Egan's Chapter 6 11th Edition PDF

Egan’s Chapter 6 11th Edition Physical Principles of Respiratory Care Physics helps our understanding of how respiratory care equipment works 2 3 States of Matter Three primary states of matter: solids, liquids, gases The air you breathe...

Egan’s Chapter 6 11th Edition Physical Principles of Respiratory Care Physics helps our understanding of how respiratory care equipment works 2 3 States of Matter Three primary states of matter: solids, liquids, gases The air you breathe, the water you drink, the food you eat are examples of states of matter. Water is the only common one between all of them. Water can exist as a gas when it is heated, remain as a liquid in a cup, or become a solid fixed item when it is frozen. The particles are unchanged in all three forms. Solids Maintain their shape because of strong mutual attractive forces (called van der Waals force) Have high degree of internal order Fixed volume and shape Strong mutual attractive force between atoms Molecules have the shortest distance to travel before collision This motion referred to as a “jiggle” 4 States of Matter (Cont.) Liquids Can move more freely, take the shape of a container, and flow Similar to solids, liquids are dense and cannot be compressed easily Have fixed volume, but adapt to shape of their container Atoms exhibit less degree of mutual attraction compared with solids Shape is determined by numerous internal and external forces Gases Molecular attractive forces are weak, can move freely and rapidly and has no boundaries. Gases can be compressed or expand and have flow No fixed volume or shape; weak attractive forces Gas molecules exhibit rapid, random motion with frequent collisions 5 Put it into perspective.. Gases have a weaker bond and move around more freely. Each popcorn kernel represents a gas molecule. What happens when we apply heat to this molecule? It expands. This is similar to our breathing because we breathe in a dry cool gas and our warm mucus membranes heat the gas causing it to expand which increases the volume we breathe in. Let’s say you breathe in a dry volume of gas of approximately 500 mL, if there was no heat that that is the volume I get. However, if we added some heat and humidity it might increase to 550 mL. Please note, these numbers are just to demonstrate and show the difference in volumes, actual volumes vary from patient to patient. This is an example of Charles Law. In Charles Law the pressure (barometric pressure) remains constant, when the gas is inhaled the temperature is increasing and the volume is increasing 6 Internal Energy of Matter All matter produces energy, there is potential and kinetic. Kinetic refers to movement or motion. So why does this matter in Respiratory Care? Our body uses energy all day long, everything from movement all the way to cellular function, muscles used for breathing, and cardiac muscles. Stretch the rubber band out, what happens when you let go of one side? It snaps back. When we breathe we are expanding our lungs (like stretching them out) and if they are healthy they should snap back. In the heart the greater the stretch the greater the contractility force. 7 Internal Energy of Matter The atoms that make up all matter are in constant motion at normal temperature This motion results from internal energy Two major types of internal energy: Potential energy Energy of position (attractive forces between molecules) Weak in gas state Makes up most of internal energy in solids and liquids Kinetic energy Energy of motion Makes up most of gases internal energy 8 9 10 Laws of Thermodynamics Thermodynamics can refer to either: The science studying the properties of matter at various temperatures The kinetics (speed) of reactions of matter at various temperatures 11 Heat Transfer (Cont.) Heat transfer When two objects of different temperature coexist, heat will move from hotter to cooler object until both are equal Heat transfer can occur in four ways: Conduction—Main method of heat transfer in solids Via direct contact between molecules Convection—Mixing of fluid molecules at different temperatures Transfers heat in liquids and gases (e.g., forced air heating in homes-fluid movements carry heat) Radiation—Occurs without direct contact between two substances Evaporation and condensation—Form of vaporization, change of state from liquid to gas, or gas to liquid 12 Conduction 1. Transfer of heat by direct contact (warm blankets on skin…) Requires direct contact (Transferring heat through matter) 2. How well the heat transfers depends on the number and force of molecular collisions 3. Most common in solids 4. Thermal Conductivity a) The measure of how well heat is transferred by an object b) Metals feel cold due to a high thermal conductivity; Metals draw heat quickly away from the skin 13 Convection Heat transfers in both liquids and gases Involves the mixing of fluid molecules at different temperatures occurs when heat is transferred through a gas or liquid by the hotter material moving into a cooler area Requires direct contact Mainly in liquids & Gases Principle behind forced air heating 14 Radiation Occurs without direct contact between objects The sun warming the earth Electrical stove burner So why does this matter? Radiant heat energy is used to keep newborns warm because they can lose their body heat quickly due to a low amount of brown fat cells. 15 16 Evaporation and Condensation Vaporization The change of state from liquid to gas Evaporation Form of vaporization where heat is taken from the air surrounding the liquid, cooling the air When we exercise and sweat evaporation is occurring to cool the skin. Condensation Opposite of evaporation Gas becomes a liquid Effective ventilation requires a balance between evaporation and condensation so the airway mucosa does not get dried out and irritated. We utilize this in the isothermic saturation boundary where gas heats in the airway causing condensation and it is rebreathed to keep our airways moist. 17 Condensation A good clinical example of condensation and evaporation is the hydroscopic condenser humidifier which is known as an “artificial nose”. The device has a water absorbent material enclosed in plastic. On exhalation the device absorbs the heat and moisture from the exhaled gas, reserving it for the next inspiration. On the next inspiration the device adds the heat and moisture back into the dry, cool inspired gas, moving it from a higher heat and moisture concentration to the lower heat and moisture concentration. 18  Temperature Temperature and kinetic energy are closely related Temperature is measurement of heat Heat is the result of molecules colliding with one another Gas temperature is directly proportional to its kinetic energy By popping popcorn you will imagine that each kernel is a gas molecule When the kernel is heated it bounces all over the place because of the increase in kinetic energy When heated the the kernel turns into a fluffy treat. For gases the heating process will increase the volume of gas. 19 Temperature (Cont.) Absolute zero (third law of thermodynamics) Concept—Lowest possible temperature that can be achieved Temperature at which there is no kinetic energy Molecules cease to vibrate; object has no measurable heat Scientists have not actually achieved it As stated by third law of thermodynamics 20 Temperature Temperature is the amount of heat, or thermal energy, present in a system. Temperature Scales oFahrenheit (° F) oCelsius (° C) oKelvin (absolute) (K) (used in Charles Law) 21  Temperature Scales Celsius to Fahrenheit F = 32+(C*1.8) OR (9/5 x C) + 32 Fahrenheit to Celsius C = (F-32)/1.8 OR C=5/9 x (F-32) Convert Celsius to Kelvin K = C + 273 Convert Kelvin to Celsius C = K - 273 22 Change of State Because RT’s work with liquids and gases we should have a good understanding of these principles. When a solid is heated, it’s molecular kinetic energy increases. This added internal energy increases molecular vibrations. If enough heat is applied, vibrations eventually weaken the intermolecular attractive forces. At some point the molecules break free of the rigid stricture, and the solid changes into liquid. Like melting white chocolate, yumm Liquid-solid phase changes (melting and freezing) Melting = changeover from solid to liquid state The point at which this happens is the melting point 23 Change of State Freezing = opposite of melting, requires large amounts of externally applied energy The energy required for freezing a substance is the same as the energy required to melt it. Sublimation = transition from solid to vapor without becoming liquid as an intermediary form Occurs because vapor pressure is low enough (e.g., dry ice) 24 Properties of Liquids We know from pouring water from one glass to another that it occurs by flowing and the water will take the shape of the new container. But liquids also exert pressure which varies with depth and density. Variations in liquid pressure within a container produce and upward supporting force, called buoyancy. Archimedes principle explains buoyancy and how objects float. In respiratory care when the baffle of a spinning nebulizer treatment the buoyancy keeps the solid particles suspended in gases. The solid particles are more buoyant than the gas. The pressure below the fluid is great than the pressure above it, causing particles to rise. In healthcare using a hydrometer measures the weight density of specific gravity of liquids such as urine, which is used for diagnostic testing. 25 Properties of Liquids Pressure—depends on height and weight density Pascal’s principle states that a confined liquid transmits pressure equally in all directions. Examples in the human body include the eyes and heart where there is pressured fluid. These concepts are related to fluid mechanics we will cover in many areas of healthcare. Buoyancy—occurs because pressure below submerged object always exceeds pressure above Gases also exert buoyant forces Helps keep solid particles suspended in gases (aerosols) Specific gravity—ratio of density of one fluid when compared with density of another reference substance (typically, water) Viscosity—force opposing fluid’s flow Blood has viscosity five times greater than water!! 26 Properties of Liquids Viscosity is the force opposing a fluid’s flow. The stronger the cohesive forces in the blood the greater the viscosity. Another way to look at viscosity is the internal friction of fluid and is independent of the density of the fluid. As the cohesive forces of a fluid increase, so does the viscosity. Blood has a viscosity of five times greater than water, the more viscous the blood the more energy it takes to make it flow. Viscosity of a gas is determined by the molecular collision of the gas molecules which we can apply using Poiseuille’s law. Higher temperatures weaken cohesive forces between molecules, which reduces viscosity. When you start your car on a cold day it is recommended that you run it a bit before you drive so the heat can reduce the oil viscosity and protect your engine. 27 Properties of Liquids In the example below polycythemia shows the RBC’s clumping together increasing viscosity, whereas the normal example demonstrates how blood flows more freely. This is a very important concept because when patients suffer from chronic hypoxemia the bone marrow produces more red blood cells in an attempt to carry more oxygen on them. We may draw an ABG on a chronically hypoxic patient and see the blood is almost like sludge. How hard do you think that would be for your heart to pump throughout your body? 28 Properties of Liquids (Cont.) Fluid’s viscosity is directly proportional to cohesive forces between its molecules The stronger the cohesive forces, the greater the fluid viscosity Heart must use more energy when blood viscosity increases, as occurs in polycythemia (increase in red blood cell concentration) 29  Properties of Liquids (Cont.) Heat will break cohesive bonds. If we heat a gas more collisions occur increasing the viscosity of the gas. A viscous gas will have more turbulent flow. As you breathe in through your nose, the gas is heated which adds to the viscosity of the gas in addition to the anatomy of the turbinates (which will be discussed in more detail later on). The difference between cohesion and adhesion is this: Adhesive forces are attractive forces between two different kinds of molecules Cohesive forces are attractive forces between two similar molecules 30 Cohesion & Adhesion The water beaker demonstrates the meniscus is a concave pattern. This is because the adhesion forces are greater than cohesion. Recall that for adhesive forces there are attractive forces between to different kinds of molecules (water and beaker) For the mercury the meniscus is convex. This is because forces within the mercury are stronger than the adhesive forces between mercury and glass. Meaning, cohesive forces are stronger than adhesive forces 31 When we are talking about surface tension we are talking about the 300 million tiny little sacks in our lungs that allow oxygen to get into our blood and allows waste to get out. 33 Surface Tension Surface tension is a force exerted by like molecules at the surface of a liquid The inward forces affect molecules on the surface This imbalance in forces causes the surface film to contract into the smallest possible surface area, usually a sphere or curve (meniscus) This is why a water droplet is a spherical shape. 34  Law of Laplace Laplaces’s law state that pressure varies directly with surface tension. Meaning if there is a high surface tension then pressures to keep the airways open will be higher. Why is the Law of Laplace and surface tension so important to respiratory care? Adult Respiratory Distress Syndrome (ARDS) may collapse the alveoli because of high surface tension. We need to understand that higher pressures are needed to keep the airway open. With newborns surfactant may be given to keep the airways open but this therapy does not work in adults. Either way we will see increased pressures during mechanical ventilation. Let’s watch a video demonstrating the this law in action. https://youtu.be/-aUZyt4a1r0 35 Properties of Liquids (Cont.) 36  Capillary Action Capillary action is a phenomenon in which a liquid in small tube moves upward against gravity. It has both adhesive and surface tension forces. The capillary action is the basis for blood samples obtained by use of a capillary tube. The absorbent wicks used in some gas humidifiers are also an application of this principle as well as some surgical dressings. Because surface tension acts to maintain the smallest possible liquid gas interface, instead, of just the edges of the liquid moving up, the whole surface is pulled upward. The strength of this force depends on the amount of liquid that contacts the tubes surface. Small capillary tube creates a more concave meniscus and a greater area of contact, liquid rises higher in tubes with smaller cross- sectional areas 37 Liquid – Vapor Changes There are two types of vaporization: boiling and evaporation Boiling occurs at the boiling point which is the temperature at which its vapor pressure exceeds atmospheric pressure. When liquids boil the molecules have enough kinetic energy to force themselves into the atmosphere against opposing pressure. The weight of the atmosphere impacts the escape of the water vapor molecules so that if the ambient pressure is higher, the greater the boiling point. On the flip side if ambient pressure is low then liquid molecules escape more easily and boiling occurs at lower temperatures. This is why cooking time must be increased in higher elevations 38  In the above figure we look at letter A (page 110 in Egans). Water can enter the atmosphere. When water is converted to vapor it acts like a gas. Molecular water obeys the same physical principles as other gases and exerts a pressure called water vapor pressure. Container B has a lid on it so water molecules can escape from below until the air at the top of the container cannot hold more water. Temperature affects evaporation in two ways (1) the warmer the air the more water vapor it can hold (2) if water is heated then kinetic energy increases and more molecules escape from the surface. EXPERIMENT: Cup your hands over your mouth and nose and breathe (not blow). What does it feel like? Is it warm and moist or is it dry and cool? 39 Water vapor pressure When using a pressure cooker, the heating of the water increase pressure inside the container. Inside our lung we have a combination of warmth and humidity (lungs don’t like to be completely dry). Therefore, if you want to measure just the partial pressure of oxygen in the lungs we have to remove the other variables like the water vapor and CO2. Those other variables are PaCO2 and PH2O (water vapor pressure at 37⁰ C creates a water vapor pressure of 47 mmHg). That is how the Alveolar air equation is calculated. This equation will help the clinician assess whether or not the oxygen the patient is breathing is actually making it into the alveoli by comparing what we think should be there versus what is actually there. Obstructions may prevent oxygen from being delivered to alveoli. This equation is the basis for other equations we will build upon. X-rays (CXR) and CT scans may explain the physical structures of the lungs or identify problems; it does not measure the severity. For example, with a pneumonia patient you can see the pneumonia on the CXR but it is not measuring how much oxygen is being delivered into the alveoli and into the blood. This would have to be determined by RT assessment via blood gas, calculations, pulse oximetry and WOB. 40 Liquid-Vapor Phase Changes (Cont.) Absolute humidity Absolute humidity (AH) is the actual mass or content of water in a measured volume of air. A common unit of measure for AH is mg/L (milligrams of water vapor per liter of gas). a.k.a. water vapor content Varies with temperature and pressure Air that is fully saturated with water vapor has absolute humidity of 43.8 mg/L at 37° C, 760 mm Hg, and water vapor pressure of 47 mm Hg 41  Liquid-Vapor Phase Changes (Cont.) On the other hand, Relative Humidity (RH)= RH of a gas = to the ratio of its actual water vapor content to its saturated capacity at a given temperature. Expressed as %. In other words, when a gas is not fully saturated the water vapor is expressed as relative humidity. RH = (Content (AH) / Saturated capacity) x 100 and it is expressed as a percent Example calculation see page 113 in Egan’s When water vapor content of a gas equals its’ capacity then RH is said to be 100%. When the RH is 100% a gas is fully saturated with water vapor. If the gas cools it causes water vapor to turn back into a liquid through a process called condensation. Let’s say your patient has a high fever and the nurse turns down the room temperature to 70 degrees Fahrenheit, the warm gas being delivered through a heated vent circuit will cool down because of the cooler air and creates condensation in the vent tubing. This creates a problem of colonization in the vent circuit. Sometimes an RT will wrap a towel or wash cloth around the heater probe so that it does not think the gas is too cool and try to heat it more which can cause injuries in the lungs. 42  At a room temperature of 22° C, air has the capacity to hold 19.4 mg/L of water vapor. If the absolute humidity in the air is 7.4 mg/L (content), then what is the relative humidity (RH)? 43  At a temperature of 20 degrees celsius, air has the capacity to hold 17.3 mg/L of water vapor. If the absolute humidity(content) is 12mg/L, what is the relative humidity? 44  When the water vapor content of a volume of gas equals its capacity, what is the relative humidity (RH) of this gas? 45 This picture demonstrates mucus plugging. Obviously the mucus is tenacious but what caused it to be so dry? We will not know in this case. However, when patients have thick mucus we should offer humidity on their oxygen to reverse any humidity deficit they may have. 46 Properties of Gases Kinetic theory says that gas molecules travel about randomly at very high speeds with frequent collisions. Velocity of gas molecules is directly proportional to temperature, meaning if I increase the temperature the velocity of the gas increases and therefore pressure increases. If the gas is cooled then the opposite happens, the kinetic energy decreases and pressure decreases. Avogadro’s law states that 1-g atomic weight of any substance contains exactly the same number of atoms, molecules or ions. This number 6.023 x 1023 is Avogadro’s constant which equals 1 mole. 47 Density Density is the ratio of the mass of a substance to its volume, basically particles packed closely together. Think about a forest with lots of trees, we might refer to it as dense forest. Some gases are less dense than others. Helium is one of them. When patients have airway obstructions (as with status asthmaticus and COPD) the helium can move through the obstruction easier because it is less dense. HELIUM MUST BE MIXED WITH OXYGEN when we provide this as therapy. We cover this material in more detail when we get to oxygen therapy. 48 Properties of Gases (Cont.) Diffusion is the process where molecules move from areas of high concentration to low concentration. When we breathe in we take in oxygen into the alveoli. Once in the alveoli the oxygen must get into the blood. It does this through diffusion. We know we just took in a fresh amount of oxygen and the blood coming back to the alveoli is less oxygenated. Therefore, if the oxygen moves from higher pressure gradients to lower pressure gradients it means the oxygen will diffuse from the alveoli into the blood. This occurs when the lungs are healthy. Diffusion is hugely important in respiratory care and we must understand this concept in order to help treat our patients. 49 50 Gas Pressure Gas Pressure: All gases exert pressure whether it is in liquid like blood. The term “tension” is used to refer to the pressure exerted by gases when dissolved in liquid. The blood carries oxygen two ways (1) attached to the red blood cell (2) dissolved in plasma. The pressure or tension of a gas depends on its kinetic activity. Gravity also affects gas pressures. This helps explain why atmospheric pressure decreases with altitude. When gas molecules collide with solid or liquid surfaces they exert pressure. Pressure is defined as the force that a gas exerts over a given area (P=Force/Area) Pressure can be measured in many different ways: PSI (pounds per square inch) as found in your tires mmHg (millimeters of mercury) – you may hear or read torr, which is the same thing as mmHg. Which you will mmHg in many aspects of healthcare INCLUDING ABG assessments. cmH2O (centimeters of water pressure). Used in many applications such as measuring cuff pressures (which we will do later this term) kPa (kilopascals) 51 Atmospheric pressure is all around the earth. At sea level the PB is 760 mmHg. However, move into higher elevations and the PB is less. Why? Because less pressure is being exerted due to gravity. 52  Boyle’s Law Body box plethesmography uses Boyle’s law to determine the volume of air remaining in the lungs after a full expiration. This is used to determine Residual Volume, Total Lung Capacity and Functional Residual Capacity Think about this, why will a potato chip bag moving from New Orleans burst open in Denver? Because of Boyle’s Law which states that if pressure decreases, volume increases and temperature is constant. This increase in volume causes the bag to burst open. What happens to the Volume? How does this apply to respiratory? When we are transporting patients via air, our cuff pressures on the endotracheal tube will lose pressure, a leak will occur and the Tidal Volumes will be decreased. Boyle’s Law in respiratory explains how we breathe. As the diaphragm moves down it decreases the pressure into the lungs causing the air to move in, which increases the volume. As we exhale the diaphragm moves up, increasing the pressure in the lung pushing the air out and decreasing the volume. 54 Dalton’s Law of Partial Pressures Duh Dalton. Dalton’s law describes the relationship among partial pressures and the total pressure in a gas mix. If oxygen is 21% of a gas mix then it will exert 21% of the pressure The total pressure in a gas mix MUST equal the sum of all pressures. Let’s look at the example below. We breathe in air which contains oxygen, nitrogen, argon, water, and carbon dioxide. 55 Dalton’s Law Oxygen is 21% Nitrogen (N2) is 78% Air is 1% (argon and carbon dioxide is a very small amount) Barometric pressure is 760 mmHg at sea level. If we multiply each gas by the Pb we get the following: Oxygen.21 x 760 = 160 mmHg Nitrogen.78 x 760 – 590 mmHg Air 0.01 x 760 = 8 (rounding) Add it all together it comes out to 758. Because CO2 and argon are so small calculate we will round this to 760 mmHg. Mount Everest Pb is 253 torr. What is the PO2? Now let’s discuss the mini clini on page 116. 56 Dalton’s Law Pressures above atmospheric are called hyperbaric pressures Usually occurs only underwater diving and in special hyperbaric chambers. At a depth of 66 feet under the sea, water exerts a pressure of 3 atm or 2280 mmHg (3 atm x 760 torr) PO2 = 2280 x.21 that would total 479 mmHg. Notice, the diver is still breathing 21% oxygen however the PO2 is significantly higher. We can create this on land by using hyperbaric chambers which were primarily used for controlled depressurization of deep-sea-divers and to treat certain types of diving accidents. Now they are used to help treat CO poisoning, gangrene https://youtu.be/nbFs9NN__Mk In traumatic brain injured patients 57 Properties of Gases (Cont.) Solubility of gases in liquids (Henry’s law) At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid Henry’s Law predicts how much of a given gas will dissolve in a liquid. According to this principle, at a given temperature, the volume of gas that dissolves in a liquid is equal to its solubility coefficient times its partial pressure. 58 An everyday example of Henry's law is given by carbonated soft drinks. Before the bottle or can of carbonated drink is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle or can is opened, some of this gas escapes, giving the characteristic hiss. Because the partial pressure of carbon dioxide above the liquid is now lower, some of the dissolved carbon dioxide comes out of solution as bubbles. Gas likes to move from areas of high concentration to low concentration. If the soda is left on the counter open then concentration of carbon dioxide in this solution will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat". Where do we apply this in respiratory? Blood. The blood carries oxygen both attached to red blood cell and dissolved in plasma. Our blood will absorb oxygen and take it to our tissues. Then the tissues will give the blood its waste (CO2). Therefore, gases can dissolve in liquid. We will apply these principles again when we get to diffusion and gas exchange. MINI CLINI Pg. 117 59 Henry’s Law and Graham’s Law Temperature plays a role is gas solubility High temps decrease solubility and low temps increase solubility As a liquid is warmed, the kinetic activity of any dissolved gas molecules is increased This increase in kinetic activity increases the escaping tendency of the molecules and partial pressure Graham’s law predicts the rate at which diffusion or movement of a gas occurs. A lighter gas diffuses faster than heavy molecules. So when you think diffusion of gases, think Graham’s law. We will apply these concepts this in RT10B when we discuss gas diffusion in more detail. 60  Critical Temperature and Pressure For every liquid, there is a temperature above which the kinetic activity of its molecules is so great that the attractive forces cannot keep them in a liquid state, this is called the critical temperature. The pressure needed to maintain equilibrium between the liquid and gas phases of a substance at this critical temperature is the critical pressure Together, the critical temperature and pressure represent the critical point of a substance O2 (a true gas) has a critical temperature so low that at room temperature and pressure that it cannot exist as a liquid. Critical temperature also helps explain how gases are liquefied. A gas can be liquefied by being cooled to below its critical temperature and then being compressed. 62 Fluid Dynamics Study of fluids in motion = hydrodynamics Both liquids and gases can flow Pressure exerted by liquid in motion depends on nature of flow itself Frictional resistance to flow exists both within the fluid itself (viscosity) and between the fluid and the tube wall. The greater the viscosity of the fluid and the smaller the cross- sectional area of the tube, the greater the decrease in pressure along the tube. 64 Fluid Dynamics (Cont.) Patterns of flow Laminar flow—fluid moving in discrete cylindrical layers or streamlines Poiseuille’s law— predicts pressure required to produce given flow using ΔP = 8nl V./ πr4 Turbulent flow—loss of regular streamlines; fluid molecules form irregular eddy currents in chaotic pattern is predicted by using Reynold`s number (NR) NR = v d2R / h Transitional flow is a mixture of laminar and turbulent flow 65 Fluid Dynamics (Cont.) Poiseuille’s Law predicts pressures required to produce a given flow. Increasing tube radius by 19% will increase the flow by 100% ACTIVITY Plug your nose with the nasal clips and try breathing through the coffee stirrer Hard to do? Now try breathing through the larger straw. Is that easier? 66 Turbulent Flow Chaotic pattern Depends on fluid density, viscosity, linear velocity, and tube radius When flow is turbulent, Poiseuille’s law no longer applies, the pressures will increase 67 Fluid Dynamics (Cont.) 68  A garden hose is a good example of this principle So is jet nebulizers, pneumatic nebulizers, gas entrainment devices (Venturi Mask) 69 Fluid Dynamics (Cont.) The Bernoulli Principle An increase in the velocity of the fluid results in a decrease in the sum of its static pressure, potential energy, and internal energy When fluids pass through a constricted tube there will be a pressure drop on the lateral wall The fluid that flows through this constriction will increase its velocity while lateral wall pressures decreases Explains why Heliox works. The lower the density, the higher the velocity (and flow) for the same inspiratory effort 70 Fluid Dynamics – Jet Entrainment Shearing forces drag in room air and cause it to move into the stream of oxygen flowing into the device The amount of air entrained depends on the diameter of the jet orifice and size of entrainment ports The greater the volume of air entrained, the higher the flow and the lower the FIO2 Let’s All see the Venturi Mask in operation 71