MODELING THE UPTAKE OF GASES BY THE DOG NASAL-PHARYNGEAL REGION - EFFECTS OF MORPHOMETRIC AND PHYSICOCHEMICAL FACTORS

A dosimetry model is used to investigate the uptake of gases by the na sal-pharyngeal region of the dog. The model accounts for cyclic air fl ow in the respiratory tract and absorption and desorption by air-blood barriers, diffusion and first-order chemical reactions in the barrier s, blood perfusion of and circulation between respiratory tract tissue s and tissues of the rest of the body, and loss of inhaled compounds b y systemic extraction. The following factors that influence nasal-phar yngeal uptake are studied: length of exposure, blood-air partitioning, respiratory tract tissue first-order reactions, systemic extraction, and lower respiratory tract (LRT) uptake. The simulation results predi ct the following: (1) The length of time for variables (e.g., regional uptakes) to reach steady state depends on the blood-air partition coe fficient and it; different for different variables for a given partiti on coefficient. Even if respiratory tract variables are in steady stat e, systemic variables may not be. (2) As the first-order tissue rate c onstant increases, nasal-pharyngeal uptake during both breathing phase s increases for a given partition coefficient. During inhalation the n asal-pharyngeal region only absorbs. On exhalation this region may des orb or absorb, depending on the rate constant and partition coefficien t; for sufficiently high rate constants, only absorption occurs. (3) N asal-pharyngeal absorption and desorption processes are not very sensi tive to systemic extraction. (4) As the thickness of the nasal-pharyng eal air-blood barrier decreases, nasal-pharyngeal uptake increases dur ing inhalation and desorption decreases during exhalation. (5) Increas ing or decreasing LRT uptake increases or decreases, respectively, bot h nasal-pharyngeal absorption and desorption. These results provide a better understanding of the role of nasal-pharyngeal morphometric and physicochemical properties and the influence of extranasal-pharyngeal factors on the uptake of gases.