Low Inflation Pressure Research Articles

Road contact stresses and forces under tires with low inflation pressure

Many field trials have been undertaken to demonstrate the benefits of reducing the inflation pressure of the tires of heavily loaded haul vehicles, but few carefully controlled laboratory studies have been performed. An earlier full scale laboratory study indicated that tire inflation pressure had far less effect on subgrade strains for unpaved, single-layer granular road structures than the tire loading itself, so attention was directed to the behaviour of the granular base at the tire tread - road surface interface. In the present paper, the results of full scale tests performed using a laboratory apparatus designed to measure the dynamic vertical, transverse, and longitudinal contact forces under tires with varying loads and inflation pressures are reported. Vertical contact forces were observed to be highly non-uniform, both across and along the contact patch.Key words: central tire inflation systems, CTI, model study, haul trucks, unbound roads, unpaved roads, access roads.

Modification of the Penlon Nuffield 200 series ventilator and IPPV with a laryngeal mask airway

There is a risk of regurgitation if a laryngeal mask airway is used with intermittent positive pressure ventilation. The lower the pressure gradient between airway and stomach, the less will be the likelihood of stomach insufflation with gas and consequent regurgitation. A flow generator ventilator, such as the Penlon Nuffield 200 which achieves a peak pressure at the end of inspiration at any given tidal volume, is likely to produce a higher peak airway pressure than a pressure generator. Replacing the expiratory valve by a venturi gives a preferable flow pattern with an inspiratory pressure plateau. At equal tidal volumes, the venturi modification provided a 10% lower inflation pressure (standard deviation 6%, P < 0.01) and a 1.8% smaller leak (P < 0.05) past the laryngeal mask airway. The same comparison but using identical inflation pressures, gave 8% larger tidal volumes (standard deviation 5.1%, P < 0.01) and a 2% smaller leak (P < 0.01) past the laryngeal mask airway.

Road contact stresses and forces under tires with low inflation pressure

Many field trials have been undertaken to demonstrate the benefits of reducing the inflation pressure of the tires of heavily loaded haul vehicles, but few carefully controlled laboratory studies have been performed. An earlier full scale laboratory study indicated that tire inflation pressure had far less effect on subgrade strains for unpaved, single-layer granular road structures than the tire loading itself, so attention was directed to the behaviour of the granular base at the tire tread - road surface interface. In the present paper, the results of full scale tests performed using a laboratory apparatus designed to measure the dynamic vertical, transverse, and longitudinal contact forces under tires with varying loads and inflation pressures are reported. Vertical contact forces were observed to be highly non-uniform, both across and along the contact patch.Key words: central tire inflation systems, CTI, model study, haul trucks, unbound roads, unpaved roads, access roads.

Capillary filtration coefficient, vascular resistance, and compliance in isolated mouse lungs.

Although many recently produced transgenic mice possess gene alterations affecting pulmonary vascular function, there are few baseline measurements of vascular resistance and permeability. Therefore, we excised the lungs of C57/BL6 mice and perfused them with 5% bovine serum albumin in RPMI-1640 culture medium at a nominal flow of 0.5 ml/min and ventilated them with 20% O(2)-5% CO(2)-75% N(2). The capillary filtration coefficient, a sensitive measurement of hydraulic conductivity, was unchanged over 2 h (0.33 +/- 0.03 ml. min(-1). cmH(2)O(-1). 100 g(-1)) in a control group ventilated with low peak inflation pressures (PIP) but increased 4. 3-fold after high PIP injury. Baseline pulmonary vascular resistance was 6.1 +/- 0.4 cmH(2)O. ml(-1). min. 100 g(-1) and was distributed 34% in large arteries, 18% in small arteries, 14% in small veins, and 34% in large veins on the basis of vascular occlusion pressures. Baseline vascular compliance was 5.4 +/- 0.3 ml. cmH(2)O(-1). 100 g(-1) and decreased significantly with increased vascular pressures. Baseline pulmonary vascular resistance was inversely related to both perfusate flow and microvascular pressure and increased to 202% of baseline after infusion of 10(-4) M phenylephrine due to constriction of large arterial and venous segments. Thus isolated mouse lung vascular permeability, vascular resistance, and the longitudinal distribution of vascular resistance are similar to those in other species and respond in a predictable manner to microvascular injury and a vasoconstrictor agent.

Can stroke patients use visual analogue scales?

Visual analogue scales (VAS) have been used for the subjective measurement of mood, pain, and health status after stroke. In this study we investigated how stroke-related impairments could alter the ability of subjects to answer accurately. Consent was obtained from 96 subjects with a clinical stroke (mean age, 72.5 years; 50 men) and 48 control subjects without cerebrovascular disease (mean age, 71.5 years; 29 men). Patients with reduced conscious level or severe dysphasia were excluded. Subjects were asked to rate the tightness that they could feel on the (unaffected) upper arm after 3 low-pressure inflations with a standard sphygmomanometer cuff, which followed a predetermined sequence (20 mm Hg, 40 mm Hg, 0 mm Hg). Immediately after each change, they rated the perceived tightness on 5 scales presented in a random order: 4-point rating scale (none, mild, moderate, severe), 0 to 10 numerical rating scale, mechanical VAS, horizontal VAS, and vertical VAS. Standard tests recorded deficits in language, cognition, and visuospatial awareness. Inability to complete scales with the correct pattern was associated with any stroke (P<0.001). There was a significant association between success using scales and milder clinical stroke subtype (P<0.01). Within the stroke group, logistic regression analysis identified significant associations (P<0.05) between impairments (cognitive and visuospatial) and inability to complete individual scales correctly. Many patients after a stroke are unable to successfully complete self-report measurement scales, including VAS.

An embolization containment device.

A coaxial catheter system for containment of distal embolization is described. Utilizing a novel 0.014" hypotube with a distal elastomeric occlusion balloon, the PercuSurge GuardWire functions as a guidewire while trapping distal embolization resulting from more proximal intervention. The particulate debris is evacuated with a single operator exchange aspiration catheter (Export catheter) prior to deflation of the distal occlusion balloon. This animal study confirmed the feasibility of concept. The system was easily delivered through tortuous coronary anatomy. The GuardWire served as an adequate rail for delivery of dilatation balloons and a multitude of stents. There was no evidence of deep wall damage from low-pressure inflation and apposition of the distal occlusion balloon.

Cutting balloon angioplasty for intrastent restenosis treatment

We describe here two patients with angiographic diagnosis of intrastent restenosis and regional myocardial ischemia. One stent restenosis was located in a native coronary artery and the other in a vein graft. Both were treated with cutting balloon angioplasty (CBA), inflated at low pressures. Angiographic success was obtained and both patients were discharged in the day after the procedure. Cutting balloon angioplasty using low inflation pressures achieved important luminal gains, in these two cases of intrastent restenosis. Further studies are necessary before the effectiveness of this procedure can be precisely defined.

High-pressure, rapid-inflation pneumatic compression improves venous hemodynamics in healthy volunteers and patients who are post-thrombotic

Purpose: Deep vein thrombosis (DVT) is a preventable cause of morbidity and mortality in patients who are hospitalized. An important part of the mechanism of DVT prophylaxis with intermittent pneumatic compression (IPC) is reduced venous stasis with increased velocity of venous return. The conventional methods of IPC use low pressure and slow inflation of the air bladder on the leg to augment venous return. Recently, compression devices have been designed that produce high pressure and rapid inflation of air cuffs on the plantar plexus of the foot and the calf. The purpose of this study is to evaluate the venous velocity response to high-pressure, rapid-inflation compression devices versus standard, low-pressure, slow-inflation compression devices in healthy volunteers and patients with severe post-thrombotic venous disease. Method: Twenty-two lower extremities from healthy volunteers and 11 lower extremities from patients with class 4 to class 6 post-thrombotic chronic venous insufficiency were studied. With duplex ultrasound scanning (ATL-Ultramark 9, Advanced Tech Laboratory, Bothell, Wash), acute DVT was excluded before subject evaluation. Venous velocities were monitored after the application of each of five IPC devices, with all the patients in the supine position. Three high-pressure, rapid-compression devices and two standard, low-pressure, slow-inflation compression devices were applied in a random sequence. Maximal venous velocities were obtained at the common femoral vein and the popliteal vein for all the devices and were recorded as the mean peak velocity of three compression cycles and compared with baseline velocities. Results: The baseline venous velocities were higher in the femoral veins than in the popliteal veins in both the volunteers and the post-thrombotic subjects. Standard and high-pressure, rapid-inflation compression significantly increased the popliteal and femoral vein velocities in healthy and post-thrombotic subjects. High-pressure, rapid-inflation compression produced significantly higher maximal venous velocities in the popliteal and femoral veins in both healthy volunteers and patients who were post-thrombotic as compared with standard compression. Compared with the healthy volunteers, the patients who were post-thrombotic had a significantly attenuated velocity response at both the popliteal and the femoral vein levels. Conclusion: High-pressure, rapid-inflation pneumatic compression increases popliteal and femoral vein velocity as compared with standard, low-pressure, slow-inflation pneumatic compression. Patients with post-thrombotic venous disease have a compromised hemodynamic response to all IPC devices. However, an increased velocity response to the high-pressure, rapid-inflation compression device is preserved. High-pressure, rapid-inflation pneumatic compression may offer additional protection from thrombotic complications on the basis of an improved hemodynamic response, both in healthy volunteers and in patients who were post-thrombotic. (J Vasc Surg 1999;29:593-9.)

Effects of increasing balloon pressure on mechanism and results of balloon angioplasty for treatment of restenosis after Palmaz-Schatz stent implantation: an angiographic and intravascular ultrasound study.

Repeat balloon angioplasty is a widely used therapeutic option for in-stent restenosis, but the optimal balloon inflation pressure has not yet been determined. We used angiography and intravascular ultrasound imaging to assess the mechanism and results of lumen enlargement at various inflation pressures. Thirteen consecutive patients with restenosis post-Palmaz-Schatz stent implantation were submitted to a four-step balloon angioplasty using increasing balloon pressure of 2, 4, 8, and >12 atm. As a global result, the lumen size was only 80% of that observed at stent implantation. Significant changes in angiographic minimal lumen diameter, minimal lumen cross-sectional area, and lumen volume were observed after each step except after the highest-pressure inflation. At low inflation pressure (<8 atm), the decrease in neointimal tissue and the stent over expansion explained the lumen enlargement, whereas after further high inflation pressure (>8 atm), only additional stent over expansion was observed. These results suggest that only moderate balloon inflation pressure (up to 12 atm) is needed for angioplasty of post-Palmaz-Schatz stent restenotic lesions.

Heavy Load, Low Tire Pressure Rutting of Unbound Granular Pavements

In a study of effects of wheels with very heavy loads but very low tire inflation pressures on unbound, single-layer granular pavements, trafficking tests were carried out on full-scale indoor pavements at the Pavement Test Facility, Transport Research Laboratory, Crowthorne, U.K. Two values of wheel load, two values of tire inflation pressure, and three subbase thicknesses were used. Testing was continued to 10,000 passes and a total of 4,704 measurements of rut depth made at intervals, providing a statistically significant data set. The development of ruts, the rut cross sections, and the effects of halving the tire inflation pressure or nearly doubling the wheel load are presented. Comparisons are made to a rut prediction equation derived by the U.S. Army Corps of Engineers Waterways Experiment Station in similar work, and conclusions are drawn.

UNBOUND ROADS TRAFFICKED BY HEAVILY LOADED TYRES WITH LOW INFLATION PRESSURE.

Keywords NEW BRUNSWICK UNIVERSITY, TRANSPORT RESEARCH LABORATORY, TRL ROADS, UNBOUND, TYRES, LOADED, HEAVY, LOADS, LOW, INFLATION, PRESSURE, TESTS, BEHAVIOUR, WHEELS, RESEARCH, VEHICLES, DESIGN, TRAFFICKING, PAVEMENTS, LAYERS, GRANULAR, MATERIALS, CLAYS, GAULT, GAULT CLAY, SUBGRADE, FWD, FALLING, WEIGHT, DEFLECTOMETERS, INSTRUMENTS, INSTRUMENTATION, RUTS, DEPTH, DEFLECTION, RUTTING, DYNAMIC, STRAIN, REDUCTION, BASES, CENTRAL, SYSTEMS, TRIALS, LABORATORIES, FORESTS, STRESS, THICKENING CANADA... Show All

Percutaneous angioplasty of arteriovenous (Brescia-Cimino) fistulae in children.

The development of a stenosis in a Brescia-Cimino fistula is a major clinical problem that threatens vascular access for dialysis. We reviewed the case notes of 46 children undergoing hemodialysis via Brescia-Cimino fistulae. Ten children (mean age 12.5 years) developed 14 stenoses located in the venous (10), anastomotic (3), or arterial (1) part of the fistula. Three (1 arterial and 2 anastomotic stenoses) of the 14 stenoses were treated surgically; the remaining 11 (10 venous and 1 anastomotic stenoses) were treated by angioplasty. Seventeen angioplasty procedures were performed by the percutaneous venous route under local anesthesia. Mean follow-up was 24 months. Restenosis within 6 months occurred in 5 patients, predominantly those who had angioplasty with low balloon inflation pressures; 1 was treated surgically; 4 underwent repeat angioplasty using higher balloon inflation pressures (3 patients) or a bigger balloon (1 patient). None subsequently developed restenosis. Angioplasty can be safely used to treat stenosis of arteriovenous fistulae, with a high initial (60% freedom from restenosis at 6 months) success rate. In summary, balloon angioplasty, repeated if necessary, is a safe and effective treatment for the majority of stenoses occurring in Brescia-Cimino fistulae. Restenosis can be safely treated by further angioplasty, which is associated with a high rate of ultimate clinical success.

Is there life outside the ERM? An evaluation of the effects of sterling's devaluation on the UK economy

This paper makes a quantitative assessment of the impact of sterling’s exit from the exchange rate mechanism (ERM) in September 1992, taking as given other events and other countries’ policies as they happened. To do this we use two different econometric models, each with its own information set. One is a UK model using current (to 1995) information; the other a multicountry model with information as known in early 1992. We therefore examine the question with the benefit of hindsight and as the policy makers could have seen it at the time. The results are the same. Sterling’s exit produced a period of recovery, real growth and little extra inflationary pressure. Excess capacity and competition in the labour markets may have led to lower inflation pressures. However, it was lower interest rates which proved growth creating in the UK, rather than sterling’s devaluation, which proved growth diverting. © 1997 John Wiley & Sons, Ltd.

Soil stress and compaction effects for four tractor tyres

Compaction effects and soil stresses were examined for four tractor tyres under three inflation pressures: 67, 100 and 150% of the recommended pressure. The four tyres were 18.4 R 38, 520/70 R 38, 600/65 R 38 and 650/60-38 and they carried a wheel load of 2590 kg. The 650/60-38 was a bias-ply tyre while the other three were radial tyres. Increased inflation pressure significantly increased all measured parameters: rut depth, penetration resistance and soil stress at 20 and 40 cm depth. The 18.4 R 38 caused a greater rut depth and penetration resistance than the other tyres, which did not differ significantly from each other. The soil stress was highest for the 18.4 R 38, followed by the 650/60-38. The low-profile tyres decreased compaction compared with the 18.4–38 tyre, mainly by allowing a lower inflation pressure. The use of low-profile tyres did not reduce compaction if not used at a lower inflation pressure. The bias-ply tyre caused a higher stress in the soil than the radial tyres when used with the same inflation pressure, but the compaction effects in terms of rut depth and penetration resistance were not greater for this tyre than for the radial low-profile tyres.

Intravascular ultrasound after low and high inflation pressure coronary artery stent implantation

We sought to characterize the differences seen after low or high pressure coronary artery stent deployment as assessed by intravascular ultrasound. Until 1992, the success of stent deployment was assessed by angiographic criteria only, but in 1993 the procedure was expanded to include postprocedural single-use intravascular ultrasound imaging. Ultrasound criteria for successful stent deployment were 1) symmetry, 2) minimal lumen diameter > 3.0 mm, 3) no echo-free spaces between the stent and the vessel, and 4) no uncovered dissections. We used mechanical 4.8F or 3.5F 20- or 30-MHz monorail single-use intravascular ultrasound catheters. Fifty-two patients were included, 28 treated in 1991 and 1992 (group A) and 24 treated in 1993 or 1994 (group B); 87% of patients underwent elective stent implantation. The number of echocardiographic studies per patient increased from 1 +/- 0.1 (mean +/- SD) in group A to 2.0 +/- 0.85 in group B. Mean maximal balloon size increased from 3.3 +/- 0.33 to 3.73 +/- 0.24 mm and maximal inflation pressure from 6.9 +/- 1.1 to 15.8 +/- 2.4 bar (p < 0.001). The eccentricity index was 0.915 +/- 0.04 in group B versus 0.87 +/- 0.05 in group A. Minimal lumen diameter measured by echocardiography increased from 2.55 +/- 0.41 mm in group A to 3.14 +/- 0.37 mm in group B. The final mean values per cross-sectional area as a percent of calculated balloon area were similar in group A (67.5 +/- 23%) and group B (66.5 +/- 22.9%). No major acute complications occurred in either group; subacute thrombosis developed in two patients, both in group A. Intravascular ultrasound data confirm that high pressure stent deployment leads to increased minimal lumen area. Despite high pressure stent deployment, homogeneous stent geometry and optimal stent expansion were not observed in all patients.

Validation of a unique concept for a low-cost, lightweight space-deployable antenna structure

Large space-deployable antennas are needed for a variety of applications that include mobile communications, radiometry, active microwave sensing, very-long-baseline interferometry, DoD space-based radar and microspacecraft. Investigators in these fields identify the need for structures up to tens of meters in size for operation from 1 to 90 GHz, based on different aperture configurations. The selection criteria common to all of the users are low cost, lightweight, high reliability and good reflector surface precision. Fortunately, a unique class of space structures has recently emerged that offers great potential for satisfying these criteria. They are referred to as inflatable deployable structures. A good example of such a concept is under development at L'Garde Inc. Serious interest from the user community will depend on realistic demonstrations of the viability of the concept. This means that large, lightweight, low-cost structures need to be developed and used to demonstrate deployment reliability in realistic service environments. The technology data base for the L'Garde inflatable concept will accommodate the development of reflector antenna structures up to 30 m in diameter. Since the concept utilizes very low inflation pressure to maintain the required geometry on orbit, gravity-induced deflection of the structure precludes any meaningful ground-based demonstrations of functional performance. Therefore this concept has been selected for a NASA In-Space Technology Experiment Program (IN-STEP) space-based experiment. The objectives of this experiment are to validate and characterize the mechanical functional performance of a 14-m-diameter inflatable deployable reflector antenna structure in the orbital operational environment. The experiment will be carried by the NASA Spartan spacecraft, which is launched, deployed and recovered by the STS. The Spartan will provide mounting, attitude control, power and data recording for the antenna experiment. The antenna concept development will benefit from both the experiment and supporting technology developments. Results of this experiment are expected to verify the feasibility of fabricating a large space structure for only a few million dollars, demonstrate the reliability of deployment, characterize the quality of the reflector surface and correlate the analytical performance prediction models with actual measured characteristics. Technology developments in support of the experiment, to be conducted at NASA Langley Research Center and the University of Colorado, will include investigation of new and advanced flexible materials, as well as system studies to assess the adequacy of this structural concept for specific classes of applications and for the development of analytical performance production tools. These combined results will be used to advance the technology of the concept with respect to improving surface precision and performance predictability and accommodating larger size structures with different configurations in different orbits.

Changes in subsoil porosity caused by heavy vehicles

Previous Swedish studies led to a recommendation to limit the load on a single axle to 6 Mg and on a tandem axle unit to 8 Mg in order to avoid permanent subsoil compaction in wet soil. In recent years large tyres that can carry large loads at low inflation pressure have been available. In a new project it was studied whether the use of such tyres may change the recommended load limits. Loads of 8–12 Mg on a single axle or 10–20 Mg on a tandem axle unit significantly reduced the porosity in the 300–400 and 400–500 mm soil layer. In the 400–500 mm soil layer in inflation pressure of 50 or 100 kPa compared with 150 kPa did not substantially reduce compaction. The results indicate that no important increase in the previously recommended limits can be proposed.

Intratracheal Perfluorocarbon Administration as an Aid in the Ventilatory Management of Respiratory Distress Syndrome

Respiratory distress syndrome carries a high morbidity and mortality when treated with mechanical ventilation with positive end-expiratory pressure. Perfluorocarbon liquids are employed in liquid ventilation due to low surface tension and high gas solubility. To assess whether intratracheal administration of the perfluorocarbon, perflubron, in combination with conventional mechanical ventilation could be of therapeutic benefit in respiratory distress syndrome, the authors tested the effects of different doses of intratracheal perflubron administration on gas exchange and lung mechanics in adult animals with respiratory failure during a 6-h observation period. Respiratory failure was induced in 30 rabbits by saline lung lavage (arterial oxygen tension < 100 mmHg at 100% oxygen with the following ventilator settings: tidal volume, 12 ml.kg-1; respiratory frequency, 30 per min; inspiratory/expiratory ratio, 1:2; and positive end-expiratory pressure of 6 cm H2O). Twenty-four rabbits were treated with different perfluorocarbon doses (3, 6, 9, and 12 ml.kg-1), and the remaining six served as controls while mechanical ventilation was continued with the aforementioned settings. Additionally, in ten healthy rabbits who were used as healthy controls, the lungs were mechanically ventilated either alone or in combination with intratracheal perfluorocarbon administration (3 ml.kg-1) for 6 h. In all treatment groups, arterial oxygen pressure increased significantly (P < 0.0001) in a dose-related fashion (193 +/- 40, 320 +/- 70, 353 +/- 125, and 410 +/- 45 mmHg at 15 min), and peak airway pressures decreased significantly (range, 18-23%; P < 0.0001) from pretreatment values. These findings were in contrast to those for the control group. The improvements were time-dependent in all four tested perfluorocarbon doses. However, the improvements in pulmonary parameters could be extended to 6 h only in groups treated with 9 ml.kg-1 and 12 ml.kg-1 perflubron. At the end of the 6-h period, the data for these two groups showed significantly higher arterial oxygen pressure (230 +/- 84 and 197 +/- 130 mmHg, respectively; P < 0.05) and lower inflation pressures than the pretreatment data for these groups and the data for the control group at 6 h. There were no clinically significant changes in pulmonary parameters in healthy animals due either to mechanical ventilation alone or mechanical ventilation in combination with intratracheal perfluorocarbon administration for 6 h. The results of this study imply that there is no association between the lung mechanics and gas exchange parameters for mechanical ventilation in combination with intratracheal perfluorocarbon administration. The data suggest that this type of perfluorocarbon administration with conventional mechanical ventilation offers a simple, alternative treatment of respiratory distress syndrome. With this technique, adequate pulmonary gas exchange can be maintained at relatively low airway pressures with high perfluorocarbon doses for several hours.

Endoluminal sealing of vascular wall disruptions with radiofrequency‐heated balloon angioplasty

Suboptimal luminal widening or acute closure secondary to arterial dissection remain significant risks of percutaneous transluminal balloon angioplasty. Non surgical techniques are often employed in an attempt to repair dissections either as temporary or definitive treatment. The aim of this study was to test the hypothesis that radiofrequency thermal balloon angioplasty at an operating temperature of 70 degrees C and low inflation pressure could seal dissections and perforations in a model of severe arterial wall damage. Dissections and perforations were created in renal (n = 4) and carotid (n = 4) arteries in four mongrel dogs. Endoluminal sealing was then attempted with conventional balloon angioplasty or radiofrequency thermal balloon angioplasty (2 atm at 70 degrees C). Contrast dye extravasation persisted in all cases following conventional balloon angioplasty but completely resolved with radiofrequency balloon angioplasty in all but one artery. Histologic examination of the arteries treated with radiofrequency balloon angioplasty showed extensive thermal injury, including transmural coagulation necrosis, flattening of the internal elastic lamina, and medial thinning. On the basis of these results, the utility of thermal balloon angioplasty for endoluminal sealing of dissections and perforations complicating angioplasty deserves further evaluation.

Finite Element Modeling of Soil Compaction by Liquid Manure Spreaders

A three-dimensional (3-D) finite element model was developed to predict the soil compaction caused by heavy liquid manure spreaders. The model includes both material and geometric nonlinearities. The updated Lagrangian method was applied to solve the geometric nonlinearity caused by large displacements. The finite element analysis was conducted with two types of tires, two different loads, and various inflation pressures. The finite element model was verified with the field test data. The results showed that the finite element model is adequate for predicting soil compaction. In agreement with observed data, the finite element results indicated that reused airplane tires with high inflation pressure resulted in the worst soil compaction, while an agricultural high floatation tire with a smaller load and lower inflation pressure caused the least soil compaction. The finite element results also demonstrated that soil compaction can be reduced by using lower tire inflation pressure.