Cardiovascular Exercise Physiology PDF

Cardiovascular Exercise Physiology Ch 9 1  Introduction One major challenges to homeostasis posed by exercise is the increased muscular demand for oxygen During heavy exercise, oxygen demands may  by 15 to 25 times Two major...

Cardiovascular Exercise Physiology Ch 9 1  Introduction One major challenges to homeostasis posed by exercise is the increased muscular demand for oxygen During heavy exercise, oxygen demands may  by 15 to 25 times Two major adjustments of blood flow are;  cardiac output Redistribution of blood flow A thorough understanding of the cardiovascular system is essential to exercise physiology 2  Cardiovascular/Respiratory Systems Components: 1. Heart 2.Vessels (arteries, capillaries, and veins) 3.Blood 4.Lungs. Circulations 1. Systemic circulation 2.Pulmonary circulation 3.Cardiac circulation Functions 1. O2/CO2 exchange between the body and environment 2.Transport O2 to tissues and removal of waste 3.Transport of nutrients to tissues 4.Regulation of body temperature 3  Cardiovascular Function Blood content in different cardiovascular compartment at rest 4  The Cardiac Cycle Systole Contraction of the ventricle Diastole Relaxation of the ventricle Fig 9.3 At very high intensity ex., cardiac out put might be compromised due to ↑HR and ↓ 5 diastolic phase. Pressure Changes During the Cardiac Cycle 6 Fig 9.4  Arterial Blood Pressure Expressed as systolic/diastolic Normal is 120/80 mmHg High is 140/90 mmHg Systolic pressure (upper number) Pressure generated during ventricular contraction (systole) while the atrial is relaxed Diastolic pressure Pressure in the arteries during ventricular relaxation (diastole) while the atrial is contracted 7  Blood Pressure Pulse pressure Difference between systolic and diastolic Pulse Pressure = Systolic - Diastolic Mean arterial pressure (MAP) Average pressure in the arteries MAP = Diastolic + 1/3(pulse pressure) 8  Mean Arterial Pressure Blood pressure of 120/80 mm Hg MAP = 80 mm Hg +.33(120-80) = 80 mm Hg + 13 = 93 mm Hg 9 Factors That Influence Arterial Blood Pressure Central factors Vascular resistance Peripheral factors increases Fig 9.6 10  Electrical Activity of the Heart Contraction of the heart depends on electrical stimulation of the myocardium Impulse is initiated in the right atrium and spreads throughout entire heart May be recorded on an electrocardiogram (ECG) 11 Conduction System of the Heart Fig 9.7 12  Electrocardiogram Records the electrical activity of the heart P-wave Atrial depolarization QRS complex Ventricular depolarization T-wave Ventricular repolarization 13 Fig 9.9 Electrocardiogram Fig 9.9 14 Cardiac Cycle & ECG Fig 9.10 15  Diagnostic Use of the ECG ECG abnormalities may indicate coronary heart disease ST-segment depression can indicate myocardial ischemia Heart attack 16 Fig 9.8 Abnormal ECG Fig 9.8 17  Cardiovascular Function Cardiovascular/respiratory endurance is the ability of the lungs, heart, and blood vessels to deliver adequate amounts of oxygen to the cells to meet the energy demands of prolonged muscular contraction associated with physical activity. At the cellular level, oxygen is used to convert food substrates, primarily carbohydrates and fats, into energy necessary to conduct body functions. Because the body needs more energy during physical exertion, the heart, lungs, and blood vessels have to deliver more oxygen to the cells. 18  Cardiovascular Function During prolonged exercise an individual with a high level of cardiovascular/respiratory endurance is able to deliver the required amount of oxygen to the tissues with relative ease. The cardiovascular/respiratory systems of a person with a low level of endurance has to work much harder. 19  Cardiovascular Function Oxygen Consumption Oxygen consumption (VO2) (Fick equation) VO2 = SV * HR * a-vO2 diff. (is a marker for CV endurance) During exercise VO2 increases as a result of the increase in all component of Fick equation. Q (SV & HR) and a-vO2 diff. atrial-venous Oxygen difference (a-vO2 diff). Peripheral component a-vO2 diff: represent the amount oxygen extracted by the muscle. Calculated as the difference between the oxygen content of arterial blood and venous blood. Increases with increasing rates of exercise as more oxygen is taken from blood. 20  Cardiovascular Function Oxygen Consumption Cardiac output (Q): Total volume of blood pumped by the left ventricle per minute. Central component SV: Volume of blood pumped per contraction. HR: Number of heart beats per minute. 21  Cardiovascular Endurance Factors Influencing Aerobic Fitness Heredity In order to become a world-class athlete, you need to choose your parents carefully!!!!!!!!!!!! Heredity accounts for Accounts for 40%-66% VO2max. Factors could be inherited: Maximal capacity of the respiratory system. Maximal capacity of the cardiovascular system. Heart size. More red cells and hemoglobin.  slow oxidative muscle fibers.  mitochondria. Muscle responsiveness to training. 22  Cardiovascular Endurance Factors Influencing Aerobic Fitness Training Potential aerobic improvement 15-25%. With lose of body fat. Adolescents may improve up 30%. Factors might improve with training: Function and capacity of cardiorespiratory system. Blood volume. Muscle ability to produce energy aerobically (more from fat than CHO).  # of mitochondria.  oxidative enzymes  fat transportation through the body 23  Cardiovascular Endurance Factors Influencing Aerobic Fitness Gender Before puberty boy and girl aerobic capacity is pretty much similar. Women are about 20–25% less than their male counterparts. Among elite athletes, female aerobic capacity is less different than their male counterparts (only 10%). Effect of training Factors might contribute to the differences:  Hemoglobin (carries O2).  blood volume (~4.5 vs. ~5.5 L).  muscle mass &  % body fat. 24  Cardiovascular Endurance Factors Influencing Aerobic Fitness Age As we age, aerobic fitness decline (after the age of ~30). Exercise & activities eases the effect of aging on VO2. Inactive  8-10%. Active  5%. Aerobically fit  2.5%. Aerobic improvement could be achieved at any age. Never too late to start. 25  Cardiovascular Endurance Factors Influencing Aerobic Fitness Body fat Fitness is related to body weight  weight  fitness. by loosing weight/fat without exercising, fitness improves. 26  Cardiovascular Endurance Assessments Because all tissues of the body need oxygen to function, higher oxygen consumption indicates a more efficient cardiorespiratory system. Cardiovascular endurance is determined by the maximal amount of oxygen (Max VO2) the human body is able to utilize per minute. Represent the maximum ceiling of O2 transport to the working muscles 27  M.A.-SM/05 Measuring Energy Costs of Exercise The most accurate way to determine energy cost during different levels of exercise is “energy chambers”. But is not efficient (i.e. expensive, training) 28  Cardiovascular Endurance Assessments Spirometer: Direct gas analysis is also considered accurate. This type of equipment is not available in most health centers or hospitals. i.e. too expensive, requires training 29  Cardiovascular Endurance Assessments Therefore, several alternative methods of estimating maximal oxygen uptake have been developed using limited equipment. Examples of submaximal tests: 1.5-Mile Run Test, 1.0-Mile Walk Test, Step Test, Astrand-Rhyming Test, 2-Minute Swim Test and YMCA cycle test. 30  Cardiovascular Endurance Assessments Usually the type of test used to determine one’s level of fitness depends on the exercise the individual has been performing or/and will be prescribed to that individual. 31  Cardiovascular Endurance Cardiovascular Response to Acute Exercise The main function of the cardiovascular system during exercise is to increase blood delivery and removal in the muscles. o VO2 increases as a result of increase in HR, SV, Q, and a-vO2 diff increase. o HR increases because the heart contract faster. o SV increase result from increase in venous return and contractility of the heart. Larger blood volume within the left ventricle and more forceful contraction. o Resting Q value is approximately 5.0 L/min. Increases directly with increasing exercise intensity to between 20 to 35 L/min. Value of increase varies with body size and endurance conditioning. When exercise intensity exceeds 40% further increases in Q are more a result of increases in HR than SV. 32  Cardiac Output (Q) Q during exercise increases in proportion to metabolic demands Mostly demands of the muscles Q decreases with aging due to decrease in maximum HR Max HR = 220-age 33  Cardiac Output (Q) The increase is due to SV & HR SV contribute up to 40% VO2max The platue is due to increased HR ↑HR ↓atrial & ventricular filling time ↓ EDV ↓ SV SV can contribute to higher % in trained individuals ↑blood volume  ↑filling volume, venous return & stroke volume Less HR at a given intensity, allowing more filling HR contribute from beginning of Ex. to 100% VO2 34  Cardiac Output (Q) Heart rate Stroke volume Cardiac output Subject (beats/min) (ml/beat) (L/min) Rest UnM 72 X 70 = 5.00 UnF 75 X 60 = 4.50 TM 50 X 100 = 5.00 TF 55 X 80 = 4.50 Max Ex. UnM 200 X 110 = 22.0 UnF 200 X 90 = 18.0 TM 190 X 180 = 34.2 TF 190 X 125 = 23.9 Table 9.1 35  Cardiorespiratory Endurance Cardiovascular Response to Acute Exercise Heart rate Stroke volume Cardiac output Subject (beats/min) (ml/beat) (L/min) Resting (supine) 55 95 5.2 Resting (standing 60 70 4.2 and sitting) Running 190 130 24.7 Cycling 185 120 22.2 Swimming 170 135 22.9 Note to students: Don’t focus much on numbers on this slide, just get the idea 36 Cardiorespiratory Endurance Cardiovascular Response to Acute Exercise Increase in HR, SV, and Q result in increase in BP. Systolic BP increases in direct proportion to increased exercise intensity. Diastolic BP changes (↑ or ↓) little if any during endurance exercise, regardless of intensity. The increase in pressure is to maintain sufficient blood flow toward the contracting muscle 37 Changes in CV Variables During Exercise Fig 9.18 38  Regulation of Heart Rate HR is controlled mainly by SA & AV nodes, which controlled by: Parasympathetic nervous system (parasympathetic tone) ↑stimulation  ↑ Ach ↓SA&AV node activities  ↓in HR ↓stimulation  ↑ in HR Initial ↑ in HR (up to 100 b/min) is due to withdraw of parasympathetic activities Fig 9.11 Faster respond because mylanated nerves 39  Regulation of Heart Rate HR is controlled mainly by SA & AV nodes, which controlled by: Sympathetic nervous system ↑stimulation  ↑ NEpi ↑SA&AV node (β-adrenergic receptors) activities  ↑in HR & force of contraction Responses of parasympathetic are faster than sympathetic Both divisions of nervous system innervate SA & AV nodes 40 Fig 9.11  Regulation of Heart Rate control of autonomic nervous system CV center in medulla oblongata Impulses (∆BP & blood PO2) are sent from various parts of the circulatory system Pressures sensors Carotid bodies (sinus) in the carotid artery Aortic sinus in the aorta Right atrium (venous return) Temperature sensors Skin Core body ↑body temp.  ↑HR (↑ circulation ↑ heat loss) Fig 9.11 41 Nervous System Regulation of HR 42 Fig 9.11 FACTORS INFLUENCING SV  Regulation of Stroke Volume Regulation of VR: Venoconstriction ↑venous emptying (propelling blood toward the heart) Muscle pump Compress veins and push blood toward the heart Respiratory pump The rhythmic pattern of respiratory muscle contraction regulate pressure in the thorax & abdominal cavities thereby regulate venous flow toward the heart. Inspiration  ↓thorax pressure & ↑abdominal pressure  ↑ venous flow from abdominal to thorax ↑ VR The role of these mechanisms are enhanced during exercise 44  Cardiac Output During Exercise Blood Shunting Maximum is based on cardiac output of 30 l/min 45 Cardiac Output During Exercise Blood Redistribution (Shunting) Fig 9.19 46  Cardiovascular Endurance Cardiovascular Response to Acute Exercise Blood Shunting: (blood redistribution) o During exercise blood is being shunted from least active tissues (abdominal) to most active tissues (muscle). Vasoconstriction (least active). increase in vascular resistance. ↓vessel diameter due to ↓parasympathetic & ↑sympathetic activities 47  Cardiovascular Endurance Cardiovascular Response to Acute Exercise Vasodilation (most active) decrease in vascular resistance (↑vessel diameter). Due to: Metabolic factors: ↓O2 tension, ↑CO2 tension, ↓pH, ↑potassium, and ↑adenosine Endothelium factors: ↑nitric oxide and prostacycline production The increase in HR, SV, Q and decrease in VR result in blood flow increase to active tissues (muscle). 48  Local Regulation of BF During Ex. ↑ in sympathetic & epi activities during exercise should result in ↑ systemic vasoconstriction!!!! How is sufficient BF is delivered to muscles? Autoregulation Blood flow increased to meet metabolic demands of tissue Local vasodilators override sympathetic vasoconstriction ↓O2 tension, ↑CO2 tension, ↓ pH, ↑potassium, ↑adenosine, ↑nitric oxide Recruitment of capillaries Only 5-10% capillaries are open at rest 49  Relationship Among Pressure, Resistance, and Flow Blood flow through the vascular system depends on: ∆Pressure Blood flow= Resistance Difference in pressure at the two ends of the circulation Blood flows from high low pressure Proportional to the difference between pressure in the aorta (MAP) and right atrial (P) 50 Fig 9.15  Relationship Among Pressure, Resistance, and Flow Vascular resistance depends on Length of the vessel Viscosity of the blood Length x viscosity Resistance = Radius of the vessel Radius4 Greatest vascular resistance occurs in arterioles ↑ in BF can be achieved by either ↑BP or ↓VR Which the body changes during ex.? A small change in vessel diameter can have a dramatic impact on resistance! Vasodilation and vasoconstriction 51 Pressure Changes Across the Systemic Circulation Fig 9.16 52 Pressure Changes Across the Systemic Circulation 53  Factors control circulatory responses to exercise Heart rate and blood pressure Depend on: Type, intensity, and duration of exercise Environmental condition Hot/humid  ↑HR & BP Emotional influence Emotionally charged environment  ↑HR & BP When patient surrounded with staff members 1st time patients Athletes performing in front of crowd 54  Transition From Rest Exercise and Exercise Recovery ↑ HR, SV, & Q within 1 second When below lactate threshold, HR, SV, Q during exercise reach plateau in 2 minutes. Recovery HR, SV, & Q depends on: Duration ↓ duration  faster recovery Intensity of exercise ↓ intensity  faster recovery Training status of subject They don’t achieve higher HR as untrained Faster replenishments of various systems Fig 9.21 55 Transition From Rest Exercise Recovery 56 Fig 9.21  Incremental Exercise Heart rate and cardiac output Increases linearly with increasing work rate ↑ is achieved by ↑ BP & ↓vascular resistance Reaches plateau at 100% VO2max Systolic blood pressure Increases with increasing work rate Double product (DP): HR x systolic BP estimation of the metabolic demands placed on the heart Increases linearly with exercise intensity Metabolic demands placed on the heart during ex. is 5Xs at rest (table 9.2) Can be used to prescribe ex. for CV patients (check book pp186) Prescribing ex. below complication threshold (ie pain, ECG abnormalities) 57  Arm vs. Leg Exercise At the same oxygen uptake arm work results in higher: Heart rate Due to higher sympathetic stimulation Blood pressure Due to vasoconstriction of large inactive muscle mass Fig 9.22. 58 Heart Rate and Blood Pressure During Arm and Leg Exercise 59 Fig 9.22  Prolonged Exercise Cardiac output is maintained Gradual decrease in stroke volume Gradual increase in heart rate Cardiovascular drift Due to ↓in blood available to deliver to the working muscles Results in ↓VR  ↓SV  ↑HR (compensation) Rising body temperature dehydration ↑ cutaneous blood flow. 60 Fig 9.23 HR, SV, and Q During Prolonged Exercise 61 Fig 9.23 Cardiovascular Adjustments to Exercise Fig 9.24 62  Cardiovascular Adjustments to Exercise Initial signal to “drive” CV system comes from higher brain centers Fine-tuned by feedback from: Chemoreceptors In the muscles Mechanoreceptors In the muscles Baroreceptors Carotid bodies (sinus) in the carotid artery Aortic sinus in the aorta Right atrium (venous return) Redundancy in CV control Fig 9.24 63 A Summary of CV Control During Exercise 64 Fig 9.25