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ECE 501 Introduction to BME ECE 501 Dr. Hang Part IV Bioinstrumentation Electrocardiogram ECE 501 Dr. Hang Introduction Number of deaths for leading causes of death in US (2004)* • • • • • • • • • • Heart disease: 654,092 Cancer: 550,270 Stroke (cerebrovascular diseases): 150,147 Chronic lower respiratory diseases: 123,884 Accidents (unintentional injuries): 108,694 Diabetes: 72,815 Alzheimer's disease: 65,829 Influenza/Pneumonia: 61,472 Nephritis, nephrotic syndrome, and nephrosis: 42,762 Septicemia: 33,464 * http://www.cdc.gov/nchs/fastats/lcod.htm ECE 501 Dr. Hang Introduction • Physiology •Instrumentation • Medicine ECE 501 Dr. Hang Physiology What is the Heart? • The heart is a very specialized muscle that pumps blood through the body, transporting oxygen, carbon dioxide, nutrients and waste. • The heart is located in the middle of the chest, between the lungs. Its bottom is tipped to the left. ECE 501 Dr. Hang Physiology The Heart as a Pump • The heart is like two pumps: one pumping blood into the body and one pumping blood out of the body. • The heart is about as big as two clenched fists put together. • The heart pumps blood in beats. ECE 501 Dr. Hang Physiology The Hard Work of the Heart ECE 501 Dr. Hang Physiology Anatomy of the Heart ECE 501 Dr. Hang Physiology Heart Chambers • Atrium is a chamber that pumps blood into the heart. • Ventricle is a chamber that pumps blood out of the heart. • The atria and the ventricles regulate blood flow by pumping blood in and out of the heart. ECE 501 Dr. Hang Physiology Heart Chambers ECE 501 Dr. Hang Physiology Heart Valves • There are four valves in the heart. • These are unidirectional valves that allow blood flow in only one direction. • They prevent blood from flowing back to the chamber that it has just left. ECE 501 Dr. Hang Physiology Heart Valves ECE 501 Dr. Hang Physiology Heart Valves • The tricuspid valve and the mitral valve are also called A-V valves, because they separate an atrium from a ventricle. • The pulmonary valve and the aortic valve are also called arterial valves, because they separate a ventricle from an artery. ECE 501 Dr. Hang Physiology Arteries and Veins • Artery is a blood vessel that delivers blood out of the heart. The two arteries of the heart are connected to ventricles. • Vein is a blood vessel that delivers blood into the heart. The two veins of the heart are connected to atria. ECE 501 Dr. Hang Physiology Arteries and Veins ECE 501 Dr. Hang Physiology Pulmonary Circulation ECE 501 Dr. Hang Physiology Pulmonary Circulation ECE 501 Dr. Hang Physiology Pulmonary Circulation ECE 501 Dr. Hang Physiology Systemic Circulation ECE 501 Dr. Hang Physiology Systemic Circulation ECE 501 Dr. Hang Physiology Systemic Circulation ECE 501 Dr. Hang Physiology Blood Vessels ECE 501 Dr. Hang Physiology Diffusion • The exchange of molecules between cells and blood occurs at the capillary level. • Capillaries are very small blood vessels with very thin walls. • Oxygen and nutrients diffuse from the blood into the cell and carbon dioxide and waste diffuse from the cell into the blood. ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase I ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase II ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase III ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase IV ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase V ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase VI ECE 501 Dr. Hang Physiology The Cardiac Cycle: Phase VII ECE 501 Dr. Hang Physiology Muscle Types: Skeletal Muscle – Fast-twitching – Voluntary control – Gets tired – Arms, legs etc. ECE 501 Dr. Hang Physiology Muscle Types: Smooth Muscle – Slow-twitching – Involuntary control – Does not get tired – Stomach, bladder, blood vessels etc. ECE 501 Dr. Hang Physiology Resting Membrane Potential ECE 501 Dr. Hang Physiology Resting Membrane Potential Goldman Equation RT PK [ K ]o PNa [ Na]o PCl [Cl ]i ln F PK [ K ]i PNa [ Na]i PCl [Cl ]o PK : Permeabili ty coefficien t of K E PNa : Permeabili ty coefficien t of Na PCl : Permeabili ty coefficien t of Cl [ K ]o : Extracellu lar concentrat ion of K [ Na]o : Extracellu lar concentrat ion of Na [Cl ]o : Extracellu lar concentrat ion of Cl [ K ]i : Intracellu lar concentrat ion of K [ Na]i : Intracellu lar concentrat ion of Na [Cl ]i : Intracellu lar concentrat ion of Cl ECE 501 Dr. Hang Physiology Action Potential Once the cell is electrically stimulated (typically by an electric current from an adjacent cell), it begins a sequence of actions involving the influx and efflux of multiple cations and anions that together produce the action potential of the cell, propagating the electrical stimulation to the cells that lie adjacent to it ECE 501 Dr. Hang Physiology Action Potential: Phase 4 Phase 4 is the resting membrane potential. This is the period that the cell remains in until it is stimulated by an external electrical stimulus (typically an adjacent cell). ECE 501 Dr. Hang Physiology Action Potential: Phase 0 Phase 0 is the rapid depolarization phase. The slope of phase 0 is determined by the maximum rate of depolarization of the cell and is known. This phase is due to opening of the fast Na+ channels and the subsequent rapid increase in the membrane conductance to Na+ and a rapid influx of ionic current in the form of Na+ ions into the cell. ECE 501 Dr. Hang Physiology Action Potential: Phase 1 Phase 1 of the action potential occurs with the closure of the fast Na+ channels. The transient net outward current causing the small downward deflection of the action potential is due to the movement of K+ and Clions. ECE 501 Dr. Hang Physiology Action Potential: Phase 2 This "plateau" phase of the cardiac action potential is sustained by a balance between inward movement of Ca2+ through calcium channels and outward movement of K+ through the potassium channels ECE 501 Dr. Hang Physiology Action Potential: Phase 3 During phase 3 of the action potential, the Ca2+ channels close, while the K+ channels are still open. This ensures a net outward current, corresponding to negative change in membrane potential, This net outward, positive current (equal to loss of positive charge from the cell) causes the cell to repolarize. ECE 501 Dr. Hang Physiology “Electrical Circuit” of the Heart ECE 501 Dr. Hang Physiology The S-A node • The S-A Node is the most important element in the electrical circuit of the heart. • It starts the cardiac cycle by periodically generating action potentials without any external stimulation. (Therefore, it is said to be autorhythmic.) • It is also known as the pacemaker of the heart. ECE 501 Dr. Hang Physiology The A-V node • The atrioventricular node periodically receives action potentials via the junctional fibers. • The most important function of the A-V node is to regulate the timing of the ventricular contraction by delaying the action potentials. • The delayed action potentials are spread over the ventricles to cause a contraction ECE 501 Dr. Hang Physiology The Electrical Cycle ECE 501 Dr. Hang Physiology The Electrical Cycle ECE 501 Dr. Hang Physiology The Electrocardiogram • The electrocardiogram (ECG) is a standardized way to measure and display the electrical activity of the heart. • Physicians can diagnose problems with the heart by analyzing its ECG and comparing it to the ECG of a healthy heart. ECE 501 Dr. Hang Physiology ECG Waves ECE 501 Dr. Hang Physiology ECG Intervals ECE 501 Dr. Hang