:: 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. As the pressure increases, the flow rate increases. The resultant aerosol size is smaller. Meanwhile, the output is greater. The time it takes to nebulizer the full dose is reduced.
- Gas density
- Gas density affects both aerosol generation and delivery to the lungs. If a carrier gas has a lower density, the flow is less turbulent. The resultant effect is decreased aerosol impaction in the upper respiratory track and higher deposition in the lungs. This phenomenon is most evident with low-density of helium-oxygen mixtures (Heliox). The use of a Heliox to nebulize albuterol causes particle size and inhaled drug mass to decrease, along with an increase in nebulization time. This has to be compensated by increasing the flow of Heliox in order to return the output to that seen with air.
- 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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