FLOW, physics, laminar, turbulant, physics

flow

1. Basic Physics and Measurement in Anaesthesia Presented by:-DR.KALYAN REGMI Moderator: DR. ANIL PRASAD NEUPANE Assistant professor,Department of anesthesiology,PAHS,Pokhara

2. Flows: Definition, types, clinical aspects Hagen- Poiseuillie equation Surface tension Laplaces law Bernoulli effect Viscosity Venturi effect Entrainment ratio Coanda effect OBJECTIVE

3. Flow is defined as the quantity of a fluid, i.e. a gas or a liquid, passing a point in unit time where F = mean flow Q = quantity (mass or volume) t = time FLOW

4. TYPES OF FLOW

5. LAMINAR FLOW Fluid moves in a steady manner and there are no eddies or turbulence. Laminar flow normally present in smooth tubes at low rates of flow. The velocity of flow is highest in the centre.

6. Flow is directly proportional to pressure under conditions of laminar flow The ratio of pressure to flow is a constant known as resistance R of the apparatus or tube concerned

7. Measurement of flow resistance

8. TURBULENT FLOW  Flow in which fluid is no longer flows in a smooth fashion but swirls in eddies. Laminar flow may change to turbulent flow if a constriction is reached which results in the increasing fluid velocity. In turbulent flow the resistance is higher for the same laminar flow

9. For turbulent flow in tubes that are rough on the inside it is found that the flow is approximately proportional to the square root of the pressure

10. The factors affecting turbulent flow are :- 1.Vicosity of fluid 2.Diameter of tube 3.Density of fluid and 4. Linear velocity of fluid

11. These factors may all be combined to give an index known as Reynolds number, which is calculated as follows

12. If Reynolds number exceeds about 2000, then turbulent flow is likely to be present. If Reynolds number is below 2000, the flow is likely to be laminar.

13. Clinical aspects of flow Changes between laminar and turbulent flow depends on the velocity of gases,which in turn depends on the volume flow and thus on the diameter of tubing and airways. In patients airway,gases are humidified, warmed (34-37 ᵒ C) and contains carbondioxide . The overall effect of these is reduction in density of gases and rises in critical flow.

14. Critical flows for anesthetic gaseous mixture of 60% nitrous oxide, oxygen and air (20 ᵒ C and patients airway)

15. As breathing is cyclical, with peak flows over 50 lit per min(turbulent flow during peak flow), laminar flow at other times in respiratory cycles Bronchi and smaller air passages in lungs: slower flow and laminar in lower respiratory tract.

16. Hegan - Poissuilles equation: Represents relationship between flow and factors affecting flow. Applied for laminar flow. Q ᵒ = π Pd4/128 η l Where, Q ᵒ = flow P = pressure across the tube d = diameter of the tube η = viscosity l = length of the tube π/128 = constant

17. Flow Rate (ml/min) 270ml 180ml 80ml 54ml 33ml 20ml Length(mm) 45mm 45mm 45mm 32mm 25mm 19mm

18. Fig. Central venous catheter Fig . Peripheral venous catheter

19. SURFACE TENSION Surface tension is a result of the attraction between molecules across the surface of a liquid. In the surface water molecules are attracted downwards and sidewise only.(air fluid interface)

20. LAPLACES LAW

21. surfactants are compounds that lower the surface tension of a liquid. Surfactant molecules are synthesized by type II pneumocytes ( cuboidal cells lining alveoli) and kept in clusters called lamilar bodies and secreted as tubular myelin. The alveoli in the lungs are lined with fluid which,comprising mainly water, has a significant surface tension. Surfactant

22. Alveoli collapse Smaller sized alveoli collapses into large sized alveoli causing ventillation perfusion mismatch Tendency of edema formation in alveoli Surface area for gaseous exchange decreases Major problems with surface tension in lungs

23. VISCOCITY Viscosity is a measure of the frictional forces acting between the layers of the fluid as it flows along the tube. Flow and viscosity are inversely proportional.

24. BERNOULLI’S PRINCIPLE : States that when a gas flowing through a tube, encounters a constriction, at that point, the pressure drops and velocity increases .

25. VENTURI EFFECT : consequence of the Bernoulli’s principle The entrainment of the air from the surroundings due to fall in the pressure at the point of constriction is called venturi effect.

26. Suction: injectors working on this venturi effect may be used to provide suction, either water or gases being used as the driving fluid. Nebulisers Venturi masks Uses of venturi effect

27. A Venturi is a simple design of valve that provide control oxygen supplied through a narrow port which allows room air to be drawn in from atmosphere The rate of flow generated by this Venturi principle and Venturi mask may be equal to peak inspiratory flow of patient. Venturi masks

28. ENTRAINMENT RATIO The entrainment ratio is defined as the ratio of entrained flow to driving flow.

29. COANDA EFFECT : If a constriction occurs at a bifurcation, due to increase in velocity and reduction of pressure, the fluid/air tends to stick to the side of the branch causing maldistribution .

30. APPLICATION: Mucus plug at the branching of tracheo -bronchial tree may cause maldistribution of respiratory gases. Unequal flow may result because of atherosclerotic plaques in the vascular tree

31. TAKE HOME MESSAGE Reynold number less than 2000 indicate laminar flow Fluid resuscitation is done via wide bored peripheral catheter Surfactant helps to prevent alveoli collapses Gas/fluid flow from higher pressure to low pressure area Gas/ fluid following through tube when encounter constriction at that point pressure drop and velocity increases.

32. THANKYOU