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Chapter 10 The Cardiovascular System and Exercise Slide Show developed by: Richard C. Krejci, Ph.D. Professor of Public Health Columbia College 10.18.11 Objectives 1. List important functions of the cardiovascular system. 2. Describe how to use the auscultatory method to measure blood pressure, and give average values for systolic and diastolic blood pressure during rest and moderate aerobic exercise. 3. Describe the blood pressure response during (1) resistance exercise, (2) upper-body exercise, and (3) exercise in the inverted position. 4. State potential benefits of aerobic exercise for treating moderate hypertension. 5. Identify the intrinsic and extrinsic factors that regulate heart rate during rest and exercise. Objectives (Cont.) 6. Identify the neural and local metabolic factors that regulate blood flow during rest and exercise. 7. Compare average values of cardiac output during rest and maximal exercise for an endurance-trained athlete and sedentary person. 8. Explain three physiologic mechanisms that affect the heart’s stroke volume. 9. Describe the relationship between maximal cardiac output and maximal oxygen uptake among individuals with varied aerobic fitness levels. Cardiovascular System Anatomy • Heart • Arteries • Capillaries • Veins Cardiovascular System Anatomy (Cont.) Heart • Provides the force to propel blood throughout the vascular circuit • Septum separates the left and right sides of the heart • Atrioventricular valves Tricuspid valve: Between right atrium and ventricle Mitral or bicuspid valve: Between left atrium and ventricle • Semilunar valves Prevent regurgitation between ventricular contractions Heart (Cont.) Heart Pumps • Functions of the chambers of the right heart pump: Receive deoxygenated blood returning from all parts of the body Pump blood to the lungs for aeration via the pulmonary circulation • Functions of the chambers of left heart pump: Receive oxygenated blood from the lungs Pump blood into the thick-walled, muscular aorta for distribution throughout the body via the systemic circulation Arteries • The high-pressure tubing that conducts oxygen-rich blood (except pulmonary arteries) to the tissues. • Because of their thickness, no gaseous exchange takes place between arterial blood and surrounding tissues. • Blood pumped from the left ventricle into the aorta circulates throughout the body via a network of arteries and arterioles. • Arteriole walls contain circular layers of smooth muscle that either constrict or relax to regulate peripheral blood flow. Capillaries • A network of microscopic blood vessels so thin they provide only enough room for blood cells to squeeze through in single file. • Gases, nutrients, and waste products rapidly transfer across the thin, porous, capillary walls. • Velocity progressively decreases as blood moves toward and into the capillaries. Veins • Venules eventually empty into the superior and inferior vena cavae. • Thin, membranous, flap-like valves spaced at short intervals within the vein permit one-way blood flow back to the heart. • Venous system acts as an active blood reservoir to either retard or enhance blood flow to the systemic circulation. Valves in Veins Blood Pressure • Systolic blood pressure Highest arterial pressure measured after left ventricular contraction • Diastolic blood pressure Lowest arterial pressure measured during left ventricular relaxation • Read as 115/70 Blood Pressure Changes During Exercise • Rhythmic Exercise: Increases systolic pressure in the first few minutes and then levels off; diastolic pressure remains relatively unchanged • Resistance Exercise: Can increase blood pressure dramatically • Upper-Body Exercise: Exercise at a given percentage of V·O2max increases blood pressure substantially more in upper-body compared with lower-body exercise • In Recovery: After a bout of sustained light- to moderateintensity exercise, systolic blood pressure decreases below pre-exercise levels for up to 12 hours in normal and hypertensive subjects Blood Pressure Changes During Exercise Heart’s Blood Supply • Coronary circulation Right coronary artery: Supplies predominantly the right atrium and ventricle Left coronary artery: Supplies the left atrium and ventricle, and a small portion of the right ventricle Heart’s Blood Supply Myocardial Oxygen Utilization • At rest, the myocardium extracts 70% to 80% of the oxygen from the blood flowing in the coronary vessels. • Because near-maximal oxygen extraction occurs in the myocardium at rest, increases in coronary blood flow provide the primary means to meet myocardial oxygen demands in exercise. In vigorous exercise, coronary blood flow increases four to six times above the resting level. Rate-Pressure Product • Provides a convenient estimate of myocardial workload • Three important mechanical factors determine myocardial oxygen uptake: 1. Tension development within the myocardium 2. Myocardial contractility 3. Heart rate • RPP = SBP x HR Heart’s Energy Supply • The myocardium relies almost exclusively on energy released from aerobic reactions. • Myocardial tissue contains the greatest mitochondrial concentration of all tissues. • Glucose, fatty acids, and lactate formed from glycolysis in skeletal muscle all provide the energy for myocardial functioning. Heart Rate Regulation: Intrinsic • Sinoatrial (S-A) node: Spontaneously depolarizes and repolarizes to provide an “innate” stimulus to the heart. • Atrioventricular (A-V) node: Delays the impulse about 0.10 seconds to provide sufficient time for the atria to contract and force blood into the ventricles • A-V bundle or Bundle of His • Purkinje Fibers: Speed the impulse rapidly through the ventricles Heart Rate Regulation: Intrinsic (Cont.) Heart Rate Regulation: Intrinsic Heart Rate Regulation: Extrinsic • Sympathetic Influence Releases catecholamines epinephrine and nor-epinephrine Leads to tachycardia (>100 beats/min) • Parasympathetic Influence Releases acetylcholine Leads to bradycardia (<60 beats/min) Heart Rate Regulation: Extrinsic Heart Rate Regulation: Extrinsic • Cortical Influence Central command provides the greatest control over heart rate Exerts its effect during exercise, at rest and in the immediate pre-exercise period Produces an anticipatory heart rate, which becomes particularly apparent prior to all-out physical effort Heart Rate Regulation: Extrinsic Heart Rate Regulation: Extrinsic • Peripheral Input Mechanoreceptors and chemoreceptors Stimuli from these peripheral receptors monitor the state of active muscle Heart Rate Regulation: Extrinsic Arrhythmias • Extrasystoles: Extra beats • Premature atrial contraction or PAC: Parts of the atria become prematurely electrically active and depolarize spontaneously prior to S-A node excitation Linked PACs can create atrial fibrillation. • Premature ventricular contraction or PVC: Premature excitation of ventricles Ventricular fibrillation Blood Distribution During Exercise • Increased energy expenditure requires rapid readjustments in blood flow that affect the entire cardiovascular system. • The vascular portion of active muscles increases through dilation of local arterioles. • At the same time, other vessels constrict to “shut down” blood flow to tissues that can temporarily compromise blood supply. Blood Flow Regulation • Flow = Pressure ÷ Resistance • Three factors determine resistance to blood flow: 1. Viscosity or blood thickness 2. Length of conducting tube 3. Radius of blood vessel • Poiseuille’s Law Flow = (Pressure gradient x Vessel radius4) ÷ (Vessel length x Fluid viscosity) Three Blood Flow Regulation Factors 1. Local: Local increases in temperature, carbon dioxide, acidity, adenosine, nitric oxide, and magnesium and potassium ions enhance regional blood flow. 2. Neural: Central vascular control via sympathetic and parasympathetic portions of the autonomic nervous system overrides vasoregulation afforded by local factors. 3. Hormonal: With sympathetic activation, adrenal glands release epinephrine and norepinephrine to cause a general constrictor response except in blood vessels of the heart and skeletal muscles. Cardiac Output • The most important indicator of the circulatory system’s functional capacity to meet the demands for physical activity • Cardiac output = Heart rate x Stroke volume • Cardiac output, mL·min-1 = [VO2, mL·min-1 ÷ avO2 diff, mL·dL blood-1] x 100 Cardiac Output Exercise Stroke Volume • Three physiologic mechanisms that increase the heart’s stroke volume during exercise: 1. Enhanced cardiac filling in diastole followed by a more forceful systolic contraction. 2. Neurohormonal influence causes normal ventricular filling with a subsequent forceful ejection and emptying during systole. 3. Training adaptations can expand blood volume and reduce resistance to blood flow in peripheral tissues. Exercise Stroke Volume Diastolic Filling and Systolic Emptying • Preload: Greater ventricular filling in diastole during the cardiac cycle from an increase in venous return • Afterload: Resistance to flow from increased systolic pressure Cardiovascular Drift • A gradual time-dependent downward “drift” in several cardiovascular responses, most notably stroke volume with a compensatory heart rate increase, during prolonged steady-rate exercise Exercise Heart Rate Trained vs. Untrained People • Heart rate increases rapidly and levels off within several minutes during sub-maximum steady-rate exercise. • Heart rate for the untrained person accelerates relatively rapidly with increasing exercise demands. • A much smaller heart rate increase occurs for the trained person so that they achieve a higher level of exercise oxygen uptake at a particular submaximal heart rate than a sedentary person. Cardiac Output and Oxygen Transport • A low aerobic capacity links closely to a low maximum cardiac output. • An increase in maximum cardiac output directly improves a person’s capacity to circulate oxygen and profoundly impacts the maximal oxygen consumption. Cardiac Output and Oxygen Transport Cardiac Output Differences • Cardiac output and oxygen consumption remain linearly related during graded exercise for boys and girls and men and women. Teenage and adult females exercise at any level of submaximal oxygen consumption with a 5-10% larger cardiac output than males. • Compared to adults, children have smaller cardiac outputs at any given submaximal exercise oxygen consumption from smaller stroke volumes. A-VO2 Difference During Exercise • VO2max = Max cardiac output x Max a-vO2 difference • The capacity of each dl of arterial blood to carry oxygen actually increases during exercise from an increased hemo-concentration from the progressive movement of fluid from the plasma to the interstitial space. • Diverting a large portion of the cardiac output to active muscles influences the magnitude of the a-vO2 difference in maximal exercise. • An increase in the capillary to fiber ratio reflects a positive training adaptation that enlarges the interface for nutrient and gas exchange during exercise. A-VO2 Difference During Exercise Cardiovascular Adjustments to Upper-Body Exercise • The highest oxygen uptake during upper-body exercise generally averages between 70% to 80% of the VO2max in bicycle and treadmill exercise. • Maximal heart rate and pulmonary ventilation remain lower in exercise with the arms from a relatively smaller muscle mass. • Any level of submaximal power output produces a higher oxygen uptake with arm compared with leg exercise. Cardiovascular Adjustments to Upper-Body Exercise The End