Cardiovascular System. Cardiovascular System. Objectives. Blood. Review of anatomy & blood flow

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1 Objectives Review of anatomy & blood flow Cardiovascular System Systemic and localized (within the heart) blood flow & blood pressure a) Rest, exercise & recovery CV regulation & integration Functional capacity of CV system Adaptations to exercise Cardiovascular System Composed of blood, the heart, and vasculature within which blood is pumped throughout the body Figure 15.3a a) Pulmonary Circulation Concerning blood flow to, within and from the lungs b) Systemic Circulation Concerning blood flow to, within and from the remainder of the body Consists of tissue/organ specific circulation beds (ex: renal, hepatic, skeletal muscle, etc.) Figure 15.1 Water, clotting proteins, transport proteins, lipoproteins, glucose, FA, antibodies, waste products Plasma the liquid component of blood & all of it s non-cellular content Blood 55% of whole blood (0.3ml O 2 ) <1% of whole blood Hematocrit: 45% of whole blood (19.7ml O 2, 15g Hb) 1

2 Blood volume ~ 5 L, but varies with: a) Body size b) Endurance training c) Exposure to extreme environments % distribution at rest Hemodynamics BF & Resistance Pressure a) Blood flows from high low pressure Resistance a) Length of the vessel b) Viscosity of the blood c) Radius of the vessel A small change in vessel diameter can have a dramatic impact on resistance! Resistance = Length x viscosity Radius 4 Blood Pressure Arterial blood pressure reflects the combined effects of arterial blood flow per minute & the resistance offered by the peripheral vasculature BP = Cardiac Output x Total Peripheral Resistance a) Systolic BP Estimate of the work of the heart and the force that blood exerts on the arterial wall during ventricular systole Figure 15.4 b) Diastolic BP Indicates the ease with which blood flows from the arterioles into the capillaries Peripheral resistance Arterial BP Classifications Hypertension Chronically elevated arterial BP > 140 mmhg systolic > 90 mmhg diastolic Treatment a) Exercise b) Drug therapy 2

3 Blood Pressure (cont.) c) Mean Arterial Pressure the average force exerted by the blood against the arterial walls during the entire cardiac cycle MAP = Diastolic BP + [0.33(Systolic BP Diastolic BP)] Blood Flow Continuum Arteries, arterial BP & arterioles Capillaries: REST EXERCISE d) Relationship between BP, Cardiac Output & TPR Cardiac Output = MAP / TPR TPR = MAP / Cardiac Output Venous system serves as blood reservoirs Blood Flow Continuum Skeletal muscle pumps & venous pooling a) Application of an active cool down Figure 15.5C BF & Pressure in the Systemic BP Response to Exercise Resistance exercise: a) Straining compresses vessels b) TPR c) Sympathetic nervous system activity, cardiac output, and MAP increase in attempt to restore muscle BF Heavy resistance training intensifies the BP response Figure

4 BP Response to Exercise (cont.) Graded Exercise: a) Systolic pressure with increases in workload b) There is a linear relationship between workload and systolic BP c) Diastolic pressure remains fairly constant BP Response to Exercise (cont.) Upper Body Exercise a) Resistance to flow is increased with upper body exercise b) Smaller vessels in upper body compress more easily Recovery BP a) Following endurance exercise, there is a hypotensive response b) BP temporarily falls below normal resting values The Heart s Blood Supply Coronary circulation: a) Right and left coronary arteries branch off the upper ascending aorta b) RCA supplies predominantly the right atrium and ventricle c) LCA supplies the left atrium and ventricle and a small portion of the right ventricle Myocardial O 2 Use At rest, myocardium extracts ~ 70 80% available O 2 from the coronary vessels During exercise flow must increase to meet O 2 demand a) Flow may increase 5 7 times Vasodilation of the coronary vessels due to: a) Adenosine (byproduct of ATP breakdown) b) Hypoxia c) Sympathetic nervous system hormones Measurement of Myocardial Work Rate Pressure Product: Systolic BP x HR = RPP Myocardial Metabolism reliant upon energy released from aerobic metabolism a) Myocardium has a significantly higher mitochondrial density compared to skeletal muscle Allows the heart to utilize available substrates depending on activity Figure

5 CV Regulation & Integration Figure Intrinsic Regulation Time sequence (seconds) for electrical impulse transmission Figure 16.1 Measuring Electrical Activity Electrocardiogram (ECG or EKG) Measuring Electrical Activity Electrocardiogram (ECG or EKG) 5

6 Extrinsic Regulation Elicit changes in HR rapidly through nerves that directly supply the heart & chemical messengers that circulate in blood Sympathetic & Parasympathetic Neural Input Extrinsic Regulation (cont.) Sympathetic neural input: a) Localized Stimulation of cardioaccelerator nerves causes the release of the catecholamines epinephrine & norepinephrine 9 Accelerate SA node depolarization which increases HR (chronotropic effect) 9 Increases contractility (inotropic effect) b) Systemically Stimulation produces vasoconstriction (except coronary vasculature) 9 Release of norepinephrine by adrenergic fibers causes vasoconstriction 9 Vasomotor tone Extrinsic Regulation (cont.) Parasympathetic neural input: a) Localized Stimulation of vagus nerves causes release of the neurohormone acetylcholine which slows sinus discharge & therefore HR 9 Slows sinus discharge & therefore HR 9 No effect on contractility Figure 16.3 Central Command Exercise Anticipation Rapid adjustments (feed-forward mechanisms) with the onset of exercise Figure Figure

7 Peripheral Input Chemoreceptors: monitor metabolites, blood gases Distribution of BF during Exercise Mechanoreceptors: monitor movement and pressure Baroreceptors: monitor blood pressure in arteries a) Aortic arch & carotid sinus Local Factors within the Muscle Nitric Oxide Autoregulatory mechanisms allow for blood flow, blood volume with only a small increase in velocity, and effective surface area for gas & nutrient exchange a) Vasodilation induced by: blood flow temperature CO2 acidity adenosine, K + & Mg 2+ NO Figure 16.7 Hormonal Factors Adrenal medulla releases: a) Larger amounts of epinephrine and smaller amounts of norepinephrine b)cause vasoconstriction (except in coronary & skeletal muscle) Minor role during exercise Functional Capacity of the CV System 7

8 Cardiac Output (Q) Q = HR x SV Methods of Measuring Q a) Direct Fick = (VO 2 ml min -1 /a-vo 2 difference) x 100 Cardiac Output (Q) Q = HR x SV Methods of Measuring Q a) Direct Fick = (VO 2 ml min -1 /a-vo 2 difference) x 100 b) Indicator dilution c) CO 2 rebreathing Q at rest a) Values vary depending upon: Emotional state (central command via cardioaccelerator nerves & nerves modulating arterial resistance) Posture b) Average male (70kg) ~ 5L min -1 c) Average female (56kg) ~ 4L min -1 ~ 25% lower in females Untrained vs. Endurance trained characteristics of Q at rest: a) Variation in resting HR Untrained: Trained: Q = 5000 ml min -1 = 5000 ml min -1 = Rest HR x 70 b min -1 x 50 b min -1 x SV 71 ml min ml min -1 Untrained (UT) vs. Endurance trained (ET) characteristics of Q during exercise: a) Both UT & ET Q rapidly with onset of exercise Subsequently a more gradual rise to meet exercise metabolic demands b) Variation between groups often observed as intensity b) Mechanisms: Increased vagal tone (parasympathetic) w/decreased sympathetic drive Increased blood volume Increased myocardial contractility and compliance of left ventricle Untrained: Trained: Maximal Exercise Q = HR x 22,000 ml = 195 b min -1 x 35,000 ml = 195 b min -1 x SV 113 ml min ml min -1 Mechanisms: a) Enhanced cardiac filling in diastole (preload) & a more forceful ejection caused by an in end diastolic volume (EDV) Starling s Law: the greater the stretch, the more forceful the contraction (contractility) b) Greater systolic emptying greater systolic ejection overcomes exercise-induced arterial blood pressures (afterload) c) Expanded blood volume & reduced peripheral resistance in tissues in ET individuals 8

9 CV Drift w/ Prolonged Exercise SV and coinciding a gradual in HR Blood Flow Rest Proposed mechanisms: a) Progressive H 2 O loss and a fluid shift from plasma to tissues Drop in PV decreases central venous cardiac filling pressure b) Increased core temperature c) Progressive increase in HR with CV drift during exercise EDV, subsequently reducing SV Figure 17.3 Blood Flow Distribution & Exercise 1. Hormonal vascular regulation 2. Local metabolic conditions Q & O 2 Transport Arterial blood carries ~ 200mL of O 2 per L of blood Resting conditions: a) If rest ~ 5L min -1, then 1000mL of O 2 would be available to the body each minute b) Resting oxygen consumption (VO 2 ) ~ 250 to 300mL min -1 c) Leaves ~ 750mL of oxygen returning to the heart unused Q & O 2 Transport (cont.) Exercise conditions: a) Even during max exercise, Hb saturation remains nearly complete, so each L of blood carries ~ 200mL of O2 Ex: a max exercise Q of 16L x 200mLO 2 L -1 ~ 3200mL b) Debate exists as to the real cause of a VO 2 max plateau Q O 2 extraction at the tissues O 2 delivery Central Peripheral Q & VO 2 max Association Figure

10 O 2 Extraction: a-vo 2 Difference From Rest to Exercise Exercise oxygen consumption increases by: a) Increased cardiac output b) Greater use of the O 2 already carried by the blood Expanding a-vo 2 difference VO 2 = Q x a-vo2 difference Figure 17.5 Factors affecting a-vo 2 difference during exercise: a) Central diversion of blood flow to working tissues b) Peripheral Increased skeletal muscle microcirculation increases extraction Increase in capillary to fiber ratio Cells ability to regenerate ATP aerobically Increased # and size of mitochondria Increased aerobic enzyme concentration CV Adaptation/ Response to Training Cardiac Hypertrophy Plasma Volume Expansion Up to 20% increase in PV (without changes in [RBC]) after 3 to 6 aerobic exercise sessions Mechanisms: a) Directly related to increased synthesis and retention of plasma albumin Increased PV: a) Increases EDV, SV, O 2 transport, & temperature regulation during exercise Figure

11 Heart Rate Stroke Volume Figure 21.9 Figure Cardiac Output a-v O 2 difference Figure Figure Blood Flow Distribution BF shunting toward Type I fibers (oxidative) during submaximal exercise Better distribution from non-active areas Enlarged cross-sectional area of arteries, veins & capillary beds Myocardial BF: a) Increased perfusion capabilities b) Mitochondrial mass & density increased Reduction in BP Figure