:: Section 5
Factors affecting SVN performance
2. Gas source
- Gas flow
- Droplet size and nebulization time are inversely proportional to gas flow through the jet. The higher the pressure and flow of gas to the nebulizer are the smaller the aerosol size generated. The output is greater and the time required to nebulize the full dose is also reduced. Nebulizers that produce smaller aerosol sizes by use of baffles may reduce the total drug output per minute compared with those without baffles and therefore require more time or nominal dose to deliver a standard dose of medication to the lungs.
- Gas density
- Gas density affects both aerosol generation and delivery to the lungs. The lower the density of a carrier gas, the less turbulent is the flow which subsequently decreases aerosol impaction in the upper respiratory track. The better result is the deposition in the lungs. This phenomenon is most evident with low-density of helium-oxygen mixtures.
- Humidity and temperature
- Humidity and temperature affect particle size and the concentration of drug remaining in the nebulizer. Evaporation of water and adiabatic expansion of gas can reduce the temperature of the aerosol to as much as 10 °C below ambient temperature. This cooling increases the solution viscosity and reduces the nebulizer output while decreasing aerosol MMAD. On the other hand, aerosols entering a warm and fully saturated gas stream increase in size due to vapor condensation. These particles also can coalesce (stick together), further increasing the MMAD. The change in aerosol size then alters the deposition pattern.
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