Laws
Boyle’s Law
What is the volume a gas occupies at a constant temperature is inversely proportional to the absolute pressure exerted on it
Temperature is constant:
- Pressure increases, volume decreases
- Pressure decreases, volume increases
The equation for Kelvin
What is K = C + 273?
Surface tension
created by cohesive forces between liquid molecules at the gas-liquid interface
- will always force a liquid to have the smallest possible surface area, usually a sphere
- surface tension decreases as temperature of a liquid increases
Difference between Absolute Humidity and Relative Humidity
Absolute Humidity: Content or weight of water in a volume of gas, expressed in mg/L
Relative Humidity:
-Comparison of absolute humidity to the maximum amount the gas can hold
- Relative humidity is 100% when the amount of water vapor is equal to the gas’s capacity also known as saturated
Breath Actuated Nebulizers
-Produce aerosol only on inspiration
- Reduces waste and delivers a dose 3-4 times that of continuous nebulization
- Ex: AeroEclipse BAN
Dalton’s Law
What is the partial pressure of a gas in a mixture proportional to its percentage in mixture: the total pressure of a system is equal to the sum of the partial pressure of all gases in the mixture?
The equation of Partial Pressure
What is Pb = PO2 (21%) + PN2 (78%) + PCO2 (0.03%) + Ptrace (0.7%)?
Viscosity
force opposing fluid’s flow
- dependent on density and cohesive forces (as cohesive forces increase, viscosity increase)
Humidity Deficit
· The difference between the water vapor content in inhaled gas and the water vapor content of the gas in the lungs
· Inspired air is not fully saturated
· Upper airway can usually overcome the deficit
Breath Enhanced Nebulizers
-Generate aerosol continuously
-An inspiratory vent allows the patient to pull room air into the nebulization chamber
-Increases inhaled drug mass and reduces aerosol waste
-Ex: Pari Neb
Fick’s Law of Diffusion
What is the flow of gas across a semi permeable membrane into membrane fluid phase is directly proportional to:
1. Surface area for diffusion
2. The pressure gradient between the compartments
3. The solubility of the gas
The flow is inversely proportional to:
1. The square root of the molecular weight of the gas
2. The thickness of the membrane
150 degrees F = _____ K
Sublimation
solid molecules change to gas molecules (bypass of liquid state). Heat is high enough that molecules gain enough energy to change directly to a gas while remaining below the melting point.
EX: solid carbon dioxide to gas (dry ice)
Air that is fully saturated with water vapor has an absolute humidity of…
What is 43.8 mg/L at 37 degrees C, 760 mmHg, and water vapor pressure of 47 mmHg?
Factors Associated with Reduced Aerosol Drug Deposition in the Lung (Box 40.7)
· Mechanical ventilation
· Artificial airway
· Reduced airway caliber (e.g., infants and children)
· Severe airway obstruction
· High gas flows
· Low minute volumes
· Poor patient compliance or technique
· Limitation of the specific delivery device
Charles’s Law
the volume of gas held at constant pressure will increase proportionately to increases in the temperature of the gas
Pressure is contant:
- temperature increases, volume increases
- temperature decreases, volume decreases
Pressure conversions
cmH2O = mmHg/0.7355
mmHg = cmH2O X 0.7355
Combined Gas Law
The absolute pressure of a gas is inversely related to the volume it occupies and directly related to its absolute temperature
Factors affecting Humidity
1. Temperature
- Increased temperature, increased water vapor carried
-Watch for thermal or mucosal injury
- Unheated humidifiers are less efficient, lose water with flow
2. Surface Area
- Increased area, increased water vapor carried
3. Time
- Increased time, increased water vapor carried
Vibrating Mesh Nebulizers
§ Electronic mico-pumping action produces a high-quality aerosol
-Liquid is drawn through 1000 tapered holes in the “aperture plate” due to vibration of the plate
- Vibrations occur at a rate of 128,000 per second
- Ex: Aerogen
Gay-Lussac’s Law
the pressure of a gas held at constant volume will rise as the absolute temperature of the gas increases
Volume is constant:
- temperature increases, pressure increases—
- temperature decreases, pressure decreases
Pb = 745 mmHg, PH20 = 33 mmHg
Calculate the partial pressure of O2, N2, CO2, and trace gases
What is
PO2 = 144.52 mmHg
PN2 = 555.36 mmHg
PCO2 = 0.2136 mmHg
Ptrace = 4.984 mmHg
Evaporation
1. liquid molecules begin to move more vigorously and escape to form a gaseous state (vapor)
a. Rate of evaporation increases with an increase in temperature, surface area, and/or a decrease in pressure
b. Vapor pressure: the force molecules exert as they hit the liquid surface to escape as a gas
Types of Humidifiers
1. Low flow humidifier
- Bubble Humidifier
2. High flow humidifier
3. Passover humidifier
- Reservior model
- Wick Humidifier
- Membrane Humidifier
Mechanisms of Aerosol Deposition
1. Inertial impaction
2. Gravity or Sedimentation
3. Brownian Diffusion