GAF, FPP, Wk12, Lect2, Cardiac Cycle 23-24.pptx

The Cardiac Cycle FPP Week 12 UH FPP Wk 12 2023-24 Learning outcomes By the end of this lecture and the appropriate independent study the successful student should be able to: •Explain the factors affecting cardiac output, heart rate and blood pressure •Review the electrical events of the cardiac...

The Cardiac Cycle FPP Week 12 UH FPP Wk 12 2023-24 Learning outcomes By the end of this lecture and the appropriate independent study the successful student should be able to: •Explain the factors affecting cardiac output, heart rate and blood pressure •Review the electrical events of the cardiac cycle •Describe a simple ECG trace UH FPP Wk 12 2023-24 Electrical and mechanical events of the cardiac cycle UH FPP Wk 12 2023-24 The conduction system of the heart Internodal pathway SA node AV node AV bundle (bundle of HIS) Right and left bundle branches Purkinje fibres Fig. 14.9 Germann UH FPP Wk 12 2023-24 Electrical Conduction UH FPP Wk 12 2023-24 The spread of the action potential UH FPP Wk 12 2023-24 Fig. 14.10 Germann Sequence of events • An action potential (AP) is generated in the Sinoatrial (SA) node in the right atrium, this passes through the atria to ….. • the Atrioventricular (AV) node transmits AP with a 0.1 sec delay allowing full atrial contraction • AP travels through the Bundle of His which then splits into left and right bundle branches • AP travels through an extensive network referred as Purkinje fibres, which spread through the ventricular myocardium from the apex upwards UH FPP Wk 12 2023-24 Reminder: Mechanical events UH FPP Wk 12 2023-24 Fig. 13.18 Stanfield Mechanical events •Diastole comprises of 3 parts (4+1) : • Isovolumetric ventricular relaxation when all valves are shut • Ventricular filling with atria relaxed with the AV valves open and the semilunar valves shut • Ventricular filling with atrial contraction to ‘top them up’ with again the AV valves open and the semilunar valves still closed •Systole comprises of 2 parts (2+3): • Isovolumetric contraction of the ventricles when both the AV and the semilunar valves are shut • Ventricular ejection when the AV valves are shut and the semilunar valves are open and blood flows into the aorta and the pulmonary artery UH FPP Wk 12 2023-24 Heart Rate control •Nervous system •Hormonal system •Useful link http://www.slideshare.net/Traceywithane/control-of-heartrate UH FPP Wk 12 2023-24 Modification of the basic heart rate The basic heart rate is modified by: • The autonomic nervous system via the cardiac centres in the medulla (brain stem) • Sympathetic input increases the heart rate and force of contraction • Parasympathetic input via the Vagus nerve, decreases the heart rate • The resting state is modified by the parasympathetic system (vagal tone) as the heart beats at around 100 beats per minute outside the body UH FPP Wk 12 2023-24 Modification of the basic heart rate Various hormones and ions affect the heart rate as well • • • Adrenaline, noradrenaline and thyroxine increase the heart rate The heart is very dependent on the concentration of potassium (K+), sodium (Na+), calcium (Ca2+), magnesium (Mg2+) Derangements in the body’s hormonal balance or ionic plasma concentrations can lead to tachycardia/bradycardia or other arrhythmias UH FPP Wk 12 2023-24 Generation of Blood Flow and Factors Contributing to this UH FPP Wk 12 2023-24 Generation and maintenance of arterial blood pressure (systolic and diastolic) • The term arterial blood pressure refers to the pressure in the arteries during systole and diastole • This is mainly dependent on: • Myocardial function • contractility and rate (cardiac output) • Resistance to forward flow in the arterial system • Elastic properties of the arterial system • Any resistance in the venous system UH FPP Wk 12 2023-24 Myocardial function Cardiac output (CO) Defined as ‘the volume of blood that each ventricle ejects in a minute’ CO= SV x HR ( ~ 70mls x 72= 5040mls) • Normal CO at rest is around 5 litres a minute • Each ventricle pumps the total body blood volume (5l) in one minute at rest UH FPP Wk 12 2023-24 Determinants of myocardial function (SV/CO) •Starlings law : reaction to venous return •Volume of venous return • role of venous system in storing blood, ‘capacitance’ vessels •Circulating hormones •Autonomic nervous system input to the myocardium •Concentration of Electrolytes in the blood (calcium, magnesium, sodium and potassium in particular) •The terms inotropic and chronotropic • An inotrope affects the contractility of the heart • A chronotrope affects the heart rate • Both can have a positive or negative effect, • e.g. Adrenaline (American – epiphrenine) has a positive inotropic and chronotropic effect on the the heart UH FPP Wk 12 2023-24 Determinants of myocardial function – Venous return affects SV/CO by influencing the preload •Systemic venous return - Dependent on: • Circulating blood volume • State of dilation/contraction of the venous vessels • RV function • if this is reduced you get back pressure through the systemic venous system and peripheral oedema •Systemic venous return - Enhanced by: • Respiratory pump • Valves in the leg veins • Muscle activity • Autonomic input to the venous musculature as needed UH FPP Wk 12 2023-24 Distribution of blood in the body at rest • Systemic venous system ~65% • Pulmonary system ~10% • In the heart ~7% • Systemic arterial system ~20% UH FPP Wk 12 2023-24 Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings UH FPP Wk 12 2023-24 Myocardial function (CO = SV x HR) Factors affecting heart rate • Autonomic nervous system • Main cardiac centres in the medulla (brain stem) • Hormones • Venous return UH FPP Wk 12 2023-24 Generation and maintenance of arterial blood pressure (systolic and diastolic) This is mainly dependent on: • Myocardial function • contractility and rate (cardiac output) • Resistance to forward flow in the arterial system • Elastic properties of the arterial system • Any resistance in the venous system UH FPP Wk 12 2023-24 Factors affecting blood flow in all the blood vessels in the peripheries • Driving pressure and pressure difference along the vessels • Vascular resistance (R) is dependent on: • Vessel diameter • Vessel length • ↑ friction with ↑ length – direct relationship • Blowing water out of a snorkel v a garden hose • Viscosity of blood (resistance to flow) • Blood is normally 4-5 x as viscous as water • Whether flow is turbulent or laminar UH FPP Wk 12 2023-24 Pulmonary versus systemic circulations and pressures Pulmonary BP ~ 25/10 mmHg (mean 15mmHg) A low pressure system • Pulmonary vascular resistance (PVR) is around 1/8th – 1/10th of the SVR (shorter vessels and much less muscle) • Right ventricle generates less force UH FPP Wk 12 2023-24 Systemic and pulmonary pressures UH FPP Wk 12 2023-24 Overall control of the CVS • Cardiac centres are in the medulla and control both HR and BP • Acceleratory and inhibitory • Have input from higher centres in the cerebrum • Input from various cardiac reflexes • Sensory fibres from the peripheral vascular system and heart • Baroreceptors • Respond to hypoxaemia and hypercapnia • Hormones UH FPP Wk 12 2023-24 Clinically - Cardiac outcome measures • Heart rate and rhythm • Blood pressure, systolic/diastolic/mean and pulse pressure • ECG (electrocardiogram) • Echocardiagram (often termed an ‘Echo’) • Cardiac output estimation • Valve function • Ejection fraction • An important measure of cardiac function ejection fraction is defined as the SV/EDV x 100 – usually 60-70% • The remaining 30-40% acts as a reserve for exercise • Ejection fraction falls in heart failure UH FPP Wk 12 2023-24 The Electocardiogram (ECG) • Records the spread of electrical activity around the heart by measuring the voltage difference between electrodes placed on the skin • Hence measures both polarisation and depolarisation of the heart • Most commonly measured with either 3 leads which gives a basic trace or 12 leads that give more detail • Depends on which lead you are looking at as to the trace Einthoven’s triangle UH FPP Wk 12 2023-24 12 lead Electrode Placement for Recording a Standard ECG UH FPP Wk 12 2023-24 Parts of an ECG • P wave - an upward deflection • atrial depolarisation (contraction) • QRS complex - a series of sharp upwards and downwards deflections • ventricular and incorporates atrial repolarisation but this is lost in the standard ECG • T wave - an upward deflection; • ventricular repolarisation (relaxation) UH FPP Wk 12 2023-24 ECG intervals and segments · P-Q (or P-R) interval: · an estimate of the time of conduction through the AV node · Q-T interval : · ventricle contraction (ventricular systole) · T-Q segment : · ventricle relaxation (ventricular diastole) · R-R interval: · time between heartbeats R-R P-Q T- Q Q-T R R T P Q S T P Q S UH FPP Wk 12 2023-24 Normal 12 lead ECG trace UH FPP Wk 12 2023-24 The main ECG abnormalities you need to know Ventricular tachycardia (VT) Ventricular fibrillation (VF) Versus atrial arrhythmias e.g. fibrillation (AF) that has QRS complexes and are less dangerous UH FPP Wk 12 2023-24 Bibliography Fox, S. I. (2009). Human physiology. (11th ed.). Boston: McGraw Hill Higher Education. Marieb, E. N. (2004). Human anatomy and physiology. (6th ed.). Pearson Benjamin Cummings. San Francisco: London. Martini, F. H. (2006). Fundamentals of anatomy and physiology. (7th ed.). San Francisco: Pearson Benjamin Cummings. Stanfield, C. L. & Germann, W. J. (2008). Principles of human physiology. (3rd ed.). San Francisco: Pearson Benjamin Cummings. Thibodeau, G. A. & Patton, K. T. (2007). Anatomy and physiology. (6th ed.). St Louis, Missouri: Mosby Elsevier. Widmaier, E. P., Raff, H. & Strang. K.Y. (2006). Vander’s human physiology: The mechanisms of body function. (10th ed.). Boston: McGraw Hill. UH FPP Wk 12 2023-24