On morphometric measurement of oxygen diffusing capacity in middle ear gas exchange

• Published in: Journal of applied physiology (1985) Vol. 98; no. 1; pp. 114 - 119
• Main Authors: Kanick, Stephen Chad, Doyle, William J, Ghadiali, Samir N, Federspiel, William J
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-01-2005; American Physiological Society
• Subjects: Animals; Biological and medical sciences; Blood Gas Analysis - methods; Capillaries - metabolism; Capillary Permeability - physiology; Computer Simulation; Diffusion; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Ear, Middle - blood supply; Ear, Middle - chemistry; Ear, Middle - metabolism; Ears & hearing; Eustachian Tube - blood supply; Eustachian Tube - chemistry; Eustachian Tube - metabolism; Finite element analysis; Fundamental and applied biological sciences. Psychology; Humans; Models, Biological; Oxygen; Oxygen - metabolism; Vertebrates: nervous system and sense organs; Oxygen; finite element analysis; Organ of hearing; Finite element method; Vertebrata; Mammalia; Ear; Diffusing capacity; diffusion length; Gas exchange; Mathematical model; Morphometry; Middle ear
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00203.2004

1 Department of Pediatric Otolaryngology, Children's Hospital of Pittsburgh; 2 Department of Chemical and Petroleum Engineering, University of Pittsburgh; and 3 Department of Otolaryngology, University of Pittsburgh School of Medicine, Pittsburgh; 4 Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem; and 5 McGowan Institute for Regenerative Medicine, Pittsburgh, Pennsylvania
Submitted 25 February 2004
; accepted in final form 10 August 2004
An accurate mathematical model of transmucosal gas exchange is prerequisite to understanding middle ear (ME) physiology. Current models require experimentally measured gas species time constants for all extant conditions as input parameters. However, studies on pulmonary gas exchange have shown that a morphometric model that incorporates more fundamental physiochemical and anatomic parameters accurately simulates transport from which the species time constants can be derived for all extant conditions. Here, we implemented a variant of that model for ME gas exchange that requires the measurement of diffusional length ( ) for the ME mucosa. That measure contributes to the mucosal diffusing capacity and reflects the resistance to gas flow between air space and capillary. Two methods for measuring have been proposed: linear distance between the air-mucosal boundary and capillary and the harmonic mean of all contributing pathway lengths. Oxygen diffusing capacity was calculated for different ME mucosal geometries by using the two measures, and the results were compared with those predicted by a detailed, two-dimensional finite element analysis. Predictive accuracy was improved by incorporating the harmonic measure, which captures important information regarding variations in capillary shape and distribution. However, compared with the oxygen diffusing capacity derived from the finite element analysis, both measures yielded nonlinear, positively biased estimates. The morphometric techniques underestimate diffusion length by failing to account for the curvilinear gas flow pathways predicted by the finite element model.
diffusion length; mathematical model; finite element analysis
Address for reprint requests and other correspondence: S. C. Kanick, Children's Hospital of Pittsburgh, 3705 Fifth Ave. @ DeSoto St., Pittsburgh, PA 15213 (E-mail: chad.kanick{at}gmail.com )