@article{segal_kepler_kimbell_2008, title={Effects of differences in nasal anatomy on airflow distribution: A comparison of four individuals at rest}, volume={36}, ISSN={["1573-9686"]}, DOI={10.1007/s10439-008-9556-2}, abstractNote={Differences in nasal anatomy among human subjects may cause significant differences in respiratory airflow patterns and subsequent dosimetry of inhaled gases and particles in the respiratory tract. This study used computational fluid dynamics (CFD) to study inter-individual differences in nasal airflow among four healthy individuals. Magnetic resonance imaging (MRI) scans were digitized and nasal-surface-area-to-volume ratios (SAVR) were calculated for 15 adults. Two males and two females, representative of the range of SAVR values, were selected for flow analysis. Nasal CFD models were constructed for each subject by a semi-automated process that provided input to a commercial mesh generator to generate structured hexahedral meshes (Gambit, Fluent, Inc., Lebanon, NH, USA). Steady-state inspiratory laminar airflow at 15 L/min was calculated using commercial CFD software (FIDAP, Fluent, Inc., Lebanon, NH, USA). Streamline patterns, velocities, and helicity values were compared. In all subjects, the majority of flow passed through the middle and ventral regions of the nasal passages; however, the amount and location of swirling flow differed among individuals. Cross-sectional flow allocation analysis also indicated inter-individual differences. Laboratory water-dye experiments confirmed streamlines and velocity magnitudes predicted by the computational model. These results suggest that significant inter-individual differences exist in bulk airflow patterns in the nose.}, number={11}, journal={ANNALS OF BIOMEDICAL ENGINEERING}, author={Segal, Rebecca A. and Kepler, Grace M. and Kimbell, Julia S.}, year={2008}, month={Nov}, pages={1870–1882} }
 @article{segal_martonen_kim_shearer_2002, title={Computer simulations of particle deposition in the lungs of chronic obstructive pulmonary disease patients}, volume={14}, ISSN={["1091-7691"]}, DOI={10.1080/08958370290084593}, abstractNote={Epidemiology data show that mortality rates for chronic obstructive pulmonary disease (COPD) patients increase with an increase in concentration of ambient particulate matter (PM). This is not seen for normal subjects. Therefore, the U.S. Environmental Protection Agency (EPA) has identified COPD patients as a susceptible subpopulation to be considered in regulatory standards. In the present study, a computer model was used to calculate deposition fractions of PM within the lungs of COPD patients. The morphology of COPD lungs was characterized by two distinct components: obstruction of airways (chronic bronchitis component), and degeneration of alveolar structure (emphysema component). The chronic bronchitis component was modeled by reducing airway diameters using airway resistance measurements in vivo, and the emphysema component was modeled by increasing alveolar volumes. Calculated results were compared with experimental data obtained from COPD patients for controlled breathing trials (tidal volume of 500 ml, respiratory time of 1 s) with a particle size of 1 µm. The model successfully depicts PM deposition patterns and their dependence on the severity of disease. The findings indicate that airway obstructions are the main cause for increased deposition in the COPD lung.}, number={7}, journal={INHALATION TOXICOLOGY}, author={Segal, RA and Martonen, TB and Kim, CS and Shearer, M}, year={2002}, month={Jul}, pages={705–720} }
 @article{segal_martonen_kim_2000, title={Comparison of computer simulations of total lung deposition to human subject data in healthy test subjects}, volume={50}, ISSN={["1047-3289"]}, DOI={10.1080/10473289.2000.10464155}, abstractNote={ABSTRACT A mathematical model was used to predict the deposition fractions (DF) of PM within human lungs. Simulations using this computer model were previously validated with human subject data and were used as a control case. Human intersubject variation was accounted for by scaling the base lung morphology dimensions based on measured functional residual capacity (FRC) values. Simulations were performed for both controlled breathing (tidal volumes [VT] of 500 and 1000 mL, respiratory times [T] from 2 to 8 sec) and spontaneous breathing conditions. Particle sizes ranged from 1 to 5 um. The deposition predicted from the computer model compared favorably with the experimental data. For example, when VT = 1000 mL and T = 2 sec, the error was 1.5%. The errors were slightly higher for smaller tidal volumes. Because the computer model is deterministic (i.e., derived from first principles of physics), the model can be used to predict deposition fractions for a range of situations (i.e., for different ventilatory parameters and particle sizes) for which data are not available. Now that the model has been validated, it may be applied to risk assessment efforts to estimate the inhalation hazards of airborne pollutants.}, number={7}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Segal, RA and Martonen, TB and Kim, CS}, year={2000}, month={Jul}, pages={1262–1268} }