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Cardiovascular Physiology I: Physiology of the Heart & The Cardiac Cycle References: Seeley, R., Stephens, T., and Tate, P., Anatomy & Physiology. 8th ed. McGraw Hill Company Inc., (2008) Guyton, A., Hall, J., Textbook of Medical Physiology. 11th ed. WB Saunders Co. (2006) • Martini, F., Fundamentals of Anatomy & Physiology. 6th ed. Benjamin Cummings Inc (2003) Part I FUNCTIONS OF THE CARDIOVASCULAR SYSTEM Function of the CV System: Blood Transport Protection Regulation Function of the CV System: Heart Generating BP Blood routing Ensuring one-way blood flow Regulating blood supply Function of the CV System: Blood Vessels Carry blood Gas & nutrient exchange Transport BP regulation Direct blood flow Part II THE CARDIAC CYCLE Cardiac cycle Events occurring from the beginning of one heartbeat to the beginning of the next Consists of 2 periods as to the activity of the ventricles Cardiac Cycle Systole – period of contraction Isovolumetric contraction Ejection Diastole – period of relaxation Isovolumetric Relaxation Passive Ventricular filling Atrial Contraction Isovolumetric Contraction Ventricular contraction causing abrupt ↑ Po AV valves close Continuous contraction to overcome aortic & pulmonary arterial Po and open SL valves Ejection (L) ventricular Po reaches 80 mmHg & ® ventricular Po reached 8 mmHg • SL valves open, then close •70% ejected in the 1st 1/3 of the period: rapid ejection • 30% ejected in the next 2/3 of the period: slow ejection Isovolumetric Relaxation Ventricular relaxation causes rapid ↓ of intraventricular Po SL valves close d/t Po increase in the large arteries Further ↓ in intraventricular Po would cause opening of AV valve. Passive Filling ~75% of the blood from the great veins AV valves are open and semilunar valves closed ↑ intraventricular Po relative to the atrium would slow down filling: Diastasis Atrial Contraction Contraction of atria will eject the remaining 25% into the ventricles Ventricular Volumes Relative to Systolic and Diastolic contractions Volume of Blood in the Ventricle END-DIASTOLIC VOLUME STROKE VOLUME OUTPUT END SYSTOLIC VOLUME EJECTION FRACTION (110-120mL) (-70mL) What remains after systole (40-50mL) Usually 60% Pressure-Volume Relationships during the cardiac cycle Summary of Pressure Volume Relationships CARDIAC CYCLE TABLE SUMMARY.pdf Heart Valves Atrioventricular valves Prevent back flow of blood between ventricles and atria Semilunar valves Prevent back flow of blood between aorta (and pulmonary artery) and ventricles Heart Valves Papillary mm Pull on the cusps of the AV valves during systole Do not help valve closure Prevent bulging into the atria Heart Valves and Heart Sounds 1st heart sound: Lub closure of the AV valves Heard during systole Relatively low in pitch and long 2nd heart sound: Dup Closure of the SL valves Heard during diastole Rapid snap Shorter Heart Valves and Heart Sounds 3rd heart sound Mid-diastole Blood oscillation as it rushes from the aorta Weak rumbling sound 4th heart sound Atrial contraction Inrush of blood into the ventricles Low frequency sound Heart Valves and Abnormal Heart Sounds Murmurs: Abnormal Heart Sounds Valvular Stenosis: Opening is too small Valvular Regurgitation: Valve does not close completely Heart Valves and Abnormal Heart Sounds SL Valve AV Valve Regurgitation Diastole High pitch, swishing Systole High pitch, swishing Stenosis Systole Loud and harsh Diastole Weak and low frequency Part III CARDIAC ELECTROPHYSIOLOGY Let’s review! Cardiac Muscle Action Potential Cardiac Muscle Action Potential RMP of cardiac muscle: -90 mV Overshoots until ~+20 mV Phase 0: Rapid Depolarization opening of fast acting Na channels and slow acting Ca channels Fast Na channels immediately close Phase 1: Partial Repolarization Closed Na channels Partially repolarized d/t efflux of K Phase 2: Plateau Full opening of Ca channels counteracting K efflux Ca influx is involved in excitationcontraction Phase 3: Rapid Repolarization Gradual in K efflux Ca channels close Phase 4: Return to Resting Membrane Potential Cardiac Muscle ExcitationContraction Coupling Phase 2 Action potential spreads to interior via T-tubules Excitation of T-tubules promote Ca release from sarcoplasmic reticulum adding to Ca influx Actin-Myosin binding Cardiac Muscle Excitation – Contraction Coupling Phase 3 Ca influx is cut Ca ions are pumped back into the sarcoplasmic reticulum relaxation Part IV CONDUCTING SYSTEM OF THE HEART Conducting System of the Heart Sinoatrial Node Superior posterolateral wall of ® atrium, below and lateral to SVC opening Non-contractile Self excitatory Conducting System of the Heart Sinoatrial node RMP of -55 to -60 mV Firing level of -40 mV Depolarization only by opening of slow Na-Ca channels Conducting System of the Heart Conducting System of the Heart Internodal pathways Anterior Tract of Bachman Middle Tract of Wenckebach Posterior Tract of Thorel Impulses converge on the Atrioventricular node Conducting System of the Heart Atrioventricular Node Posterior wall of ® atrium, adjacent to coronary sinus Delay of impulse conduction allows full contraction of atrium Conducting System of the Heart Bundle of His Located on either side of interventricular septum Conducts impulses from atria to ventricles Conducting System of the Heart Purkinje Fibers Conducting tissues of the ventricles Conducting System of the Heart Why is the SA node the pacemaker of the heart? Frequency of impulse production is faster Structure Impulses/min SA 70-80 AV 40-60 Purkinje Fibers 15-40 Greater rhythmicity depresses other potential pacemakers The Electrocardiogram a graphic representation of the electrical activity generated by the atria and ventricles. The Electrocardiogram Strip Small block = 1mm TIME (x-axis) Small block = 0.04 second Bold block = 0.20 second The Electrocardiogram Strip AMPLITUDE (yaxis) Small block = 0.1 mV Rate: 22mm/second The Electrocardiogram: Einthoven’s Triangle The Electrocardiogram: Precordial Leads The Electrocardiogram When a positive wave of depolarization within the heart cells moves toward a positive skin electrode, there is an upward deflection on the ECG The Electrocardiogram The Electrocardiogram The Electrocardiogram P-WAVE The first positive deflection on the ECG. Atrial depolarization The Electrocardiogram PR INTERVAL time required for the impulse to travel from the SA node through the conduction system to the Purkinje fibers The Electrocardiogram QRS Complex Ventricular depolarization Atrial repolarization is not seen The Electrocardiogram ST SEGMENT represents the beginning of ventricular muscle repolarization The Electrocardiogram T WAVE representing ventricular repolarization The Electrocardiogram Interpreting the Electrocardiogram Heart Rate # of QRS complexes is a 6 second strip x 10 # of QRS complexes in a 3 second strip x 20 Interpreting the Electrocardiogram Heart Rate = 300 / # of big squares between 2 QRS complex Triplicate system 300 – 150 – 100 – 75 – 60 - 50 Anatomic Representation in the ECG Inferior wall II, III, AVF Anterior Wall V1, V2, V3, V4 Lateral Wall I, AVL, V5, V6 Superior Wall AVR Part V CARDIAC REGULATION Intrinsic Cardiac Regulation Largely determined by Preload The degree to which the ventricular walls are stretched at the end of diastole Determined by venous return (amount of blood returning to the heart) Intrinsic Cardiac Regulation Starling’s Law of the Heart Relationship between preload and force of cardiac contraction preload = contraction force = SV Intrinsic Cardiac Regulation Starling’s Law of the Heart Major influence on stroke volume (amount of blood ejected by the heart every cardiac cycle) and cardiac output (amount of blood ejected by the heart in one minute) CO = SV x HR = 5* L/min Stroke Volume and Inotropic regulation Inotropic effects Force of Contraction ↑ inotropic effect = ↑ force of contraction = ↑ amount of blood ejected Intrinsic Cardiac Regulation Intrinsic Cardiac Regulation Afterload pressure against which the ventricles must pump blood afterload= work of cardiac mm = SV Extrinsic Cardiac Regulation Hormonal Catecholamines Neuronal Autonomic nervous system Cardiorespiratory centers of the medulla Extrinsic Cardiac Regulation Other control mechanisms Barorecpetor and chemoreceptor Temperature Electrolyte levels (K, Na, Ca) Extrinsic Cardiac Regulation: Neuronal influences Sympathetic Cardioaccleratory center stimulation = HR and contractility (SV) Extrinsic Cardiac Regulation: Neuronal Influences Parasympathetic Cardioinhibitory center stimulation = HR and contractility (SV) Extrinsic Cardiac Regulation: Hormonal influences Catecholamines Norepinephrine and Epinephrine : sympathetic stimulation Extrinsic Cardiac Regulation: Reflex Mechanisms Baroreceptor & Chemoreceptor reflex Extrinsic Cardiac Regulation: Other Control Mechanisms Na & Ca levels Direct relation with HR K levels Inverse relation with HR Extrinsic Cardiac Regulation: Other Control Mechanisms Temperature 1 oC = 4 bpm Coronary blood flow coronary blood flow = contractility Extrinsic Cardiac Regulation: other Control Mechanisms Bainbridge reflex relationship of venous return with heart rate VR = HR Heart Rate and Chronotropic Regulation Chronotropic effects Speed of contraction ↑ chronotropic effects = ↑ speed of contraction = ↑ amount of blood ejected Ejection Fraction and Heart Function Determines how much of the blood entering the ventricles is pumped (End-Diastolic ventricular Volume - Endsystolic ventricular volume) End diastolic ventricular volume (N) 63-77% for males and 55-75% for females The Hypoeffective Heart Inhibition of nervous excitation AbN heart rhythm Valvular heart disease Hypertension Cardiac anoxia Myocardial damage THE END