Ultrasound system to measure esophageal varix pressure: an in vitro validation study.
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We report our experience with an ultrasound system to measure esophageal varix pressure in an in vitro model. The ultrasound system consists of a 12.5 MHz frequency intraluminal ultrasound probe, a water infusion catheter, and a manometry catheter, all contained within a nondistensible latex bag. Esophagi and external jugular veins were harvested from five pigs. The vein and ultrasound system were placed inside the esophagus. One end of the vein was connected to a water reservoir to modulate its pressure; the other end was connected in two different ways to simulate hydrodynamic and hydrostatic flow conditions. The bag was inflated with water until vein occlusion was discernible on the ultrasound images. The influences of vein pressure, vein cross-sectional area and esophageal elasticity on the ultrasound measurement of vein pressure were assessed. A total of 108 trials were performed at nine different vein pressures. Complete vein occlusion occurred when the bag pressure was slightly greater (1.4 +/- 0.7 mmHg) than the vein pressure. For a vein pressure of 25 mmHg, the average occlusion and opening pressures were 27 +/- 0.2 and 25.7 +/- 0.3 mmHg, respectively (P < .05) suggesting that the vein opening pressure on the ultrasound images is more accurate than the vein closing pressure. In conclusion, the ultrasound technique can accurately measure intravariceal pressure in vitro. The bag pressure at the point of vein reopening is the best determinant of the vein pressure. (+info)
Monitoring respiratory mechanics during mechanical ventilation: where do the signals come from?
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Graphical patient data have become essential to the understanding and management of ventilator-dependent patients. These electronically generated data often reveal clues to subtle complications that, if corrected, could lead to improved patient-ventilator harmony. The apparent precision of the waveforms and the 3- or 4-place display of numeric data imply high accuracy. Laboratory devices and equipment, with their required certification, generally exhibit accuracies of approximately 2% for flow and significantly less than 1% for pressure. But the cost constraints placed on hospital-grade medical equipment dictate the use of commercial sensors-transducers, which means that pressure measurements will range between 3% and 5% of reading, and flow measurements will range between 6% and 10% (+/- 3 standard deviations of the mean). Other direct and indirect influences, such as temperature, humidity, absolute pressure, system pressure, type of gas, contamination, and myriad additional effects further interfere with the transformation of the variable of interest into an electrically equivalent signal. The abundance of viewable information pertinent to the management of the ventilated patient can be traced to the availability of the many types of transducers combined with microprocessor electronics. The process of capturing a variable of interest (sensing and signal transduction), converting it to a digitized electronic signal (analog-to-digital-conversion), operating on that signal (such as for control of the breathing algorithm and checking for violation of alarm thresholds), and finally converting it back to an analog signal that appears on a monitor generally receives scant appreciation. The process, however, lies at the core of data management in modern ICU ventilators. (+info)
A novel method for assessing effects of hydrostatic fluid pressure on intracellular calcium: a study with bovine articular chondrocytes.
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Chondrocytes in articular cartilage are exposed to hydrostatic pressure and distortional stress during weight bearing and joint loading. Because these stresses occur simultaneously in articular cartilage, the mechanism of mechanosignal transduction due to hydrostatic pressure alone in chondrocytes is not clear. In this study, we attempted to characterize the change in intracellular calcium concentration ([Ca2+]i) in response to the application of hydrostatic fluid pressure (HFP) to cultured bovine articular chondrocytes isolated from defined surface (SZ) and middle zones (MZ) by using a fluorescent indicator (X-rhod-1 AM), a novel custom-made pressure-proof optical chamber, and laser confocal microscopy. Critical methodology implemented in this experiment involved application of high levels of HFP to the cells and the use of a novel imaging apparatus to measure the peak [Ca2+]i in individual cells. The peak [Ca2+]i in MZ cells cultured for 5 days showed a significant twofold increase after the application of HFP at constant 0.5 MPa for 5 min. The peak [Ca2+]i in SZ cells was lower (43%) than that of MZ cells. The peak was suppressed with an inhibitor of dantrolene, gadolinium, or a calcium ion-free buffer, but not with verapamil. This study indicated that the increase in [Ca2+]i in chondrocytes to HFP is dependent on the zonal origin. HFP stimulates calcium mobilization and stretch-activated channels. (+info)
A determination of bite force in northern Japanese children.
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The bite force of 2594 school children (1248 males and 1346 females) living in northern Japan was investigated during oral health examinations in May and June 2001, using a new type of occlusal force gauge. The subjects were recruited from a variety of educational institutes and comprised: 73 nursery (3-5 years old), 1019 primary (6-11 years old), 902 junior high (12-14 years old) and 600 high (15-17 years old) school children. The measuring apparatus consisted of a hydraulic pressure gauge, with a bite element encased in a plastic tube. The bite force was measured at the first molar or second primary molar in the children presenting in the permanent and primary dentitions, respectively. The findings revealed significant variations in bite force between children of different ages. The average bite force was 186.2 N in males and 203.4 N in females of nursery school children; 374.4 N in males and 330.5 N in females of primary school children; 514.9 N in males and 448.7 N in females of junior high school children; and 545.3 N in males and 395.2 N in females of high school children. The prevalence of malocclusion in the nursery school children was found to be less than 30 per cent, which contrasted with almost 70 per cent in the high school children. (+info)
Molar bite force in relation to occlusion, craniofacial dimensions, and head posture in pre-orthodontic children.
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The present study examined bite force in relation to occlusion, craniofacial dimensions, and head posture. The sample comprised 88 children (48 girls, 40 boys) aged 7-13 years, sequentially admitted for orthodontic treatment of malocclusions entiling health risks. Bite force was measured in the molar region by means of a pressure transducer. Angle classification, number of teeth and contact in the intercuspal position (ICP) were recorded and dental arch widths were measured on plaster casts. Craniofacial dimensions and head posture were recorded from lateral cephalometric radiographs taken with the subject standing with their head in a standardized posture (mirror position). Associations were assessed by Spearman correlations and multiple stepwise regression analyses.The maximum bite force increased significantly with age in girls, with teeth in occlusal contact in boys, and with increasing number of erupted teeth in both genders. Bite force did not vary significantly between the Angle malocclusion types. Only in boys was there a clear correlation between bite force and craniofacial morphology: cranial base length (n-ba, n-ar), posterior face height (s-tgo, ar-tgo), vertical jaw relationship (NL-ML), mandibular inclination (NSL-ML), form (ML-RL) and length (pg-tgo), and inclination of the lower incisors (Ili-ML). Multiple regression analysis showed that the vertical jaw relationship (P < 0.001) and the number of teeth present (P < 0.01) were the most important factors for the magnitude of bite force in boys. In girls, the most important factor was the number of teeth present (P < 0.001). No correlations between bite force and head posture were found. (+info)
The use of pressure change on standing as a surrogate measure of the stiffness of a compression bandage.
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OBJECTIVES: To measure interface pressure and stiffness of short-stretch and long-stretch bandages applied with variable strength. These parameters have a deciding influence on the efficacy of compression therapy in chronic venous disease. DESIGN: Prospective experimental study. MATERIALS AND METHODS: Compression bandages constructed of different materials were applied with light, moderate and high pressure. Interface pressure was measured over the medial aspect of leg in 12 healthy individuals. Long-stretch bandages were compared to short-stretch bandages. The difference between standing and supine pressure was used to characterise stiffness. RESULTS: In the low pressure range the median pressure of the final bandage in the supine position was between 18 and 30 mmHg for the long-stretch and 25-33.5 mmHg for the short-stretch bandages (p<0.01, Mann-Whitney U-test). The median differences between standing and supine pressure were between 2.0 and 8.5 for the long-stretch and 6.0-10.5 mmHg for the short-stretch material. In the group of moderate pressure the median values in the supine position were in a range 33.0-58.0 mmHg, for long-stretch and 39.0-49.5 mmHg for short-stretch bandages, with an increase after standing of 6.0-7.0 mmHg with long-stretch, and 14.0-21.0 mmHg with short-stretch bandages (p<0.01, Mann-Whitney U-test). The median supine pressure values in the high pressure group were between 52.0 and 67.0 mmHg for long-stretch and 59.5-67.0 mmHg for short-stretch material. The median increase during standing ranged between 8.5 and 14.5 mmHg in the elastic group and 23.0-33.0 in the inelastic group (p<0.01, Mann-Whitney U-test). CONCLUSION: A bandage applied with light pressure corresponds to the moderate pressure category of stockings. The difference between the sub-bandage pressure from supine to standing can be used to characterise the stiffness of a bandage. (+info)
Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction: an experimental study on the rabbit lumbar spine model.
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Intervertebral disc (IVD) pressure measurement is an appropriate method for characterizing spinal loading conditions. However, there is no human or animal model that provides sufficient IVD pressure data. The aim of our study was to establish physiological pressure values in the rabbit lumbar spine and to determine whether temporary external disc compression and distraction were associated with pressure changes. Measurements were done using a microstructure-based fibreoptic sensor. Data were collected in five control rabbits (N, measurement lying prone at segment L3/4 at day 28), five rabbits with 28 days of axial compression (C, measurement at day 28) and three rabbits with 28 days of axial compression and following 28 days of axial distraction (D, measurement at day 56). Disc compression and distraction was verified by disc height in lateral radiographs. The controls (N) showed a level-related range between 0.25 MPa-0.45 MPa. The IVD pressure was highest at level L3/4 (0.42 MPa; range 0.38-0.45) with a decrease in both cranial and caudal adjacent segments. The result for C was a significant decrease in IVD pressure (0.31 MPa) when compared with controls (P=0.009). D showed slightly higher median IVD pressure (0.32 MPa) compared to C, but significantly lower levels when compared with N (P=0.037). Our results indicate a high range of physiological IVD pressure at different levels of the lumbar rabbit spine. Temporary disc compression reduces pressure when compared with controls. These data support the hypothesis that temporary external compression leads to moderate disc degeneration as a result of degradation of water-binding disc matrix or affected active pumping mechanisms of nutrients into the disc. A stabilization of IVD pressure in discs treated with temporary distraction was observed. (+info)
A simple method for measuring interstitial fluid pressure in cancer tissues.
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A novel procedure using a polyurethane transducer-tipped catheter (Millar) is described that allows reliable measurement of interstitial fluid pressure (IFP) in cancer tissues. Before and after each use, the transducer is calibrated at 37 degrees C by a water column. After calibration, the transducer is passed through the lumen of a surgical needle. The sensor is kept in the lumen of the needle during penetration into the tumor. The sensor tip is then introduced into the center core of the tumor as the needle sleeve is withdrawn from the tumor surface. Our new technique is simple and provides IFPs equal to those provided by the well-established, wick-in-needle technique. Using our new technique, we compared IFP in skin melanoma grafts in NG2 knockout and wild-type mice. Knocking out NG2 proteoglycan on vasculogenic and angiogenic pericytes reduced interstitial fluid pressure in melanoma from +4.9 cm H2O to -0.4 cm H2O (P=0.0054 Mann-Whitney U test). (+info)