Peak Pressure (peak + pressure)

Distribution by Scientific Domains


Selected Abstracts


Scaling of plantar pressures in mammals

JOURNAL OF ZOOLOGY, Issue 3 2009
F. Michilsens
Abstract The interaction of the limbs with the substrate can teach a lot about an animal's gait mechanics. Unlike ground-reaction forces, plantar pressure distributions are rarely studied in animals, but they may provide more detailed information about the loading patterns and locomotor function of specific anatomical structures. With this study, we aim to describe pressures for a large and diverse sample of mammalian species, focusing on scaling effects. We collected dynamic plantar pressure distributions during voluntary walking in 28 mammal species. A dynamic classification of foot use was made, which distinguished between plantiportal, digitiportal and unguliportal animals. Analysis focused on scaling effects of peak pressures, peak forces and foot contact areas. Peak pressure for the complete mammal sample was found to scale to (mass)1/2, higher than predicted assuming geometric similarity, and we found no difference between the different types of foot use. Only the scaling of peak force is dependent on the dynamic foot use. We conclude that plantar peak pressure rises faster with mass than expected, regardless of the type of foot use, and scales higher than in limb bones. These results might explain some anatomical and behavioural adaptations in graviportal animals. [source]


A Single Ventilator for Multiple Simulated Patients to Meet Disaster Surge

ACADEMIC EMERGENCY MEDICINE, Issue 11 2006
Greg Neyman MD
Objectives To determine if a ventilator available in an emergency department could quickly be modified to provide ventilation for four adults simultaneously. Methods Using lung simulators, readily available plastic tubing, and ventilators (840 Series Ventilator; Puritan-Bennett), human lung simulators were added in parallel until the ventilator was ventilating the equivalent of four adults. Data collected included peak pressure, positive end-expiratory pressure, total tidal volume, and total minute ventilation. Any obvious asymmetry in the delivery of gas to the lung simulators was also documented. The ventilator was run for almost 12 consecutive hours (5.5 hours of pressure control and more than six hours of volume control). Results Using readily available plastic tubing set up to minimize dead space volume, the four lung simulators were easily ventilated for 12 hours using one ventilator. In pressure control (set at 25 mm H2O), the mean tidal volume was 1,884 mL (approximately 471 mL/lung simulator) with an average minute ventilation of 30.2 L/min (or 7.5 L/min/lung simulator). In volume control (set at 2 L), the mean peak pressure was 28 cm H2O and the minute ventilation was 32.5 L/min total (8.1 L/min/lung simulator). Conclusions A single ventilator may be quickly modified to ventilate four simulated adults for a limited time. The volumes delivered in this simulation should be able to sustain four 70-kg individuals. While further study is necessary, this pilot study suggests significant potential for the expanded use of a single ventilator during cases of disaster surge involving multiple casualties with respiratory failure. [source]


Plantar pressures in diabetic patients with foot ulcers which have remained healed

DIABETIC MEDICINE, Issue 11 2009
T. M. Owings
Abstract Aims, The recurrence of foot ulcers is a significant problem in people with diabetic neuropathy. The purpose of this study was to measure in-shoe plantar pressures and other characteristics in a group of neuropathic patients with diabetes who had prior foot ulcers which had remained healed. Methods, This was an epidemiological cohort study of patients from diabetes clinics of two Swedish hospitals. From a database of 2625 eligible patients, 190 surviving patients with prior plantar ulcers of the forefoot (hallux or metatarsal heads) caused by repetitive stress were identified and 49 patients agreed to participate. Barefoot and in-shoe plantar pressures were measured during walking. Data on foot deformity, activity profiles and self-reported behaviour were also collected. Results, Mean barefoot plantar peak pressure at the prior ulcer site (556 kPa) was lower than in other published series, although the range was large (107,1192 kPa). Mean in-shoe peak pressure at this location averaged 207 kPa when measured with an insole sensor. Barefoot peak pressure only predicted ,35% of the variance of in-shoe peak pressure, indicating variation in the efficacy of the individual footwear prescriptions (primarily extra-depth shoes with custom insoles). Conclusions, We propose that the mean value for in-shoe pressures reported in these patients be used as a target in footwear prescription for patients with prior ulcers. Although plantar pressure is only one factor in a multifaceted strategy to prevent ulcer recurrence, the quantitative focus on pressure reduction in footwear is likely to have beneficial effects. [source]


Indentation of a free-falling lance penetrometer into a poroelastic seabed

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2005
Derek Elsworth
Abstract A solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a blunt penetrometer that self-embeds from freefall into the seabed. Arrest from freefall considers deceleration under undrained conditions in a purely cohesive soil, with constant shear strength with depth. The resulting decelerating velocity field is controlled by soil strength, geometric bearing capacity factors, and inertial components. At low impact velocities the embedment process is controlled by soil strength, and at high velocities by inertia. With the deceleration defined, a solution is evaluated for a point normal dislocation penetrating in a poroelastic medium with a prescribed decelerating velocity. Dynamic steady pressures, PD, develop relative to the penetrating tip geometry with their distribution conditioned by the non-dimensional penetration rate, UD, incorporating impacting penetration rate, consolidation coefficient and penetrometer radius, and the non-dimensional strength, ND, additionally incorporating undrained shear strength of the sediment. Pore pressures develop to a steady peak magnitude at the penetrometer tip, and drop as PD=1/xD with distance xD behind the tip and along the shaft. Peak induced pressure magnitudes may be correlated with sediment permeabilities, post-arrest dissipation rates may be correlated with consolidation coefficients, and depths of penetration may be correlated with shear strengths. Together, these records enable strength and transport parameters to be recovered from lance penetrometer data. Penetrometer data recorded off La Palma in the Canary Islands (J. Volcanol. Geotherm. Res. 2000; 101:253) are used to recover permeabilities and consolidation coefficients from peak pressure and dissipation response, respectively. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Buccal and lingual activity during mastication and swallowing in typical adults

JOURNAL OF ORAL REHABILITATION, Issue 1 2003
M. J. Casas
summary, A non-invasive protocol was developed to assess tongue and cheek movements during mastication and to evaluate the temporal relationship between mastication and the initiation of pharyngeal swallowing. Typical adults (three males and three females) were monitored during chewing. Miniature pressure transducers were bonded unilaterally to the buccal and lingual surfaces of the first mandibular molar and the buccal surface of the first maxillary molar on each subject's preferred chewing side. Surface electromyography of the ipsilateral masseter muscle was recorded as an indicator of jaw-closing activity. Pressure and electromyography (EMG) recordings were time-linked to simultaneous B-mode ultrasound imaging of the oral cavity using a submental, coronal view aligned with the first mandibular molar. The intervals between peak pressure recorded at each pressure transducer and peak jaw-closing activity for each masticatory cycle were not statistically different [analysis of variance (anova), P=0·9856] and displayed large statistical variation. These intervals were not different at the beginning of the trials (hard biscuit) than they were at the completion of mastication when the cookie had been broken down to a paste/puree consistency bolus. The interval between the last chewing stroke and the initiation of swallowing was 0·92 ± 0·34 s). No significant difference existed among subjects for this time interval (anova, P=0·382). [source]


Scaling of plantar pressures in mammals

JOURNAL OF ZOOLOGY, Issue 3 2009
F. Michilsens
Abstract The interaction of the limbs with the substrate can teach a lot about an animal's gait mechanics. Unlike ground-reaction forces, plantar pressure distributions are rarely studied in animals, but they may provide more detailed information about the loading patterns and locomotor function of specific anatomical structures. With this study, we aim to describe pressures for a large and diverse sample of mammalian species, focusing on scaling effects. We collected dynamic plantar pressure distributions during voluntary walking in 28 mammal species. A dynamic classification of foot use was made, which distinguished between plantiportal, digitiportal and unguliportal animals. Analysis focused on scaling effects of peak pressures, peak forces and foot contact areas. Peak pressure for the complete mammal sample was found to scale to (mass)1/2, higher than predicted assuming geometric similarity, and we found no difference between the different types of foot use. Only the scaling of peak force is dependent on the dynamic foot use. We conclude that plantar peak pressure rises faster with mass than expected, regardless of the type of foot use, and scales higher than in limb bones. These results might explain some anatomical and behavioural adaptations in graviportal animals. [source]


A shock-produced (Mg, Fe)SiO3 glass in the Suizhou meteorite

METEORITICS & PLANETARY SCIENCE, Issue 11 2004
Ming CHEN
The glass is surrounded by a thick rim of polycrystalline majorite and is identical in composition to the parental low-Ca pyroxene and majorite. These ovoid grains are surrounded by a fine-grained matrix composed of majorite-pyrope garnet, ringwoodite, magnesiowüstite, metal, and troilite. This study strongly suggests that some precursor pyroxene grains inside the shock veins were transformed to perovskite within the pyroxene due to a relatively low temperature, while at the rim region pyroxene grains transformed to majorite due to a higher temperature. After pressure release, perovskite vitrified at post-shock temperature. The existence of vitrified perovskite indicates that the peak pressure in the shock veins exceeds 23 GPa. The post-shock temperature in the meteorite could have been above 477 °C. This study indicates that the occurrence of high-pressure minerals in the shock veins could not be used as a ubiquitous criterion for evaluating the shock stage of meteorites. [source]


Pes planovalgus in RA: a descriptive and analytical study of foot function determined by gait analysis

MUSCULOSKELETAL CARE, Issue 1 2003
Deborah E. Turner BSc SRCh
Abstract Objective: To compare gait and foot function between rheumatoid arthritis (RA) patients with painful pes planovalgus deformity and healthy age- and sex-matched adults. Methods: Gait analysis was undertaken in 23 RA patients (14 female and 9 male, mean age 52.3 years, mean disease duration 6.6 years) and 23 healthy adults (14 female and 9 male, mean age 49.5 years). Gait measurements included temporal and spatial parameters, plantar pressures and three-dimensional (3D) kinematics at the ankle joint complex (AJC). The mean differences between the groups and associated confidence intervals were calculated using the t distribution. Results: RA patients showed longer gait cycle (mean difference 0.15 sec and 0.14 sec for right and left limbs, respectively) and double-limb support times (mean difference 8.3% and 7.9% for right and left limbs, respectively), shorter stride length (mean difference ,0.31 m for right and left limbs), slower walking speed (mean difference ,0.39 m/sec) and lower cadence (mean difference ,16.6 steps/min). In comparison with the normal group, RA patients had greater AJC dorsi/plantarflexion range of motion (ROM) (mean difference 5.7 °) and inversion/eversion ROM (mean difference 2.9 °). The frontal plane position of the AJC was more everted at specific stance periods (mean difference at heel strike ,2.4 ° and at midstance ,4.0°). Furthermore, both the peak eversion (mean difference ,4.1 °) and summated eversion motion as a function of time (mean difference ,313.9 °) were greater in the RA group. The pes planovalgus foot in RA was characterized by increases in peak pressure (mean difference 34.3 kPa), pressure,time integral (mean difference 18.2 kPa.sec), peak force (mean difference 1.7 N), force,time integral (mean difference 0.7 N.sec), contact time (mean difference 9.8% roll over process) and contact area (mean group difference 3.4 cm,2) in the medial midfoot. Further changes in the load pattern in the forefoot were observed in the RA patients, namely increases in the peak pressure (mean difference 96.4 kPa), pressure,time integral (mean difference 58.4 kPa.sec), and contact area (mean difference 1.7 cm,2) in the medial forefoot region and reduction in contact area (mean difference ,3.9 cm,2), peak force (mean difference ,7.2 N) and force,time integral (mean difference ,1.6 N.sec) in the lateral forefoot. Conclusions: Painful pes planovalgus deformity in RA is associated with global changes in gait, and localized structural and functional changes in the foot which can be accurately measured using clinical gait analysis. Copyright © 2003 Whurr Publishers Ltd. [source]


The design of duct venting of gas explosions

PROCESS SAFETY PROGRESS, Issue 2 2008
Almerinda Di Benedetto
Abstract Venting systems are useful for the mitigation of accidental explosions. Vent ducts should be used if equipment is located indoors, as NFPA 68 (2007) suggests, for discharging combustion products to safe location. However, the presence of a duct is likely to increase the severity of the explosion with respect to simply vented vessels. Up to now, no reliable correlations are available for the sizing of ducted vented systems. The only correlation available was developed by Bartknecht in 1993 for gas explosion, also acknowledged by NFPA 68. In this study, we propose an engineering correlation based on semi-empirical engineering methodologies, which is able to quantify the relations between geometric properties and the peak pressure occurring in the combustion chamber in the presence of a duct fitted on the vent panel. To this aim, we have regressed all the available experimental data on gas explosion in ducted-vented vessels. © 2007 American Institute of Chemical Engineers Process Saf Prog, 2008 [source]


Association between Attributes of a Cyclist and Bicycle Seat Pressure

THE JOURNAL OF SEXUAL MEDICINE, Issue 10 2010
Eadric Bressel PhD
ABSTRACT Introduction., Bicycle seat pressure is thought to be the principal risk factor for bicycle seat injuries such as erectile dysfunction; however there is a lack of understanding regarding the characteristics of a cyclist that predict bicycle seat pressure. Aim., The purpose of this study was to determine if select attributes of a cyclist are associated with seat pressure during stationary bicycling. A secondary purpose was to determine which of the associated attributes were the best predictors of seat pressure and if they were consistent between two different seats. Methods., There were two data collection phases to this correlational study in which 40 males between the ages 20 and 50 years volunteered. For the first phase, select attributes of the cyclist (age, weight, flexibility, experience level, and ischial tuberosity width) were measured. The second phase required participants to ride a stationary cycle ergometer while pelvic tilt angles and seat pressures were measured on two different traditional seats. Main Outcome Measure., The main outcome is the mean and peak bicycle seat interface pressure over the anterior and total seat. Results., Body weight explained up to 50% of the variance in mean total seat pressure (P = 0.001). Regarding peak total pressure, pelvic tilt angle and flexibility explained 43% and 17% of the variance, respectively, for the two seats tested (P = 0.01). Conclusion., These results indicate that predictors of mean seat pressure are not the same for peak pressure. Body weight alone accounted for the most variance in mean pressure whereas pelvic tilt and flexibility accounted for the most variance in peak pressure. These variables related to seat pressure may give some guidance to cyclists and clinicians who intend to prevent or alleviate the symptoms associated with bicycle seat injuries that include erectile dysfunction. Bressel E, Nash D, and Dolny D. Association between attributes of a cyclist and bicycle seat pressure. J Sex Med 2010;7:3424,3433. [source]


A compliant tip reduces the peak pressure of laparoscopic graspers

ANZ JOURNAL OF SURGERY, Issue 7 2002
Damian D. Marucci
Background: Previous studies have demonstrated that high pressures are generated at the tips of laparoscopic graspers, which can cause tissue injury. This study examines the effect of a compliant edge on tip pressure. Methods: One of a pair of identical laparoscopic graspers was modified by refashioning the tip out of silicone. A thin film pressure transducer (I-scan 6900 sensor) was deployed between the jaws of the grasper and a simulated tissue (leather strap). Load and handle pressures were kept constant. Peak tip pressure readings were taken as the load orientation was increased from the perpendicular to 135° (n = 10). The data was analysed using anova and a post-hoc Duncan's multiple range test. Results: Peak tip pressures generated by the compliant tipped grasper were significantly less than those developed by the unmodified grasper, particularly at high-load orientations. Conclusion: High pressures generated at the tip of laparoscopic graspers can be reduced by altering the mechanical properties (compliance) of the tip. [source]


78 Use of a rabbit model to investigate the feasibility of using an innervated neosphincter transplant for the treatment of stress urinary incontinence.

BJU INTERNATIONAL, Issue 2006
A.D. SHAFTON
Aim:, To examine the feasibility of using an innervated smooth muscle wrap as a neosphincter in a rabbit model of urinary incontinence. Methods:, Rabbits were rendered incontinent surgically by lesion of the proximal urethral wall to the level of the submucosa (n = 20). In twelve animals a strip of dartos smooth muscle was wrapped around the lesioned urethra to create a new urethral sphincter and stimulating electrodes were inserted into the muscle. After a recovery period of at least one-week cystometrograms were established for control (urethra intact), lesioned and lesion plus neosphincter animals. Results:, Infusion of saline into the bladder of control animals caused a slow rise in bladder pressure until, at approximately 20,30 ml, there was an increase in pressure that rose steeply and was associated with bladder emptying. The threshold for this reflex emptying was 2,3 cm H2O, and the maximum pressure during the reflex was 6,15 cm H2O. After the bladder emptied, the pressure dropped to 0,2 cm H2O. In rabbits with lesioned sphincters, it was not possible to obtain a normal cystometrogram because there was leakage of fluid from the urethral opening before a volume and pressure sufficient to elicit a reflex was achieved. The loss of the majority of fluid often occurred without a significant pressure increase, that is, there was no true emptying reflex. Similar results were observed in animals in which the urethra had been lesioned and implanted with the smooth muscle neosphincter. Prior to electrical stimulation of the neosphincter, with constant current pulses at 2 Hz, substantial leak occurred at 11.4 ± 2.5 ml, whereas during stimulation voiding occurred at 17.8 ± 1.4 ml. At void or emptying, the peak pressure was 6.1 ± 0.1 cm H20 in control, 0.7 ± 0.2 in operated but not stimulated and 3.5 ± 0.6 in the same animals during stimulation. A satisfactory improvement of continence was observed for a period of up to 6½ months postsurgery. At the end of the study, histological examination confirmed the neosphincter to be both healthy and viable. Conclusion:, Smooth muscles of the dartos display contractile properties which make them suitable for use as transplantable sphincters. A smooth muscle neosphincter, controlled by electrical stimulation, can restore continence after urethral damage. [source]


Shock wave induced cytoskeletal and morphological deformations in a human renal carcinoma cell line

CANCER SCIENCE, Issue 4 2006
S. Fatemeh Moosavi-Nejad
Effects of shock waves on the morphology and cytoskeleton of a human renal carcinoma cell line (ACHN) were investigated in vitro. ACHN monolayer cultured on a cover slide glass was treated with 10 shots of focused underwater shock waves, with 16 MPa peak pressure at the focal area of a piezoceramic shock wave generator. After exposure to the shock wave, based on the severity of morphological deformations of the treated cells, the monolayer was divided into three morphological areas; focal, marginal and intact. Morphological deformations were found to be associated with disorganization of the intracellular cytoskeletal filaments. Deformation of the cytoskeletal proteins in the treated cells were separately studied with respect to the location of the cells within the three morphological areas. Among three major cytoskeletal proteins, actin and tubulin, but not vimentin, were affected by the shock waves. The deformed cells reorganized their cytoskeletal network within 3 h with a pattern similar to the control, indicating the transient characteristic of the shock wave induced cytoskeletal damage in the surviving cells. The remaining cell fragments on the slide glass, which contained short actin filaments, indicated the important role of shear stress in damaging the cytoskeletal fibers by shock waves. (Cancer Sci 2006; 97: 296,304) [source]


Plantar pressure distribution analysis in normal weight young women and men with normal and claw feet: A cross-sectional study

CLINICAL ANATOMY, Issue 4 2005
G. Gravante
Abstract We analyzed the plantar support in 72 normal-weight young voluntaries (46 women, 26 men), by a baropodometric platform. We considered subjects with claw foot (CFS) and subjects with normal foot (NFS). We found a significant reduction of total plantar support surface in the CFS (P < 0.0001 for women, P < 0.001 for men), due to the reduction of the forefoot and rear foot areas of both plantar imprints. Indeed, CFS of both sexes exhibited higher values of both plantar pressure and peak pressure, compared to the NFS. Moreover, the load per units of plantar surface increased in CFS compared to the NFS. In conclusion, the reduction of plantar support surfaces in CFS of both sexes was associated to a major load per units of plantar surface in the forefoot and rear foot areas, and this may be a risk factor to lower extremity overuse injuries. Clin. Anat. 18:245,250, 2005. © 2005 Wiley-Liss, Inc. [source]


Performance of neonatal ventilators in volume targeted ventilation mode

ACTA PAEDIATRICA, Issue 2 2007
Atul Sharma
Abstract Aim: To test the hypothesis that in volume targeted ventilation modes, ventilator performance would vary according to ventilator type. Methods: Four neonatal ventilators: Draeger Babylog 8000 (Draeger Medical, Germany), SLE 5000 infant ventilator (SLE systems, UK), Stephanie paediatric ventilator (F. Stephan Biomedical, German) and V.I.P. Bird gold (Viasys Healthcare, USA) were assessed using a lung model. Delivered peak pressure, inflation time, mean airway pressure (MAP) and volume were measured. Results: At the same preset ventilator settings, the Stephanie and V.I.P. Bird ventilators delivered significantly lower peak pressures and tended to deliver lower MAPs than the other two ventilators. At a volume targeted ventilation level of 5 mL, the SLE and the V.I.P. Bird delivered significantly shorter inflation times. The above differences related to differences in the airway pressure waveforms delivered by the four ventilators. The V.I.P. Bird had a less variable volume delivery, but this was always significantly lower than the preset volume guarantee level but higher than the volume displayed by the ventilator. Conclusion: In volume targeted ventilation modes, performance differs between neonatal ventilator types; these results may have implications for clinical practise. [source]


Metal Objects Mapping After Small Charge Explosions.

JOURNAL OF FORENSIC SCIENCES, Issue 3 2006
A Study on AISI 304Cu Steel with Two Different Grain Sizes
ABSTRACT: Evidence of exposure of a metal component to a small charge explosion can be detected by observing microstructural modifications; they may be present even if the piece does not show noticeable overall plastic deformations. Particularly, if an austenitic stainless steel (or another metal having a face-centered cubic structure and a low stacking fault energy) is exposed to an explosive shock wave, high-speed deformation induces primarily mechanical twinning, whereas, in nonexplosive events, a lower velocity plastic deformation first induces slip. The occurrence of mechanical twins can be detected even if the surface is damaged or oxidized in successive events. In the present research, optical metallography (OM) and scanning electron microscopy (SEM), and scanning tunneling microscopy (STM) were used to detect microstructural modifications caused on AISI 304Cu steel disks by small-charge explosions. Spherical charges of 54.5 or 109 g TNT equivalent mass were used at explosive-to-target distances from 6.5 to 81.5 cm, achieving peak pressures from 160 to 0.5 MPa. Explosions induced limited or no macro-deformation. Two alloy grain sizes were tested. Surface OM and SEM evidenced partial surface melting, zones with recrystallization phenomena, and intense mechanical twinning, which was also detected by STM and X-ray diffraction. In the samples' interior, only twins were seen, up to some distance from the explosion impinged surface and again, at the shortest charge-to-sample distances, in a thin layer around the reflecting surface. For forensic science locating purposes after explosions, the maximum charge-to-target distance at which the phenomena disappear was singled out for each charge or grain size and related to the critical resolved shear stress for twinning. [source]


Garnet,chloritoid,kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts

JOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2010
A. J. SMYE
Abstract The assemblage garnet,chloritoid,kyanite is shown to be quite common in high-pressure eclogite facies metapelites from orogenic belts around the world, and occurs over a narrowly restricted range of temperature ,550,600 °C, between 20 and 25 kbar. This assemblage is favoured particularly by large Al2O3:K2O ratios allowing the development of kyanite in addition to garnet and chloritoid. Additionally, ferric iron and manganese also help stabilize chloritoid in this assemblage. Pseudosections for several bulk compositions illustrate these high-pressure assemblages, and a new thermodynamic model for white mica to include calcium and ferric iron was required to complete the calculations. It is extraordinary that so many orogenic eclogite facies rocks, both mafic eclogites sensu stricto as well as metapelites with the above assemblage, all yield temperatures within the range of 520,600 °C and peak pressures ,23±3 kbar. Subduction of oceanic crust and its entrained associated sedimentary material must involve the top of the slab, where mafic and pelitic rocks may easily coexist, passing through these P,T conditions, such that rocks, if they proceed to further depths, are generally not returned to the surface. This, together with the tightly constrained range in peak temperatures which such eclogites experience, suggests thermal weakening being a major control on the depths at which crustal material is decoupled from the downgoing slab. [source]


Petrogenetic modelling of strongly residual metapelitic xenoliths within the southern Platreef, Bushveld Complex, South Africa

JOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2010
T. E. JOHNSON
Abstract Xenoliths of quartz-absent Fe-rich aluminous metapelite are common within the platinum group element-rich mafic/ultramafic magmatic rocks of the Platreef. Relative to well-characterized protoliths, the xenoliths are strongly depleted in K2O and H2O, and have lost a substantial amount of melt (>50 vol.%). Mineral equilibria calculations in the NCKFMASHTO system yield results that are consistent with observations in natural samples. Lower-grade rocks that lack staurolite constrain peak pressures to ,2.5 kbar in the southern Platreef. Smaller xenoliths and the margins of larger xenoliths comprise micro-diatexite rich in coarse acicular corundum and spinel, which record evidence for the metastable persistence of lower-grade hydrous phases and rapid melting consequent on a temperature overstep of several hundred degrees following their incorporation in the mafic/ultramafic magmas. In the cores of larger xenoliths, temperatures increased more slowly enabling progressive metamorphism by continuous prograde equilibration and the loss of H2O by subsolidus dehydration; the H2O migrated to xenolith margins where it may have promoted increased melting. According to variations in the original compositional layering, layers became aluminosilicate- and/or cordierite-rich, commonly with spinel but only rarely with corundum. The differing mineralogical and microstructural evolution of the xenoliths depends on heating rates (governed by their size and, therefore, proximity to the Platreef magmas) and the pre-intrusive metamorphic grade of the protoliths. The presence or absence of certain phases, particularly corundum, is strongly influenced by the degree of metastable retention of lower-grade hydrates in otherwise identical protolith bulk compositions. The preservation of fine-scale compositional layering that is inferred to be relict bedding in xenolith cores implies that melt loss by compaction was extremely efficient. [source]


The P,T path of the ultra-high pressure Lago Di Cignana and adjoining high-pressure meta-ophiolitic units: insights into the evolution of the subducting Tethyan slab

JOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009
C. GROPPO
Abstract The Lago di Cignana ultra-high-pressure unit (LCU), which consists of coesite,eclogite facies metabasics and metasediments, preserves the most deeply subducted oceanic rocks worldwide. New constraints on the prograde and early retrograde evolution of this ultra-high pressure unit and adjoining units provide important insights into the evolution of the Piemontese,Ligurian palaeo-subduction zone, active in Paleocene,Eocene times. In the LCU, a first prograde metamorphic assemblage, consisting of omphacite + Ca-amphibole + epidote + rare biotite + ilmenite, formed during burial at estimated P < 1.7 GPa and 350 < T < 480 °C. Similar metamorphic conditions of 400 < T < 650 °C and 1.0 < P < 1.7 GPa have been estimated for the meta-ophiolitic rocks juxtaposed to the LCU. The prograde assemblage is partially re-equilibrated into the peak assemblage garnet + omphacite + Na-amphibole + lawsonite + coesite + rutile, whose conditions were estimated at 590 < T < 605 °C and P > 3.2 GPa. The prograde path was characterized by a gradual decrease in the thermal gradient from ,9,10 to ,5,6 °C km,1. This variation is interpreted as the evidence of an increase in the rate of subduction of the Piemonte,Ligurian oceanic slab in the Eocene. Accretion of the Piemontese oceanic rocks to the Alpine orogen and thermal relaxation were probably related to the arrival of more buoyant continental crust at the subduction zone. Subsequent deformation of the orogenic wedge is responsible for the present position of the LCU, sandwiched between two tectonic slices of meta-ophiolites, named the Lower and Upper Units, which experienced peak pressures of 2.7,2.8 and <2.4 GPa respectively. [source]


Scaling of plantar pressures in mammals

JOURNAL OF ZOOLOGY, Issue 3 2009
F. Michilsens
Abstract The interaction of the limbs with the substrate can teach a lot about an animal's gait mechanics. Unlike ground-reaction forces, plantar pressure distributions are rarely studied in animals, but they may provide more detailed information about the loading patterns and locomotor function of specific anatomical structures. With this study, we aim to describe pressures for a large and diverse sample of mammalian species, focusing on scaling effects. We collected dynamic plantar pressure distributions during voluntary walking in 28 mammal species. A dynamic classification of foot use was made, which distinguished between plantiportal, digitiportal and unguliportal animals. Analysis focused on scaling effects of peak pressures, peak forces and foot contact areas. Peak pressure for the complete mammal sample was found to scale to (mass)1/2, higher than predicted assuming geometric similarity, and we found no difference between the different types of foot use. Only the scaling of peak force is dependent on the dynamic foot use. We conclude that plantar peak pressure rises faster with mass than expected, regardless of the type of foot use, and scales higher than in limb bones. These results might explain some anatomical and behavioural adaptations in graviportal animals. [source]


Manual digital pressures during knuckle-walking in chimpanzees (Pan troglodytes)

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009
R.E. Wunderlich
Abstract Considerable attention has been given to hand morphology and function associated with knuckle-walking in the African apes because of the implications they have for the evolution of bipedalism in early hominins. Knuckle-walking is associated with a unique suite of musculoskeletal features of the wrist and hand, and numerous studies have hypothesized that these anatomical features are associated with the dynamics of load distribution across the digits during knuckle-walking. We collected dynamic digital pressures on two chimpanzees during terrestrial and simulated arboreal locomotion. Comparisons were made across substrates, limb positions, hand positions, and age categories. Peak digital pressures were similar on the pole and on the ground but were distributed differently across the digits on each substrate. In young animals, pressure was equally high on digits 2,4 on the ground but higher on digits 3 and 4 on the pole. Older animals experience higher pressures on digits 2 and 3 on the ground. Hand posture (palm-in vs. palm-back) influenced the distribution and timing of peak pressures. Age-related increases in body mass also result in higher overall pressures and increased variation across the digital row. In chimpanzees, digit 5 typically bears relatively little load regardless of hand position or substrate. These are the first quantitative data on digital pressures during knuckle-walking in hominoids, and they afford the opportunity to develop hypotheses about variation among hominoids and biomechanical models of wrist and forearm loading. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source]


Functional analysis of the gibbon foot during terrestrial bipedal walking: Plantar pressure distributions and three-dimensional ground reaction forces

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2005
Evie Vereecke
Abstract This paper gives a detailed analysis of bipedal walking in the white-handed gibbon, based on collected pressure and force data. These data were obtained from four gibbons in the Wild Animal Park, Planckendael, Belgium, by using a walkway with integrated force plate and pressure mat. This is the first study that collects and describes dynamic plantar pressure data of bipedally walking gibbons, and combines these with force plate data. The combination of these data with previously described roll-off patterns of gibbons, based on general observations, video images, force plates, and EMG data, gives us a detailed description of foot function during gibbon bipedalism. In addition, we compare the observed characteristics of hylobatid bipedalism with the main characteristics of bonobo and human bipedalism. We found that gibbons are midfoot/heel plantigrade, and lack the typical heel-strike of other hominoids. The hallux is widely abducted and touches down at the onset of the stance phase, which results in an L-shaped course of the center of pressure. The vertical force curve is trapezoid to triangular in shape, with high peak values compared to humans. The braking component is shorter than the accelerating component, and shortens further at higher walking velocities. Speed has a significant influence on the forefoot peak pressures and on most of the defined gait parameters (e.g., vertical force peak), and it alters the foot contact pattern as well. The investigation of existing form-function relationships in nonhuman primates is essential for the interpretation of fossil remains, and might help us understand the evolution of habitual bipedal walking in hominids. Am J Phys Anthropol, 2005. © 2005 Wiley-Liss, Inc. [source]


Comparison of breathing tube connectors during invasive bronchial procedures,

ANAESTHESIA, Issue 6 2009
N. Rahe-Meyer
Summary Bronchoscopy and bronchial suctioning during intra-operative artificial ventilation often causes leakage from the ventilation circuit with a decrease in ventilatory parameters and possible workplace contamination with anaesthetic gases. Different connectors have been developed to reduce gas leakage. We evaluated the following connectors : VBM 2 mm, 3 mm and 5 mm, Bodai Suction-Safe, Bodai Bronch-Safe and Bodai Trach-Safe, as well as the BE 105-7, BE 105-8 and SH 7-45. Invasive bronchial instruments (catheters, bronchoscopes and bronchial blockers) with 1.67,7.33 mm diameter were used. Pressure-controlled ventilation was performed on a test lung using a ventilator. Sevoflurane concentration in the room was measured 0.2 and 1.5 m from the connector using a photo-acoustic infrared-spectroscope. The VBM connectors caused the least gas leak and ensured stability of ventilation parameters even at peak pressures when combined with smaller instruments. With instruments > 6 mm, BE 105-7, BE 105-8 and SH 7-45 connectors performed best. The Bodai connectors showed a reduced ability to prevent leakage and to keep ventilatory parameters stable. All connectors, excluding the Bodai Trach-Safe, prevented exposure to anaesthetic gases beyond the current safety recommendations when combined with the fitting instruments. The connectors showed different ranges of tightness, equivalent to different ranges of compatibility with the instruments used. [source]


Performance of neonatal ventilators in volume targeted ventilation mode

ACTA PAEDIATRICA, Issue 2 2007
Atul Sharma
Abstract Aim: To test the hypothesis that in volume targeted ventilation modes, ventilator performance would vary according to ventilator type. Methods: Four neonatal ventilators: Draeger Babylog 8000 (Draeger Medical, Germany), SLE 5000 infant ventilator (SLE systems, UK), Stephanie paediatric ventilator (F. Stephan Biomedical, German) and V.I.P. Bird gold (Viasys Healthcare, USA) were assessed using a lung model. Delivered peak pressure, inflation time, mean airway pressure (MAP) and volume were measured. Results: At the same preset ventilator settings, the Stephanie and V.I.P. Bird ventilators delivered significantly lower peak pressures and tended to deliver lower MAPs than the other two ventilators. At a volume targeted ventilation level of 5 mL, the SLE and the V.I.P. Bird delivered significantly shorter inflation times. The above differences related to differences in the airway pressure waveforms delivered by the four ventilators. The V.I.P. Bird had a less variable volume delivery, but this was always significantly lower than the preset volume guarantee level but higher than the volume displayed by the ventilator. Conclusion: In volume targeted ventilation modes, performance differs between neonatal ventilator types; these results may have implications for clinical practise. [source]