Influence of Thermal Plume on Particle Inhalability of a Lying Mannequin in a Room

In this study, the dispersion and deposition of particles in the respiratory system attached to a mannequin lying down inside a room were investigated numerically. The respiratory system model was prepared by processing the CT scan images of a volunteer and was attached to a mannequin lying in the middle of a room. The flow field around the mannequin and effects of the thermal plume on the particle aspiration by the mannequin model was simulated using the Ansys-Fluent software. The aspiration efficiency of spherical particles in the airway was studied with the Lagrangian particle trajectory analysis, including the turbulence dispersion effects. For validation of numerical simulations, the aspiration efficiency of the particles obtained from the numerical solution was compared with the case of a standing mannequin. The results are presented for two different modes with upward and downward thermal plumes. For the first mode, due to the strong effect of the thermal plume in the upward direction, the aspiration efficiency of midrange particles increases. However, the aspiration efficiency of large micro-particles decreases for the first mode. For the second mode, with the downward thermal plume, the aspiration efficiency of small micro-particles increases significantly.

Particle Transport and Deposition in a Ventilated Room With a Standing Mannequin

This study presents the results of a series of numerical simulations for airflow field and particle dispersion and deposition around a mannequin standing inside a ventilated room. A 3-D airway model was constructed from the nostril inlet to the end of 4th lung generation and was integrated into the standing mannequin model in the room. The computational domain included the region around the mannequin and inside the respiratory system. The room was ventilated by a mixing air-conditioning system that supplied air with a speed of 3m/s from a diffuser mounted on the top of the sidewall and exited from a damper mounted at the bottom of the side or front walls. In the first mode, the diffuser and damper were located on the wall in front of the mannequin and in the second mode on the wall at the right side of the mannequin. The mean airflow field inside the room was obtained by solving the Navier-Stokes and continuity equations using the Ansys-Fluent software. The k-ω SST transitional model was employed for turbulence modeling. Then, spherical particles with 5, 10, 20, and 40 μm diameter and unit density were released into the room, and their trajectories were tracked by using the Lagrangian trajectory analysis approach. Aspiration efficiency and deposition of particles for inhalation flow rates of 15 and 30 lit/min were analyzed with the improved discrete random walk (DRW) stochastic model using a user-defined function (UDF) coupled into the Ansys-Fluent discrete phase model. Simulation results for the mean airflow showed the formation of a large recirculation zone inside the room. In the first mode, the main recirculation zone formed behind mannequin that carried the flow streamlines toward the mannequin breathing zone. In the second mode, the recirculation formed in front of the mannequin face that led the streamlines out of the breathing zone. The simulation results for particle inhalation showed that the aspiration efficiency of particles is higher in the first ventilation mode compared to the second mode. Results also showed that the total deposition of particles in the airway passage increases as particle size increases.

Development of an Empirical Formula for Describing Human Inhalability of Airborne Particles at Low Wind Speeds and Calm Air

Based on experiments conducted in low wind speed and calm air environments, the current International Organization for Standardization (ISO) and European Committee for Standardization (CEN) convention modeling human aerosol inhalability (i.e. aspiration efficiency) may not be valid when wind speeds are less than 0.5 ms−1. Additionally, the convention is based primarily on mouth breathing data and aerosols with aerodynamic diameters smaller than 100 µm. Since the convention's development, experimental inhalation data at wind speeds lower than 0.5 ms−1 for nose, mouth, and oronasal breathing have been generated for aerosols in a wider range of sizes (1.5–135 µm). These data were gathered and modeled with the intention of providing a simple convention recommendation for inhalability in low wind speed (>0 to <0.5 ms−1) and calm air (~0 ms−1) conditions to the ISO Technical Committee (TC) 146, Subcommittee 2, Working Group (WG) 1 (‘Particle Size-Selective Sampling and Analysis'), as it relates to standard ISO 7708, and to CEN TC 137/WG 3, as it relates to standard EN 481. This paper presents several equations as possibilities, all relating aspiration efficiency to aerodynamic diameter. The equation AE=1+0.000019dae2−0.009788dae stands out as a possible new convention. This polynomial model balances simplicity and fit while addressing the weakness of the current convention.

Accelerated gastric emptying is associated with improved aspiration efficiency in obesity

BackgroundThe overall effectiveness of aspiration therapy (AT) for obesity relies on optimal aspiration timing after a meal, which can vary depending on a patient’s rate of gastric emptying (GE). Our aim was to identify if baseline GE rates were associated with differences in aspiration efficiency (AE).MethodsSubjects from an ongoing AT clinical trial were enrolled in this study. AE was calculated as the absolute gastric residual and calories aspirated at 20 and 40 min. Participants were then divided by baseline GE rate into two groups (slow vs fast). Wilcoxon rank-sum test was used to compare AE at 20 and 40 min between the groups. Exploratory linear regression was used to assess relationship between GE and AE.Results7 patients (85% female) were coenrolled in the study. Mean age and body mass index were 39.8±9.44 and 43±5, respectively. AE did not significantly differ between the 20 and 40 min time points for the group as a whole (34.3% vs 36.9%; p>0.5). However, those with fast GE aspirated more calories than those with slow GE (20 min: 200 kcal vs 72.5 kcal; 40 min: 154 kcal vs 63 kcal) (p=0.05). On linear regression, delayed GE was associated with poorer aspiration (20 min: β=−107 calories; p=0.019; R2=0.7). 4/7 patients had significant differences in residual/caloric aspiration across the two time points.ConclusionPatients undergoing AT may benefit from a GE test to optimise their AE. Paradoxically faster GE times saw better aspiration. Prospective studies are revealing a personalised approach to obesity.

Evaluating Aerosol Aspiration Efficiency in Fast-moving Air

Sampling representative aerosol particles in fast-moving air is a challenging task. Aerosols are significantly more massive than gas molecules, thus they might not follow air streamlines well and could be more easily subjected to sampling errors. This work examines the physical factors that govern the aspiration efficiency of an aerosol sampling probe in unidirectional moving air, and explores the plausible sampling deviations under various high air velocity scenarios. The particle sizes of 0.5 and 5 μm are of particular interest due to their use in defining air cleanliness levels in ISO 14644-1[1] and FED-STD-209.[2]* Our analytical results indicate that significant sampling errors could occur for 5-μm particles when a thick-walled sampling probe is used, or when the air velocity at the sampling probe inlet does not match the velocity of the incoming air (i.e., anisokinetic sampling). The aspiration efficiency of 0.5-μm particles, on the other hand, is nearly 100% due to sufficiently small inertia of these particles.