Disposition of Mulberry Pollen in the Human Respiratory System: A Mathematical Model

Inhaled particle deposition sites must be identified to effectively treat human airway diseases. We have determined distribution patterns of a selected aeroallergen, mulberry pollen, among human extrathoracic (ET: i.e., oronasopharyngeal) regions and the lung. A predictive model validated by inhalation exposure data from human subjects was utilized. Deposition locations were primarily functions of (1) mulberry particle parameters (geometric size, 11–18 μm; shape, spherical; and density, 1.14 g cm−3), and (2) mode of breathing. In the general population, two styles of inhalation are prevalent, normal augmentors (NAs) and mouth breathers (MBs). Their clinical definitions are based on intra-ET airflow divisions. For a NA-mode breathing sedentary (minute ventilation = VE = 10 L min−1) adult, 93% of inhaled mulberry pollen was removed by the ET compartment and 7% collected within the lung. For a MB, the respective deposition efficiencies were 75% and 25%. To apply the model, we used a daily springtime mulberry pollen concentration of 1748 grains m−3 and an exposure time of 0.5 hour to calculate actual doses for the respiratory system. Under the stipulated conditions, a MB would inhale 524 pollen grains per day and 131 would be deposited in the lung; the value is 37 grains for a NA. Preliminary epidemiological results suggest 15% of the study population are MBs in whom such pollen deposits are likely contributors to airway disease.