Week 5 Review Chem/Phys Flashcards
Mnemonic for relating gas laws with the variable and constant.
Could These Guys Possibly Be Violent?
What is Fick’s Law?
- Fick’s law is an application of Graham’s law in physiologic states
- Fick’s law for diffusion of a gas across a tissue plane is an encompassing law that accounts for molecular weight, concentration gradient, solubility, and membrane interactions
- The rate of diffision of a substance across a membrane is directly proportional to:
- concentration gradient (partial pressure difference of gas across the membrane)
- membrane surface area
- diffusion coefficient (solubility)
- and inversely proportional to
- thickness of the membrane
- molecular weight
- thickness of the membrane
Vgas = Area x Solubility x Partial pressure difference
Molecular Wt x Distance
Name 3 factors that change flow from laminar to turbulent.
- increased velocity
- bend > 20 degrees
- irregularity in the tube
Describe how viscosity and density relate to laminar and turbulent flow.
- Viscosity is a determinant of flow when flow is laminar (low flow rates)
-
Density is a determinant of flow when flow is turbulent (high flow rates)
- D=mass/volume
- Determines rate of flow in flow meters when rate of gas flow is high through variable orifice flow meter
- i.e. Heliox
- Heliox is used to improve ventilation in patient’s with narrow airways. It has lower diffusability, able to get better oxygenation by using carrier of helium
1 bar = ____ psi
14.7 psi
Discuss a few Clinical Applications of Fick’s Law.
**Allows determination of pulmonary gas exchange**
-
2nd gas effect
- Nitrous can almost act like a carrier gas
- the rapid uptake of high concentrations of nitrous at induction of inhalation anesthesia produces an increase in alveolar concentrations of oxygen and the accompanying volatile anesthetic agent
-
Diffusion hypoxia
- more likely to displace oxygen
- during emergence from nitrous, rapid elimination of nitrous from the lungs dilutes other alveolar gases, producing alveolar “diffusion hypoxia.” (This phenomenon is driven by the same mechanism as the second gas effect—-but in reverse direction)
-
COPD - reduced alveoloar surface tension
- slower induction
- indirectly proportional relationship of membranes
-
placental drug transfer - of drugs and oxygen
- Fick’s describes passive diffusion of molecules down a concentration gradient
- expansion of endotracheal tube cuff (when nitrous is in use)
-
expansion of air pockets (when nitrous is in use)
- N2O is 34x more soluble in blood than nitrogen
- Therefore, volume of nitrous oxide diffusing IN > volume nitrogen OUT
- N2O is 34x more soluble in blood than nitrogen
What is critical temperature?
The temperature above which a gas cannot be liquefied regardless of how much pressure is applied
A gas cannot be liquefied if the ambient temperature is greater than critical temperature
A gas can be liquefied if sufficient pressure is applied at ambient temp below the critical temperature
Describe Charle’s Law and give a practical application.
Volume of a gas is directly proportional to the temperature (K)
Pressure remains constant
So, as temp increases, volume increases
Application: LMA cuff ruptures in an autoclave
Effects of 1 mA.
Macroshock
skin tingling/perception
Effects of 10-20 mA.
Macroshock
let go of source
Effects of 50 mA.
Macroshock
pain, LOC, mechanical injury
1 atm = ____ mmHg = ____ torr = ____ bar = ____ kPa = ____cm H20 = _____ psi
1 atm = 760 mmHg = 760 torr = 1 bar = 100 kPa = 1020 cm H2O = 14.7 psi
Effects of 100-300 mA.
Macroshock
V fib, resp intact
1 atm = _____ torr
760 torr
Formula for O2 delivery
DO2 = CO x [(1.34 x hgb x SpO2) + (.003 x PaO2)] x 10
Effects of 5 mA.
Macroshock
maximal “harmless” current
Describe Adiabatic Cooling.
- occurs when matter changes phase
- the term adiabatic implies a change in temperature of the matter without gain or loss of heat
- Clinical Application: N2O cylinder opened fully - frost can form on the outlet due to cooling
What is the solubility coefficient for O2?
.003 ml/100ml blood/mmHg partial pressure
**CO2 is 20 more soluble in blood than O2**
How do stereoisomers differ from structural isomers?
-
structural isomers
- have the same molecular formula, but their atoms are located in different places
- i.e. enflurane and isoflurane
- truly different molecules with differing physical and chemical properties
-
stereoisomers
- molecules that have a similar geometric arrangement of atoms but differ in their spatial position
- may be enantiomers or diastereomers
What is a concentration solution?
grams per ____ cc
i.e. 1:100,000 Epinephrine = 1 gram per 100,000 cc
= 1 gram Epi in 100,000 mL
= 1000 mg in 100,000 mL
= 1 mg in 100 mL
= 1000 mcg in 100 mL
= 10 mcg in 1 mL
What is a clinical application of Beer’s law and how does it work?
- Clinical Application
- spectroscopy - pulse oximetry
- 2 LEDs
- one (RED) - emits light at 660 nm
- deoxy Hgb at 660 nm
- one (INFARED) - emits light at 940 nm
- oxy Hgb at 940 nm
- shine across a pulsatile tissue bed
- measure the absorption on opposite side
- Compare RED vs INFARED light
- calculate oxygen saturation
- one (RED) - emits light at 660 nm
7.5 mmHg = _____ cm H2O
10.2 cm H2O
What is a percentage solution?
grams per 100 mL
i.e. 2% Lidocaine = 2 grams of Lidocaine per 100 mL
= 2000 mg in 100 mL
= 20 mg in 1 mL
Describe a few clinical applications of Bernoulli and Venturi.
- lateral pressure of rapidly flowing fluid in a constricted tube can be subatmospheric, hence a sidearm on that portion of the tube can be used to aspirate another fluid into the tube
- nebulizers
- venturi oxygen masks (24-40%)
- Jet ventilation
Name 3 clinical applications of La Place’s Law.
- normal alveoli and the need for surfactant during expiration
- vascular pathology - aneurysm rupture due to increased wall tension
- ventricular volume and work of the heart - a dilated ventricle has greater tension in its wall (end diastolic pressure rises)
What is Avogadro’s Hypothesis and Number?
6.02 x 1023 molecules = 1 mole
Hypothesis: If you have 2 different gas containers containing 2 different gases at the same temp and pressure, then they contain the same number of molecules
1 mole is 1 gram multiplied by the molecular weight:
i.e. 1 mole O2 = 32 grams
1 mole of any substance occupies 22.4 L, so 6.02 x 1023 molecules of O2 = 32 grams and occupies 22.4 L
Explain Dalton’s Law of Partial Pressures.
Total pressure of a gas mixture is the sum of the partial pressure of each gas
In a mixture of gases, the pressure exterted by each gas is the same as that which it would exert if it alone occupied the container
Explain how a thorpe tube works at high and low flows.
- Thorpe Tube is an older term for flowmeters
-
At low flows
- annular shaped orifice around the float is relatively tubular so (according to Poiseuille’s Law) flow is governed by viscoisity
-
At high flows
- (indicated on the wider top part of the float tube), the annular opening is more like an orifice, and density governs flow
Explain how a venturi tube is an application of Bernoulli’s equation to meausure fluid flow.
- fluid flows through different cross sectional areas in different portions of the tube
- as tube narrows (V2), velocity of fluid increases, thus dropping pressure
- Velocity of the fluid can be found by measuring the pressure
Describe the relationship of tension, radius, and pressure in the Law of La Place.
-
pressure gradient across the wall of a SPHERE or TUBE/CYLINDER (blood vessel, ventricle, alveolus) is related to
- wall tension (T) - directly
- radius (r) - inversely
