1 / 48

Physics – insights

Physics – insights. Dr. S. Parthasarathy MD., DA., DNB, MD ( Acu ), Dip. Diab.DCA , Dip. Software statistics PhD ( physio ) Mahatma gandhi medical college and research institute, puducherry , India. Definitions.

murphy-waters
Download Presentation

Physics – insights

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics – insights Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab.DCA, Dip. Software statistics PhD (physio) Mahatma gandhi medical college and research institute, puducherry, India

  2. Definitions • What is a gas?A gas is a substance that is in its gaseous phase, but is above its critical temperature. Critical temperature is the temperature above which a gas cannot be liquefied no matter how high the pressure. A vapouris a substance in the gaseous phase but is below its critical temperature. 

  3. For example • 20 degrees – gas – apply 50 PSI – liquifies • 30 degrees gas – apply 500 PSI – liquifies • 36.1 degrees – apply any PSI does not • 36 – critical temperature

  4. Pressure, volume and temperature • Pressure = f/a • Units = 1 bar = 1 atm = 100 kpa = 760 mmHg= 14.7 PSI • 138 bar = 2000 psi • Temperature – units – 00 C = 320F = 2730k • Volume == litres or Cubic cm ( cc = ml)

  5. There are some gas laws which inter relate the three variables • Boyle’s law • “For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume” P is proportional to 1 / V or PV = K  

  6. Volume decrease – pressure increase

  7. Application in anaesthetic practice Oxygen cylinder of volume 10 L, molybdenum steel – 138 bars. So how much oxygen is stored ? P1V1 = P2V2 138*10 = 1*V2 So, V2 = 1380 L

  8. Transfer • 100 bar – 15 litre cylinder • P1 V1 = P2V2 one • 1500 litres of oxygen • 5 litres / minute --- 300 minutes approx

  9. Charles law • “For a fixed mass of gas at a constant pressure, the volume is directly proportional to the temperature” V is proportional to T or V / T = K 

  10. Charles’ Law (Temperature-Volume Law)Gas volume varies directly with temperature at a constant pressure V1/T1=V2/T2

  11. Application of charles law • Respiratory gas measurements of tidal volume & vital capacity etc are done at ambient temperature while these exchanges actually take place in the body at 37 OC.

  12. Pressure law- Gay lussac law • “For a fixed mass of gas at a constant volume, the pressure is directly proportional to the temperature” P is proportional to T or P / T = K 

  13. Gay lussac law

  14. Cylinders are kept in high temperature?? • Volume same • Pressure raises to explode • Molybdenum steel can withstand 210 bars , if there is any damage , temperature rise ??

  15. Universal gas law • PV = nRT • Look at the gauge of the oxygen cylinder • Pressure • Volume, R, temperature constant • P ∝ n • Look at the gauge and tell • But for nitrous ??

  16. Is there a pneumonic ?? • Pakistan Tele Vision -- Can Be Good • P constant – C • T constant – B • V constant – G

  17. Avogadro’s hypothesis • Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules. • One mole of a gas • Oxygen (O2) = 32 • 32 grams of oxygen will have 6.022 * 1023 atoms

  18. If we describe in volume • One mole of a gas will occupy 22.4 litres • Gram molecular weight –( Oxygen – 16 ) =O2- 32 • i.e 44 gm of CO2, 2 gram of hydrogen, 32 gm. O2, • Will occupy ?? • 22.4 litres

  19. Take sevoflurane as example • MW = 200 • i.e. 200 gm of sevo will occupy 22.4 litres • 20 gm = 2.24 litres • flow of oxygen through vaporizer of 224 litres this 2.24 will be 1 %

  20. Nitrous oxide ?? • N2O is stored in cylinder as liquid. • Exists partly as liquid and partly as gas. • So customary to weigh the cylinder along with its contents. • From known cylinder wt. and measured wt. amount of N2Oand usage is found out using Avogadro’s hypothesis

  21. E.g. Wt of cylinder with N2O - 5.6kg Tare wt. - 4.5kg So, wt of N2O - 1.1kg 44 g of N2O = 22.4 l Therefore 1.1 kg of N2O = = 560 l So, if we give 2 liters of N2O / min, this cylinder will come for 280 min or 4.6 hrs

  22. Dalton’s law • total pressure of a gas mixture was the sum of the pressures of each of the gases if they were to exist on their own.  • P = p1+p2+p3….. • If a cylinder of air = 100 kPa • Nitrogen is 79 kPa and oxygen 21 kPa Entonox 100 kPa == ??

  23. Dalton’s law • What is the partial pressures of O2 and N2O if you are administering a ratio of 70/30? N20 70% X 760 mmHg = 532 mmHgO2 30% X 760 mmHg = 228 mmHg 760 mmHg • Would this differ if you were administering anesthesia at Ooty General Hospital? N20 70% X 630 mmHg = 441 mmHgO2 30% X 630 mmHg = 189 mmHg 630 mmHg

  24. Dalton’s law

  25. Graham’s law of diffusion • rate of diffusion was inversely proportional to the square root of the molecular mass of the gas Applications: • Flow meters: each gas with its own phy property must pass through its own calibrated flow meter. • Rate of diffusion is slower in liquids and thus local anaesthetics, if not injected in close proximity to the nerve fibre will not be effective. • Helium, a lighter gas is used in airway obstruction to improve diffusion and gas exchange

  26. Gas B more mass than A • A will effuse out of the alveolus quicker than B, leaving behind more of B and so raising its concentration. • for example, halothane is more massive than nitrous oxide, • Graham’s law will indicate that the nitrous will diffuse quicker and so raise the concentration of the halothane in the alveolus.

  27. Fick law • Diffusion – concentration gradient pressure gradient 1. DLCO 2. vapour into circuits 3. Nitrous into cuffs and air filled cavities Carbondioxide is 20 times more soluble than oxygen – membrane defects affect oxygenation

  28. Henry’s Law • Henry’s law states that for a gas-liquid interface the amount of the gas that dissolves in the liquid is proportional to its partial pressure. • So Henry’s law helps to predict how much gas will be dissolved in the liquid. • The actual amount also depends on the solubility of the gas.

  29. Adiabatic expansion • Adiabatic, when applied to expansion or compression of a gas, means that energy is not added or removed when the changes occur. • Compression of gas – temperature rises • Expansion of gas – temperature falls • Think there are no pressure regulators in Boyle s machine

  30. Reynolds number • whether flow is laminar or turbulent Where – Reynold’s number density of fluid v – velocity of fluid d – diameter of tube and – viscosity of fluid

  31. Reynold s number • Reynold s number of 2000 – borderline • When • Re < 2000 – laminar • Re > 2000 – turbulent • Viscosity is the important property of laminar flow • Density is the important property of turbulent flow • Reynold’s number of 2000 delineates laminar from turbulent flow

  32. Applications of reynold number • 1- undersized ETT may cause a tremendous decrease in the flow of gases • 2- Every piece of anaesthetic equipment; because of diameters & shape of connectors,FGF affected • 3- In respiratory tract obstruction, oxygen – helium mixtures are given to reduce density and improve the flow. • 4- Laminar flow during quiet breathing is changed to turbulent during speaking & coughing- dyspnea. • Flow meter – low flows – laminar flow – density • High flows – turbulent flow – viscosity

  33. Roughly speaking • Numerical value for critical value in l/min for O2 + N2O is same as ID of ETT in mm. • Flow changes to turbulent from laminar. • Flow – 5 litres , ok for 5 mm ID ET tube

  34. Hagen poiseille equation • Flow – Q is determined by a few factors

  35. Pressure bags and height • Viscosity of common infusions: • 1.0 centipoise - Lactated Ringers • 4.0 cP- Hetastarch • 40.0 cP- 5% albumin • Warming decrease viscosity

  36. Joule-Thompson Effect • When a compressed gas is allowed to escape freely into an open space, cooling occurs. • Condensation of water or frost may accumulate on the cylinder valve. • A cryoprobe operates on the Joule-Thompson effect.

  37. (Joule-Thompson Effect) • As gas escapes from a N2O cylinder, the liquid N2O in the cylinder vaporizes. • Heat is lost as the liquid vaporizes (latent heat of vaporization) • the temperature in cylinder falls Hot summer – what is necessary ??

  38. Bernoulli principle • An increase in the flow velocity of an ideal fluid will be accompanied by a simultaneous reduction in its pressure. Kinetic + potential = same

  39. Venturi • The effect by which the introduction of a constriction to fluid flow within a tube causes the velocity of the fluid to increase, therefore, the pressure of the fluid to fall.

  40. Venturi -- clinical uses • Suction • Scavenging • Venturi mask • Nebulizers • Checking Bains circuit

  41. Coanda effect • This effect was named after a Romanian aircraft designer Henri Coanda, after an aircraft he designed went up in flames as a consequence of this effect. 

  42. Coanda Effect If a constriction occurs at bifurcation because of increase in velocity and reduction in the pressure, fluid (air, blood) tends to stick to one side of the branch causing maldistribution.

  43. Coanda effect • 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 • Fluid logic used in ventilators employs this principle to replace valves or mobile parts.

  44. Boyle law, charles law , Gay lussac, universal • Graham s law • Fick law • Bernoulli and venturi • Reynold number • Poiseulli • Joule thomson effect • Coanda effect

  45. Thank you all

More Related