Physiological Factors Affecting Lung Deposition

Ventilation and mechanics of breathing are an integral part of respiratory physiology that directly affect aerosol transport and deposition in the lung. Although natural breathing pattern varies widely among individuals, breathing pattern is controllable, and by using an appropriate breathing pattern, aerosol deposition can be substantially modified for desired purposes. Effects of breathing pattern have been investigated under carefully controlled inhalation conditions covering a wide range of tidal volumes (V_T) and breathing frequencies (f) or respiratory times (T = 1/f). The studies have shown that lung deposition can increase or decrease as much as two times by changing the breathing pattern. Specific functional relationships have been found between lung deposition and breathing pattern parameters such that lung deposition can be estimated for any given breathing pattern. Both V_T and T have shown strong effects on lung deposition, but their influence is variable depending on particle size, particularly, ultrafine vs. micron-sized particles. V_T is more influential than T for micron-sized particles whereas V_T and T are equally influential for ultrafine particles. Although effects of lung morphology are difficult to study systematically, comparison between normals and patients with obstructive airway disease has shown that lung deposition is closely related with the degree of airways obstruction and can be 2-3 times greater in patients with obstructive airway disease compared to normals. Thus, breathing pattern and the status of airways obstruction should be carefully considered in designing aerosol delivery and estimating deposition dose.