Pressure Transducer Research Articles

PO-02-206 A MECHANISM FOR PACING-INDUCED REGIONAL CONTRACTILE DYSFUNCTION MEDIATED BY RELEASED CATECHOLAMINES

We have previously shown that non-excitatory epicardial stimulation (NES) increases measures of cardiac function mediated by local release of norepinephrine. In this further investigation we focused on the effects of NES on the local myocardial contractile pattern. Farm pigs were anesthetized and instrumented with a LV high-fidelity pressure/volume conductance transducer, thoracic aortic pressure transducer, left atrial (LA)/ LV epicardial electrodes, and sonomicrometer segment length (SL) gauges placed proximal (lateral base) and distal (posterior mid LV) to the LV stimulation site. During constant LA pacing, LV pulses (0.8ms, 2-3x threshold volts) were applied during the absolute refractory period before and after β-receptor blockade (BB, metoprolol). Regional contractile function was analyzed by constructing LVP vs. SL loops in a beat-by-beat fashion thus allowing characterization of local cardiac function in relation to LV pressure over the entire cardiac cycle. NES resulted in a local contractile dysfunction characterized by an early shortening, subsequent lengthening, and re-shortening pattern during the cardiac cycle in the SL gauge proximal (middle tracing), but not remote to the stimulation site (bottom tracing). The onset of early lengthening in the proximal SL coincided with peak pressure generation, followed by re-shortening as LV pressure fell. The LVP vs. SL loop was markedly altered. This contractile effect rapidly waned within 10-15 seconds after cessation of electrical stimulation and was abolished by BB. The NES induced dysfunction developed within an average of 5-10 seconds of stimulation onset and was accompanied by increases in several global indices of cardiac function (dP/dt, peak LVP, early aortic valve opening) which were also abrogated by B-blockade. These findings demonstrate that pacing elicits local catecholamine release that may cause dyssynergy and mimic the regional pacing-induced contractile dysfunction seen at pacing sites in man.

Neuromuscular coupling of obligatory respiratory muscles to inspiratory pressure is reduced in dystrophic (mdx) mice

Neuromuscular coupling (NMC) is a recognised clinical index of inspiratory muscle function which reflects the efficiency of conversion of neural activation to inspiratory pressure. Duchenne muscular dystrophy (DMD) is characterised by respiratory insufficiency culminating in respiratory failure. We investigated inspiratory pressure generating capacity and electrical activation of obligatory inspiratory muscles in X-linked muscular dystrophy ( mdx) mice, to evaluate NMC of diaphragm, external intercostal and parasternal intercostal to inspiratory pressure across a range of behaviours in early established to late progressive disease.In urethane anaesthetised mice (1.7 g/kg i.p.), inspiratory pressure was recorded via a pressure transducer positioned in the thoracic oesophagus. Diaphragm EMG activity was recorded using needle electrodes. Studies were performed in male wildtype (WT) and mdx mice at 4, 8, 12 and 16 months old. Recordings were made at baseline and during sustained tracheal occlusion to task failure, defined as an inability to sustain peak pressure. Peak pressure was determined from the average of five successive peak efforts at the maximum response. The corresponding peak inspiratory EMG activities were determined. Two factor (age x genotype) analysis of variance was performed.Obligatory muscle EMG activities were significantly lower in mdx mice from 4 months of age. Peak inspiratory pressure was significantly greater in mdx at 4 months of age. At 8 months, peak inspiratory pressure was equivalent between WT and mdx followed by a significant decrease in peak inspiratory pressure in 12- and 16-month-old mdx. NMC was lower in mdx mice across the ventilatory and non-ventilatory range, emerging early in dystrophic disease.Reduced NMC of obligatory muscles to inspiratory pressure in mdx mice reveals a greater reliance on accessory muscles to support respiratory performance in dystrophic disease. Remarkably, this burden is adequately accommodated in early disease with a preserved capacity to generate peak inspiratory pressure. We reason that the loss of compensation afforded by accessory muscles to peak inspiratory pressure generation underpins the emergence of respiratory compromise in advanced disease. Our results may have implications for the understanding and treatment of DMD. Funded by Science Foundation Ireland SFI/19/6628 INSPIRE DMD. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cardio-centric hemodynamic management with and without adjuvant ethyl nitrite improves mean arterial pressure in rodents with chronic high-thoracic traumatic spinal cord injury

Objective: Traumatic spinal cord injury (SCI) causes an initial injury followed by a protracted phase of spinal cord tissue hypoxia. This tissue hypoxia contributes to secondary injury, leading to worse motor and cardio-autonomic outcomes in the chronic setting. No neuroprotective agents to mitigate secondary injury have been identified as efficacious in clinical trials. However, we have demonstrated that taking a cardio-centric approach to hemodynamic management following SCI by augmenting cardiac output and mean arterial pressure (MAP) with the b1-adrenoceptor agonist dobutamine (DOB), and further coupling DOB infusion with the inhalation of ethyl nitrite (ENO), an S-nitrosylating agent, is associated with improved spinal cord oxygenation in the acute phase post-SCI. Aim: To determine the influence of a cardio-centric approach to hemodynamic management with adjuvant ENO inhalation following SCI on long term outcomes. We hypothesized that treatment with DOB and ENO in the acute phase following SCI would mitigate secondary injury and improve cardiovascular outcomes in the chronic setting. Methods. A total of 34 male Wistar rats underwent a T3 contusion injury (300 kdyn) and were assigned into 4 treatment groups: control (n=6), ENO (n=6), DOB (n=12), and combined DOB and ENO (n=10). At 11-weeks post-SCI, a locomotor assessment was conducted using the Basso, Beattie and Bresnahan (BBB) locomotor rating scale. At 12-weeks post-SCI, rodents were anesthetized with intravenous urethane (2.44±0.50 g/kg) and instrumented with a solid-state pressure transducer in the carotid artery to measure MAP. Results. We observed a higher MAP in both DOB (113.6 ± 11.4 mmHg; p = 0.030) and ENO+DOB (116.7 ± 14.6 mmHg; p=0.013) treated groups when compared with controls (94.65 ± 11.62 mmHg). The MAP of ENO treated animals (91.6 ± 7.3 mmHg; P= 0.97) was not different from controls. No differences in BBB scores were found between DOB (15.17 ± 4.49), ENO+DOB (13.95 ± 3.86), ENO (12.5 ± 2.5) and control (11.8 ± 2.7)(P=0.29). Collectively, these data suggest that DOB treatment, alone or in combination with ENO, improves systemic hemodynamics in the chronic high-thoracic SCI setting US Department of Defense, ICORD Seed Grant, Craig H. Neilsen Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Intra-renal pressures during warm arterial and venous ischemia-reperfusion in rats

Red blood cell (RBC) trapping presents as the expansion- and obstruction of-, the outer-medullary capillaries of the kidney with tightly packed RBCs. RBC trapping has been shown to contribute to kidney injury and glomerular filtration rate decline, however, the mechanisms mediating RBC trapping remain unclear. It has previously been proposed that swelling of tubular cells during warm-ischemia initiates RBC trapping by increasing intra-renal pressure. This increase in pressure is thought to compresses the vasa recta capillaries that drain the renal medulla, initiating RBC trapping in the medullary circulation during reperfusion. In the current study we tested the hypothesis that ‘Intra-renal pressure is increased during warm ischemia-reperfusion’. We tested our hypothesis using young male Wistar-Kyoto rats (n=6). We examined pressure changes in the left kidney during ischemia-reperfusion from warm arterial (n=3) and venous (n=3) clamping using micro-serrefines. Rats were anesthetized with isoflurane (2-5%), a midline abdominal incision performed and the left artery and vein isolated. The left kidney was then cleared of connective tissue and placed in a kidney-cup to prevent movement. Intra-renal pressure was measured using a Millar micro-tip catheter pressure transducer which was inserted into the kidney outer-medulla. Intra-renal pressure was recorded during baseline and following 45 minutes of ischemia and 1 hour of reperfusion. Body temperature was maintained throughout the study using a servo-controlled heating table and heat lamp. At the end of the study, the left kidney was harvested and correct catheter placement confirmed. The kidneys were then fixed for later histological analysis. Data were compared using 2-way RM ANOVA (Graphpad Prism).Arterial clamping significantly increased intra-renal pressure (p<0.001). Following arterial clamping, intra-renal pressure rapidly increased reaching a peak of ~30mmHg above baseline after ~6 minutes. Intra-renal pressure then fell slightly averaging 17±3mmHg above baseline over the clamp period. Upon release of the arterial clamp, intrarenal pressure fell to below baseline levels within 270 seconds. Following clamping of the renal vein, intrarenal pressure increased, reaching a peak of 28mmHg above baseline. The increase in average intrarenal pressure across the clamp period was significantly greater with venous compared to arterial clamping (p<0.001), averaging 25±1mmHg. Similar to arterial clamping, intra-renal pressure rapidly fell to baseline levels following removal of the venous clamp.Our data indicate that both arterial and venous clamping increase intra-renal pressure during the clamp/ischemic period. As intra-renal pressure rapidly returns to baseline following removal of the clamp, however, compression of the venous vessels that drain the renal medulla by high intra-renal pressures is unlikely to mediate RBC trapping during reperfusion. NIH NIDDK ISAC 21AU4231, NIH NHLBI P01 HL134604 and an American Heart Association Transformational Project Award 970585 to P.O. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Experimental monitoring of vibrations and the problem of amplitude quantification

Experimental monitoring of blade vibration in turbomachinery is typically based on blade-mounted strain gauges. Their signals are used to derive vibration amplitudes which are compared to previously determined modal scope limits, including a safety factor. According to industrial guidelines, this factor is chosen conservatively to ensure safe operation of the machine.For the experimental campaign with the open test case fan ECL5, which is representative for modern lightweight UHBR architectures, it is planned to conduct measurements close to the stability limit. These investigations require a close approach to the limit and hence demand for accurate quantification of vibration amplitudes to ensure secure operation without exhaustive safety margins. It is required that the surveillance is possible in real time and not only in post-processing.Historically, short-time Fourier transformations of vibration sensors are used, but the complex nature of coupled phenomena near the stability limit has an influence on the amplitude accuracy, depending on evaluation parameters. This was demonstrated in a previous study using fast response wall pressure transducers. The present study investigates the influence on blade vibration data of a modern composite material transonic fan. Different methods are compared, sensitivity to evaluation parameters is analyzed and guidelines are given for fast and robust surveillance of critical vibration modes.

Study of right ventricular outflow tract gradient in immediate postoperative period following intracardiac repair for tetralogy of Fallot

ABSTRACT Background: Surgical repair of tetralogy of Fallot (TOF) consists of adequate ventricular septal defect closure and relief of right ventricular outflow tract (RVOT) obstruction to the greatest extent possible. The residual RVOT gradient can be due to dynamic and fixed obstruction, and high gradient is sometimes seen even after a satisfactory RVOT resection often confirmed with intraoperative TransEsophageal Echocardiogram (TEE). Aim: The present study was conducted to study the changes in RVOT residual gradient in the early postoperative period. We analyzed the change in residual gradient by invasive monitoring intraoperatively after separating from cardiopulmonary bypass (CPB) in a case of intracardiac repair (ICR) for TOF and compared the readings 24 h after extubating the patients in intensive care unit (ICU). Materials and Methods: This was an observation study done in the Department of CTVS, Advanced Cardiac Centre, PGIMER, and Chandigarh from February 2018 to March 2019. A total of thirty patients with preoperative diagnosis of TOF were included in the study. After ICR for TOF, postseparation from CPB, RVOT gradient was measured using 23G needle connected to pressure transducer and compared with RVOT gradient measured 24 h postextubating using invasive line kept intraoperatively in pulmonary artery and RVOT. Results: There was a significant decrease in residual RVOT gradient postoperatively in ICU after 24 h of extubating, in comparison to intraoperative postbypass residual RVOT gradient. Postbypass residual RVOT gradient was 11.33 ± 1.39 that decreased to 7.81 ± 1.29 24 h after extubating (P < 0.05). Patients in whom pulmonary valve was preserved had greater postbypass residual RVOT gradient (12.44 ± 1.13) than patients with transannular patch (10.5 ± 0.90). However, both decreased after 24 h of extubating (9 ± 0.7 and 6.9 ± 0.8, respectively). Conclusion: Once satisfactory RVOT resection for fixed obstruction is done and is confirmed using TEE, the residual gradient, if marginally high, can be ignored as residual gradient significantly decreases after extubation and hemodynamic improvement is seen in postoperative period.

Naltrindole Pretreatment Elicits Potent Dose Dependent Effects on Reducing Infarct Size During Ischemia Reperfusion In-Vivo

Over one million individuals experience a myocardial infarction (MI) every year. Currently, no therapeutic is available to salvage necrotic cardiac tissue following an MI. The use of a prophylactic agent to reduce infarct size in patients at high risk for an MI would attenuate the development of heart failure. Interventional cardiologists state that a 25% reduction in infarct size is clinically meaningful to reduce heart failure. Previously, a 5 min pretreatment with high dose (HD) naltrindole (NTI) (7.5 mg/kg x 5 min = 37.5 mg/kg, n=3) resulted in a robust 74% (15±6%) reduction in infarct size compared to control in an in-vivo model of ischemia reperfusion injury (IRI). This effect was accompanied by a reduction in irreversible hypercontracture known as rigor. However, it caused a transient reduction in cardiac function during the infusion period. In this study, we aim to determine the effect of intermediate (ID; 3.75 mg/kg x 5 min = 18.75 mg/kg) and low dose (LD; 0.2-1.0 mg/kg x 5 min = 1.0-5.0 mg/kg) NTI pretreatment on infarct size and cardiac function in a rat in vivo model of IRI.Female Sprague-Dawley rats (~250g) were divided into four cohorts: non-treated control (n=15), LD (n=18), ID (n=5), and HD (n=5) NTI groups. All cohorts were anesthetized with Ketamine-xylazine (90 mg/kg, 9 mg/kg). Control rats received normal saline (0.9% NaCl), while treatment groups received either HD, ID, or LD NTI infused through the jugular vein (0.4mL/min) over 5 mins before inducing regional ischemia by occluding the left descending coronary artery for 30 min followed by 3 hr reperfusion. Cardiac function was measured through a pressure transducer catheter placed into the left ventricle (LV) in NTI treated groups. Planimetered photographs of heart slices were used to determine infarct size. Data were analyzed via ANOVA, Bonferroni-Dunn, and post-hoc analysis. Probability values <0.05 were considered statistically significant.HD, ID, and LD NTI reduced infarct size by 81% (11±4%) p<0.05, 55% (26±7%) p<0.05, and 4% (55±4%) respectively compared to control (57±2%). Cardiac function parameters such as dP/dt min, the maximal rate of LV pressure relaxation, was not significantly affected by ID NTI compared to LD NTI in contrast to the cardiac depression elicited by HD NTI. These results indicate that the cardiac depressive effects of NTI are dose dependent and the infarct reducing effects of NTI can be achieved through doses that spare cardiac function. Therefore, ID NTI prophylaxis may be an effective strategy to limit cardiac tissue death in populations at high risk of an MI. Future studies will be conducted on porcine cardiac IRI models. Funding was supported by Young Therapeutics LLC and internal grants from Philadelphia College Of Osteopathic Medicine This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A Systematic Review of Methods Used to Determine the Work of Breathing during Exercise.

Measurement of the work of breathing (Wb) during exercise provides useful insights into the energetics and mechanics of the respiratory muscles across a wide range of minute ventilations. The methods and analytical procedures used to calculate the Wb during exercise have yet to be critically appraised in the literature. The aim of this systematic review was to evaluate the quality of methods used to measure the Wb during exercise in the available literature. We conducted an extensive search of 3 databases for studies that measured the Wb during exercise in adult humans. Data were extracted on participant characteristics, flow/volume and pressure devices, oesophageal pressure (Poes) catheters, and methods of Wb analysis. A total of 120 articles were included. Flow/volume sensors used were primarily pneumotachographs (n = 85, 70.8%), whereas the most common pressure transducer was of the variable reluctance type (n = 63, 52.5%). Oesophageal pressure was frequently obtained via balloon-tipped catheters (n = 114, 95.0%). Few studies mentioned calibration, frequency responses and dynamic compensation of their measurement devices. The most popular method of measuring the Wb was pressure-volume integration (n = 51, 42.5%), followed by the modified Campbell (n = 28, 23.3%) and Dean & Visscher diagrams (n = 26, 21.7%). Over one-third of studies did not report the methods used to process their pressure-volume data, and the majority (60.8%) of studies used the incorrect Wb units and/or failed to discuss the limitations of their Wb measurements. The findings of this systematic review highlight the need for the development of a standardized approach for measuring Wb which is informative, practical, and accessible for future researchers.

An Interface Pressure Detection Method of Cable Silicone Rubber-XLPE Based on Nonlinear Ultrasound

The interface pressure between the cable attachment and the body is crucial for the stable long-term operation of the cable. To solve the issue of interface insulation characteristics’ damage caused by the pressure transducer measurement method, a non-destructive testing method of silicone rubber interface pressure using nonlinear ultrasound is presented. Initially, the study analyzes the propagation characteristics of ultrasonic waves at the interface of cross-linked polyethylene and silicone rubber. The study also establishes the relationship between the nonlinear coefficient and the interface pressure. Subsequently, a nonlinear ultrasonic test platform is constructed using the pulse reflection method to measure the interface pressure of flat silicone rubber and cross-linked polyethylene through nonlinear ultrasonic testing. Theoretical and experimental results indicate that the fundamental amplitude of the frequency domain of the interface reflection wave decreases, and the second harmonic amplitude and nonlinear coefficient both increase as pressure increases. These results demonstrate that the nonlinear ultrasound, non-destructive testing method can accurately evaluate the interfacial pressure state of the cable accessories.

Numerical study of piezoball dissipation test with penetration under partially drained conditions

The piezoball, a full-flow penetrometer equipped with a pore pressure transducer, is increasingly being used in in-situ investigations due to its advantages of characterizing soft soils relative to the piezocone. The operative coefficient of consolidation, ch, can be estimated by monitoring the dissipation of excess pore pressures after piezoball penetration. However, the determination of ch from the dissipation test becomes complicated if the piezoball is penetrated under partially drained conditions. The performances of piezoball penetration and subsequent dissipation are investigated using a coupled large deformation finite-element approach. The numerical results are verified by comparing with existing centrifuge tests, against both undrained and partially drained conditions. A comprehensive interpretation method is then presented for inferring ch from piezoball tests against various drainage conditions. It is found that the variation of ch with drainage conditions is essentially dependent on the distribution of pore pressures before dissipation. Two backbone curves determining the nominal initial excess pore pressure at the equator of the probe and the coefficient of consolidation are obtained to assess the effect of partial drainage, which capture the influences of the piezoball geometry, stress level and over-consolidation ratio.

Experimental Study on Potential Influence of the Invasive Hedychium coronarium J. König on the Evapotranspiration of Riparian Plant Community.

The balance between precipitation and evapotranspiration (ET) has direct effect on vegetation, and any change in its structure and composition can influence it. The aim of this study is to determine experimentally the daily evapotranspiration (ET) of the invasive species, Hedychium coronarium, and to compare with a group of four native species of the riparian forest. The experiment was carried out in a greenhouse with three different treatments: (1) only the invasive species; (2) only native species; and (3) a mixture of invasive and native species. In each lysimeter, pressure transducers recorded the water level at every 15 min along 14 months. Daily ET was calculated by the method of Gribovszki et al. (2008) and varied according to the treatment, indicating that different species (invasive or native) use the water differently. The maximum accumulated daily ET occurred for mixture treatment (2540.16 mm), while the treatment with the invasive plant presented the lowest value (2172.53 mm). H. coronarium, in monodominant stands, can reduce evapotranspiration on invaded areas and increase it when immersed in the riparian forest.

APR1400 원자로 축소모델 구조해석을 위한 상관길이

The correlation length for structural analysis can be calculated by installing several dynamic pressure transducers and evaluating the measured values in scale model testing. This study was conducted under the normal operating condition of the reactor in KHNP-STAR, which was designed and manufactured as a 1/7 scale-down model for APR1400. To verify conservative design at APR1400 reactor internals, the correlation length was evaluated at two locations: (1) the downcomer of the reactor coolant, and (2) the control element assembly guide tube. The correlation length calculated in this study will be used for the structural analysis aspect in the scale model testing of the APR1400 reactor internals.

Optical study of knocking phenomenon in a spark-ignition engine by using high-speed OH* chemiluminescence imaging: A multiple ignition sites approach

Knock in a spark-ignition (SI) engine is a complicated combustion phenomenon that stimulates high-pressure oscillations inside the combustion chamber and restricts engine performance. This study presents a high-speed OH* chemiluminescence imaging technique to investigate the knock mechanism resulting from firing multiple spark plugs. The experiment was performed using a customized liner having three spark plugs installed at equal spacing, and to compare the results with conventional SI conditions, in which one spark plug was mounted at the center of the cylinder head. In addition, multiple pressure transducers were used at various locations to record the frequencies induced by the pressure oscillations inside the cylinder during knocking events. The results showed that firing a single central spark plug generated mild knock with late combustion phasing and lower power output. However, adding more spark plugs could advance the initiation of autoignition and produce higher knock intensity along with lower combustion duration for the same operating conditions. Additionally, a weak OH* chemiluminescence intensity oscillation was monitored before the autoignition of the unburned charge occurred. The crank angle location of peak OH* intensity and peak HRR showed a good linear curve fit with a positive slope. Furthermore, the larger amount of unburned mass fraction produced stronger pressure waves due to multiple autoignition sites, and the unburned mass fraction exhibited a good linear relationship with unburned temperature and end-gas area at the knock onset point. Moreover, the frequency spectrum recorded by the multiple pressure sensors illustrated that in the case of a single central spark plug only circumferential acoustic waves were formed with low power intensity. However, multiple ignition sites promoted both circumferential and radial pressure waves inside the combustion chamber because of multiple autoignitions occurring both near the center and cylinder wall.

Design and Development of an MRI Compatible Circuit Suitable for Pre-Clinical Physiological Monitoring in a 4.7T Magnetic Resonance Imaging

As monitoring preclinical MRI is essential, it is important that the equipment used must be MRI-compatible. This is because interaction with an MRI radiofrequency (RF) transmitting field can cause RF burns due to inappropriate equipment. And non-compatible MRI monitoring equipment can give inaccurate readings in the MRI system if the equipment has ferromagnetic components. Preclinical MRI is designed for animals, the model used to study diseases related to humans. Animal models are imaged using a smaller scanner with high magnetic fields like the 4.7T. The main parameters of interest are the respiratory rate, the temperature, the pressure transducer and the electrocardiogram (ECG), this is because the animal model is used as a laboratory experiment for human disease. An MRI-compatible lead Ⅱ ECG simulator, with approximately 0.5 mV output amplitude was attached to the input of the ECG preamplifier to represent a small animal’s signal. The transmitted signal is the ECG, the pressure sensor, the temperature, and the battery (voltage), these are all linked to different channels (outside, near and inside magnet) and were acquired with the pressure sensor pad taped on a male adult volunteer’s thumb to record the human pulse of 70 bpm, which is similar to the respiration rate of an anaesthetized mouse or rat. The use of a signal gating generator should be explored in future work, this could make the monitoring parameters to be independent of the RF pulse influence. Finally, fibre optics should be included in the design process.

Flow Pressure Characteristics of the Ahmed Glaucoma Valve and Possible Effect of Entrapped Air in the Tube.

The purpose of this study was to assess the pressure characteristics of the Ahmed Glaucoma Valve (AGV) and possible effects of air trapped in the tube. Physiologic saline was pumped through 17 AGVs using a syringe infusion pump, and the flow pressure was measured by a set of pressure transducers. During the infusion at a rate of 2µL/minute, the pressure measurement was repeated twice in each AGV to determine the repriming pressures with/without air (1µL) in the tube. After a pressure surge occurred during the initial priming, the pressure decreased suddenly and then became constant. The repriming pressure, determined as the peak pressure before valve opening, was significantly (P < 0.0001, paired t-test) higher with air (26.5 ± 6.8 mm Hg) than without air (12.1 ± 3.8 mm Hg), whereas the constant pressures after repriming was equivalent between with (10.6 ± 3.7 mm Hg) and without (10.4 ± 2.9 mm Hg) air conditions (P = 0.68). Air in the AGV tube causes increased repriming pressure of about two-fold compared to repriming without air. This pressure increment caused by air in the capillary-sized tube might occur because of the effects of viscosity pressure and capillary pressure. To ensure stable surgical results, surgeons are advised to not allow air to remain in the tube. Pars plana tube insertion of the AGV combined with gas tamponade surgery may result in higher-than-expected intraocular pressure. Conversely, injection of air/gas can avoid postoperative hypotony when the AGV is implanted in eyes with a high risk of hypotony.

Investigations of shock–boundary layer interaction dynamics using high-bandwidth pressure field imaging

The large-scale pulsations of shock-induced separation with length scale that significantly exceeds the incoming boundary layer thickness are investigated. The shock–boundary layer interaction (SBLI) unit is generated by an inward-turning axisymmetric compression ramp at an inflow Mach number of 2.5. A substantial region surrounding the centre azimuth exhibited mean and dynamic flow features that are consistent with two-dimensional separation. Two-dimensional highly resolved maps of surface pressure field are obtained using fast-response pressure-sensitive paint fluorescence imaging at 40 kHz repetition rate. The measurement domain covered significant regions of the incoming boundary layer through the relaxing boundary layer downstream of the reattachment as well as over 25 boundary layer thicknesses in the azimuthal direction. These measurements provide new insights into the spanwise coupling of the SBLI unit in addition to its inherent dynamics. The power spectral density (PSD) of the centreline pressure exhibits very good agreement with theoretical models and complementary measurements using fast-response pressure transducers, which served to validate the pressure field measurements. Detailed examination of the PSD reveals strong agreement with the literature, which includes the peak Strouhal number of the separation and reattachment shock motions as well as the downward frequency shift along the separation bubble. Furthermore, the pressure fluctuation maps reveal streamwise-elongated structures just downstream of the ramp leading edge that persist well downstream of the reattachment. A time sequence of conditional average pressure fluctuation maps is constructed surrounding isolated pressure excursions in the intermittent region. This sequence, along with two-point cross correlation analysis, provides critical information about the flow processes that drive the separation bubble pulsations in the SBLI units with large separation scales. Overall, the imbalance in the mass within the separation bubble appears to be the critical mechanism that drives the separation bubble pulsations. Furthermore, the pressure perturbations originating at azimuthally offset locations are also observed to influence the separation bubble dynamics.

Very lean hydrogen vapor cloud explosion testing

AbstractHydrogen is a key energy carrier for modern society. The breaking of the hydrogen bonds within traditional hydrocarbon molecules has been the primary mode of energy utilization since the industrial revolution. An increased focus on “net‐zero” greenhouse gas emissions, specifically carbon dioxide and methane, has resulted in a global push for lower carbon energy vectors, including pure hydrogen. Accurately modeling the dispersion, fire, and explosion hazards associated with new and existing hydrogen production, distribution and transportation networks, and consumption is a key component to the safe expansion of these networks. BakerRisk performed a series of very lean hydrogen‐air vapor cloud explosion (VCE) tests as part of an internal research effort. The goal of these tests was to better understand the VCE hazards associated with very lean hydrogen‐air mixtures (≤14% H2). Flame speeds and blast loads were measured using high‐speed video and an array of dynamic pressure transducers. This paper discusses the test setup and test results, including a comparison with data from prior tests. The measured flame speeds are compared to those predicted using computational fluid dynamics analysis and referenced to deflagration‐to‐detonation criteria. Discussion regarding the application of these test results to facility siting studies is also provided.

Slug flows of gas and shear-thinning fluids in horizontal pipes

Experiments on slug flow are carried out with air and three solutions of carboxymethylcellulose (CMC)(0.05, 0.1 and 0.2% w/w) in a 44.2 mm ID horizontal pipe. The lengths, velocities and frequency of passage of the large bubbles are obtained through a high-speed digital camera. The gas fraction and length of liquid slugs are also estimated. Pressure changes along the pipe are measured with a differential pressure transducer. Particle Image Velocimetry is used to obtain the mean velocity of the continuous liquid field in the film and slug regions. The combination of tested gas and liquid superficial velocities and of distinct fluid rheology results in 48 different experimental conditions. The flow behavior is found to be strongly dependent on the rheological properties of the continuous phase. In particular, the gas volume fraction within the liquid slug (α=1−Rs), the passage frequency of the large bubbles (νt) and the pressure changes are increased. New expressions are proposed for α and νt to account for the rheology of the liquid phase. Predictions of the flow parameters obtained through two modified mechanistic models are compared with the experimental data. The friction coefficient expression proposed by Anbarlooei et al. (Phys. Rev. E, 92(6), 5–9, 2015) is also tested. The impact of the proposed modifications on the calculated properties of slug flow is assessed; typical RMS-errors of less than 15% are obtained for parameter predictions.

Noninvasive Assessment of Arterial Pulse-Pressure Variation During General Anesthesia: Clinical Evaluation of a New High-Fidelity Upper Arm Cuff

To compare noninvasive pulse-pressure variation (PPV) measurements obtained from a new high-fidelity upper arm cuff using a hydraulic coupling technique to corresponding intraarterial PPV measurements. The authors used prospective multicenter comparison and development studies for the new high-fidelity upper arm cuff. The study was performed in the departments of Anesthesiology at the Ludwig-Maximilians-Universität München Hospital, the University Hospital of Bonn, and the RoMed Hospital in Rosenheim (all Germany). A total of 153 patients were enrolled, undergoing major abdominal surgery or neurosurgery with mechanical ventilation. For the evaluation of PPV, 1,467 paired measurements in 107 patients were available after exclusion due to predefined quality criteria. Simultaneous measurements of PPV were performed from a reference femoral arterial catheter (PPVref) and the high-fidelity upper arm cuff (PPVcuff). The new device uses a semirigid conical shell. It incorporates a hydraulic sensor pad with a pressure transducer, leading to a tissue pressure-pulse contour with all characteristics of an arterial- pulse contour. The comparative analysis of the included measurements showed that PPVref and PPVcuff were closely correlated (r=0.92). The mean of the differences between PPVref and PPVcuff was 0.1 ± 2.0%, with 95% limits of agreement between -4.1% and 3.9%. To track absolute changes in PPV >2%, the concordance rate between the 2 methods was 93%. The new high-fidelity upper arm cuff method provided a clinically reliable estimate of PPV.

Radar-based measurements of the solids flow in a circulating fluidized bed

The aim of this work is to demonstrate the value of radar technology for studying experimentally the solids flows in gas-solids fluidized beds. The work presents original results regarding the solids concentration and velocity acquired in a non-intrusive manner from a cold flow model. The tailored radar setup operates at submillimeter wave frequencies (0.34THz) and can measure the location of solids with a spatial resolution of 1/8 mm−1 in the direction of the radar beam, and of 40–60 mm across the radar beam. The solids velocity in the direction of the beam propagation is determined through measurement of the Doppler shift caused by the reflection of the transmitted radar signal by solids moving in relation to the antenna. The measurements were performed in both the horizontal and vertical directions in the riser of a circulating fluidized bed (cross-sectional area of 0.45 m2 and height of 3.1 m) operated with glass beads (mean particle size of 106 µm, and particle density of 2,486 kg/m3) and using air at ambient temperature as the fluidization agent, with superficial velocities in the range of 0.3–1.3 m/s. The measurements are used to assess the validity of the technique and are not intended to characterize the unit fluid dynamically. The solids concentrations derived from the radar measurements follow the qualitative trends derived from pressure-drop measurements, resembling the expected changes that occur in the concentration profiles as the fluidization velocity increases. Concentrations in the range from 10-6 m3/m3 to 10-1 m3/m3 are measurable. In quantitative terms, for low concentrations of solids (<5·10-3 m3/m3, approximately) the radar measurements exhibited the ability to provide more consistent measurements of the solids concentration than those obtained from pressure transducers, for which the small pressure differences lead to unstable and even negative values for solids concentrations. The two measurement methods were in quantitative agreement for solids volume fractions higher than the threshold. Concentrations ≥ 1·10-1 m3/m3, though measurable, strongly attenuate the radar signal, thereby reducing the beam penetration to a depth of centimeters. For each position along the radar beam, the distribution of solids velocity measured from the Doppler effect was found to be within the expected ranges and allowed observations of solids back-mixing. The radar technique applied in this work is a promising technique for detailed characterization of the solids flow influidized beds, offering high spatial and temporal resolutions, allowing the determination of both solids velocity and concentration, and having a reasonably high penetration depth.