HEAMODYNAMICS DEFINITIONBlood flow BLOOD FLOW Velocity of blood

• • HEAMODYNAMICS DEFINITION=Blood flow BLOOD FLOW Velocity of blood flow=Quantity of blood/cross -sectional area of blood vessel Method of study: Doppler flowmeter Plethysmograph-use to measure volumeenclosed organ Venous occlusion plethysmograph

• Fick pricinple : dye dilution method • Types of blood flow • Laminar flow: silent flow, occur at velocities up to a critical level • Turbulent flow: • noisy flow, • occurs when the velocity is above critical level, • increase resistance to forward flow • Both forward and backflow

• CRITICAL VELOCITY at which blood flow become turbulent is known as REYNOLD’S NUMBER • REPRESENTED AS • NR=PDV/ɳ • NR-Reynolds number • P- density of the blood • D-Diameter of the vessel • V-velocity of the flow • ɳ-viscosity

• Factors influencing blood flow 1. PRESSURE GRADIENT=BF directly proportional to PG 2. RESISTANCE TO BLOOD FLOW(peripheral resistance)= • inversely proportional to BF • Increases away from the heart e. g resistance in aorta<artery<arteriole

FACTOR AFFECTING PERIPHERAL RESISTANCE • Radius of blood vessels: PR inversely proportional radius • Pressure gradient: ∆Pressure/volume of blood flow • Viscosity

• 3. VISCOSITY: the friction of blood against the wall of the blood vessels, the thickness of blood • inversely proportional to blood flow • Increases with Hemoconcentration from burn, polycythemia • Decreases with aneamia

4. DIAMETER OF BLOOD VESSELS BV flow is directly proportional to the diameter of the blood vessel(cross sectional) Factors influencing diameter of blood vessel Physiological and pathological factors

PHYSIOLOGICAL FACTORS • Elasticity of blood vessel: • Integrity of endothelium(the inner lining of blood vessel) • Sympathetic innervation of blood vessels (vascular tone; vasomotor tone)

PATHOLOGICAL FACTORS I. Damage to endothelium II. Blockade of blood vessel (artheroscleroris) III. Increase in vascular tone(↑sympathetic nerve) IV. Increase adrenaline during stress

5. Velocity of blood flow BF volume is directly proportional to velocity of blood flow

• FACTORS MAINTAINING blood flow VELOCITY I. Cardiac output II. Cross-sectional area of the blood vessel III. Viscosity of blood

• Conditions decreasing flow I. Hypothyrodism II. Polycythemia III. Cardiac failure

• Condition increasing blood flow velocity I. Exercise II. Adrenaline injection III. Hypethyrodism IV. Anemia V. Decrease in peripheral resistance eg by antihypertensive drug VI. Nitric oxide supplement

• Local regulation of blood flow • This is the regulation of blood flow to organs initiated by the organ • It is Intrinsic • Theories of autoregulation • Myogenic theory-stretching of blood vessel by blood, intrisically results in the contraction (constriction) of the vessel =reduced blood flow • Metabolic theory=metabolites generated in working tissues increases the cross-sectional area of the vessel (vaodilators)

• Examples of metabolic vasodilator I. ↑ Temperature II. ↑CO 2 or PCO 2 III. ↓Po 2 IV. ↑Lactate V. ↑Hydrogen ion (↓p. H) VI. ↑ADP

• AUTOREGULATION IS PROMINENT IN I. HEART II. KIDNEYS III. BRAIN