Lung deposition depending on duration of inhalation and particle concentration
Substance output of an aerosol generating device determines the number of particles deposited in the lungs. Deposition is therefore influenced by the duration of aerosol generation and the amount of aerosol generated per time unit. During permanent aerosol generation the length of inhalation determines the amount of applied substance. Consequently a long anddeep breath is more effective than rapid and shallow inhalation.
In pressurized metered dose inhalers (pMDI) substance output per time unit is irrelevant since the aerosol is dispensed very rapidly. Still lung deposition increases the slower and deeper the breathing. On the contrary in dry powder inhalers (DPI) a sufficient flow rate must be achieved to desagglomerate powder particles. Due to van der Waals´ forces smaller particles agglomerate to a greater extent than larger. Consequently higher forces are necessary to separate particles from one another.
On the other hand higher air flows cause a higher grade of impaction resulting in higher rates of oropharyngeal deposition. Therefore lung deposition in most DPI does not exceed 25% although considerable differences exist between particular devices.
Voshaar T. Therapie mit Aerosolen. 2005. Uni-Med: Bremen