The Heart and Exercise Blood Flow Superior and Inferior Vena Cava's Right Atrium Atrioventricular (AV) valve ( or Tricuspid valve) Right Ventricle Pulmonary semilunar valve Pulmonary Aorta (Trunk) to Pulmonary Arteries Lungs Pulmonary Veins Left Atrium Mitrial (or Bicuspid) valve Left Ventricle Aortic Semilunar Valve Aorta Cardiac Cycle (P, Q, R, S, T, and U waves) P wave = Atrial Depolarization QRS = Ventricular Depolarization - much more energy (height of ECG reading) - much more rapid (closer together ECG for more muscle) T wave = Ventricular Repolarization Atrial Repolarization occurs during QRS Complex 1. right ventricle contracts with 1/5 less force than left ventricle 2. left ventricle covers a wider spectrum of pressure 3. atria's are always at a low pressure 4. aorta is always at a high pressure a) when the aortic semi-lunar valve closes, this produces a rebound effect 5. an isometric ventricle contraction occurs when the semi-lunar valves are not open and the ventricles start to contract, raising blood pressure in the ventricles and the atria 6. A Phonocardiogram measures noise in the heart a) lubb = dull noise at low pressure occurs when the a-v valves close a) dubb = crisp noise at high pressure occurs when the s-l valves close Distribution of the Electrical Signal Regulated by the sinoatrial node (SA node - "pacemaker") special fibers located at base of heart impulse generated at regular intervals causes the atria to contract at distal end of atria is Atrioventricular Node (AV node) AV node transmits impulse across septum to Bundle of His Bundle of His Accelerates Impulse Bundle of His divides to Right/Left Bundle Branches Run to the apex of the heart Bundle branches divide to the Purkinje Fibers Purkinje Fibers transmit impulse to muscle Cause contraction from Apex upward More efficient movement of blood In Depth on the Electrical Signal 1. S-A Node (Pacemaker) a) area that initiates the electrical current b) the tissues around the node(s) are more permeable to Na+ than other areas of the heart. During contraction, Na+ is forced out, then it slowly seeps back in. When is returns, the polarity of the node is changed and it generates another electrical signal for a contraction to occur. 2. Internodal Fibers a) these fibers conduct the electrical activity faster than the cardiac tissue b) moves the signal from the S-A node to the A-V node 3. A-V node a) responsible for transmitting electrical signal to the ventricles b) it is nearer the S-A node than other parts of the atria's, so it may get electrical activity faster than some of the atria. For this reason (to prevent incomplete ventricular filling), the A-V node has a delay before it fires. 4. A-V Bundle (Bundle of His) a) carries electrical signal from atria to ventricles across A-V junction b) this forks off to the left and right bundle branches 5. Purkingie Fibers a) these are "twigs" that run off the branches and serve to enervate the ventricle b) this enervation causes a contraction from the apex upward, and then the sides squeeze in Ectopic Pacemakers (abnormalities) 1. If the bundle branches break or do not transmit past a certain point, syncitium (passing of the signal from fiber to fiber) takes over and the contraction takes slightly longer. This may be seen as a blip on the "Q" wave. 2. If the S-A node loses its ability to enervate: a) the A-V node may take over I) HR slows to about 40-45 beats /minute b) or the bundle branches may take over if the A-V node does not 3. An area of the cardiac muscle may be irritable, and may generated a contraction of its own. This can be seen as either PAC's or PVC's (depending upon location) Some Terms 1. Diastole period of time when the heart is not contracting or relaxing 2. Systole period of time when the heart is contracting or relaxing 3. End Diastolic Volume amount of blood in the ventricle at the end of diastole (just before contraction) 4. End Systolic Volume amount of blood in the ventricle at the end of systole (just after contraction) 5. Stroke Volume End Diastolic minus End Systolic (amount of blood ejected by contraction) Cardiac Output (Q) 1. Major concern in cardiac function 2. Def: the amount of blood ejected from the left ventricle over a period of time (usually 1 minute) 3. At rest: a) Q is about 5 L/min (1 1/4 gallons) - based on 70 kg (154 lb) male b) right ventricle is about the same 4. At maximal exercise: a) average is about 18-24 L/min (4-5 times rest) b) endurance athletes are near 30-35 L/min - huge difference between trained endurance athlete and untrained 5. Researchers can look at Q and see: a) is his / her heart in good shape b) how close is person working as compared to max 6. Q can be determined: a) invasively (Fick equation: Q = VO2 / A-V diff) b) non-invasive measures (rebreathing) c) or, Q = Heart Rate (HR) times Stroke Volume (SV) Factors that influence HR 1. Neural Factors (Nervous system) a) Medulla has a: 1) cardiac center 2) respiratory center 3) vasomotor center b) Autonomic Nervous System 1) Vagus Nerve (10th Cranial Nerve) I) is the parasympathetic nerve to the heart II) distributes the electrical activity to the S-A node, A-V node, and the muscle fibers in the atrium. III) the increased activity of the nerve slows down the discharge rate of the S-A node which slows down the HR 2) Sympathetic Nerves (T1 - L3) I) collectively known as the accelerator nerves II) they increase permeability of the S-A node III) they distribute electrical activity to the atria and ventricles IV) they cause muscle cells to get more excited and therefore contract more forcefully c) Under Normal Conditions 1) receive both sympathetic and parasympathetic signals 2) with excitation, sympathetic increases and parasympathetic decreases 3) afterwards, the inverse happens 2. Humeral Factors (Hormonal System) a) Adrenal Glands release chemicals to increase the rate and strength of the contraction 1) epinephrine 2) norepinephrine b) Thyroid releases Thyroxin 1) accelerates the HR c) Chemoreceptors in carotid and aortic sinuses 1) sensitive to changes in: I) Blood pH II) CO2 III) O2 2) increases or decreases HR depending upon pH, CO2, and O2 I) lower pH increases HR, higher pH lowers II) lower CO2 lowers HR, higher CO2 increases III) lower O2 increases HR, higher O2 lowers 3. Emotions (apprehension, etc) a) usually result in increased HR 4. Temperature of the environment a) more blood to pump when environment is hot, so the HR increases 5. Temperature of the body a) more blood to pump when body is hot, so the HR increases 6. Humidity a) cooling is less effective in humid environment, so HR increases 7. Stretching of the S-A Node - influences the rate of Na+ in and out 8. Electrolyte Balance (mostly Na+ and K+) - a disruption in balance = a disruption in HR Ways to measure Heart Rate 1. Stethoscope a) need a quiet environment b) need a still subject 2. Palpate an artery a) wrist = radial artery b) neck = carotid artery 1) however, when measuring the heart rate here, the carotid sinus reflex tells the brain the blood pressure has risen, thus lowering the heart rate 3. Photoelectric Pulse Transducer a) this records the heart beat by sending light into the capillary bend (through the skin) and recording how much light comes back. When more blood is present, less light comes back. 4. Telemetry a) this involves a radio transmitter and a receiver b) usually works well within a range of 150 feet 5. Direct (Hard) Wiring a) gives the best results b) invasive: requires use of needle c) has the subject grounded 6. Electrocardiograms a) connect 10 electrodes to get a 12-lead picture of heart b) allows cardiologist to determine if areas of heart are functioning properly c) only three electrodes required to measure HR alone Factors affecting Stroke Volume (SV) 1. Acute bouts of exercise increase SV as the intensity increases a) caused by 1) a more forceful contraction of the ventricles (result of adrenaline) 2) the skeletal muscle pump (returning blood to the heart faster) 2. As intensity increases, SV increases rapidly then plateaus a) any increases in Q after that point are due to increases in HR b) max SV occurs before Hrmax c) at a high HR, SV may decrease due to an incomplete filling between contractions Effects of Training 1. Heart Rate a) decreased resting HR with improved aerobic fitness level 1) HR decreases because SV is increased (more efficient) b) max HR may decrease slightly 1) males = 220 - age 2) females = 226 - age 3) standard deviation is +/- 12 beats /minute 2. Heart Size a) heart is a muscle, so it grows 1) type of growth depends upon type of exercise (of course) b) weight is the biggest growth 1) is due to an increase in muscle mass 2) aerobic training results in increased volume of heart I) probably does not occur past age 25 3) anaerobic training results in thicker walls I) referred to as a "weightlifters heart" 3. Age a) young people 1) endurance training is not physically harmful 2) may be psychologically harmful I) get sick of sport II) low enthusiasm b) older people 1) increases strength and endurance of heart 2) maintains elasticity of vascular system 3) may improve collateral circulation (reduce clogged arteries) by: I) increasing amount of blood vessels in the heart II) changing the blood lipid profiles - reducing the cholesterol and triglyceride levels III) changing the way cholesterol is transported - LDL's are most likely to be deposited when the LDL-C is high - HDL bonds to the Cholesterol, so HDL-C is beneficial as it takes the cholesterol to the liver IV) exercise increases HDL-C, and decreases LDL-C Heart Murmurs 1. Def: Strange sound in the heart caused by a) mechanical factors (valves) b) unknown factors 2. Types a) Functional: no problems with heart b) Pathological: may lead to problems 3. Some Causes a) Stenosis 1) valve does not open all the way 2) caused by a growing together of valves, so valves don't fold back completely 3) streptococci and rheumatic fever may cause b) Regurgitation 1) valve does not close all the way 2) blood leaks back into previous chamber ??