:: Section 5
Factors affecting SVN performance
3. Solution
A typical saline has a 0.9% strength. A more concentrated saline solution (e.g., 1 N) is hypertonic relative to body fluid. Aerosol generated from such a concentrated solution may cause bronchial irritation. Furthermore, the aerosol will capture moisture, resulting in growth in mist size until it reaches equilibrium. The deposition pattern of the aerosol will therefore also be affected.
On the other hand, short term application of highly concentrated hypertocnic saline (3-10%) aerosol is used for Sputum induction, i.e. to assist in mobilizing pulmonary secretions for evacuation and recovery. The exact mechanism by which high-density hypertonic aerosols aid mucociliary clearance is unknown. However, an increased volume of surface fluid, combined with stimulation of the irritant (cough) reflex, is the likely factor.
If a drug formulation is very viscous, common SVNs may not be able to draw the liquid through the capillary. The dense and viscous fluid also requires much higher energy to break it into fine droplets.
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