Theoretical deposition of variably sized platelets in the respiratory tract of healthy adults

Abstract

Background: Numerous types of airborne particles representing by-products of mechanical processes such as milling, abrading or polishing are characterized by platelet-like shapes. Besides these particles of the micrometer scale also nanoplatelets consisting of single or multiple layers of graphene sheets can be theoretically dispersed in the atmosphere. The present study describes the theoretical behavior of variably sized platelets in the airways of the human respiratory tract. Methods: Aerodynamic characteristics of inhaled platelets belonging to the nano- or micrometer scale were approximated by application of the projected-area diameter concept describing particle orientation in the air-conducting lung structures and by calculation of the related aerodynamic diameter. Particle transport was assumed to take place in a stochastic lung architecture with respective variability of morphometric determinants in single airway generations. Deposition mechanisms used for the computations included Brownian motion, inertial impaction, interception, and gravitational settling. Calculations were conducted for three different breathing scenarios (sitting, light-exercise, and heavy-exercise breathing) and for platelets ranging in thickness from 10 nm to 1 µm and in maximal projected-area diameter from 1 to 30 µm. Results: Under sitting breathing conditions platelets with a thickness of 10 nm deposit in the airways by 21% to 40%, whereby a “hot spot” of deposition can be observed in airway generation 20. In the case of platelets with a thickness of 100 nm, deposition fractions ranging from 20.9% to 78.3% (maximum in airway generation 20) can be predicted. Platelets adopting a thickness of 1 µm deposit in the airways by 54.2% to 99.6% (maximum in airway generation 21). Increase of the breathing intensity can have either a reducing or enhancing effect on local deposition. Conclusions: Due to the partly high deposition fractions of platelets measured in the lung airways, these particles may bear the potential to act as serious health hazards that have to be subjected to further studies in the future.