I RELATIONSHIP BETWEEN BLOOD FLOW PRESSURE GRADIENT VISCOSITY

I. RELATIONSHIP BETWEEN BLOOD FLOW, PRESSURE GRADIENT, VISCOSITY OF BLOOD, RADIUS & LENGTH OF VESSEL

POISEUILLE – HAGEN FORMULA Q = ( P 1 – P 2 ) x πr 4 8 ηL Q – flow P 1 -P 2 – pressure difference between two ends of vessel r – radius of vessel; L – length of vessel η – viscosity of blood;

Contd: Q = ( P 1 – P 2 ) x Ohm’s law: Q = ( P 1 – P 2 ) R πr 4 8 ηL Substitute the value of Q from Poiseulle’s equation to Ohm’s law: R= 8 ηL πr 4

Factors affecting flow of fluid: F 1 = x F 2 = 2 x P 1 – P 2 1 r 1 2 ½L 1 F 3 = 16 x 3 F 4 = 32 x 2 r 1 4 2 r 1 ½L 1

II. RELATIONSHIP BETWEEN FLOW & PRESSURE: Flow Critical closing pressure (CCP): Rigid tubes Flow Pressure CCP Blood vessels Pressure

VALUES OF CCP: • Sympathetic stimulation – • Sympathetic inhibition –

III. RELATIONSHIP BETWEEN DISTENDING PRESSURE & TENSION Law of Laplace: Tension in the wall of a cylinder is equal to the product of transmural pressure (P) and radius (r) divided by the thickness of the wall P x r T= W P= T r

contd Distending pressure (P) Wall tension (T) T P T

Pressure (mm. Hg) PRESSURE – VOLUME RELATIONSHIP IN ARTERIES Volume (m. L)

Pressure (mm. Hg) PRESSURE – VOLUME RELATIONSHIP IN VEINS Volume (m. L)

Mean Velocity Pressure (mm Hg) (cms/s) 0 40 80 120 CHANGES IN PRESSURE & VELOCITY IN SYSTEMIC CIRCULATION Systolic Diastolic Total cross sectional area of the vessel Velocity 1 2 3 Relative resistance 4 5 6 7

BLOOD FLOW MEASUREMENT 1. Methods based on Fick’s principle: 2. PAH acid clearance method: 3. Plethysmography: 4. Electromagnetic flowmeter: 5. Ultrasonic Doppler flowmeter:

3. PLETHYSMOGRAPHY: Volume recorder Water Rubber sleeve

4. ELECTROMAGNETIC FLOWMETER:

5. ULTRASONIC DOPPLER FLOWMETER: Crystal Transmitted wave Reflected wave

Control of peripheral circulation: A. Intrinsic (local) control – Vasodilator theory Oxygen lack theory Metabolic mechanism Myogenic mechanism Reactive hyperemia Active hyperemia Endothelial derived factors

A. INTRINSIC CONTROL: I. Acute – 1) Autoregulation – 2) Factors increasing blood flow – 3) E. D. R. F. –

Blood flow (m. L / min) Hyperaemia Occlusion Time (secs)

II. Long term control: • Mechanism: 1) Tissue vascularity – 2) Collateral blood vessels – • Angiogenesis: Sites – Factors released from – Stimulators – Inhibitors –

B. EXTRINSIC REGULATION: I. II. Nervous: a) Sympathetic stimulation – b) Parasympathetic stimulation – c) Vascular reflexes – Humoral: Hormones – a) Constrictors – b) Dilators –

FACTORS AFFECTING CALIBER OF ARTERIOLES: FACTORS CONSTRICTORS DILATORS Local: Local hormones: Circulating hormones: Neural factors: Ions:

HUMORAL REGULATION OF BLOOD FLOW • VASOCONSTRICTORS • • • Angiotensin II Vasopressin Nor-epinephrine Prostaglandins Endothelins Neuropeptide Y • VASODILATORS • • • Bradykinin Histamine Prostacyclin VIP Endothelium derived relaxing factor