Cardiovascular System 2 PDF

Cardiovascular System 2  Objectives Basic cardiac anatomy Skeletal Muscle vs Cardiac Muscle Correlate electrical activity with ECG Cardiac cycle Cardiac output and regulation Differences - Skeletal and Cardiac Muscle  Cardiac muscle Two kinds of myocytes Cont...

Cardiovascular System 2  Objectives Basic cardiac anatomy Skeletal Muscle vs Cardiac Muscle Correlate electrical activity with ECG Cardiac cycle Cardiac output and regulation Differences - Skeletal and Cardiac Muscle  Cardiac muscle Two kinds of myocytes Contractile cells: responsible for contraction Pacemaker cells: noncontractile cells that spontaneously depolarize – Initiate depolarization of entire heart – Do not need nervous system stimulation, in contrast to skeletal muscle fibers Intrinsic cardiac conduction system Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway 2 The impulses Left atrium pause (0.1 s) at the atrioventricular (AV) node. 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje fibers) to the ventricles. 4 The bundle branches conduct the impulses Inter- through the ventricular interventricular septum. septum 5 The subendocardial conducting network depolarizes the contractile cells of both ventricles. Action potential Tetanic contractions cannot occur in cardiac muscles Cardiac muscle fibers have longer absolute refractory period than skeletal muscle fibers Benefit of longer AP and contraction – Sustained contraction ensures efficient ejection of blood – Longer refractory period prevents tetanic contractions Intrinsic cardiac conduction system Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway 2 The impulses Left atrium pause (0.1 s) at the atrioventricular (AV) node. 3 The Subendocardial atrioventricular conducting (AV) bundle network connects the atria (Purkinje fibers) to the ventricles. 4 The bundle branches conduct the impulses Inter- through the ventricular interventricular septum. septum 5 The subendocardial conducting network depolarizes the contractile cells of both ventricles.  Pacemaker sets Heart Rate SA node firing rate: 75/min AV node firing rate: 40-60/min ventricular cells firing rate: 30/min SA node firing rate - sets Heart Rate If SA node defective? Implant mechanical pacemaker!  Electrocardiogram- ECG Surface electrodes: record electrical activity heart ECG: electrical activity of whole heart, not of single cell ECG: not a single action potential- composite of all electrical potentials generated by all cells of heart at any given moment Signal very weak by time it gets to skin Good conductor of electricity to skin surface 12 Lead ECG  ECG A lead is a tracing of the electrical activity of the heart between two electrodes Each lead provides an electrical “photograph” of the heart’s activity from a different angle Together, the 12 leads, or “photographs,” facilitate a thorough interpretation of the heart’s activity Limb electrodes Chest electrodes  QRS complex Ventricular depolarization Ventricular repolarization Atrial depolarization T P P-R S-T Interval Segment Q-T Interval 0 0.2 0.4 0.8 0.6 PR interval: 0.2 sec  SA node R P T Q S 1 Atrial depolarization, initiated by the SA node, causes the P wave. R AV node P T The sequence of depolarization Q S and 2 With atrial depolarization complete, the impulse is delayed at the AV node. R repolarization of the heart P T related to the deflection waves Q S of an ECG tracing 3 Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. R P T Q S 4 Ventricular depolarization is complete. R P T Q S 5 Ventricular repolarization begins at apex, causing the T wave. R P T Q S Depolarization 6 Ventricular repolarization is complete. Repolarization  ECG 1. Heart Rate 2. Rhythm 3. Abnormalities – Waves (P, QRS, T) – Segments (PR, ST) – Intervals (wave‐ segment combinations: PR, QT)  Rate Rule of 300 - Divide 300 by the number of big boxes between each QRS = rate Number of big Rate boxes 1 300 2 150 3 100 4 75 5 60 6 50  Rate HR : 60 -100/min is normal HR < 60 = bradycardia HR > 100 = tachycardia  Rhythm Sinus – Originating from SA node – P wave before every QRS – P wave in same direction as QRS Heart Blocks – 1st degree – 2nd degree (2 types) – 3rd degree Normal sinus rhythm First degree Heart Block PR interval >0.2 sec Second degree Heart Block Second degree Heart Block Mobitz Type 2, Third degree Heart Block Atrial Fibrillation Ventricular Tachycardia  Ventricular fibrillation Electrical activity is disorganized. Action potentials occur randomly throughout the ventricles. Results in chaotic, grossly abnormal ECG deflections. Seen in acute heart attack.  Mechanical Events of Heart Systole: Period of heart contraction Diastole: Period of heart relaxation Cardiac cycle: blood flow through heart during one complete heartbeat – Atrial systole and diastole are followed by ventricular systole and diastole – Cycle represents series of pressure and blood volume changes – Mechanical events follow electrical events seen on ECG Cardiac cycle 1. Ventricular filling (Mid-late diastole) 2. Ventricular systole (Systolic phase) 3. Isovolumetric relaxation (Early Diastole)  Measure of Cardiac Performance Stroke volume (SV): blood pumped per ventricular contraction (70ml in adult, at rest) SV = End diastolic volume (EDV) ‐ End systolic volume (ESV) = 120 ml ‐ 50 ml = 70ml Cardiac output (CO): blood pump out/min CO = SV X HR CO = SV (70 ml/beat) ×HR (75 beats/min) = 5.25 L/min Ejection Fraction (EF)= % of EDV that is actually ejected  Factors affecting stroke volume Preload Contractility Afterload Frank Starling Law: Relationship between preload and SV  Factors affecting stroke volume Afterload: back pressure exerted by arterial blood – Afterload is pressure that ventricles must overcome to eject blood Back pressure from arterial blood pushing on SL valves is major pressure – Aortic pressure is around 80 mm Hg – Pulmonary trunk pressure is around 10 mm Hg  Heart Sounds Two sounds - associated with closing of valves First sound, S1 is closing of AV valves at beginning of ventricular systole Second sound, S2 is closing of SL valves at beginning of ventricular diastole Pause between them indicates heart relaxation  Aortic valve sounds heard in 2nd intercostal space at right sternal margin Pulmonary valve sounds heard in 2nd intercostal space at left sternal margin Mitral valve sounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle Areas of the thoracic surface Tricuspid valve sounds where the sounds of individual typically heard in right valves are heard most clearly sternal margin of 5th intercostal space  Clinical – Homeostatic Imbalance Heart murmurs: abnormal sounds heard when blood hits obstructions Usually indicate valve problems – Incompetent valve: fails to close completely, allowing backflow of blood – Stenotic valve: fails to open completely, restricting blood flow through valve  Blood Pressure Systolic pressure: 120 mmHg Diastolic pressure: 80 mmHg Pulse Pressure = Systolic pressure - Diastolic pressure A single value for driving pressure: Mean arterial pressure (MAP) MAP= Diastolic pressure +1/3 Pulse pressure  120 100 ::c 80 E e::, Diastolic 60· pFessure ,:g CD 40 0 IVC Aorta (and other elastic arteries) experiences widest variation in pressure. Thick tunica media with elastin allows aorta to stretch and recoil to accommodate pressure changes as heart pumps blood into it and then relaxes. @2003 Benjamin Cummings and adam.com® sphygmomanometer  Maintaining BP Short term mechanism – Neural Long term mechanism – Renal Short term mechanism - Neural Short term mechanism-Neural Long Term