Positive Pressure and Negative Pressure Irrigation Dynamics with Different Needle Designs Using Computational Fluid Dynamics

To compare using computational fluid dynamics (CFD) the flow pattern, irrigant velocity, apical pressure and shear stress produced by negative (MiC) and positive pressure with different types of needles (side-vented (SV), front-vented (FV) and notched (N)) at two insertion depths in the apical ramification of oval root canals. The micro-CT of a mandibular molar with an oval root canal with an apical ramification was used for computational analysis after preparation and geometric reconstruction. Geometries with the needles in two positions (1 and 3mm from WL) were created to run the simulations. Key parameters of irrigation were displayed with CFD and compared. The penetration depth of the needle in the root canal strongly influenced shear stress and apical pressure. The three needles revealed that the highest shear stress, velocity and apical pressure were 1mm from the WL and generated medium velocities. In N simulations, the fluid flow did not reach the apical ramification and the lowest shear stress values for positive pressure needles were found. The predominant axial component for FV revealed a different pattern of irrigation with high shear stress values and higher apical pressures than those exerted by other needles. SV simulations had generalized fluid flow in most of the main canal, the highest shear stress values and lower apical pressure than the threshold determined for risk of extrusion. MiC was associated with low velocity, shear stress and apical pressure. The SV needle demonstrated a combination of low positive pressure and high shear stress; while N had the lowest shear stress and FV the highest apical pressure. MiC generated fluid flow in part of the apical ramification with negative apical pressure values but low shear stress and velocity.

Objective:Periapical extrusion is frequently observed during endodontic therapy. It can lead to acute injury of periapical tissues, resulting in interappointment pain or swelling. The effect is pronounced in teeth with immature teeth which are more susceptible to the extrusion of irrigant. The aim of this study was to evaluate the effect of gravity on apical extrusion of irrigating solution with different irrigation protocols in immature anterior teeth.Methods:An extracted maxillary central incisor was modified to simulate an open apex with an apical diameter of 1.3 mm and parallel canal walls. The tooth was subjected to a cone-beam computed tomographic scan, and the image data set was utilized to prepare 30 resin tooth models with a 3D printer. These resin teeth were used to form an open-ended Myers and Montgomery extrusion models. These were then randomly divided into two groups to simulate their orientation in the jaw during endodontic therapy, i.e., group I (maxillary arch, n=15) models fixed at 45° inclined plane and group II (mandibular arch, n=15) models placed at a plane parallel to the floor. Five models from each group (n=5) were tested by three different irrigation protocols: positive pressure (PP) Irrigation, passive ultrasonic irrigation (PUI), and negative pressure (NP) irrigation. The extruded irrigating solution was collected in glass vials, and the volume was measured.Results:The volume of extruded irrigating solution in groups I and II was compared using Mann–Whitney U-test. The median values for PP, PUI, and NP irrigation protocols were 0.6, 1, and 0 ml and 10, 10, and 0.5 ml for groups I and II, respectively. PP and PUI protocols were associated with significantly less extrusion in group I when compared to group II (P=0.004). There was no statistically significant difference in the volume of irrigating solution extruded in groups I and II (P=0.007) for NP irrigation protocol.Conclusion:Gravitation force has an influence on periapical extrusion of irrigant in immature permanent teeth irrespective of the irrigant system used. NP performed better when compared to PP or PUI irrigation protocol irrespective of the tooth orientation.

This study aims to determine the characteristics of fluid flow through root canal irrigation using positive and negative pressure methods used CFD (Computational Fluid Dynamic) software by modeling root canals and needle insertion in the root canals. This modeling used a steady flow, an incompressible flow, and uniform flow at the inlet side, and the roughness of the root canal wall surface is neglected (smooth wall). The open-ended needle with different insertion lengths applied for each method with a flow rate of 0.2 mL/s or about 6.63 m/s and the Reynolds number is 1376 (Laminar). The fluid has 2.5% of NaOCl with the density of 1060 kg/m3 and 0.001 Pa.s of fluid viscosity. After considering factors such as velocity, dynamic pressure, and wall shear stress in both methods, a greater velocity value in the apical region is determined by using a positive pressure method. Meanwhile, the negative pressure method shows the ability to lift higher due to shear stress, which is more evenly distributed upwards. However, both methods are qualified for irrigation replacement in the apical region.

Objective: To evaluate the irrigation performance of a modified flat-side open-ended needle (FS needle) in comparison with a traditional flat needle (F needle) and a side-vented needle (S needle), aiming to optimize clinical irrigation strategies. Methods: A 3% sodium hypochlorite solution was selected as the irrigant. Idealized root canal and three irrigation needle geometries were modeled using FreeCAD. Mesh generation and computational setup were performed using Fluent software to simulate the irrigation process with three needle types at working depths of 1, 3, and 5 mm (nine groups in total). Apical pressure, wall shear stress, and velocity data were extracted. Data were processed using Python, and flow field characteristics and irrigation efficacy were comparatively analyzed based on velocity and wall shear stress distributions, as well as four evaluation metrics: apical pressure, effective replacing depth, and effective shear stress depth and span. Results: The apical pressures of the FS needle were 14.22, 11.79, and 9.43 kPa at working depths of 1, 3, and 5 mm, respectively, which were lower than those of the F needle (35.09, 25.04, 17.78 kPa) and close to those of the S needle (9.49, 7.66, 5.92 kPa). The effective replacing depths of the FS needle were 1.25, 1.65, and 1.95 mm, slightly lower than those of the F needle (1.30 mm) but much higher than those of the S needle (0.15 mm) at 1 mm working depth, and comparable to the S needle (1.95 mm) at 5 mm working depth. The effective shear stress depths were 5.07, 3.36, and 1.56 mm, with spans of 3.18, 1.93, and 1.40 mm, respectively, slightly lower than those of the F needle in depth but close to or higher than the S needle in span. Conclusions: At working depths of 1-3 mm, the FS needle was associated with low apical pressure and superior fluid replacement capacity, indicating a favorable balance between pressure control and irrigation efficiency.

To assess reliability of wall shear stress (WSS)calculations using computational fluid dynamics (CFD) dependent on inflow in internal carotid artery aneurysms (ICA). Six unruptured ICA aneurysms were studied. 3D computational meshes were created from 3D digital subtraction angiographic images (Axiom Artis dBA, Siemens Medical Solutions). Transient CFD simulations(Fluent, ANSYS Inc.) were performed for two inflow conditions: (1) idealized averaged waveform from normal subjects (ID) and (2) patient-specific waveform (PS)measured with 2D phase contrast magnetic resonance imaging. Stability of calculation was assessed by comparing mean WSS (<WSS>), temporal wall shear stress magnitude variation (Delta WSS), and oscillatory shear index(OSI, a measure of variation in the WSS direction) on the aneurysmal wall for both conditions. For all cases, mean relative difference (PS-ID) of WSS (<WSS>) was -15% (range -32% to 11%). Mean Delta WSS difference was -29.3% ( -100% to 67%). Mean OSI difference was 7.5% (-12% to 40%). Large variations in histograms of these parameters were noted. For accurate calculations of WSS parameters,patient-specific information on physiological flow may be necessary. Results obtained with averaged or idealized flow waveforms may have to be interpreted with caution.

Middle ear pressure changes have been thought to cause sensori-neural loss as well as conductive hearing loss. To clarify the degree and mechanism, we used electrocochleography in guinea pigs to investigate electrophysiological changes in the inner ear while positive or negative pressure changes were applied only to the middle ear cavity (middle ear group), or to the external auditory canal and middle ear cavity simultaneously (external-middle ear group).1) Significant reductions in action potential (AP) amplitude were found in the middle ear group receiving either positive or negative pressure, but there was no significant difference between the two groups. No significant reductions were found in the external-middle ear group regardless of whether positive or negative pressure was applied.2) Significant reductions in summating potential (SP) amplitude and SP/AP ratio were found in the middle ear group receiving positive pressure. There was wide variation in the changes observed in the middle ear group receiving negative pressure. The external-middle ear group receiving negative pressure showed greater reductions in SP amplitude and SP/AP ratio than the group receiving positive pressure, implying a difference in the changes in stiffness of the inner ear windows between the two groups.3) Rebound phenomenon in SP amplitude and SP/AP ratio was found in the middle ear group when positive pressure in the middle ear cavity was released, implying secondary effects on hearing due to inner ear pressure changes.

Linear brakes are devices used to restrict relative linear motions between two points. The use of soft robotic technology has enabled the fabrication of lightweight linear brakes making use of frictional forces generated by a vacuum on jamming layers. This kind of device has significant potential for wearable devices as they are lightweight yet produce significant linear tensions which can be used to transfer loads or to selectively prevent certain motions of the body. However, vacuum-based devices have limitations in terms of maximum pressure and due to the decreasing frictional forces as the jamming layers decrease in contact area as they separate during the motion. This article introduces a positive and negative pressure linear brake where both positive and negative pressure is applied to jamming layers located inside of a pouch motor which is pressurized using positive pressures. This results in a soft linear brake capable of large braking forces and of adjusting its behavior through the variation of both positive and negative pressures. The proposed brake could sustain a linear tensile force approaching 500 N even at lower pressures and was implemented as a lower back support device intended for factory and healthcare workers.

Complexities in root canal anatomy and surface adherent biofilm structures remain as challenges in endodontic disinfection. The ability of an irrigant to penetrate into the apical region of a canal, along with its interaction with the root canal walls, will aid in endodontic disinfection. The aim of this study was to qualitatively examine the irrigation dynamics of syringe irrigation with different needle tip designs (open-ended and closed-ended), apical negative pressure irrigation with the EndoVac® system, and passive ultrasonic-assisted irrigation, using a computational fluid dynamics model. Syringe-based irrigation with a side-vented needle showed a higher wall shear stress than the open-ended but was localised to a small region of the canal wall. The apical negative pressure mode of irrigation generated the lowest wall shear stress, while the passive-ultrasonic irrigation group showed the highest wall shear stress along with the greatest magnitude of velocity.

Mechanical insufflation-exsufflation (MI-E) uses positive and negative pressures to assist weak cough and to help clear airway secretions. Laryngeal visualization during MI-E has revealed that inappropriate upper airway responses can impede its efficacy. However, the dynamics of pressure transmission in the upper airways during MI-E are unclear, as are the relationships among anatomic structure, pressure, and airflow. Can airflow resistance through the upper airway and the larynx feasibly be calculated during MI-E, and if so, how are the pressures transmitted to the trachea? Cross-sectional study of 10 healthy adults, where MI-E was provided with and without active cough using pressure settings+20/-40cm H2O and ± 40cm H2O. Airflow and pressure at the level of the facemask were measured using a pneumotachograph, whereas pressure transducers (positioned via transnasal fiber-optic laryngoscopy) recorded pressures above the larynx and within the trachea. Upper airway resistance (Ruaw) and translaryngeal resistance (Rtl) were calculated (in centimeters of water per liter per second) and were compared with direct observations via laryngoscopy. Positive pressures reached the trachea effectively, whereas negative tracheal pressures during exsufflation were approximately one-half of the intended settings. Insufflation pressure increased slightly when passing through the larynx. Participant effort influenced tracheal pressures and the resistances, with findings consistent with laryngoscopic observations. During MI-E, resistance seems to be dynamic, with Ruaw exceeding Rtl. Inappropriate laryngeal closure increased Rtl during both positive and negative pressures. We found that Ruaw and Rtl can be calculated feasibly during MI-E. The findings indicate different transmission dynamics for positive and negative pressures and that resistances are influenced by participant effort. The findings support using lower insufflation pressures and higher negative pressures in clinical practice.

Volumetric hemodynamic analysis has previously demonstrated robustness to surface irregularities and noise; however, quantitative evaluation methods remain limited. The authors introduce a novel approach to assess intradome velocity distributions in intracranial aneurysms by applying radiomics texture and pattern analysis to time-step data derived from transient computational fluid dynamics (CFD) simulations. Angiographic volumes from catheter 3D rotational angiography were available for 75 aneurysms (33 ruptured). Transient CFD simulations were performed on aneurysm models over an entire cardiac cycle. Intradome volumetric velocity distributions were exported for consecutive time points, followed by maximum intensity projection (MIP) to 2D images and logarithmic transformation to enhance discrimination analysis at the intensity extrema. Two-dimensional images representing consecutive time points were used as input to radiomics as 3D DICOM volumes. Univariate and multivariate analyses assessed rupture status discrimination accuracy of 93 histogram, texture, and pattern radiomics features. Radiomics analysis of MIP velocity texture and pattern revealed that, compared with unruptured aneurysms, ruptured aneurysms have lower intensity patterns (higher energy and total energy of logarithmic values), reflecting dominant low-velocity regions. These regions exhibit consistent intensity textures (higher correlation and inverse difference, with lower cluster shade and difference entropy) with recurrent patterns of similar intensities (higher maximum probability and long-run emphasis). Localized high-velocity runs are also present (higher high gray-level run emphasis) in ruptured aneurysms, suggesting a heterogeneous flow profile. Stepwise regression multivariate analysis achieved rupture status discrimination with an area under the curve of 0.88 (sensitivity 0.91, specificity 0.74). The automatic analysis of transient velocity using radiomics, incorporating pattern and texture analysis, demonstrated strong discriminating performance for rupture status. This innovative application of radiomics expands its utility beyond tumor and aneurysm shape analysis, enabling evaluation of velocity changes throughout the entire cardiac cycle. It provides valuable insights into rupture characteristics and paves the way for exploring future research possibilities.

To evaluate hemodynamic changes during aneurysmal dilatation in chronic type B aortic dissections compared to hemodynamic parameters in the healthy aorta with the use of computational fluid dynamics (CFD). True lumen (TL)/false lumen (FL) dimensional changes, changes in total pressure (TP), and wall shear stress (WSS) were evaluated at follow-up (FU) compared to initial examination (IE) with transient CFD simulation with geometries derived from clinical image data and inflow boundary conditions from magnetic resonance images. The TL/FL pressure gradient between ascending and descending aorta (DAo) and maximum WSS at the site of largest dilatation was compared to values for the healthy aorta. Hemodynamic changes at site of largest FL dilatation included 77% WSS reduction and 69% TP reduction. Compared to the healthy aorta, pressure gradient between ascending and DAo was a factor of 1.4 higher in the TL and a factor of 1.5 in the FL and increased at FU (1.6 and 1.7, respectively). Maximum WSS at the site of largest dilatation was a factor of 3 lower than that for the healthy aorta at IE and decreased by more than a factor of 2 at FU. The FL dilatation at FU favorably reduced TP. In contrast, unfavorable increase in pressure gradient between ascending and DAo was observed with higher values than in the healthy aorta. Maximum WSS was reduced at the site of largest dilation compared to healthy aorta.

Exercise increases muscle microvascular flow via vasodilation from both endothelial dependent and independent mechanisms. Altered transmural pressure also affects blood flow in muscle. For example, lower body negative pressure decreases and lower body positive pressure increases blood flow. PURPOSE: To determine muscle microvascular blood flow (MBF) during post-exercise hyperemia at negative and positive lower body pressure (LBP). It was hypothesized that the post-exercise hyperemic response would not be present at increased levels of positive LBP. METHODS: Eight healthy subjects (6 male, 2 female; ages 21–41) were placed supine in a LBP chamber that was sealed at the waist. Photoplethysmography was used to noninvasively measure MBF of the tibialis anterior muscle and skin microvascular blood flow (SBF) of overlying skin during exposure to a series of LBP levels (−30, −20, −10, 0, 10, 20, 30mmHg) with and without dorsiflexion exercise. At each pressure level MBF was allowed to stabilize for one minute prior to a one minute baseline data collection. Subjects then performed a one minute isometric dorsiflexion at a resistance of 41N and MBF was recorded for one minute following dorsiflexion. Subjects were given a 5 minute rest period between pressure levels to ensure MBF return to baseline. All microvascular flow data were normalized to the control value obtained at ambient pressure without exercise and presented as percentages (mean±SE) to compare between conditions. Data were analyzed using two-way repeated measures ANOVA to determine exercise effect and pressure effect on MBF. RESULTS: MBF and SBF increased at all LBP levels with exercise compared to no exercise (p=0.001 and p=0.005). MBF significantly decreased with negative pressure and increased with positive pressure (p=0.003 and p<0.001). The lowest MBF was at −30mmHg (52±9% w/o exercise, 61±9% w/ exercise) and the highest was at 10mmHg (137±15% w/o exercise, 145±12% w/ exercise). CONCLUSION: Post exercise hyperemia occurs at all lower body pressure levels studied. Elevation of microvascular flow after isometric exercise adds to changes measured at different levels of LBP. Regimens for exercise training and post-injury rehabilitation may benefit from exercise at low levels of positive LBP. Supported by NIH Training Grant 2 T32AR07484-22 to GCM.

Water hammer is a transient flow in pipes that was created by sudden changesof velocity in pipe lines. This phenomenon can cause strong positive and negative pressures in water conveyance pipes and usually it poses pipeline to danger. Overall, water hammer creates by rapidly closing valves, shutting off or suddenly restarting pumps. It has destructive hydrodynamic effects in pressurized pipelines. In this study, governing equations of water hammer is numerically simulated using MATLAB software. Then, the sensitivity analysis in negative and positive pressures by changing some variables such as pipe diameter, pipe length and also wave velocity in pipewas investigated. Numerical simulation is based on characteristic method. Sensitivity analysis help designers to have well understand of water hammer phenomenon.

Rheumatoid arthritis (RA) is an autoimmune disease characterised by an attack on healthy cells in the joints. Blood flow and wall shear stress are crucial in angiogenesis, contributing to RA's pathogenesis. Vascular endothelial growth factor (VEGF) regulates angiogenesis, and shear stress is a surrogate for VEGF in this study. Our objective was to determine how shear stress correlates with the location of new blood vessels and RA progression. To this end, two models were developed using computational fluid dynamics (CFD). The first model added new blood vessels based on shear stress thresholds, while the second model examined the entire blood vessel network. All the geometries were based on a micrograph of RA blood vessels. New blood vessel branches formed in low shear regions (0.840-1.260 Pa). This wall-shear-stress overlap region at the junctions was evident in all the models. The results were verified quantitatively and qualitatively. Our findings point to a relationship between the development of new blood vessels in RA, the magnitude of wall shear stress and the expression of VEGF.

Peristaltic contraction of the embryonic heart tube produces time- and spatial-varying wall shear stress (WSS) and pressure gradients (∇P) across the atrioventricular (AV) canal. Zebrafish (Danio rerio) are a genetically tractable system to investigate cardiac morphogenesis. The use of Tg(fli1a:EGFP)y1 transgenic embryos allowed for delineation and two-dimensional reconstruction of the endocardium. This time-varying wall motion was then prescribed in a two-dimensional moving domain computational fluid dynamics (CFD) model, providing new insights into spatial and temporal variations in WSS and ∇P during cardiac development. The CFD simulations were validated with particle image velocimetry (PIV) across the atrioventricular (AV) canal, revealing an increase in both velocities and heart rates, but a decrease in the duration of atrial systole from early to later stages. At 20-30 hours post fertilization (hpf), simulation results revealed bidirectional WSS across the AV canal in the heart tube in response to peristaltic motion of the wall. At 40-50 hpf, the tube structure undergoes cardiac looping, accompanied by a nearly 3-fold increase in WSS magnitude. At 110-120 hpf, distinct AV valve, atrium, ventricle, and bulbus arteriosus form, accompanied by incremental increases in both WSS magnitude and ∇P, but a decrease in bi-directional flow. Laminar flow develops across the AV canal at 20-30 hpf, and persists at 110-120 hpf. Reynolds numbers at the AV canal increase from 0.07±0.03 at 20-30 hpf to 0.23±0.07 at 110-120 hpf (p< 0.05, n=6), whereas Womersley numbers remain relatively unchanged from 0.11 to 0.13. Our moving domain simulations highlights hemodynamic changes in relation to cardiac morphogenesis; thereby, providing a 2-D quantitative approach to complement imaging analysis.