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6 Cards in this Set

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  • Back
Explain fractional concentration of a gas.
Fraction of a gas is the % concentration, F --> expressed as a decimal (ie FiO2 = -.21 for inspired O2 at RT)

always dry gas, without water vapor
Define the partial pressure of gases
Partial pressure = fractional concentration x total gas pressure

Dalton's Law of Partial Pressure = in a mixture of gases the partial pressure exerted by each gas is the same as if that gas were alone

example: PO2 in the atmosphere at sea level = -.21 x 760 mmHg = 160 mmHg

At high altitude, atmospheric pressure will be lower and therefore PO2 will be lower
Water vapor in inspired air in lungs accounts for 47 mmHg --> PO2 = 0.21(760-47) = 150 mmHg
Understand how gases dissolve in liquids
1) Partial pressure of a gas = partial pressure of gas in the gas phase
- however, overall gas content in liquid depends on both solubility and partial pressure of the gas
- Henry's Law: max gas dissolved in liquid = Pgas x solubility
- Therefore, a gas with high partial pressure may have low dissolved content if solubility is low

2) Gas may bind to molecules such as oxygen binding to Hb
- bound gas molecules do not contribute to partial pressure in liquid
- gas must first dissolve into the liquid before it can bind the carrier molecule

3) Driving force from gas into liquid is the partial pressure difference between the two phases and not the difference in content
- gas content in liquid = dissolved gas + bound gas
Define the lung volumes and capacities and describe how they are measured

Measuring lung volumes and capacities:
1) spirometry: measures volumes of air that a person can inspire and expire, cannot measure RV and therefore cannot be used to measure or calculate the FRC
2) respirometry: measure flow using mechanical rotors or turbines, calculated volumes displayed electronically or on a dial --> cannot measure RV or FRC
3) pneumotachographs: measure pressure gradient across laminar resistance, pressure drop is proportional to flow rate and flow volumes are calculated --> cannot measure RV or FRC
4) gas dilution (helium): used for indirectly measuring RV and FRC
- person starts at FRC and breathes an insoluble gas of known concentration and volume from a spirometer
-Rebreathe until Helium is well mixed into the lungs
-Helium is now distributed between FRC of lung and spirometer
- measured concentration of He --> use formula V1C1=V2C2 to calculate FRC
- all values known, solve for V2
-caveat: only measures the part of FRC that is in continuity with the gas breathed in
- trapped gas in airways cannot be accounted for
5) Body Plethysmography: person placed in air-tight booth and changes in pressures are measured to find FRC
- measures all gases of the body, even trapped air
State the normal values for TLC, FRC, TV, and VC
FRC: 3.0L
TV: 0.5L
VC: 4.5L
Recite the formula for the ideal gas law and be able to convert a lung volume measured at one set of conditions to another set of conditions.
PV = nRT

P1V1/T1 = P2V2/T2

Temperature in Kelvins

- PH20 = 0 mmHg

- PH20 @ 23C = 21 mmHg
- PH20 @37C = 47 mmHg