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Hematocrit
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hematocrit is the percentage of whole blood which is composed of solid material –cells, platelets etc the blood is composed primarily of water (~55 %) called plasma –the hematocrit would be 45 can vary between 40 and 50
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Pressure Difference Drives Blood Flow in the Systemic Circuit
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Pressure Changes Across the Systemic Circulation
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Why the pressure change? Blood flow = change in pressure / resistance increases in pressure at the beginning or decreases in pressure at the end will increase blood flow this could result in increased resistance to compensate (homeostasis)
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Resistance the most important factor determining blood flow is resistance the most important factor determining resistance is the radius of the vessel Resistance = Length X viscosity / radius 4
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Cardiac Output during Exercise Q increases in direct proportion to the metabolic rate required to perform task linear relationship between Q and VO2 remember... Q = HR x SV
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Stroke Volume and Heart Rate during Exercise in untrained or moderately trained individuals stroke volume plateaus ~ 40% VO2 max at work rates > 40% VO2 max, Q increases by HR alone See fig 9.17
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Changes in Cardiovascular Variables During Exercise
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The Fick Equation VO2 = Q x (a-vO2 diff) VO2 is equal to the product of cardiac output and arterial-mixed venous difference an increase in either Q or a-vO2 difference will result in an increase in VO2max
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Redistribution of Blood Flow Increased blood flow to working skeletal muscle Reduced blood flow to less active organs –Liver, kidneys, GI tract
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Changes in Muscle and Splanchnic Blood Flow During Exercise
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Increased Blood Flow to Skeletal Muscle During Exercise Withdrawal of sympathetic vasoconstriction Autoregulation –Blood flow increased to meet metabolic demands of tissue –O 2 tension, CO 2 tension, pH, potassium, adenosine, nitric oxide
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Redistribution of Blood Flow During Exercise
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Circulatory Responses to Exercise Heart rate and blood pressure Depend on: –Type, intensity, and duration of exercise –Environmental condition –Emotional influence
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Transition From Rest Exercise and Exercise Recovery Rapid increase in HR, SV, cardiac output Plateau in submaximal exercise Recovery depends on: –Duration and intensity of exercise –Training state of subject
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Cardiovascular Responses during Transitions
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Incremental Exercise Heart rate and cardiac output –Increases linearly with increasing work rate –Reaches plateau at 100% VO 2max Systolic blood pressure –Increases with increasing work rate Double product –Increases linearly with exercise intensity –Indicates the work of the heart Double product = heart rate x systolic BP
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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.
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Heart Rate and Blood Pressure During Arm and Leg Exercise
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Prolonged Exercise Cardiac output is maintained –Gradual decrease in stroke volume –Gradual increase in heart rate Cardiovascular drift –Due to dehydration and increased skin blood flow (rising body temperature).
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HR, SV, and CO During Prolonged Exercise
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Summary of Cardiovascular Adjustments to Exercise
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Summary of Cardiovascular Control During Exercise Initial signal to “drive” cardiovascular system comes from higher brain centers Fine-tuned by feedback from: –Chemoreceptors –Mechanoreceptors –Baroreceptors
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A Summary of Cardiovascular Control During Exercise
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