Sports Physiology Unit 4 - Cardiovascular PDF

SPORTS PHYSIOLOGY UNIT 4 - CARDIOVASCULAR Christopher James Keating, PhD, ACSM-EP® The Cardiovascular System  Serves a number of important functions in the body.  Most of which support other physiological systems.  Virtually all bodily functions depend in some way on the proper...

SPORTS PHYSIOLOGY UNIT 4 - CARDIOVASCULAR Christopher James Keating, PhD, ACSM-EP® The Cardiovascular System  Serves a number of important functions in the body.  Most of which support other physiological systems.  Virtually all bodily functions depend in some way on the proper function of this system.  Important to understand that circulatory and respiratory systems are coupled closely together and cannot function without the other.  Plays a large role in exercise and performance.  One of themajor challenges to homeostasis brought on by exercise is the increased muscular demand for oxygen. 15-25 times greater  Will see many adaptations to the system with chronic exercise. 2 The Cardiovascular System (cont.) Functions 3 Components: Delivery of oxygen and other 1. Heart – serves as the pump. nutrients. 2. Vasculature – serve as Removal of CO and other 2 channels for transport. waste products. 3. Blood – fluid which circulates Transportation of hormones. throughout the body and Maintenance of homeostasis serves to transport nutrients, (body temperature, pH). etc. Prevention - plays a role in immune function response to infection. 3 4 The Cardiac Arteries and Veins 5 Myocardium (cont.)  Myocardium = cardiac muscle  Cardiac muscle fibers are highly aerobic. Contain large numbers of mitochondria. Much more than Type I (slow-twitch) muscle fibers.  Thickness of myocardium varies with the stress placed on its wall. Exercise can increase the thickness of the myocardium (as can hypertension).  The left ventricle has the thickest wall. 6 Myocardium Myocardium = cardiac muscle  Cardiac muscle fibers are shorter than skeletal muscle fibers. Striated due to intercalated discs (contain actin & myosin just like skeletal muscle) Branched rather than elongated in series.  Contains specialized structures that hold muscle together and spread electrical signals. Desmosomes – hold cells together Pay attention to cadherin in the video below What do these structures provide? Gap Junctions –intercalated discs. What do gap junctions allow for? Good cardiac video 7 8 Cellular Structure of Cardiac Muscle 9 How does the Heart Contract?  The heart uses the cardiac conduction system to signal a contraction.  Spontaneously generates its own electrical signal to contract (autoconduction).  No external signal or stimulus is required.  Intrinsic rate of contraction will be between 60 and 100 beats per minute.  AV Node = 40-60 bpm  Ventricular Cells = 20-40 bpm  Heart beats as a functional syncytium  Atria beat ahead of ventricles to send blood to ventricles  Walls of left ventricle 4-5X thicker than walls of right ventricle 10 Cardiac Conduction System 11 Cardiac Cycle  Includes all events that occur between two consecutive heart beats. 1. Systole – contraction period of the heart. 2. Diastole – relaxation period of the heart, allows chambers to fill with blood.  All chambers of the heart undergo a period of systole and diastole during each cardiac cycle.  2/3 spent in diastole 12 13 Regulation of Heart Rate The two most prominent factors that influence HR are the parasympathetic and sympathetic nervous systems. Vagus Nerve Parasympathetic fibers innervate the heart through this cranial nerve. When stimulated, these nerve endings release ACh which causes a decrease in the activity of both the SA and AV nodes due to hyperpolarization. Hyperpolarization: moving the resting membrane potential further away from threshold. Parasympathetic control is called what? 14 Regulation of Heart Rate (cont.) Initial increases in HR during exercise (up to 100 bpm) is due to withdrawal of vagal tone. At higher work rates, stimulation of the SA and AV nodes by the sympathetic nervous system is responsible for further increase in HR. The sympathetic nervous system (through norepinephrine) innervates the heart through β receptors in the heart. Excitation of the β receptors leads to an increase in both HR and force of contraction. 15 The Vascular System Arteries Venules  Carry blood away from heart to Blood passes from capillaries to arterioles. venules. Arterioles  Smaller branches of arteries Veins  Surrounded by smooth muscle.  As venules move back towards the  Blood passes through these into heart they increase in size and capillaries. become veins.  Carry blood towards the heart.  Contain valves that prevent back- Capillaries  Narrow (one cell thick) flow of blood.  Exchange between tissues and the  Most of your blood is in veins at blood occurs here. any one time. 16 17 Blood  3rd Component of the cardiovascular system Functions of the Blood 1. Transports gas, nutrients, and wastes. 2. Regulates temperature. 3. Buffers and balances acidity and helps to maintain the proper pH of efficient use of metabolic processes. Blood Volume  Varies across people  Highly related to body size and state of aerobic training.  5 – 6 liters in men and 4 – 5 liters in women. 18 The Composition of the Blood Total blood volume is composed of plasma and formed elements (blood cells). Plasma  Mostly made up of water.  Contains numerous dissolved ions, proteins, and hormones.  Typically 55 – 60% of blood volume.  Levels can change acutely due to water loss and can also increase greatly in response to exercise training. Hematocrit  Total blood volume red cells, white cells and platelets.  Typically 40 – 45% of volume. 19 Red Blood Cells  Erythrocytes  Constantly destroying and producing new cells.  Main function is to transport oxygen. How do they transport oxygen?  Hemoglobin  4 oxygen molecules bind to each hemoglobin  250 million hemoglobin per RBC How many molecules of O2 can bind to a RBC? 20  Blood Cell component - red and white blood cells, and platelets constitutes ~45% of blood volume = hematocrit polycythemia - excess production of red blood cells causing an abnormal increase in red blood cells anemia - abnormally low red blood cell counts Liquid component - water, clotting proteins, transport proteins, lipoproteins, glucose, fatty acids, antibodies, transferrin, waste products (eg. urea, ammonia, etc.), etc. plasma - the liquid component of blood and all of it’s non-cellular content serum - what remains of plasma after blood has clotted. Blood Distribution Where is blood sent in the body?  Metabolically active tissues receive the greatest amount of blood. 1. At rest the liver (27%) and the kidneys (22%) receive almost half of all the circulating blood 2. Skeletal muscle receives only 15% What happens with exercise?  Blood goes to the muscles (80% or more)  Cardiac output and blood flow to active muscle can increase up to 25 L/min compared to that at rest. Other conditions that can alter distribution 1. Eating – blood moves to digestive system. 2. Heat Stress – blood moves to skin to dissipate heat. 22 Blood Distribution (cont.) 23  Blood Distribution  At rest, the veins serve as a reservoir for blood (64%).  When a need arises (exercise) sympathetic neural input can cause the veins to constrict and push more blood back to the heart and arteries. Summary  Not only can blood be directed to certain tissues and away from others when the need arises, but a greater percentage of blood can also be made available for use. 24 Control of Blood Distribution  Primarily done by the arterioles. Why the arterioles? 1. Smooth Muscle 2. Respond to “Input” Vasodilation – increase in artery diameter Vasoconstriction – decrease in artery diameter 25 26 Control of Vessel Diameter 1. Auto-regulation  Local control of blood distribution.  Arterioles self-regulate the amount of blood a given tissue receives.  Increased oxygen demand, elevated K+, H+, lactic acid, all lead to…? ↑ velocity → shear stress → NO 2. Extrinsic Neural Control  Nervous system (sympathetic) input controls blood distribution.  Smooth muscle has receptors that control dilation and constriction. 27 Mechanism for how NO regulates local blood flow 29 Stroke Volume  Stroke Volume (SV)  Volume of blood pumped/ejected from the left ventricle during each contraction of the heart End-Diastolic Volume (EDV)  Volume of blood in the left ventricle at the end of diastole (just prior to contraction) End-Systolic Volume (ESV)  Volume of blood remaining in the left ventricle at the end of systole (after contraction). So how do we get SV? SV = EDV – ESV 30. Cardiac Output (Q) Cardiac Output: Volume of blood pumped by the left ventricle per minute. Q = Heart Rate (HR) ´ Stroke Volume (SV) Q = beats/min × ml/beat = ml/min  typically expressed as L/min Cardiac output is normally about 5 L/min at resting. 31. Q Calculations of SV and 32  Factors that Increase Return of Blood to the Heart During Exercise 3 Mechanisms 1. Breathing  Pressure changes aid in the return of blood. 2. Muscle Pump  Contractions squeeze veins and force blood back toward the heart. 3. Valves  Located in veins and allow for flow only toward the heart. 33 Frank-Starling Law of the Heart 1. Increase in EDV results in a lengthening of cardiac fibers, which improves the force of contraction in a manner similar to that seen in skeletal muscle. 2. An increase in the length of cardiac fibers then increases the number of myosin cross-bridge interactions with actin. 3. An increase in number of cross-bridges results in an increased force production. What else? 4. Rise in contractility leads to an increased amount of blood pumped each beat. 34  Regulation of Stroke Volume In order to eject blood, the pressure generated by the LV must exceed the pressure in the aorta. How does the body control this during exercise? Typically, afterload is minimized during exercise due to arteriole dilation, reducing afterload and making it easier for the heart to pump a large volume of blood. Regulation of Stroke Volume In order to eject blood, the pressure generated by the LV must exceed the pressure in the aorta. Aortic pressure (called afterload) represents a barrier to the ejection of blood from the ventricles. An increase in afterload produces a decrease in SV. Typically afterload is minimized during exercise due to arteriole dilation, reducing afterload and making it easier for the heart to pump a large volume of blood. 36 Blood Pressure Mean arterial pressure (MAP)  Average pressure exerted by What is Blood Pressure? the blood as it travels through arteries.  Thepressure exerted by the  MAP = DBP + [0.333 ´ (SBP – blood against the vessel wall DBP)]  SBP + (2 x DBP) / 3 1.Systolic blood pressure (SBP) Why is this calculation only  Highest pressure relevant during rest?  Occursduring contraction of the heart Control of Blood Pressure  Bloodvessel constriction 2.Diastolic blood pressure (DBP)  Lowest increases blood pressure, pressure dilation reduces blood  Occurs during “filling” of the pressure. heart 37 Blood Pressure & Hypertension Hypertension: high blood pressure. Hypertension increases the workload on the left ventricle, resulting in an adaptive increase in the muscle mass of the left ventricle. This is called left ventricular hypertrophy Initially, this increase in cardiac mass helps to maintain the heart’s pumping ability. With time, this hypertrophy changes the organization and function of cardiac muscle fibers, resulting in diminished pumping capacity of the heart which can lead to heart failure. 38 Normal & Abnormal Blood Pressure (at resting) Blood Pressure Systolic pressure = greatest pressure during contraction Normal range at rest = 100-140 mmHg Diastolic pressure = lowest pressure during filling stage Normal range = 70-90 mmHg Normotensive Blood Pressure Limits ACSM 250 mmHg = max systolic pressure 120 mmHg = max diastolic pressure Low systolic = 70 mmHg Abnormal Blood Pressures Hypertension Hypertension: > 140 systolic and/or > 90 diastolic Severe headache. “essential hypertension” – no Fatigue or confusion. known cause Vision problems. Chest pain. “secondary hypertension” – cause Difficulty breathing. Irregular heartbeat. Hypotension Blood in the urine. < 100 mmHg systolic and/or < 70 mmHg diastolic Pounding in your chest, neck, or ears. Causes of Hypertension Several factors increase BP, including (1) obesity, (2) insulin resistance, (3) high alcohol intake, (4) high salt intake, (5) aging (6) sedentary lifestyle, (7) stress, (8) low potassium intake, (9) low calcium intake. 43 44 Hypertension BP = CO x R or QxR Hypertension is either the result of increased CO or increased resistance  Relationship Between Pressure, Resistance, & Flow Blood flow = difference in pressure resistance Resistance = Length of vessel x Viscosity of fluid Radius4 Blood flow can be increased by either an increase in BP or a decrease in resistance. Difference in pressure between arteries and veins is what drives circulation of blood. 46 Artery Size and Blood Distribution Ohm’s Law Flow = ∆Pressure / Resistance Resistance = (viscosity x L)/ r4 Poiseuille’s Equation - Flow (distr.) = K x P x r4 L K = viscosity P = pressure r = vessel radius L = vessel length Small change in r = large change in flow 47 48 49 What happens with exercise? 50 Cardiovascular Response to Acute Exercise What changes? 1. HR, SV, and Q all increase. 2. Blood distribution changes. Why are these changes important? To meet the increased metabolic rate. Provide more oxygen, more nutrients, and remove waste. Help regulate temperature. 51 Heart Rate Resting Heart Rate  60 to 80 (100) bpm  30-40 bpm (highly trained) to above 100 bpm (sedentary) Exercise  HR will increase in direct proportion to exercise intensity.  Easy measure to use to estimate exercise intensity.  Will typically reach a “steady-state” during submaximal exercise within 10 seconds of workload increase. Max Heart Rate  The highest value achieved in an all-out effort  Constant day-to-day  220 – age = age predicted max HR (AP-HRmax) 52 Heart Rate and Exercise Intensity 53 Threshold (Target) Heart Rate Threshold Heart Rate or Target Heart Rate THR =.75 (220-age) Karvonen’s HRR Method: THRR = 75-85% THR=.75(max HR – RHR) + RHR THR=.85(max HR – RHR) + RHR Stroke Volume SV & Exercise  Increases with exercise up to intensities of 40% to 60% of max.  SV is the primary determinant of cardiorespiratory endurance capacity at maximal rates of work. Why is having a higher SV an advantage?  Everyone can increase HR, but only up to a certain point.  Cardiac output (Q) = HR x SV  Bigger SV  bigger Q  more blood to muscles 55 Stroke Volume and Exercise Intensity 56  Factors that Increase SV with Exercise 1. Volume of Returning Venous Blood  Increased by the muscle pump. 2. Ventricle Size  Body Size  Training Why does it Plateau? 3. Ventricle Contractility  Frank Starling Mechanism  Nervous system input 4. Total Peripheral Resistance  Vasodilation to working muscles.  Aortic Pressure (Decreased BP at a given load) 57 Exercise & Cardiac Output  Remember: Cardiac Output (Q) Determines the amount of blood “presented” to working muscles.  Exercise Intensity increase leads directly to an increase in Q. Why?.  HR and SV both increase.  However, at intensities over 40% to 60% of max, HR is the only mechanism that can increase Q.  Cardiovascular drift – after about 15 minutes at steady state exercise -HR increases; SV decreases 58 Cardiac Output and Exercise Intensity 59 Cardiovascular Drift  Cardiovascular Drift Describes the gradual time-dependent downward “drift” in several cardiovascular responses, most notably stroke volume with concomitant heart rate increase, during prolonged steady-state exercise Under these circumstances, a person must exercise at lower intensity than if cardiovascular drift did not occur Submaximal exercise for >15 minutes decreases plasma volume, which decreases stroke volume A reduced stroke volume initiates a compensatory heart rate increase to maintain a nearly constant cardiac output Blood Plasma Volume & Exercise Reduces with onset of exercise (fluid moves to interstitial space). More fluid is lost with the greater degree of sweating. Excessive loss of fluid (water) can result in declines in performance. Reduction in plasma volume results in hemoconcentration. Loss in plasma volume results in higher concentration of red blood cells per unit of blood. Increased hematocrit Increases oxygen carrying capacity of the blood, but also increased viscosity. Endurance training can lead to increases in overall plasma volume. How? 62 Blood Pressure & Exercise Endurance Exercise Systolic BP increases in direct response to increases in intensity. Diastolic BP changes very little, if any, during endurance exercise regardless of intensity. Sometimes it even decreases slightly. Resistance Exercise Exaggerated BP response to sometimes as high as 480/350 Why so high? 63 Blood Pressure Response to Exercise With arm exercise, dilation of vessels occurs in the upper body but the leg blood vessels have increased constriction. More muscle mass is active during leg exercise therefore more arterioles are dilated which leads to less increase in blood pressure. 64 Arterial-Venous Oxygen Difference, or (a-v)O2 diff What is it?  Amount of oxygen extracted from the blood as it travels through the capillaries How is it calculated?  The difference in oxygen content between arterial blood and venous blood What happens during exercise?  Increases as more oxygen is taken from blood and Q increases.  TheFick Haveequation less oxygen in venous represents theblood (arterial relationship of oxygen the O remains constant). body’s oxygen consumption R (VO2), to the arterial-venous oxygen difference (a-vO2 diff) and cardiac output (Q)... - - VO2 = Q x a-vO2 = (HR × SV) x a-vO2 65 66 Central Command Theory & Cardiac Output 1. Within one second after the initiation of muscular contraction there is a withdrawal of the vagal (parasympathetic) tone to the heart. 2. This is then followed by an increase in sympathetic stimulation of the heart. 3. At the same time, there is a vasodilation of arterioles in active skeletal muscles and a reflex increase in the resistance of vessels in less-active areas. 4. End result is an increase in cardiac output to ensure that blood flow to muscle matches the metabolic needs. Central Command Theory proposes that the initial signal to the CV system at the beginning of exercise comes from higher brain centers. Fine-tuning of the CV response to a given exercise increase is accomplished through a series of feedback loops from muscle chemoreceptors, mechanoreceptors, and arterial baroreceptors. 67 68 Vascular Remodeling Response to aerobic training Collateral circulation – additional vessels opened and Larger arteries – increased formed about heart lumen diameter Protectiveto heart muscle – prevent large myocardial Improved ability to dilate infarction Endothelial lining produces nitrous oxide (in healthy heart) DECREASED RESISTANCE Coronary circulation 71 72 Varicose Veins A condition in which the valves within a vein fail to maintain their one-way blood flow and blood gathers in them so they become excessively distended and painful Usually occurs in the surface veins of the lower extremities In severe cases, phlebitis occurs where the venous wall becomes inflamed and progressively deteriorates Those with varicose veins should avoid static, straining-type exercises that accompany resistance training Exercise does not prevent varicose veins but regular exercise can minimize complications because repeated muscle actions continually propel blood toward the heart 74 Warm-down Implications Warm down following strenuous to increase the use of the muscle pump so as to: 1. Distribute blood back to organs from which it came 2. Maintain increased circulation to carry metabolic wastes away from cell Warm-up Implications Increase temperature of soft tissue Redistribute blood from inactive to active areas Increase heart rate from a resting rate to a higher rate that approximates exercise HR Dynamically stretch muscles connective tissue Increase speed of nerve impulses  77 Describe five factors that affect blood pressure.