Pressure Spikes Research Articles

A trial of topical prednisolone acetate before intravitreal triamcinolone acetonide decreases intraocular pressure spikes

Objective: To compare adverse intraocular pressure (IOP) spikes in patients receiving intravitreal triamcinolone acetonide (IVTA) in 2 cohorts: ( i) patients who underwent a topical prednisolone acetate trial (PAT) without incurring a short-term IOP rise, and ( ii) control patients who did not undergo a PAT. Design: Retrospective cohort study. Participants: Charts of all patients who underwent any intravitreal injection during the study period were reviewed ( n = 1150). Methods: Patients in the PAT group received a 6-week course of prednisolone acetate 1% 4 times per day and had an IOP that did not rise above 25 mm Hg or above 8 mm Hg over the IOP in the contralateral eye. Patients undergoing a PAT and having a short-term IOP rise were not studied. Control patients did not receive a PAT. All patients received 12-20 mg of IVTA. Patients were followed for a minimum of 6 weeks and follow-up lasted for I year or until intraocular surgery or another IVTA injection was performed. Results: There were 97 patients in the PAT cohort and 75 control patients. Patients in the PAT cohort had a lower proportional rise between maximum IOP and baseline (43%) compared with controls (64%) ( p = 0.035). Patients in the PAT group also had a lower risk of incurring a 40% ( p = 0.05), 60% ( p = 0.0I8), and 100% ( p = 0.045) increase in maximum IOP (vs baseline) compared with controls and were less likely to require glaucoma filtration surgery ( p = 0.035). Conclusions: Patients undergoing a PAT who did not have a subsequent short-term IOP rise had a lower risk of severe IOP spikes after IVTA compared with those patients receiving IVTA but not having undergone a PAT.

SRF cryostat dynamics at the Canadian Light Source

This work includes the creation of a computer model of the superconducting radio frequency cryostat located at the Canadian Light Source (CLS) in Saskatoon, Canada. This cryostat requires careful pressure and level modulation to ensure proper radio frequency control. A detailed mathematical model of the cryostat is generated based on gas and liquid mass balances for a boiling vessel, along with pressure–volume–temperature relations. Model results are compared with experimental data taken from the actual cryostat at the CLS to determine the accuracy of the simulation. Finally, cryostat performance is explored using the model, and it is demonstrated that there are no significant advantages in pressure modulation when reducing the level operating point, and in fact a reduction in operating level slightly increases the maximum value of pressure spikes due to heat loading.

Investigation of transient cavitating flow in viscoelastic pipes

A study on water hammer in viscoelastic pipes when the fluid pressure drops to liquid vapour pressure is performed. Two important concepts including column separation and the effects of retarded strains in the pipe wall on the fluid response have been investigated separately in recent works, but there is some curiosity as to how the results for pressure and discharge are when column separation occurs in a viscoelastic pipe. For pipes made of plastic such as polyethylene (PE) and polyvinyl chloride (PVC), viscoelasticity is a crucial mechanical property which changes the hydraulic and structural transient responses. Based on previous developments in the analysis of water hammer, a model which is capable of analysing column separation in viscoelastic pipes is presented and used for solving the selected case studies. For the column-separation modelling the Discrete Vapour Cavity Model (DVCM) is utilised and the viscoelasticity property of the pipe wall is modelled by Kelvin-Voigt elements. The effects of viscoelasticity play an important role in the column separation phenomenon because it changes the water hammer fundamental frequency and so affects the time of opening or collapse of the cavities. Verification of the implemented computer code is performed for the effects of viscoelasticity and column separation – separately and simultaneously – using experimental results from the literature. In the provided examples the focus is placed on the simultaneous effect of viscoelasticity and column separation on the hydraulic transient response. The final conclusions drawn are that if rectangular grids are utilised the DVCM gives acceptable predictions of the phenomenon and that the pipe wall material's retarded behaviour strongly dampens the pressure spikes caused by column separation.

Avaliação da acuidade visual e da pressão intraocular no tratamento do edema macular diabético com triancinolona intravítrea

To evaluate the effect of intravitreal triamcinolone acetonide in patients with diffuse diabetic macular edema on the visual acuity and intraocular pressure. To report the potential adverse events and to analyze the potential relationship between age and visual acuity and intraocular pressure variability. This clinical controlled study included 14 patients (28 eyes), 14 of the eyes received an intravitreal injection of 4 mg triamcinolone acetonide for the treatment of diabetic macular edema. The study group was compared to a control group of 14 eyes, without diabetic macular edema. The follow-up period was of 3 months. Pressure spikes >21 mmHg occurred in 28.7% of eyes, with a significant difference of intraocular pressure between the study group and the control group in the first week after treatment. Visual acuity showed a significant improvement when compared with the control group since the second day after the treatment. There was no association between age and variability of visual acuity and intraocular pressure. Intravitreal triamcinolone acetonide showed to be effective for improving visual acuity in patients with diabetic macular edema, in the first three months of treatment. The incidence of intraocular hypertension was 28.7%, easily manageable.

INTRAOCULAR PRESSURE INSTABILITY AFTER 23-GAUGE VITRECTOMY

The purpose of this study was to describe outcomes, trends, risk factors, and protective factors for intraocular pressure (IOP) spikes in patients undergoing 23-gauge pars plana vitrectomy. A retrospective review in an academic institution was performed on all eyes undergoing 23-gauge vitrectomy with at least 1-month follow-up. The main outcome measures included IOP and operative complications. Ninety-seven eyes of 93 patients were included. Intraocular pressure spikes >22 in the first month occurred in 73% of eyes with or suspect for glaucoma versus 46% of eyes without (P = 0.017); 76% of eyes with a gas fill versus 44% of eyes with a fluid fill (P = 0.0036); and 21% of eyes started on IOP-lowering drops on postoperative day 1 versus 49% of eyes who were not (P = 0.0033). Complications included retinal tears (3%), intraoperative retinal detachment (2%), and postoperative retinal detachment (2%). Fifteen percent of eyes required suturing of at least one sclerotomy. There were no cases of postoperative hypotony or endophthalmitis. Patients with or suspect for glaucoma or those with a gas fill may be at risk for high postoperative IOP during the first month. Aggressive early treatment of IOP may prevent IOP spikes in the early postoperative period.

Unilateral Decompression Retinopathy After Laser Iridotomy in a Patient with Bilateral Acute Angle-Closure Glaucoma.

Acute angle closure glaucoma is an ocular pathology characterized by a severe increase of intraocular pressure (IOP) that requires the realization of a peripheral Nd:YAG laser iridotomy as a treatment. Several complications have been described after a peripheral laser iridotomy such as hyphema, endothelial corneal damage, intraocular pressure spikes or cataract. Furthermore, retinal and subhyaloid haemorraghes have been observed after the treatment. This uncommon finding has been named decompression retinopathy. The case of an unilateral decompression retinopathy in a 67-year-old woman after the resolution of a bilateral episode of acute angle closure glaucoma was presented.

薄膜センサによる2円筒転がり接触圧力計測の研究(機械要素,潤滑,設計,生産加工,生産システムなど)

In order to investigate the durability of sliding or rolling parts of machinery or to apply appropriate heat and surface treatment conditions to such parts, it is important to know the oil-film pressure and to evaluate the stress distribution of the parts. Regarding the contact pressure between the gear teeth flanks and cam followers, the maximum pressure and stress distribution can be calculated theoretically. However, the real contact pressure does not always agree with calculated ones due to the different configuration of contact surface, misalignment and etc. In this study, the authors developed a thin film pressure sensor with a thickness of 4.2μm, and the high oil-film pressure of the order of GPa under the line contact was measured. For the experiment, a test rig was developed with two-rollers to which a thin-film pressure sensor for the pressure measurement and additionally two-thin-film pressure sensors for checking the contact condition were deposited. The measured maximum pressure agreed comparatively well with Hertzian maximum pressure. Except the pressure spike, the measured pressure distribution also agreed rather well with the EHL calculation.

Cataract surgery in pseudoexfoliation syndrome

To discuss the preoperative, intraoperative and postoperative considerations and techniques for cataract surgery in pseudoexfoliation syndrome. Pseudoexfoliation syndrome is a common disorder worldwide that has been linked to the lysyl oxidase-like-one (LOXL1) gene. Its identification in patients undergoing cataract surgery has become important in preventing complications through proper preoperative planning. The management of the small pupil found in pseudoexfoliation can be achieved using various pharmacological and mechanical techniques. There are now several devices available to support the weak zonules that commonly accompany pseudoexfoliation. Postoperatively, pseudoexfoliation patients need to be followed closely to monitor for complications such as intraocular pressure spikes, inflammation and intraocular lens dislocation. With proper preoperative preparation, intraoperative use of appropriate adjunctive devices, and close postoperative follow-up, favorable outcomes can be achieved in cataract surgery in pseudoexfoliation syndrome.

Clinical Presentation and Conservative Management of Tympanic Membrane Perforation during Intrapartum Valsalva Maneuver

Background. Tympanic membrane perforation may occur when ear pressures are excessive, including valsalva maneuver associated with active labor and vaginal delivery. A pressure differential across the eardrum of about 5 psi can cause rupture; the increased intraabdominal pressure spikes repeatedly manifested by “pushing” during second-stage labor easily approach (and may exceed) this level. Material and Method. We describe a healthy 21-year old nulliparous patient admitted in active labor at 39-weeks' gestational age. Results. Blood appeared asymptomatically in the left ear canal at delivery during active, closed-glottis pushing. Otoscopic examination confirmed perforation of the left tympanic membrane. Complete resolution of the eardrum rupture was noted at postpartum check-up six weeks later. Conclusion. While the precise incidence of intrapartum tympanic membrane rupture is not known, it may be unrecognized without gross blood in the ear canal or subjective hearing loss following delivery. Only one prior published report on tympanic membrane perforation during delivery currently appears in the medical literature; this is the first English language description of the event. Since a vigorous and repetitive valsalva effort is common in normal vaginal delivery, clinicians should be aware of the potential for otic complications associated with the increased intraabdominal pressure characteristic of this technique.

Ab interno trabeculectomy

Anterior chamber drainage angle surgery, namely trabeculotomy and goniotomy, has been commonly utilized in children for many years. Its’ reported success has ranged between 68% and 100% in infants and young children with congenital glaucoma. However, the long-term success of these procedures has been limited in adults presumably due to the formation of anterior synechiae (AS) in the postoperative phase. Recently, ab interno trabeculectomy with the Trabectome™ has emerged as a novel surgical approach to effectively and selectively remove and ablate the trabecular meshwork and the inner wall of the Schlemm’s canal in an attempt to avoid AS formation or other forms of wound healing with resultant closure of the cleft. This procedure seems to have an appealing safety profile with respect to early hypotony or infection if compared to trabeculectomy or glaucoma drainage device implantation. This might be advantageous in some of the impoverish regions of the Middle East and Africa where patients experience difficulties keeping up with their postoperative visits. It is important to note that no randomized trial comparing the Trabectome to other glaucoma procedures appears to have been published to date. Trabectome surgery is not a panacea, however, and it is associated with early postoperative intraocular pressure spikes that may require additional glaucoma surgery as well as a high incidence of hyphema. Reported results show that postoperative intraocular pressure (IOP) remains, at best, in the mid-teen range making it undesirable in patients with low-target IOP goals. A major advantage of Trabectome surgery is that it does not preclude further glaucoma surgery involving the conjunctiva, such as a trabeculectomy or drainage device implantation. As prospective randomized long-term clinical data become available, we will be better positioned to elucidate the exact role of this technique in the glaucoma surgical armamentarium.

Thermoelastohydrodynamics of grease-lubricated concentrated point contacts

Isothermal and thermoelastohydrodynamic lubrication (TEHL) analyses of grease lubricated bearings are presented. A grease plug flow is formed in the conjunction that, with no shear at the boundaries with the solid surfaces, adheres to them in the region of high pressures under isothermal conditions. The elastohydrodynamic lubrication grease pressure distribution conforms fairly closely to that of its base oil alone, with the exception of inlet trail and pressure spike regions. The dependency of film thickness on speed (rolling viscosity) and load parameters for the base oil agrees with previously reported findings of the research community. For grease there are subtle differences with the base oil film thickness load and speed dependencies. However, it is clear that extrapolated oil film thickness formulae for oils can be used reasonably for the prediction of grease films, at least as a first approximation. The results presented agree well with optical interferometric measurements reported in the literature for grease-lubricated contacts at low temperatures and low surface velocities. TEHL analysis shows breakdown of the plug flow and significant reduction in film thickness, which can lead to changes in the regime of lubrication to mixed or boundary conditions.

Temperature and pressure spikes in ion-beam cancer therapy

The inelastic thermal spike model is applied to liquid water in relation to high-energy 12C6+ beams (hundreds of MeV/u) used for cancer therapy. The goal of this project is to calculate the heat transfer in the vicinity of the incident-ion track. Thermal spike calculations indicate a very large temperature increase in the vicinity of ion tracks near the Bragg peak during the time interval from 10(-15) to 10(-9) s after the ion's passage and an increase in pressure, as large as tens of MPa, can be induced during that time. These effects suggest a possibility of thermomechanical pathways to disruption of irradiated DNA. An extension of the model for hydrogen, beryllium, argon, krypton, xenon, and uranium ions around the Bragg peak is presented as well.

TUNNELLED VERSUS STRAIGHT INTRAVITREAL INJECTION

To compare tunnelled scleral intravitreal injection with straight scleral intravitreal injection concerning short-term intraocular pressure (IOP) changes, occurrence and amount of vitreous reflux, and patient discomfort. Sixty patients were randomly allocated to two groups (tunnelled intravitreal injection and straight intravitreal injection). IOP was measured before and directly (<1 minute) after the injection of 0.05 mL of an antivascular endothelial growth factor agent and then every 5 minutes until IOP was <30 mmHg. Occurrence and amount of vitreous reflux were recorded. Patient discomfort during injection was assessed with a Wong-Baker faces pain rating scale. IOP (mmHg +/- SD) increased significantly directly after injection to 35.97 +/- 8.13 (tunnelled intravitreal injection) and 30.19 +/- 12.14 (straight intravitreal injection). These pressure spikes differed significantly between both groups (P = 0.01, mean difference: -7.11). Five minutes after injection, there was no significant difference in IOP increase between the groups. All IOP measurements were <30 mmHg after 15 minutes. Occurrence and amount of vitreous reflux were significantly higher with straight intravitreal injection. There was no significant difference in Wong-Baker faces pain rating scale score between both groups. Tunnelled intravitreal injection seems to be the technique of choice for low-volume intravitreal injection (0.05 mL). There is neither a difference in patient discomfort nor a difference in IOP increase 5 minutes after injection between both groups. Significantly less vitreous reflux with tunnelled intravitreal injection should lead to less postinjectional drug loss.

Intraocular pressure changes during injection of microincision and conventional intraocular lenses through incisions smaller than 3.0 mm

To compare intraocular pressure (IOP) during insertion of a new microincision intraocular lens (IOL) (Akreos AO MI60) and a conventional IOL (AcrySof Natural SN60AT) and to determine the minimum incision sizes for insertion in a cadaver eye model. John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA. After phacoemulsification in phakic cadaver eyes, multiple IOL insertions were attempted through 1.8 mm to 2.5 mm wounds. The final incision size and insertion success were evaluated in each case. A pressure transducer placed in the vitreous cavity measured real-time IOP changes (100 readings per second), including the mean and peak IOP during IOL implantation. The minimum incision size for the microincision IOL insertion was 1.9 mm using a wound-assisted technique and 2.2 mm using a cartridge-insertion technique. The minimum incision size for wound-assisted implantation of the conventional IOL was 2.4 mm. During successful implantation, the mean and peak IOPs were similar between the 2 IOL types. The peak IOPs exceeded 60 mm Hg (retinal perfusion pressure). In unsuccessful attempts, the mean and peak IOPs were higher for the conventional IOL, reaching 306.05 mm Hg in 1 eye. Monitoring during implantation of both IOL types confirmed that IOP increases during insertion, including during microincision surgery using a wound-assisted technique. Further studies are necessary to evaluate the effect of pressure spikes on the optic nerve during IOL insertion.

Viscoanaesthesia in cataract surgery: a prospective, randomized clinical trial

We aimed to compare viscoanaesthesia (VisThesia) with intracameral lidocaine in cataract surgery carried out under topical anaesthesia. In this prospective study 98 patients were randomly assigned to receive VisThesia (group 1, n = 49) or 0.5 cc of 1% unpreserved lidocaine (group 2, n = 49). All surgery was carried out by one surgeon using clear corneal technique. Pachymetry, the status of the cornea and anterior chamber, and intraocular pressure (IOP) were checked pre- and postoperatively. Mean pain scores were 0.12 (maximum: 3) in group 1 and 0.37 in group 2; the difference between the groups was not statistically significant (95% confidence interval [CI] 0.003-0.487; p = 0.05). A total of 48 patients in group 1 (98%) and 49 in group 2 (100%) reported no discomfort or only mild discomfort. No significant differences in flare and cells in the anterior chamber or IOP were found between the two study groups. There was a significantly greater frequency of corneal oedema in group 1 (p = 0.001). Postoperative central corneal thickness values were also significantly higher in group 1 (95% CI 11.64-57.24; p = 0.003). Results suggest that viscoanaesthesia provides a level of comfort during cataract surgery under topical anaesthesia similar to that facilitated by intracameral lidocaine. However, patients who are given viscoanaesthesia may have increased risk for postoperative corneal oedema.

Development and demonstration flight of a fuel cell system for high-altitude balloons

Proton exchange membrane fuel cell offers higher energy density than the existing battery technologies for high-energy applications, and it is a promising power source for various industries including aerospace vehicles. We have been developing and testing a non-external humidified fuel cell system for high-altitude balloons, which require simple, light, and easy-to-operate power systems. This system consists of three major subsystems—a fuel cell stack, a reactant supply subsystem, and an electrical control subsystem. Ground performance testing in a vacuum chamber simulating the high-altitude vacuum condition was performed before the flight. Then, a demonstration flight of the fuel cell system was launched using a large balloon for verifying its performance under practical high-altitude conditions. Cell voltage variations synchronized with oxygen pressure spikes were observed that were probably caused by condensed product water plugging the flow passages of the back pressure regulator. Flight results indicated that the fuel cell system operated better when water was expelled as vapor, rather than in the liquid form. In addition, a back pressure regulator should be installed to avoid the accumulation of water droplets for realizing a stable performance.

Intracameral Fibrin Tissue Sealant as an Adjunct in Tectonic Lamellar Keratoplasty for Large Corneal Perforations

To report a technique of intracameral injection of Tisseel fibrin sealant as an adjunct in the performance of tectonic deep anterior lamellar keratoplasty in cases with preexisting or intraoperative macroperforation. Patients with corneal perforations up to 4 mm in greatest dimension first had the defect sealed externally with cyanoacrylate adhesive or fibrin sealant. An air bubble was injected into the anterior chamber (AC), followed by intracameral Tisseel fibrin sealant. This was injected via a 21-G cannula or needle, introduced into the AC from the limbus, with the tip positioned just under the perforation. Fibrin sealant was injected to completely cover the perforation site. Deep anterior lamellar keratoplasty then proceeded with a manual technique without chamber loss. Postoperatively, slit-lamp examination to assess resolution of fibrin sealant and graft status was performed, and visual acuities and intraocular pressures were recorded. Two patients with preexisting corneal perforations and 1 patient with an intraoperative perforation were included. In all patients, lamellar dissection proceeded uneventfully after intracameral fibrin injection. Fibrin sealant in the AC spontaneously resorbed by the second postoperative week. There were no postoperative intraocular pressure spikes and no cases of severe anterior uveitis. All grafts were clear at last follow-up with no evidence of endothelial decompensation. Intracameral fibrin sealant injection seems to be a safe adjunct to allow completion of deep anterior lamellar keratoplasty in cases with corneal perforation with the aim of avoiding higher risk penetrating keratoplasty. Cases were characterized by a lack of complications postoperatively, and no cases of persistent double AC were encountered.

Modification of polyurethane to reduce occlusion of enteral feeding tubes

Feeding tubes are used to supply nutritional formula to immobilized patients. The most common cause for failure of enteral feeding tubes is their occlusion. The purpose of this study was to examine whether occlusion of enteral feeding tubes could be minimized using an additive. An open, intermittent enteral feeding system was simulated in the laboratory and data were collected over a period ranging from 2 to 6 days. Feeding formula was cycled through a feeding tube in either the presence or absence of simulated gastric acid in an effort to generate a reproducible occlusion. Pressures in the tube were measured frequently throughout these cycles. We observed pressure spikes with each cycle, but never a complete occlusion. Pressure spikes formed only when simulated gastric acid was mixed with the feeding solution. Large amounts of feeding formula adsorbed onto polyurethane (PU) surfaces in the presence of gastric acid. Also, this subtle change in surface chemistry significantly affected the number of pressure spikes observed. The maximum pressure required to maintain flow in the tube was reduced by about half from 2.0 psi to 0.8 psi when polyvinyl alcohol (PVA) was added. The addition of PVA to PU also reduced the contact angle from 83 degrees (untreated) to approximately 64 degrees in the presence of PVA. Furthermore, when formula was added to PU in the presence of PVA the thickness of the layer that remained on the surface was almost 10 times greater in controls than on PVA-treated surfaces. These results suggest that a treatment that increases the hydrophilicity of the feeding tube may help minimize clogging.

Inverse approach for calculating temperature in EHL of line contacts

This paper proposes a thermal elastohydrodynamic lubrication (TEHL) inverse approach to estimate the pressure, temperature rise, and apparent viscosity distributions in an EHL line contact. Once the film shape is measured, the pressure and estimated film thickness distributions can be calculated from force balance and elastic deformation theories. By using these smoothing pressure and film thickness distributions, the Gauss–Seidel iteration is employed to calculate the temperature rise distribution from energy, surface temperature, and rheology equations. This approach overcomes the problems of pressure and temperature rise fluctuations, and generates accurate results of pressure and temperature rise distribution from a small number of measured points of film thickness, which also saves computing time. Results show that the direct inverse method requires a lot of measured points to establish the amplitude and location of the pressure and temperature rise spikes, whereas the inverse approach can obtain the accuracy results with only 31 measured points. With the error from the resolution in the film thickness measurements, this approach also presents a smooth curve of the pressure and temperature rise distributions with a small error. Furthermore, this approach still provides a good solution in apparent viscosity, whereas the direct method provides a much larger error in apparent viscosity.

Suppression of reflex urethral responses by sacral dermatome stimulation in an acute spinalized feline model

Reflex contractions of the external urethral sphincter (EUS) are a major component of voiding dysfunction after neurological injury or disease. Aberrant urethral reflexes can prevent voiding and cause serious medical complications. Characterizing these urethral reflexes during genitourinary studies is necessary for evaluating novel pharmacological or neuroprosthetic approaches. The objectives of the present study were to generate urethral reflexes in the acute spinal feline, to quantify these reflexes, and to suppress them with electrical stimulation of the sacral dermatomes. This study comprised eight male cats. Anaesthesia was maintained with alpha-chloralose or sodium pentobarbital. The spinal cord was transected between T10 and T12, and nerve cuff electrodes were placed on the extradural S2 sacral roots to provide bladder activation. Bladder and urethral pressures were recorded during and after bladder contractions. Electrical stimulation was applied non-invasively to the sacral dermatomes with commercial surface electrodes. Urethral reflexes were elicited consistently in six cats. The corresponding urethral pressure spikes were quantified. Putative metrics of urethral reflex activity such as the rate and average magnitude of reflex pressure spikes correlated significantly with standard urodynamic variables. Electrical stimulation of the sacral dermatomes suppressed urethral reflexes in three cats. These findings in an acute spinal feline preparation demonstrate a non-invasive means of suppressing undesirable urethral reflexes. Translation of this work to clinical use could improve neuroprostheses for restoring bladder function and enhance treatment of aberrant urethral reflexes in humans.