CIRCULATION MEDICAL PHYSICS PRESSURE FLOW RESISTANCE Distribution of

CIRCULATION MEDICAL PHYSICS PRESSURE FLOW RESISTANCE

Distribution of blood to the body organs Figure 15 -13: Distribution of blood in the body at rest

Blood vessel functions: overview Strong and elastic arteries Arterioles control blood flow and pressure Caps: thin and with large area for diffusional exchange Compliant, large, low R veins with valves assures blood return Figure 15 -1: Functional model of the cardiovascular system

Pulse and Mean Arterial Pressures Figure 15 -5: Pressure throughout the systemic circulation

Systolic pressure Mean pressure Diastolic pressure Left ventricle Large arteries Arterioles Capillaries Venules and veins Fig. 10 -8, p. 283

Some Physics of Fluid Movement: Blood Flow • Flow rate: (L/min) • Flow velocity = rate/C-S area of vessel Figure 14 -6: Flow rate versus velocity of flow

Poiseuille’s Law Flow = P/R R = length · viscosity / radius 4 CO = art. bp/TPR Flow proportional to P • Resistance reduces flow • Reduce vessel diameter – Increase viscosity or tube – length With constant flow, R can – affect P Figure 14 -4 c: Pressure differences of static and flowing fluid

Arteriolar constriction alters blood flow

Arterioles: large and variable R Flow = P/R R = P/Flow Parterioles and Rarterioles largest in CV system Figure 14 -2 : Pressure gradient in the blood vessels

Capillary Blood Flow Lowest velocity • Largest total • cross sectional area Hydrostatic • pressure drops slightly Figure 15 -17: The velocity of flow depends on the total cross-sectional area

Velocity of flow (mm/sec) 0. 5 500 Anatomical distribution Total cross-sectional area (cm 2) 4. 5 Blood flow rate (liters/min) 6, 000 5 Aorta Arteries Arterioles Capillaries Venules Veins Venae cavae Fig. 10 -14, p. 291

P 1 > P 2 P 1 mm Hg FLOW P 2 P = FLOW x R FLOW = P R R= L/min or ml/sec P FLOW mm Hg ml/sec Peripheral Resistance Units (PRU)

POISEUILLE’S LAW GOVERNING FLUID FLOW(Q) THROUGH CYLINDRIC TUBES (FLOW)Q = DIFFERENCE IN PRESSURE (Pi - Po) r 8 n. L VISCOSITY 4 LENGHT RADIUS

LAMINAR VS TURBULENT FLOW THE REYNOLD’S NUMBER LAMINAR FLOW TURBULENT FLOW Nr = p. Dv / n laminar = 2000 or less p = density D = diameter v = velocity n = viscosity

RESISTANCE AND BLOOD FLOW 1. RESISTANCE • 2. CODUCTANCE =1/ RESISTANCE • 3. DIAMETER OF THE BLOOD VESSELS • 4. CRITICAL CLOSING PRESSURE •

Total peripheral resistance Blood viscosity Arteriolar radius Number of red blood cells Local (intrinsic) control Concentration of plasma proteins Extrinsic control Myogenic responses to stretch Vasopressin Heat, cold application (therapeutic use) Angiotensin II Histamine release (involved with injuries and allergic responses) Epinephrine and norepinephrine Local metabolic Sympathetic activity changes in O 2, (exerts generalized vasoconstrictor CO 2, other effect) metabolites Major factors affecting arteriolar radius Fig. 10 -12, p. 290

1. DISTENSIBILITY=^VOL/^P x ORIGINAL VOL • 2. VASCULAR • COMPLIANCE(CAPACITANCE)=^VOL/^P 3. DELAY COMPLIANCE • 4. VOLUME PRESSURE CURVE • 5. ARTERIAL PRESSURE PULSATION • 6. TRANSMISSION OF PRESSURE PULSES • 7. DAMPING OF THE PRESSURE PULSES •

CLINICAL METHOD FOR MEASURING BP 1. PALPATION METHOD • 2. AUSCULTATORY • METHOD(KORTKOFF SOUNDS) A. SYSTOLIC BP • B. DIASTOLIC BP • C. MEAN ARTERIAL BP •

Pressure-recording device Stethoscope Inflatable cuff Fig. 10 -7 a, p. 282

When cuff pressure is between than 120 and 80 mm Hg: Blood flow through the vessel is turbulent whenever blood pressure exceeds cuff pressure. Intermittent sounds are heard as blood pressure fluctuates throughout the cardiac cycle. Fig. 10 -7 c (middle), p. 282

Cuff pressure Blood pressure Fig. 10 -7 b, p. 282

Effects of gravity on arterial and venous pressures. Each cm of distance produces a 0. 77 mm. Hg change. Veins Arteries 0 100 mm Hg 190 mm Hg Sphincters protect capillaries VENOUS PUMP keeps PV < 25 mm Hg

Pressure = 0 mm Hg Pressure = 100 mm Hg 90 mm Hg caused by gravitational effect 10 mm Hg caused by pressure imparted by cardiac contraction Pressure = 90 mm Hg Fig. 10 -26, p. 301

VEINS AND THEIR FUNCTION 1. VENOUS PRESSURE • 2. RIGHT ATRIAL PRESSURE • 3. EFFECT OF GRAVITY ON VENOUS • PRESSURE 4. PRESSURE REFERENCE • 5. BLOOD RESERVOIRS •