Effects of Exercise on CVS - PDF

The Heart Components of the cardiovascular system List the components of CVS and function of each: 1. Heart 2. Blood vessels Structural functional relationship of the heart SA node is the normal pace maker of the heart  Fast response fibers...

The Heart Components of the cardiovascular system List the components of CVS and function of each: 1. Heart 2. Blood vessels Structural functional relationship of the heart SA node is the normal pace maker of the heart  Fast response fibers Slow response fibers (atria, ventricles and Purkinje fibers) (SAN, AVN) MEMBRANE POTENTIAL (mV) VENTRICULULAR SAN CELL 1 2 0 0 0 3 0 3 -50 -50 4 4 -100 -100 Compare fast and slow response fibers Factors affecting Autorhythmicity Positive chronotropic Negative chronotropic factor factors Sympathetic stimulation Parasympathetic stimulation Fever Hypothermia Mild alkalosis Mild acidosis Mild hypoxia Severe hypoxia  Conductivity It is the ability of cardiac muscle to transmit action potential from one cell to the next. Explain conductivity. SA N AVN Although the cardiac muscle is conductive , the heart is provided with a conductive system. List its parts and explain its function  Contractility It is the ability of cardiac muscle to convert chemical energy into mechanical energy in the form of tension, work and pressure. Contraction is triggered by increased intracellular Ca⁺⁺.There are two sources of Ca⁺⁺: A. Extracellular fluid (ECF). B. Sarcoplasmic reticulum (SR) Factors affecting contractility: Positive inotropic factors Negative inotropic factors Sympathetic stimulation Parasympathetic stimulation decrease atrial contractility Catecholamines, digitalis Ether chloroform and bacterial toxins, ischemia Mild heat, ↑Ca⁺⁺ in ECF Mild cold, ↑K⁺ in ECF  Contractility Afterload Preload Extent of myocardial fiber shortening 1. Preload , Frank -Starling law (length tension relationship). ↑ preload → More shortening of cardiac muscle 2. Contractility. 3. Afterload (aortic pressure).↑ afterload → less shortening of cardiac muscle  Cardiac Output It is the volume of blood pumped by right or left ventricle /minute. Normally it equals 5.5 L/minute under basal or resting conditions. As long as the CO is satisfactory to body needs , the heart is considered functionally normal Cardiac index (CI) is cardiac output/body surface area. It equals 3.2 L/min./m². Body surface area is an important determinant of metabolic rate  The Two determinants of CO are stroke volume & HR. Alterations in cardiac output can be brought about by alterations in either or both determinants. Stroke volume ( SV) is the CO/beat. It averages 80 ml. It is affected by: 1. Preload. ↑ preload →↑ SV 2. Contractility. ↑ contractility →↑ SV 3. Afterload. ↑ afterload →↓SV  Arterial Blood Pressure By the end of this lecture you should be able to:- 1. Define arterial blood pressure and mention its functions. 2. Recognize determinants of arterial blood pressure. 3. Discuss regulation of arterial blood pressure Systolic & diastolic blood pressure Determinants of arterial blood pressure ABP=CO X PR Arterial blood pressure is determined by cardiac output and peripheral resistance. How does the cardiovascular system respond to exercise?  The Circulatory System Works with the pulmonary system Cardiopulmonary or cardiorespiratory system Purposes of the cardiorespiratory system Transport O2 and nutrients to tissues Removal of CO2 wastes from tissues Regulation of body temperature Two major adjustments of blood flow during exercise Increased cardiac output Redistribution of blood flow  Organization of the Circulatory System The heart is two pumps in one. The right side of the heart pumps blood through the pulmonary circulation, while the left side of the heart delivers blood to the systemic circulation.  Exercise Training Protects the Heart Regular exercise is cardioprotective Reduce incidence of heart attacks Improves survival from heart attack Exercise reduces the amount of myocardial damage from heart attack Improvements in heart’s antioxidant capacity Improved function of ATP-sensitive potassium channels  Cardiac Output The amount of blood pumped by the each ventricle each minute Product of heart rate and stroke volume Heart rate Number of beats per minute Stroke volume Amount of blood ejected in each beat Depends on training state and gender Q = HR x SV Factors that Regulate Cardiac Output  Resting cardiac output is typically ~ 5 l/min. At VO2max it will be ~ 35 l/min in a well-trained ~ 25 l/min in a healthy aerobic athlete, and up but not especially to 45 l/min in a ultra- trained young man elite performers Dynamic exercise  ↑ Muscle pump + ↑ sympathetic vasoconstriction  ↑ Venous return  ↑ stroke volume  ↑ cardiac output. HR Cardiac output Cardiac contractility Maintenance of Muscle ventricular filling “pump” Skin and Venous splanchnic blood return volume  Cardiac output (CO) increase Increased CO can be achieved by raising either stroke volume (SV) or heart rate (HR) steady-state HR rises essentially linearly with work rate over the whole range from rest to VO2max : - increased sympathetic and decreased parasympathetic discharge to the cardiac pacemaker + catecholamines - reflex signals from the active muscles - blood-borne metabolites from these muscles - temperature rise  Heart rate Maximum HR is predicted to endurance training, within 10 b.p.m., in normal especially if maintained people who are not endurance over many years, lowers trained, by the rule: this maximum by up to 15 HR (b.p.m.) = 220 - age b.p.m. it also, of course, lowers resting HR Blood Pressure (BP) also rises in exercise systolic pressure (SBP) goes up to 150-170 mm Hg during dynamic exercise; diastolic scarcely alters in isometric (heavy static) exercise, SBP may exceed 250 mmHg, and diastolic (DBP) can itself reach 180  Muscle chemoreflex Heavy exercise ↑ muscle lactate  muscle chemorec. and afferent nerves medullary cardiovascular center ↑ sympathetic neural outflow ↑ HR and cardiac output per minute + vasoconstriction (viscera, non working skeletal muscles) + vasodilation in working skeletal muscles Endurance training Strength training  Blood flow redistribution is achieved partly by sympathetic nerve activity, and partly chemically  Redistribution of Blood Flow During Exercise Increased blood flow to working skeletal muscle At rest, 15–20% of cardiac output to muscle Increases to 80–85% during maximal exercise Decreased blood flow to less active organs Liver, GI tract Redistribution depends on metabolic rate Exercise intensity  Increased blood flow to working skeletal muscle because of vasodilatory metabolites such as AMP, adenosine, H+, and K+ acting on pre-capillary sphincters, which override the vasoconstrictor effects of norepinephrine. Changes in Muscle and Splanchnic Blood Flow During Exercise The Muscle thoracic Pump Helps Venous Return  During exercise the muscle pump functions to return blood to the heart, or increase venous return; the muscles contract and squeeze the veins to push blood back up to the heart  the thoracic or respiratory pump serves the same function, i.e, as you breath in and out this compresses veins in the chest and abdomen to increase venous return to the heart  Nitric Oxide Is an Important Vasodilator Produced in the endothelium or arterioles Promotes smooth muscle relaxation Results in vasodilation and increased blood flow Important in autoregulation With other local factors One of several factors involved in blood flow regulation during exercise Increases muscle blood flow  Coronary artery Coronary blood flow Rest ↑ Cardiac output  ↑ Coronary flow (fivefold) ↑ Endothelial cell Coronary artery shear stress  Nitric oxide Prostacyclin ↑ Endothelial-dependent vasodilation + cholinergic fibers stimulation (sympathetic system) Exercise Nitric oxide Vasodilator Prostacyclin capacity  Circulatory Responses to Exercise Heart Rate and Blood Pressure During Arm and Leg Exercise  The long term effect of exercise – the heart Aerobic exercise strengthens the heart. The heart becomes bigger. The walls become thicker and stronger. The stroke volume increases. The result is that the heart becomes a more efficient pump. Your resting heart rate gets slower as you get fitter, because the heart needs fewer beats to pump blood round the body. Training also results in new capillaries growing to improve the supply of blood to the muscles.  Circulatory Responses to Exercise Cardiovascular Changes During Prolonged Exercise Summary of Cardiovascular Responses to Exercise