Hematocrit

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

Pressure Difference Drives Blood Flow in the Systemic Circuit

Pressure Changes Across the Systemic Circulation

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)

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

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

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

Changes in Cardiovascular Variables During Exercise

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

Redistribution of Blood Flow Increased blood flow to working skeletal muscle Reduced blood flow to less active organs –Liver, kidneys, GI tract

Changes in Muscle and Splanchnic Blood Flow During Exercise

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

Redistribution of Blood Flow During Exercise

Circulatory Responses to Exercise Heart rate and blood pressure Depend on: –Type, intensity, and duration of exercise –Environmental condition –Emotional influence

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

Cardiovascular Responses during Transitions

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

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.

Heart Rate and Blood Pressure During Arm and Leg Exercise

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).

HR, SV, and CO During Prolonged Exercise

Summary of Cardiovascular Adjustments to Exercise

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

A Summary of Cardiovascular Control During Exercise