Analysis of the airflow features and ventilation efficiency of an Ultra-Clean-Air operating theatre by qDNS simulations and experimental validation.

Ultra-Clean-Air (UCA) operating theatres aim to minimise surgical instrument contamination and wound infection through high flow rates of ultra-clean air, reducing the presence of Microbe Carrying Particles (MCPs). This study investigates the airflow patterns and ventilation characteristics of a UCA operating theatre (OT) under standard ventilation system operating conditions, considering both empty and partially occupied scenarios. Utilising a precise computational model, quasi-Direct Numerical Simulations (qDNS) were conducted to delineate flow velocity profiles, energy spectra, distributions of turbulent kinetic energy, energy dissipation rate, local Kolmogorov scales, and pressure-based coherent structures. These results were also complemented by a tracer gas decay analysis following ASHRAE standard guidelines. Simulations showed that contrary to the intended laminar regime, the OT's geometry inherently fosters a predominantly turbulent airflow, sustained until evacuation through the exhaust vents, and facilitating recirculation zones irrespective of occupancy level. Notably, the occupied scenario demonstrated superior ventilation efficiency, a phenomenon attributed to enhanced kinetic energy induced by the additional obstructions. The findings underscore the critical role of UCA-OT design in mitigating MCP dissemination, highlighting the potential to augment the design to optimise airflow across a broader theatre spectrum, thereby diminishing recirculation zones and consequently reducing the propensity for Surgical Site Infections (SSIs). The study advocates for design refinements to harness the turbulent dynamics beneficially, steering towards a safer surgical environment.

Impact of human body shape on forced convection heat transfer.

Predicting human thermal comfort and safety requires quantitative knowledge of the convective heat transfer between the body and its surrounding. So far, convective heat transfer coefficient correlations have been based only upon measurements or simulations of the average body shape of an adult. To address this knowledge gap, here we quantify the impact of adult human body shape on forced convection. To do this, we generated fifty three-dimensional human body meshes covering 1st to 99th percentile variation in height and body mass index (BMI) of the USA adult population. We developed a coupled turbulent flow and convective heat transfer simulation and benchmarked it in the 0.5 to 2.5 m·s-1 air speed range against prior literature. We computed the overall heat transfer coefficients, hoverall, for the manikins for representative airflow with 2 m·s-1 uniform speed and 5% turbulence intensity. We found that hoverall varied only between 19.9 and 23.2 W·m-2 K-1. Within this small range, the height of the manikins had negligible impact while an increase in the BMI led to a nearly linear decrease of the hoverall. Evaluation of the local coefficients revealed that those also nearly linearly decreased with BMI, which correlated to an inversely proportional local area (i.e., cross-sectional dimension) increase. Since even the most considerable difference that exists between 1st and 99th percentile BMI manikins is less than 15% of hoverall of the average manikin, it can be concluded that the impact of the human body shape on the convective heat transfer is minor.

A Review on Methods for Measurement of Free Water Surface.

Turbulent free-surface flows are encountered in several engineering applications and are typically characterized by the entrainment of air bubbles due to intense mixing and surface deformation. The resulting complex multiphase structure of the air-water interface presents a challenge in precise and reliable measurements of the free-water-surface topography. Conventional methods by manometers, wave probes, point gauges or electromagnetic/ultrasonic devices are proven and reliable, but also time-consuming, with limited accuracy and are mostly intrusive. Accurate spatial and temporal measurements of complex three-dimensional free-surface flows in natural and man-made hydraulic structures are only viable by high-resolution non-contact methods, namely, LIDAR-based laser scanning, photogrammetric reconstruction from cameras with overlapping field of view, or laser triangulation that combines laser ranging with high-speed imaging data. In the absence of seeding particles and optical calibration targets, sufficient flow aeration is essential for the operation of both laser- and photogrammetry-based methods, with local aeration properties significantly affecting the measurement uncertainty of laser-based methods.

Robust operation of distribution network based on photovoltaic/wind energy resources in condition of COVID-19 pandemic considering deterministic and probabilistic approaches.

In this paper, optimal allocation and planning of wind and photovoltaic energy resources are performed in a distribution network with the objective of reducing losses, improving reliability, and minimizing energy generation cost in terms of changes in load consumption pattern during the COVID-19 pandemic condition. The main goal is identifying the best operating point, ie the optimal location and size of clean energy resources in the worst load change conditions, which ensures the best network operation in all conditions during the COVID-19 condition via the turbulent flow of water-based optimization (TFWO). First, the deterministic approach is implemented in Hybrid and Distributed cases before and during COVID-19 conditions. The probabilistic approach is performed considering generation uncertainty during the COVID-19 conditions. The results showed better performance in the Distributed case with the lowest losses and higher reliability improvement. Moreover, the losses are significantly reduced and the reliability is improved during the COVID-19 pandemic conditions. The findings indicate that the allocation and planning during the COVID-19 conditions is a robust option in network operating point changes. Also, the probabilistic results showed that considering the uncertainty has increased active and reactive losses (4.67% and 5.82%) and weakened the reliability (10.26%) of the deterministic approach.

Exploration of the form factors of turbulence kinetic energy transfer for shear exfoliation of graphene.

Mass production of defect-free and large-lateral-size 2D materials via cost-effective methods is very important. Recently, shear exfoliation has shown great promise for large-scale production due to its simple operation, environmental-benignity and wide adaptability. However, a long-standing challenge is that with the production of more nanosheets, a ceiling yield and shattered products are encountered, which significantly limits their wider application. The method and efficiency of energy transfer in fluid is undoubtedly the key point in determining exfoliation efficiency, yet its in-depth mechanism has not yet been described. Thus, a thorough investigation of turbulence energy transfer is critically necessary. Herein, we identify two main factors that critically determine the exfoliation yield and provide a statistical analysis of the relationship between these factors and the exfoliation yield. In the initial shearing process, the coexistence of the 2D nanosheets and raw particles is the dominant factor; as time passes, the dimensional change of raw materials gradually has a greater influence on the energy transfer. These factors together lead to attenuated efficiency and a power function relationship between yield and exfoliation time. This investigation gives a statistical explanation of shear exfoliation technology for 2D material preparation and provides valuable insights for mechanical exfoliating high-quality 2D materials.

Automated sample preparation for the detection and confirmation of hypoxia-inducible factor stabilizers in urine.

As hypoxia-inducible factor stabilizers (HIFs) can artificially enhance an athlete's erythropoiesis, the World Anti-Doping Agency prohibits their use at all times. Every urine sample for doping control analysis has to be evaluated for the presence of HIFs and therefore sensitive methods that allow high sample throughput are needed. Samples suspicious for the presence of HIFs need to be confirmed following the identification criteria established by the World Anti-Doping Agency. Previous work has shown the advantages of using turbulent flow online solid-phase extraction (SPE) procedures to reduce matrix effects and retention time shifts. Furthermore, the use of online SPE allows for automation and high sample throughput. Both an initial testing procedure (ITP) and a confirmation method were developed and validated, using online SPE liquid chromatography-tandem mass spectrometry (LC-MS/MS), with limits of detection between 0.1 ng/ml (or possibly lower) and 4 ng/ml (or higher for GSK360a) and limits of identification between 0.1 ng/ml (or possibly lower) and 1.17 ng/ml. The ITP only takes 6.5 min per sample. To the best of our knowledge, these are the first ITP and confirmation methods that include more than three HIFs without the need for manual sample preparation.

Facility for Calibrating Anemometers as a Function of Air Velocity Vector and Turbulence.

NIST calibrates anemometers as a function of airspeed vector and turbulence intensity (Tu). The vector capability (sometimes called "3-D") is particularly important for calibrating multi-hole differential-pressure probes that are often used to quantify pollution emitted by smokestacks of coal-burning electric power plants. Starting with a conventional "1-D" wind tunnel, we achieved vector and Tu capabilities by installing translation/rotation stages and removable turbulence generators (grids or flags). The calibration ranges are: yaw angle ±180°; pitch angle ±45°; airspeed 1 m/s to 30 m/s; turbulence intensity 0.07 ≤ Tu ≤ 0.25; average data collection rate: 300 points/hour at fixed Tu. The system's expanded uncertainties corresponding to 95 % confidence level are: airspeed 0.0045×|V|+(0.036/|V|)2 where |V| is the magnitude of the airspeed in m/s; pitch and yaw angles 0.3°; and turbulence intensity 0.03 Tu. The airspeed working standard is a Laser Doppler Anemometer that is traced to SI unit of velocity via a spinning disk. Calibrations are corrected for blockage by the instrument under test and its supports.

Turbulent Flow in a Cavernous Sinus Lesion: Does It Suggest Something?

A 14-year-old boy who had been complaining of double vision for the previous month was referred for neuro-ophthalmological evaluation. He was carrying a diagnosis of a cavernous sinus haemangioma causing a right VIth nerve palsy, based on imaging elsewhere. He reported having a boil at the angle of his mouth, which was associated with left-sided facial cellulitis, two weeks before the onset of the diplopia. His blood investigations showed a leukocytosis with elevated inflammatory markers. Re-evaluation of the magnetic resonance imaging suggested a sac-like out-pouching in the intracavernous part of the right internal carotid artery with differential intensity suggestive of turbulent flow. On the basis of the clinico-radiological findings, a diagnosis of mycotic aneurysm of the cavernous sinus part of internal carotid artery was made. A high index of suspicion is required to detect this rare clinical entity, which is associated with a potentially catastrophic clinical course.

Frictional drag measurements of large-scale plates in an enhanced plane channel flowcell.

This paper describes the design of an enhanced, plane channel, flowcell and its use for testing large-scale coated plates (0.6 m × 0.22 m) in fully developed flow, over a wide range of Reynolds numbers, with low uncertainty. Two identical, hydraulically smooth plates were experimentally tested. Uniform biofilms were grown on clean surfaces to test skin friction changes resulting from different biofilm thickness and densities. A velocity survey of the flowcell measurement section, using laser Doppler anemometry, showed a consistent velocity profile and low turbulence intensity in the central flow channel. The skin friction coefficient was experimentally determined using a pressure drop method. Results correlate closely to previously published regression data, particularly at higher speeds. Repeated measurements indicated very low uncertainty. This study demonstrates this flowcell's applicability for representing consistent frictional drag of ship hull surfaces, enabling comparability of hydrodynamic drag caused by surface roughness to the reference surface measurements.

A rapid, automatic and accurate assay for quantifying temocillin in human serum and CSF using turbulent flow liquid chromatography coupled to high-resolution mass spectrometry. Clinical application.

Temocillin is a ß-lactamase-resistant penicillin used for the treatment of multiple drug-resistant Gram-negative bacteria. To maximize efficacy and avoid adverse effects, the dose regimen has to be quickly adjusted to the clinical situations. This necessitates the development of a rapid, reliable and accurate analytical method. Temocillin and the stable isotopically labeled internal standard ([13 C6 ]-amoxicillin) were extracted from either serum or cerebrospinal fluid by a turbulent flow liquid chromatographic method and eluted onto an octadecyl-silica phase with polar endcapping. Mass spectrometry was conducted using an exact mass determination method by electrospray positive ionization high-resolution mass spectrometry. The LLOQ and ULOQ of the present method were determined to be 0.4 and 200 µg/ml for serum and cerebrospinal fluid samples, respectively. The total analysis time was <7 min. The recovery ranged from 87.7 to 120.8%. Intra- and inter-day precision and trueness were tested at four concentration levels: 0.4, 8, 40 and 160 µg/ml. Values were 6.33 ± 1.53, 8.8 ± 1.3, 8.8 ± 0.36 and 2.1 ± 0.76%, and 5.0 ± 0.54, 9.9 ± 1.0, 5.8 ± 1.6 and 0.1 ± 1.1%, for inter- and intra-day analysis, respectively. Temocillin was found to be stable under all relevant laboratory conditions. The method was cross-validated with a microbiological assay. This method is suitable for accurate measurement of temocillin concentration in small volumes of serum or cerebrospinal fluid. Thanks to the online extraction procedure, the overall analytical time is compatible with high-throughput analysis for clinical application.

Surgical treatment results of secondary tunnel-like subaortic stenosis after congenital heart disease operations: A 7-year, single-center experience in 25 patients.

OBJECTIVE: To summarize the surgical results of secondary tunnel-like subaortic stenosis (STSS) after congenital heart disease (CHD) operations, the pathogenesis of STSS is analyzed and its operative effect and prognosis are evaluated. METHODS: We analyzed clinical data from 25 patients who underwent surgical repair for STSS in Fuwai Hospital from 1 January 2009 to 31 December 2015. There were 17 males and 8 females. The types of CHD included a double outlet right ventricle (DORV), a ventricular septal defect (VSD), and partial atrioventricular septal defects (PAVSDs). The median age of the patients at the time of their first CHD operation was 1 year (1 month to 42 years). The median age of the patients at the time of STSS repair was 5 years and 8 months (2 years and 10 months to 48 years). The surgical types included the modified Konno procedure, Konno procedure, fibromuscular resection (FMR), and removal and reconstruction of the intraventricular baffle (RRIB). RESULTS: All patients successfully received STSS repair. There were no surgical deaths in this study. The preoperative gradient across the left ventricular outflow tract was 81 (43-159) mm Hg, and the postoperative gradient was 8.2 (4-46.2) mm Hg. On the basis of the surgical techniques used for subaortic stenosis repair, we divided the patients into three subgroups: the Konno group (n = 11), the FMR group (n = 11), and the RRIB group (n = 3). Preoperatively, there was no significant difference in the gradient between the Konno group and the FMR group (ΔP, P = .287), but the Konno group was significantly better than the FMR group postoperatively (ΔP, P = .022). There were no significant statistical differences between the RRIB group and the other two groups in all these data. A third-degree atrioventricular block occurred in two patients after the operation, and both patients required a permanent pacemaker. All patients were followed up after discharge for a median duration of 5 years (3-9 years). During the follow-up period, none of the patients had any clinical symptoms or subaortic restenosis, and there was no late death. CONCLUSIONS: Secondary subaortic stenosis (SSS) occurs after DORV surgery. The Konno operation or the RRIB can be selected for surgical correction, which is more satisfactory and safer for the treatment of stenosis. For patients with SSS after the operation of VSD or PAVSD, the FMR can be chosen for the operation. The operation is relatively simple, the operation time is short and the effect is satisfactory. Existing problems include that the incidence of a third-degree atrioventricular block is slightly higher after the operation.

Calciprotein Particles Cause Endothelial Dysfunction under Flow.

Calciprotein particles (CPPs), which increasingly arise in the circulation during the disorders of mineral homeostasis, represent a double-edged sword protecting the human organism from extraskeletal calcification but potentially causing endothelial dysfunction. Existing models, however, failed to demonstrate the detrimental action of CPPs on endothelial cells (ECs) under flow. Here, we applied a flow culture system, where human arterial ECs were co-incubated with CPPs for 4 h, and a normolipidemic and normotensive rat model (10 daily intravenous injections of CPPs) to simulate the scenario occurring in vivo in the absence of confounding cardiovascular risk factors. Pathogenic effects of CPPs were investigated by RT-qPCR and Western blotting profiling of the endothelial lysate. CPPs were internalised within 1 h of circulation, inducing adhesion of peripheral blood mononuclear cells to ECs. Molecular profiling revealed that CPPs stimulated the expression of pro-inflammatory cell adhesion molecules VCAM1 and ICAM1 and upregulated transcription factors of endothelial-to-mesenchymal transition (Snail, Slug and Twist1). Furthermore, exposure to CPPs reduced the production of atheroprotective transcription factors KLF2 and KLF4 and led to YAP1 hypophosphorylation, potentially disturbing the mechanisms responsible for the proper endothelial mechanotransduction. Taken together, our results suggest the ability of CPPs to initiate endothelial dysfunction at physiological flow conditions.

On the limitations of partial Fourier acquisition in phase-contrast MRI of turbulent kinetic energy.

PURPOSE: To investigate limitations of partial Fourier acquisition in phase-contrast MRI of turbulent kinetic energy (TKE). METHODS: To assess the validity of partial Fourier reconstruction of TKE and phase images, computational fluid dynamics data of mean and turbulent velocities in a stenotic U-bend phantom was used. Partial Fourier acquisition with 75% k-space coverage was simulated and TKE data were reconstructed using zero-filling, homodyne reconstruction, and the method of projections onto convex sets (POCS). Results were compared to data from fully sampled k-space and 75% symmetric sampling. In addition, compressed sensing (CS) reconstruction was compared for a standard variable density sampling pattern and a variable density sampling pattern combined with 75% partial Fourier. For illustration purposes, in vivo examples of velocity magnitude and TKE maps of aortic flow reconstructed with the different methods are provided. RESULTS: In accordance with theory, partial Fourier reconstruction of TKE maps from phase-contrast data results in artifacts relative to fully sampled data. It is demonstrated that neither homodyne reconstruction nor POCS can improve reconstruction of TKE data with respect to zero-filling reconstruction when compared to ground-truth (RMS error: 4.70%, 4.34%, and 2.45% for homodyne, POCS, and zero-filling reconstruction of in vivo data, respectively). CS reconstruction from data acquired with partial Fourier did not recover the resolution loss incurred by partial Fourier sampling. CONCLUSION: Partial Fourier reconstruction of TKE maps from phase-contrast data does not yield a benefit over zero-filling reconstruction. In consequence, symmetric sampling is preferred over partial Fourier acquisition for a given number of phase-encodes in phase-contrast MRI.

Current status and future trends on automated multidimensional separation techniques employing sorbent-based extraction columns.

Determination of target analytes present in complex matrices requires a suitable sample preparation approach to efficiently remove the analytes of interest from a medium containing several interferers while at the same time preconcentrating them aiming to improve the output signal detection. Online multidimensional solid-phase separation techniques have been widely used for the analysis of different contaminants in complex matrices such as food, environmental, and biological samples, among others. These online techniques usually consist of two steps performed in two different columns (extraction and analytical column), the first being employed to extract the analytes of interest from the original medium and the latter to separate them from the interferers. The extraction column in multidimensional techniques presents a relevant role since their variations as building material (usually a tube), sorbent material, modes of application, and so on can significantly influence the extraction success. The main features of such columns are subject of constant research aiming improvements directly related to the performance of the separation techniques that utilize multidimensional analysis. The present review highlights the main features of extraction columns online coupled to chromatographic techniques, inclusive for in-tube solid-phase microextraction, online solid phase and turbulent flow, aiming the determination of analytes present at very low concentrations in complex matrices. It will critically describe and discuss some of the most common instrumental set up as well as comments on recent applications of these multidimensional techniques. Besides that, the authors have described some properties and enhancements of the extraction columns that are used as first dimension on these systems, such as type of column material (poly (ether ether ketone), fused silica, stainless steel, and other materials) and the way that the extractive phase is accommodated inside the tubing (filled and open tubular). Practical applications of this approach in fields such as environment, food, and bioanalysis are also presented and discussed.

Evaluation of energy dissipation rate as a predictor of mechanical blood damage.

A long-standing goal in the field of biofluid mechanics has been to reliably predict hemolysis across the wide range of flows that can occur in prosthetic cardiovascular devices. A scalar representation of the complex three-dimensional fluid stresses that are exerted on cells is an attractive alternative for the simplicity that it lends to the computations. The appropriateness of the commonly used von-Mises-like scalar stress as a universal hemolysis scaling parameter was previously evaluated, finding that erythrocyte membrane tensions calculated for laminar shear and extensional flows and for three cases of turbulent flow were widely divergent for the same value of scalar stress. The same techniques are applied in this study to laminar and turbulent flows that each have the same energy dissipation rate. Results showed that agreement of membrane tension between laminar shear and turbulent shear inside an eddy was improved relative to the common scalar stress cases, but disagreement between laminar shear and laminar extension remained the same and disagreement between laminar shear and other turbulent flows increased. It is therefore concluded that energy dissipation rate alone is also likely not sufficient to universally scale blood damage across the range of different flows that can be encountered clinically.

Aquatic animal colors and skin temperature: Biology's selection for reducing oceanic dolphin's skin friction drag.

There is currently a growing interest in the area of drag reduction. In this work, the thermal effects of body color of some species of aquatics like Orcas and Dusky dolphins are investigated with respect to their swimming routes and geometric and behavioral characteristics. Considering the marine and atmospheric characteristics of these aquatics' routes, a thermal analysis is performed. The surrounding fluxes including the water flux, sun irradiation, and core temperature are considered in an energy balance to determine the skin temperature of the top side of the animal/organism's body. To study the effects of color on the surface temperature of the aquatic species, an experiment is carried out in the water on a flat plate with black and white color. Applying a turbulent analytical solution for heated boundary layers, it will be shown that the black color on the top of the bodies of these marine organisms is very efficient in terms of skin drag reduction. Moreover, to investigate the effects of the temperature on underwater skin friction drag reduction, the turbulent flow is simulated around a flat plate and a 2- dimensional modeled Killer whale at different temperatures. The results show that the top black body color of Orca and Dusky dolphin decreases their skin friction drag by 7%. This study will also provide the reason for this evolution of color scheme of other extremely fast marine animals, such as billfish, whales, and sharks. This method of drag reduction can be considered as one of the effective factors in skin drag reduction of underwater robots.

The Influence of Internal Intermittency, Large Scale Inhomogeneity, and Impeller Type on Drop Size Distribution in Turbulent Liquid-Liquid Dispersions.

The influence of the impeller type on drop size distribution (DSD) in turbulent liquid-liquid dispersion is considered in this paper. The effects of the application of two impellers, high power number, high shear impeller (six blade Rushton turbine, RT) and three blade low power number, and a high efficiency impeller (HE3) are compared. Large-scale and fine-scale inhomogeneity are taken into account. The flow field and the properties of the turbulence (energy dissipation rate and integral scale of turbulence) in the agitated vessel are determined using the k-ε model. The intermittency of turbulence is taken into account in droplet breakage and coalescence models by using multifractal formalism. The solution of the population balance equation for lean dispersions (when the only breakage takes place) with a dispersed phase of low viscosity (pure system or system containing surfactant), as well as high viscosity, show that at the same power input per unit mass HE3 impeller produces much smaller droplets. In the case of fast coalescence (low dispersed phase viscosity, no surfactant), the model predicts similar droplets generated by both impellers. In the case of a dispersed phase of high viscosity, when the mobility of the drop surface is reduced, HE3 produces slightly smaller droplets.

Determination of UV filters in human breast milk using turbulent flow chromatography and babies' daily intake estimation.

UV filters (UV-Fs) are a group of hormonally active chemical compounds used to protect against the deleterious effects of UVA and UVB solar radiation, which are currently present in most consumer goods (personal care products, plastics, fabrics, paints, etc). Last years the concern about these emerging contaminants has been on the rise, and increasing efforts are being taken in order to properly asses the hazard that the exposure to these compounds in the early stages of life may pose. In this study, a new method for the analysis of 11 UV-Fs residues in human breast milk samples has been developed. The method is based on turbulent flow chromatography coupled to liquid chromatography-tandem mass spectrometry (TFC-HPLC-MS/MS). The validated method was successfully applied to 79 human breast milk samples from mothers in Barcelona (Spain). Twenty-four per cent of the samples contained UV-Fs, with major contributors being oxybenzone (benzophenone 3, BP3), its metabolite 4,4'-dihydroxybenzophenone (4DHB), and UV320 showing maximum concentrations of 779.9, 73.3, and 523.6ngg-1 milk, respectively. Additionally, the plastic containers of the milks were also analysed, revealing high concentrations of BP3 and 4DHB, up to 10.6µgg-1 plastic. The calculated mean ΣUV-Fs were useful to estimate the daily intake (EDI) by babies, which were 69.1µg d-1kg-1 body weight.

On-line approaches for the determination of residues and contaminants in complex samples.

The determination of residues and contaminants in complex matrices such as in the case of food, environmental, and biological samples requires a combination of several steps to succeed in the aimed goal. At least three independent steps are integrated to provide the best available situation to deal with such matrices: (1) a sample preparation technique is employed to isolate the target compounds from the rest of the matrix; (2) a chromatographic (second) step further "purifies" the isolated compounds from the co-extracted matrix interferences; (3) a spectroscopy-based device acts as chromatographic detector (ideally containing a tandem high-resolution mass analyzer) for the qualitative and quantitative analysis. These techniques can be operated in different modes including the off-line and the on-line modes. The present report focus the on-line coupling techniques aiming the determination of analytes present in complex matrices. The fundamentals of these approaches as well as the most common set ups are presented and discussed, as well as a review on the recent applications of these two approaches to the fields of bioanalytical, environmental, and food analysis are critically discussed.

Role of tube size and intranasal compression of the nasotracheal tube in respiratory pressure loss during nasotracheal intubation: a laboratory study.

BACKGROUND: Small nasotracheal tubes (NTTs) and intranasal compression of the NTT in the nasal cavity may contribute to increasing airway resistance. Since the effects of size, shape, and partial compression of the NTT on airway resistance have not been investigated, values of airway resistance with partial compression of preformed NTTs of various sizes were determined. METHODS: To determine the factors affecting the respiratory pressure loss during the nasotracheal intubation, physical and fluid dynamics simulations were used. The internal minor axes of NTTs in the nasal cavity of intubated patients were measured using dial calipers. In physical and fluid dynamics simulations, pressure losses through the tubular parts, compressed parts, and slip joints of NTTs with internal diameters (IDs) of 6.0, 6.5, 7.0, 7.5, and 8.0 mm were estimated under partial compression. RESULTS: The median internal minor axes of the 7.0- and 7.5-mm ID NTTs in the nasal cavity were 5.2 (4.3-5.6) mm and 6.0 (4.2-7.0) mm, respectively. With a volumetric air flow rate of 30 L/min, pressure losses through uncompressed NTTs with IDs of 6.0-, 6.5-, 7.0-, 7.5- and 8.0-mm were 651.6 ± 5.7 (6.64 ± 0.06), 453.4 ± 3.9 (4.62 ± 0.04), 336.5 ± 2.2 (3.43 ± 0.02), 225.2 ± 0.2 (2.30 ± 0.00), and 179.0 ± 1.1 Pa (1.82 ± 0.01 cmH2O), respectively; the pressure losses through the slip joints were 220.3 (2.25), 131.1 (1.33), 86.8 (0.88), 57.1 (0.58), and 36.1 Pa (0.37 cmH2O), respectively; and the pressure losses through the curvature of the NTT were 71.6 (0.73), 69.0 (0.70), 64.8 (0.66), 32.5 (0.33), and 41.6 Pa (0.42 cmH2O), respectively. A maximum compression force of 34.1 N increased the pressure losses by 82.0 (0.84), 38.0 (0.39), 23.5 (0.24), 16.6 (0.17), and 9.3 Pa (0.09 cmH2O), respectively. CONCLUSION: Pressure losses through NTTs are in inverse proportion to the tubes' IDs; greater pressure losses due to slip joints, acute bending, and partial compression of the NTT were obvious in small NTTs. Pressure losses through NTTs, especially in small NTTs, could increase the work of breathing to a greater extent than that through standard tubes; intranasal compression further increases the pressure loss.