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心臟生理學 Cardiac Physiology 生理學科 鍾文彬 助理教授 TEL: # 3183 E.mail: [email protected] 1 Overview of the Heart: 1. Structure of the heart and its components 2. Excitation of the heart (cardiac muscles) 3. Conducting pathways of action potentials 4. Cardiac cycle and Rhythm of the heart 5. Works and regulations of the heart 6. ECG 2 Circulation System Circulation 1. 2. 3. system consists of: Heart Blood vessels Blood Two separate circulation: 1. Systemic circulation 2. Pulmonary circulation 3 The heart is a dual pump 4 From Sherwood 2007 Course overview of the Heart: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart 6. ECG 5 From Sherwood 2007 6 Spread of Cardiac Excitation From Sherwood 2010 7 Action potential conduction and excitatory contraction of the Heart SA Node Conducting System of the Heart Interatrial pathway Internodal pathway Interatrial pathway AV node AV node Bundle of His SA node LA RA Purkinje system Ventricular Muscle Left branch of bundle of His Internodal pathway Right branch of bundle of His LV RV Purkinje fibers From Sherwood 2010 8 Thickness of Ventricle Walls Ventricular Wall thickness: R/L= 2:10 mm Work: R/L=1:7 Work of the heart? Cardiac output (L/min) From Sherwood 2010 9 Structure of Heart Valves Atrioventricular Fibrous tissue Four valves Left AV valve (bicuspid, mitral) Right AV valve (tricuspid) Aortic semilunar valve Pulmonary semilunar valve From Sherwood 2010 10 One-way Valves Valve opened When pressure is greater behind the valve, it opens. Valve closed When pressure is greater in front of the valve, it closes. From Sherwood 2010 11 Actions of AV and Semilunar valves 12 From Sherwood 2010 Characteristics of Myocardium 1. Automaticity 2. Excitability 3. Contractility 4. Conductivity 13 Course overview of the Heart: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart 6. ECG 14 Three Types of Myocardium Pacemaker cells (autorhythmic cells) Electrical conducting cells (1%) Contractile cells (99%) (pump cells) 15 How dose the rhythm of heart beat make up by Pacemaker? 心跳的節率是如何產生的? 16 The action potential of an autorhythmic pacemaker cell. SA node cell 1. Sodium ions “ leaking”in through the F-type [funny, sodium] channels PLUS calcium ions moving in through the T [transient, calcium] channels cause a threshold graded depolarization. 2. The rapid opening of voltagegated calcium channels is responsible for the rapid depolarization phase. 3. Reopening of potassium channels PLUS closing of calcium channels are responsible for the repolarization phase. 17 Electrical properties of cardiac auto-rhythmic pacemaker cells (3) 1. Threshold potential 2. Peacemaker potential 3. Action potential (1) (2) P: permeability From Sherwood 2010 18 Contractile Myocardium (Cardiac muscle) (Pump cardiac muscle) 收縮型心肌細胞(幫浦細胞)的 興奮(去極化)是如何產生的? 19 The action potential of a myocardial pumping cell. Contractile cell 1. The rapid opening of voltage-gated sodium channels is responsible for the rapid depolarization phase. 2. The prolonged “ plateau”of depolarization is due to the slow but prolonged opening of voltage-gated calcium channels PLUS closure of potassium channels. 3. Opening of potassium channels results in the repolarization phase. 20 Refractory period (RP): 心肌的不反應期 Prevention of cardiac muscle from tetanus contraction Absolute refractory period : 95% RP Relative refractory period : 5% RP 21 From Sherwood 2010 How does the rapid transduction of action potential from excited cell to its around (next) cells ? 心肌細胞的興奮是如何傳導/散佈到 周圍的細胞的? The Gap Junction between cells Presence of the Gap Junction: Yes: Cardiac & smooth muscle cells No: Skeletal muscle cells 22 Striated muscle Thin / Thick filaments Myofiber branches From Sherwood 2010 Intercalated disks Desmosomes: Resist stress Gap junctions: Contract as unit (Functional Syncytium) Gap junction 23 一大團心肌細胞如何產生一致性 的心肌興奮與縮收作用? 24 Functional Syncytium (功能之一致性) Upon fast action potential conductance through Gap Junctions, a mass of cardiac muscle simultaneously contracting 25 心肌細胞興奮如何產生 機械性的縮收作用? 26 How dose the action potential control the mechanical contraction of pump cardiac muscle? E-C coupling 27 E-C Coupling: Action potential Excitation-Contraction Coupling Contractile response 28 Calcium ions regulate the contraction of cardiac muscle Opening L-type Calcium channel about 95% of Ca2+ is from intracellular poor: SR CICR (Calcium-Induced Calcium Release) 29 Course overview of the Heart: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart 6. ECG 30 How dose the action potential conduct throughout the heart rapidly? Highway system 心肌細胞興奮如何快速 傳遍整個心房或心室? 31 Spread of Cardiac Excitation 32 Conducting System of the Heart Interatrial pathway SA Node AV node SA node LA RA Left branch of bundle of His Internodal pathway Internodal pathway Interatrial pathway AV node Bundle of His Purkinje system Ventricular Muscle Right branch of bundle of His LV RV From Sherwood 2010 Purkinje fibers 33 Dose the rhythmic action potential flow throughout a full heart at the same conducting velocity ? 心肌的電興奮傳導途徑的 傳導速率一樣嗎? 34 Transmission of the cardiac impulse Conductive Tissue Conduction Rate (m/s) SA node 0.05 Atrial pathway 1 AV node ( delay ) 0.05 His bundle 1 Purkinje fibers 4 Ventricular muscle 1 35 AV nodal delay Insulation: cause A & V contractions independently deceleration: Narrow down the wide of conducting route 36 Is SA node the “only one” pacemaker of the heart ? NO !! The frequency determination of the autorhythm of the heart Conductive tissues Action potential /min SA node 70-80 AV node 40-60 His Bundle & 20-40 Purkinje Fibers 20-40 37 How to determine the peacemaker of the heart? 該由誰帶領心肌的興奮頻 率呢?如何決定? 38 From Sherwood 2010 39 From Sherwood 2010 40 Cardiac Cycle 1. 腔室與大動脈之壓力變化? 2. 瓣膜開閉狀況? 41 Systole (ventricles) = 1 x isovolumetic contraction + 1 x ejection 等容積性縮收期 心室射血期 42 Diastole (ventricles) = 1 x isovolumetic relaxation + 1 x filling 等容積性舒張期 心室充血期 < > 43 Aortic pressure (mmHg) Left ventricular pressure (mmHg) Left atrial pressure (mmHg) Left ventricular volume (mL) Heart sound 44 From Sherwood 2010 Course overview of the Heart: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart Stroke volume, heart rate; Modulations by ANS, hormones, EDV 6. ECG 45 How can we evaluate the WORK a heart done or doing? Cardiac Output (CO) 46 Cardiac Output (CO) CO = SV x HR SV, stroke volume; HR, heart rate Average CO = 5 L/min at rest Average HR = 72 beat/min, at rest Average SV = 70 mL Average blood volume = 5.5 L 47 Controls of Cardiac Output CO HR Parasympathetic activity Sympathetic Activity & (epinephrine) SV EDV Venous return From Sherwood 2010 48 SV: 1. Intrinsic control: EDV, effecter of Frank-Starling Rule 2. Extrinsic control: Sympathetic stimuli: enhance myocardium contraction Epinephrine & norepinephrine: increase contraction force HR: extrinsic ANS control only • Sympathetic stimuli: increase HR • Parasympathetic stimuli: decrease HR 49 ANS Inputs to the Heart 50 The regulation of “SV” SV的調控因子 51 Sympathetic Effect on Cardiac Contraction Sympathetic nor-/epinephrine: •stronger contraction •more rapid of contraction •more rapid relaxation 52 Ventricular Volume and Stroke Volume 1. EDV, volume of blood in ventricle at end of diastole 2. ESV, volume of blood in ventricle at end of systole 3. SV = EDV - ESV 53 Sympathetic effects on SV EDV 175 ml EDV 135 ml SV ? SV,70 ml ESV 65 ml EDV 135 ml Sympathetic stimulation (B) SV, 100 ml SV, 140 ml Sympathetic stimulation (A) Sympathetic stimulation (A) ESV 35 ml ESV 35 ml 54 Frank-Starling Mechanism (Rule) EDV 175 ml EDV 135 ml SV= ? 70 ml ESV 65 ml 100 ml ESV 65 ml To increase the heart’ s SV: Fill it more fully with blood. The increased stretch of the ventricle will align its actin and myosin in a more optimal pattern of overlap. 55 Frank-Starling Mechanism (Rule) To further increase the SV: Fill it more fully with blood. Deliver sympathetic signals (norepinephrine and epinephrine); It will also relax more rapidly, allowing more time to refill. 56 Intrinsic and extrinsic controls of SV Stroke volume Extrinsic control Strength of cardiac contraction Intrinsic control Sympathetic activity (and epinephrine) EDV Intrinsic control Extrinsic control From Sherwood 2010 Venous return 57 The regulation of “HR” HR 的調控因子 58 Polarized potential: hyper-/ hypo-polarization HR regulations: ANS Pacemaker potential: in-/ de-creased slope parasympathetic stimulation sympathetic stimulation 59 From Sherwood 2010 Control of Cardiac Output CO HR Parasympathetic activity Sympathetic Activity & (epinephrine) SV EDV Venous return From Sherwood 2010 60 Course overview of the Heart: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart 6. ECG waves, intervals, segments 61 ElectroCardioGraph ECG, EKG 62 ECG ST interval 63 The SA node is the heart’ s pacemaker because it initiates each wave of excitation with atrial contraction. The Bundle of His and other parts of the conducting system deliver the excitation to the apex of the heart so that ventricular contraction occurs in an upward sweep. 64 ECG: bipolar leads Bipolar Leads: Lead I Lead II Lead III I III II I + III = II 65 ECG: unipolar leads aVR aVL Uni-polar Leads: Chest leads: V1, V2, V3, V4, V5, V6 Augmented Limb leads: aVR, aVL, aVF aVF 66 67 Significant criteria of ECG Three waves : P, QRS, T Two segments: PR, ST Four intervals: PR, QRS, ST, QT ST interval 0.04 s 0.1 mV 68 ECG: Two segments PR (AV node delay) End of atrial depolarization till beginning of ventricular depolarization ST End of ventricular depolarization till beginning of ventricular repolarization PR ST 69 ECG: Three obvious waves P Atrial depolarization QRS Ventricular depolarization T Ventricular repolarization QRS P T 70 ECG: Four intervals Interval Electrical Events PR Atrial depolarization and conduction of AP to AV node QRS Ventricular depolarization and atrial repolarization ST Ventricular depolization and Ventricular repolarization QT Ventricular depolarization plus ventricular repolarization 71 Electrical Activity Abnormalities in heart rate: 1. Tachycardia: HR>100 bpm 2. Bradycardia: HR<60 bpm NORMAL RATE AND RHYTHM ABNORMALITIES IN RATE From Sherwood 2007 Tachycardia 72 Electrical Activity Abnormalities in rhythm: 1.Rhythm: regularity of the ECG waves 2.Arrhythmia: any variation from the normal rhythm 73 Electrical Activity Atrial fibrillation: 1. Rapid, irregular, uncoordinated atrial depolarizations with no definite P waves 2. Irregular ventricular response 3. Pulse deficit 74 Electrical Activity Complete heart block 1. Complete atrial and ventricular dissociation 2. Atrial rate > ventricular rate (escape rhythm) Heart block 75 Electrical Activity Ventricular fibrillation: 1. Irregular with no detectable pattern or rhythm, serious and lethal arrhythmia 2. Irreversible brain damage: >4 mins Ventricular fibrillation From Sherwood 2007 76 Summary: 1. Structure of the heart and its components cardiac muscles, valves, pacemakers, conductive pathways 2. Excitation of the heart (cardiac muscles) excitation of pacemakers and contractile muscles 3. Conductive spread of the action potential speed and properties of the conductive pathways 4. Cardiac cycle and heart rhythm 5. Works and regulations of the heart 6. ECG and electrical Activity of the heart 77 References: 1. Sherwood: Human Physiology –from cells to systems, ed.7 2. Widmaier, Raff &.Strang: Vander’ s Human Physiology- the mechanisms of body function, ed.11 3. Fox: Human Physiology, ed.11 78