Circulation / Haemodynamics

Objectives At the end of this Lecture You would Know: 1. Different Types of Vessels and their role in Vascular physiology 2. Different aspects of Controlling Mechanisms of circulatory system

Circulation/Haemodynamics Haem------Blood Dynamics- Motion or Flow

Importance Management of Hemodynamic in every surgery is one of the most important aspect of management Leading cause of death in most of the major surgeries is hemodynamic failure

Major Divisions Systemic Circulation Pulmonary Circulation Supplies blood to all parts of the body Also called greater circulation or peripheral circulation Pulmonary Circulation Circulation in the lungs For the oxygenation of the blood (Hb)

Circulatory System Heart- Pumps blood Arterioles- Resistance vessels Aorta – Elastic vessel. Windkessel vessel Arteries-Conducting vessels. Carry blood away from heart Arterioles- Resistance vessels Metarterioles- Regulatory vessels Regulates blood flow

Circulatory System Capillaries- Exchange vessels Exchange of nutrients with & metabolites of tissues Veins and venules – Capacitance vessels Storage & Carrying blood toward the heart

 Capacitance of blood vessels describes the distensibility of blood vessels located within the body. It is inversely proportional to elasticity.

Volume of blood in circulation Systemic circulation 84 % Veins 64 % Arteries 13 % Arterioles & capillaries 7 % Heart & Lungs 16 % Heart 7 % Pulmonary vessels 9 %

More than 64 % of the blood is in the systemic veins

Flow = Pressure/R Flow = P1-P2 /R P2 P1 FLOW Pressure Distance Force ( Pressure Head ) FLOW Flow = P1-P2 /R

Poiseuille and Resistance Poiseuille’s Equation Flow= ∆P.∏r4 8ŋL Where ∆ P= Driving Pressure r = radius ŋ=Viscosity L= Length of the tube

Poiseuille and Resistance Radius or diameter is KEY Factor.  radius by 1/2  resistance by 16 FOLD -

Laminar / Turbulent Flow Reynold’s Number Re=v.d.p ŋ Where V=mean vel of blood flow d= diameter in cm p= density ŋ = viscosity of blood > 2000

Blood Pressure Defined as: Pressure exerted by the flowing blood laterally on the vessel wall per unit area. Importance; Maintaining pulsatile blood flow to all tissues of the body

Types of Blood Pressure: A. Systolic B. Diastolic C. Pulse Pressure D. Mean Arterial Pressure DIASTOLE 120 80 mmHg 120 mmHg 80 SYSTOLE

Determinants of B.P B.P= COP x TPR

Determinants of Systolic BP 1. Stroke Volume 2. Distensibility ARTERIES (LOW COMPLIANCE) Determinants of Systolic BP 1. Stroke Volume 2. Distensibility Determinants of Diastolic BP 1. Elasticity of Aorta 2.TPR DIASTOLE 80 mmHg 120 mmHg SYSTOLE

Brachial Artery Pressure curve, showing Systolic / Diastolic & MAP DIASTOLE Mean Art Pr = DBP + 1/3rd PP Pulse Pressure = SBP- DBP = 120-80=40 80 mmHg 120 mmHg SYSTOLE

Flow in Rigid tube Pump ON Water Pump OFF X X- No Flow Water

Flow in Aorta Pump Pump Rubber tube Water Terminal end Narrowed Pump Rubber tube Water Continous Flow Both during systole & Diastole

Stretching of Elastic Vessel(Aorta) during Systole & Recoil during Diastole

Bernoulli’s Principal, Application

Total Peripheral Resistance, (TPR) Flow = P1-P2 R Total Peripheral Resistance=100-0 =100 mmHg (TPR) 100 ml /Sec (COP) TPR (in systemic Circulation) = 1 PRU TPR (In Pulmunary Circulation) = 16-2 =14/100 = 0.14 PRU

Effect of Gravity on Arterial & Venous Pressures