Atrial systole forces blood into the ventricles Atrial contraction causes additional 20% filling of the ventricles f In Fourth part of VENTRICULAR DIASTOLE  The cardiac cycle CARDIAC CYCLE VIDEO: https://www.youtube.com/watch?v=qmpd82mpVO4 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%) 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 The remaining volume in each ventricle is called END SYSTOLIC VOLUME CARDIAC OUTPUT is the total volume ejected by the heart per minute The cardiac cycle v3 GEE  The cardiac cycle 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 The Wiggers’ Diagram Carl J. Wiggers (1883-1963) American Physiologist Questions?