A computational fluid dynamics approach to assess interhuman variability in hydrogen sulfide nasal dosimetry

Human exposure to hydrogen sulfide (H₂S) gas occurs from natural and industrial sources and can result in dose-related neurological, respiratory, and cardiovascular effects. Olfactory neuronal loss in H₂S-exposed rats has been used to develop occupational and environmental exposure limits. Using nasal computational fluid dynamics (CFD) models, a correlation was found between wall mass flux and olfactory neuronal loss in rodents, suggesting an influence of airflow patterns on lesion locations that may affect interspecies extrapolation of inhaled dose. Human nasal anatomy varies considerably within a population, potentially affecting airflow patterns and dosimetry of inhaled gases. This study investigates interhuman variability of H₂S nasal dosimetry using anatomically accurate CFD models of the nasal passages of five adults and two children generated from magnetic resonance imaging (MRI) or computed tomography (CT) scan data. Using allometrically equivalent breathing rates, steady-state inspiratory airflow and H₂S uptake were simulated. Approximate locations of olfactory epithelium were mapped in each model to compare air:tissue flux in the olfactory region among individuals. The fraction of total airflow to the olfactory region ranged from 2% to 16%. Despite this wide range in olfactory airflow, H₂S dosimetry in the olfactory region was predicted to be similar among individuals. Differences in the 99th percentile and average flux values were <1.2-fold at inhaled concentrations of 1, 5, and 10 ppm. These preliminary results suggest that differences in nasal anatomy and ventilation among adults and children do not have a significant effect on H₂S dosimetry in the olfactory region.