Exit Exit Home Home BASIM ZWAIN LECTURE NOTES BASIM ZWAIN LECTURE NOTES Cardiac Cardiac Physiology Physiology Anatomy of the Anatomy of the heart heart Location Location : : Within mediastinun of medial cavity Within mediastinun of medial cavity of thorax, anterior to vertebral of thorax, anterior to vertebral column, posterior to sternum, column, posterior to sternum, superior to diaphragm (at rest), superior to diaphragm (at rest), superior margin (2nd rib), inferior superior margin (2nd rib), inferior margin (5th intercostal space), 60% margin (5th intercostal space), 60% of mass to the left of midline, base of mass to the left of midline, base (posterior surface) faces right (posterior surface) faces right shoulder, apex points inferiorly shoulder, apex points inferiorly toward left hip (contacts chest wall toward left hip (contacts chest wall Pericardium Pericardium 1. Fibrous pericardium: Tense 1. Fibrous pericardium: Tense connective tissue, protects heart, connective tissue, protects heart, anchors heart to surrounding anchors heart to surrounding tissues, prevents over filling tissues, prevents over filling 2. Serous pericardium: Parietal 2. Serous pericardium: Parietal layer (Internal surface of fibrous layer (Internal surface of fibrous pericardium), Visceral layer pericardium), Visceral layer (epicardium: part of heart wall) (epicardium: part of heart wall) 3. Pericardial cavity: Between 3. Pericardial cavity: Between Layers of the Layers of the heart heart 1. Three layers 1. Three layers a. Epicardium a. Epicardium b. Middle b. Middle myocardium myocardium c. Deep c. Deep endocardium endocardium Myocardium: Myocardium: a. Cardiac muscle arranged in a. Cardiac muscle arranged in circular bundles circular bundles b. Fibrous skeleton: Holds cardiac b. Fibrous skeleton: Holds cardiac muscle together muscle together Endocardium: Endocardium: a. Inner myocardial surface a. Inner myocardial surface b. Lines heart & connective tissues b. Lines heart & connective tissues of valves of valves Chambers of the Chambers of the Heart Heart Four chambers: Two atria & two Four chambers: Two atria & two ventricles, heart is divided ventricles, heart is divided longitudinally: Interatrial & longitudinally: Interatrial & interventr-icular septa, atria interventr-icular septa, atria receive returning blood (i.e., receive returning blood (i.e., veins), auricles are appendages to veins), auricles are appendages to increase atrial volume, fossa ovalis increase atrial volume, fossa ovalis is residual impression of fetal is residual impression of fetal foramen ovale foramen ovale Veins of right atrium: Veins of right atrium: a. Superior vena cava: Return flow a. Superior vena cava: Return flow from regions superior to diaphragm from regions superior to diaphragm b. Inferior vena cava: Return flow b. Inferior vena cava: Return flow from regions inferior to diaphragm from regions inferior to diaphragm c. Coronary sinus: Drain blood from c. Coronary sinus: Drain blood from myocardium myocardium Veins of left atrium Veins of left atrium Four pulmonary veins: Lungs back to Four pulmonary veins: Lungs back to heart, most of the posterior surface heart, most of the posterior surface of the heart of the heart Ventricles: Ventricles: 1. 1. Blood leaving the Blood leaving the heart, heart, 2. 2. Most of mass of heart, Most of mass of heart, right: anterior surface, left: right: anterior surface, left: inferior surface, inferior surface, 3. 3. Muscles: Muscles: Trabeculae carneae (cross-bars), Trabeculae carneae (cross-bars), papillary muscles (valve function, papillary muscles (valve function, project into heart cavity), project into heart cavity), 4. 4. Pulmonary trunk: Right ventricle, Pulmonary trunk: Right ventricle, routes blood to lungs, routes blood to lungs, 5. 5. Aorta: Aorta: Left ventricle, systemic circulation Left ventricle, systemic circulation Blood Flow Through the Blood Flow Through the Heart Heart Two circuits: Two circuits: 1. Pulmonary: 1. Pulmonary: Right Right side of the heart side of the heart a. Blood to lungs for gas exchange a. Blood to lungs for gas exchange b. Right ventricle to left atrium of b. Right ventricle to left atrium of the heart the heart c. Blood returns from body to right c. Blood returns from body to right atrium, low O2 concentration, atrium, low O2 concentration, relatively high CO2 concentration relatively high CO2 concentration d. Rt. Atrium to right ventricle d. Rt. Atrium to right ventricle e. Rt. Ventricle to lungs: Take O2 & e. Rt. Ventricle to lungs: Take O2 & give CO2, pulmonary arteries (away give CO2, pulmonary arteries (away from heart, not CO2) from heart, not CO2) 2. Systemic: 2. Systemic: left side of the heart left side of the heart a. Left atrium to left ventricle a. Left atrium to left ventricle b. Left ventricle into aorta b. Left ventricle into aorta c. Aorta to body through systemic c. Aorta to body through systemic arteries: Gases and nutrients are arteries: Gases and nutrients are exchanged exchanged d. Systemic veins to right atrium d. Systemic veins to right atrium 3. Work loads 3. Work loads a. Equal volumes a. Equal volumes b. Unequal work loads b. Unequal work loads c. Systemic: Five times as much c. Systemic: Five times as much resistance to blood flow, longer resistance to blood flow, longer route route d. Left ventricle is much larger & d. Left ventricle is much larger & thicker to do more work thicker to do more work Heart Heart Valves Valves A. A. Atrioventricular (AV) valves Atrioventricular (AV) valves 1 1 . . Valves at atrium-ventricular Valves at atrium-ventricular junction junction 2 2 . . Prevent backflow into atria Prevent backflow into atria 3 3 . . Closed during ventricular Closed during ventricular contraction (systole) contraction (systole) B. B. Right AV valve: tricuspid: Three Right AV valve: tricuspid: Three cusps (reinforced endocardium) cusps (reinforced endocardium) C. C. Left AV valve:Bicuspid:Mitral Left AV valve:Bicuspid:Mitral valve:Two cusps valve:Two cusps D. D. Chordae tendineae (heart Chordae tendineae (heart strings): Collagen cords attached to strings): Collagen cords attached to cusps, anchor cusps to papillary cusps, anchor cusps to papillary muscles during ventricular muscles during ventricular contraction, intraventr-icular contraction, intraventr-icular pressure rises forces blood against pressure rises forces blood against valve flaps, chordae tendinea anchor valve flaps, chordae tendinea anchor flaps in closed postion flaps in closed postion E. E. Semilunar (SL) valves: Two: Semilunar (SL) valves: Two: Aortic Aortic : Between left ventricle & : Between left ventricle & aorta & aorta & pulmonary pulmonary :Between right :Between right ventricle & pulmonary trunk. Open ventricle & pulmonary trunk. Open during ventr-icular contraction during ventr-icular contraction (systole): Intraventricular press- (systole): Intraventricular press- ure exceeds BP in aorta & pulmonary ure exceeds BP in aorta & pulmonary trunk. Three crescent shaped cusps trunk. Three crescent shaped cusps open against arterial walls open against arterial walls . . F. F. No valves between atria & venae No valves between atria & venae cavae & pulm-onary veins . Atrial cavae & pulm-onary veins . Atrial Blood Flow to the Blood Flow to the Heart Heart Heart requires its own circulatory Heart requires its own circulatory system. Myocar-dium is too thick to system. Myocar-dium is too thick to permit diffusion. Coronary cir- permit diffusion. Coronary cir- culation: Arterial supply: culation: Arterial supply: Right & Right & left coronary arteries left coronary arteries (arise at (arise at base of aorta). base of aorta). Left Left : (supplies left : (supplies left side of heart by marginal branches: side of heart by marginal branches: anterior inter-ventricular & anterior inter-ventricular & circumflex arteries). circumflex arteries). Right: Right: (supplies right side of heart: (supplies right side of heart: Marginal & posterior interven- Marginal & posterior interven- Cardiac veins: Cardiac veins: Follow course of Follow course of coronary arteries, join to form coronary arteries, join to form coronary sinus to empty into right coronary sinus to empty into right atrium. Tributaries: Great, middle & atrium. Tributaries: Great, middle & small cardiac veins. small cardiac veins. Anterior Anterior cardiac veins empty directly into cardiac veins empty directly into right atrium. right atrium. Patholo Patholo gy gy Angina pectoris Angina pectoris : Temporary deficient : Temporary deficient blood flow to myocardium, thoracic blood flow to myocardium, thoracic pain is symptom pain is symptom Myocardial infarction (MI) Myocardial infarction (MI) : Heart : Heart attack, Cardiac cells are amitotic, attack, Cardiac cells are amitotic, O2 deficiency causes necrosis (cell O2 deficiency causes necrosis (cell death), dead cells are replaced by death), dead cells are replaced by noncontra-ctile scar tissue. noncontra-ctile scar tissue. Cardiac Cardiac Muscle Muscle Characteristics Characteristics 1. Branched, short, and 1. Branched, short, and interconnected fibers interconnected fibers 2. Striated 2. Striated 3. Cardiac muscle fibers are 3. Cardiac muscle fibers are functionally connected functionally connected (intercalated discs, desmosomes, (intercalated discs, desmosomes, electrical coupling via gap electrical coupling via gap junctions) junctions) 4. Functional syncytium: Entire 4. Functional syncytium: Entire myocardium acts as a single unit myocardium acts as a single unit Contraction Contraction 1. All cardiac muscle cells contract 1. All cardiac muscle cells contract as a single unit as a single unit 2. Self-excitable ( 2. Self-excitable ( i.e., i.e., autorhytmic): Initiate APs, autorhytmic): Initiate APs, independent of nervous innervation independent of nervous innervation 3. Long refractory period: No 3. Long refractory period: No tetanic contractions tetanic contractions Autorhythmic fibers: Pace maker Autorhythmic fibers: Pace maker cells: 1% of heart muscle, cells: 1% of heart muscle, depolarize spontaneously depolarize spontaneously Contractile muscle fibers: Contractile muscle fibers: Depolarize in response to pacemaker Depolarize in response to pacemaker cell activities cell activities Heart Heart Physiology Physiology Intrinsic conduction system: Intrinsic conduction system: Noncontractile card-iac cells that Noncontractile card-iac cells that initiate & distribute impulses from initiate & distribute impulses from atria to ventricles. Autorhythmic, atria to ventricles. Autorhythmic, unstable RMP: Drift towards unstable RMP: Drift towards threshold. Pacemaker potentials: threshold. Pacemaker potentials: Membrane potential changes Membrane potential changes spontaneously spontaneously Events Events : Na+ influx (slow) offset by : Na+ influx (slow) offset by K K + efflux (slow), K efflux (slow), K + permeability permeability gradually decreases, Influx of Na gradually decreases, Influx of Na + + depolarizes cardiac cells, depolarizes cardiac cells, Depolarization opens fast Ca Depolarization opens fast Ca 2+ 2+ channels, Ca channels, Ca 2+ 2+ influx from ECS causes influx from ECS causes rising phase of AP, Repolarization rising phase of AP, Repolarization increases K increases K + permeab-ility (cardiac permeab-ility (cardiac cells repolarize), K cells repolarize), K + channels channels inactivate, Cycle starts again inactivate, Cycle starts again Location of autorhythmic cells Location of autorhythmic cells 1. 1. Sinoatrial (SA) node: Pacemaker: Sinoatrial (SA) node: Pacemaker: Fastest rate of depolarization, Fastest rate of depolarization, characteristic (sinus) rhythm. characteristic (sinus) rhythm. Located in right atrial wall, after Located in right atrial wall, after depolarization is initiated, depolarization is initiated, depolarization wave sweeps via gap depolarization wave sweeps via gap junctions throughout atria junctions throughout atria 2. 2. Atrioventricular (AV) node: Atrioventricular (AV) node: Depolarization wave initiated by SA Depolarization wave initiated by SA node reaches AV node, AV node is node reaches AV node, AV node is located in interatrial septum near located in interatrial septum near tricuspid valve, dia. of fibers is tricuspid valve, dia. of fibers is smaller (slows impulse conduction smaller (slows impulse conduction ‘0.1 s’ & permits completion of ‘0.1 s’ & permits completion of atrial contraction), impulse passes atrial contraction), impulse passes to bundle of His to bundle of His 3. 3. Atrioventricular bundle (of His): Atrioventricular bundle (of His): Functional passage of impulse from Functional passage of impulse from atria to ventricles (no gap atria to ventricles (no gap junctions between cells in atria & junctions between cells in atria & ventricles), Located in inferior ventricles), Located in inferior interatrial septum, very short interatrial septum, very short (branches to form bundle branches) (branches to form bundle branches) 4. 4. Bundle branches: Course Bundle branches: Course interventricular septum toward apex interventricular septum toward apex of heart of heart 5. 5. Purkinje fibers: Reach apex then Purkinje fibers: Reach apex then branch super-iorly into ventricular branch super-iorly into ventricular walls, impulses in fibers moves walls, impulses in fibers moves faster than cell to cell contact faster than cell to cell contact (ensures greater pumping efficacy) (ensures greater pumping efficacy) Pathology of Intrinsic Pathology of Intrinsic Conductance System Conductance System Arrhythmias: Uncoordinated Arrhythmias: Uncoordinated contractions B. Fibrillation: Rapid, contractions B. Fibrillation: Rapid, irregular contractions irregular contractions Ectopic focus: Excitable tissue Ectopic focus: Excitable tissue other than SA node controls heart other than SA node controls heart contractions contractions Heart block: Damage to AV node: Heart block: Damage to AV node: Impulse cannot reach ventricles Impulse cannot reach ventricles Extrinsic Control of Extrinsic Control of the Heart the Heart Brain-based control Brain-based control 1. Cardioaccelatory center in 1. Cardioaccelatory center in medulla, sympathetic NS control, medulla, sympathetic NS control, innervate SA and AV nodes innervate SA and AV nodes 2.Cardioinhibitory center, X nerve, 2.Cardioinhibitory center, X nerve, parasympathe-tic system, innervate parasympathe-tic system, innervate SA & AV nodes, slows HR SA & AV nodes, slows HR Electrocardiogr Electrocardiogr aphy aphy Electrical changes during heart Electrical changes during heart activity (ECG): activity (ECG): Deflection waves Deflection waves 1. 1. P wave: Depolarization moving P wave: Depolarization moving from SA node through atria from SA node through atria 2. 2. QRS complex: Ventricular QRS complex: Ventricular depolarization: Precedes contraction depolarization: Precedes contraction 3. 3. T wave: Ventr. repolarization, T wave: Ventr. repolarization, occurs slower than depolarization: occurs slower than depolarization: more spread out than QRS more spread out than QRS Intervals Intervals 1. 1. P-R: Interval from beginning of P-R: Interval from beginning of atrial excitation &ventricular atrial excitation &ventricular excitation, (includes: atrial excitation, (includes: atrial depolariz-ation & contraction, depolariz-ation & contraction, passage of impulse through intrinsic passage of impulse through intrinsic conduction system), lasts 0.16 s conduction system), lasts 0.16 s 2. 2. Q-T: Ventricular depolarization Q-T: Ventricular depolarization through repola-rization, includes: through repola-rization, includes: time of ventricular contraction time of ventricular contraction Mechanical Events during Heart Mechanical Events during Heart Contraction Contraction Cardiac cycle Cardiac cycle Systole (contraction) & diastole Systole (contraction) & diastole (relaxation), Length: Total 0.8 s, (relaxation), Length: Total 0.8 s, atrial systole 0.1 s, ventricular atrial systole 0.1 s, ventricular systole 0.3 s & quiescent period 0.4 systole 0.3 s & quiescent period 0.4 s s Events Events 1. 1. Start point: Atria & ventricles Start point: Atria & ventricles are relaxed (mid-to-late diastole) are relaxed (mid-to-late diastole) 2. 2. Ventricular filling: Mid-to-late Ventricular filling: Mid-to-late diastole, AV valves are open, diastole, AV valves are open, semilunar valves are closed, vent- semilunar valves are closed, vent- ricles begin to fill (70% occurs ricles begin to fill (70% occurs prior to atrial cont-raction), prior to atrial cont-raction), atrial systole (atria contract atrial systole (atria contract “preceded by P wave”, increased “preceded by P wave”, increased atrial pressure propels Bd from atrial pressure propels Bd from 3. 3. Ventricular systole: As Ventricular systole: As contraction begins, intra- contraction begins, intra- ventricular BP increase(AV valves ventricular BP increase(AV valves close, semilunar valves close, semilunar valves closed),isovolumetric contraction closed),isovolumetric contraction phase“vol-ume constant” (BP in phase“vol-ume constant” (BP in aorta&pulm. trunk exceeds aorta&pulm. trunk exceeds intraventricular pressure, pr. in intraventricular pressure, pr. in ven. increases without volume ven. increases without volume changing), ven. ejection phase changing), ven. ejection phase (intraventr. pressure exceeds (intraventr. pressure exceeds 4. 4. Isovolumetric relaxation: Occurs Isovolumetric relaxation: Occurs during early diastole, T wave, during early diastole, T wave, ventricles relax, intraventricular ventricles relax, intraventricular pressure drops, Bd in vessels pressure drops, Bd in vessels outside heart begins to flow back outside heart begins to flow back into ventricles (semilunar valves into ventricles (semilunar valves close, aortic pr. Increases close, aortic pr. Increases “dicrotic notch”), AV valves still “dicrotic notch”), AV valves still closed (isovolumetric relaxation) closed (isovolumetric relaxation) 5. 5. AV valves open when pr. in atria AV valves open when pr. in atria exceeds pr. against AV valves exceeds pr. against AV valves