Differences In Pressure Measurements Research Articles

Evaluation of Optimal Esophageal Catheter Balloon Inflation Volume in Mechanically Ventilated Children.

Accuracy of esophageal pressure measured by an air-filled esophageal balloon catheter is dependent on balloon filling volume. However, this has been understudied in mechanically ventilated children. We sought to study the optimal filling volume in children receiving ventilation by using previously reported calibration methods. Secondary objectives included to examine the difference in pressure measurements at individualized optimal filling volume versus a standardized inflation volume and to study if a static hold during calibration is required to identify the optimal filling volume. An incremental inflation calibration procedure was performed in children receiving ventilation, <18 y, instrumented with commercially available catheters (6 or 8 French) who were not breathing spontaneously. The balloon was manually inflated by 0.2 to 1.6 mL (6 French) or 2.6 mL (8 French). Esophageal pressure (Pes) and airway pressure tracings were recorded during the procedure. Data were analyzed offline by using 2 methods: visual determination of filling range with the calculation of the highest difference between expiratory and inspiratory Pes and determination of a correctly filled balloon by calculating the esophageal elastance. We enrolled 40 subjects with median (interquartile range [IQR]) age 6.8 (2-25) months. The optimal filling volume ranged from 0.2 to 1.2 mL (median [IQR] 0.6 [0.2-1.0] mL) in the subjects with a 6 French catheter and 0.2-2.0 mL (median [IQR] 0.7 [0.5-1.2] mL) for 8 French catheters. Inflating the balloon with 0.6 mL (median computed from the whole cohort) gave an absolute difference in transpulmonary pressure that ranged from -4 to 7 cm H2O compared with the personalized volume. Pes calculated over 5 consecutives breaths differed with a maximum of 1 cm H2O compared to Pes calculated during a single inspiratory hold. The esophageal elastance was correlated with weight, age, and sex. The optimal balloon inflation volume was highly variable, which indicated the need for an individual calibration procedure. Pes was not overestimated when an inspiratory hold was not applied.

Straws Don't Suck: Are Straws Dangerous after Endoscopic Skull Base Surgery?

Objective Patients undergoing endoscopic endonasal surgery have historically been restricted from using straws postoperatively, due to the concern that this activity generates negative pressure. The objective of this study is to evaluate the pressure dynamics in the sinonasal cavity associated with the use of a straw. Methods Intracranial pressure catheters were placed in the nasal cavity of 20 healthy individuals. Pressure measurements were then recorded while participants drank liquids of different viscosities from a cup and from a straw. Measurements were recorded with and without subjects occluding their nose to simulate postoperative nasal obstruction. Results The average pressure in the nasal cavity while drinking water from a cup was -0.86 cmH 2 O, from a straw was -1.09 cmH 2 O, and while occluding the nose and using a straw was -0.81 cmH 2 O. The average pressure in the nasal cavity while drinking a milkshake from a cup was -0.98 cmH 2 O, from a straw was -1.88 cmH 2 O, and while occluding the nose and using a straw was -1.37 cmH 2 O. There was no statistically significant difference in pressure measurements when comparing either task or consistency ( p > 0.05). Conclusion Straw use is not associated with the generation of significant negative pressure in the nasal cavity. The pressure generated when drinking from a straw is not significantly different from that of drinking from a cup. This data suggest that straw use may be safe for patients following endoscopic skull base surgery, but further investigation is warranted.

Ankle joint contact loads and displacement in syndesmosis injuries repaired with Tightropes compared to screw fixation in a static model

BackgroundThe effect of syndesmotic fixation on restoration of pressure mechanics in the setting of a syndesmotic injury is largely unknown. The purpose of this study is to examine the contact mechanics of the tibiotalar joint following syndesmosis fixation with screws versus a flexible fixation device for complete syndesmotic injury. MethodsSix matched pairs of cadaveric below knee specimens were dissected and motion capture trackers were fixed to the tibia, fibula, and talus and a pressure sensor was placed in the tibiotalar joint. Each specimen was first tested intact with axial compressive load followed by external rotation while maintaining axial compression. Next, syndesmotic ligaments were sectioned and randomly assigned to repair with either two TightRopes® or two 3.5 mm cortical screws and the protocol was repeated. Mean contact pressure, peak pressure, reduction in contact area, translation of the center of pressure, and relative talar and fibular motion were calculated. Specimens were then cyclically loaded in external rotation and surviving specimens were loaded in external rotation to failure. ResultsNo differences in pressure measurements were observed between the intact and instrumented states during axial load. Mean contact presure relative to intact testing was increased in the screw group at 5 Nm and 7.5 Nm torque. Likewise, peak pressure was increased in the TightRope group at 7.5 Nm torque. There was no change in center of pressure in the TightRope group at any threshold; however, at every threshold tested there was significant medial and anterior translation in the screw group relative to the intact state. ConclusionEither screws or TightRope fixation is adequate with AL alone. With lower amounts of torque, the TightRope group appears to have contact and pressure mechanics that more closely match native mechanics.

Measuring gastrointestinal pH and pressure in cribbing and non-cribbing horses with a wireless gastrointestinal monitoring capsule

s / Journal of Equine Veterinary Science 33 (2013) 321-399 355 drum using a tapered element oscillating microbalance sampler (1400a; Thermo Fisher Scientific, Waltham MA). Instantaneous TSP concentrations were recorded every 60 sec for 30 min. Measurements were averaged over 30 minutes; and the average expressed on a weight (kg) basis. Differences between preand post-steaming dust concentrations were evaluated using PROC MIXED of SAS with P 0.05 considered significant. Initial dust content measurements were different between the two hays; 758 and 406 mg/m3 per kg DM for MM and LM, respectively (P 1⁄4 0.030). Steaming reduced the dust content of the MM hay to 345 mg/m3 per kg DM (P 1⁄4 0.043); however, dust content in the LM hay was not significantly affected by steaming (257 mg/ m3 per kg DM, P 1⁄4 0.445). Limited data is available regarding typical, or acceptable, concentrations of dust in feedstuffs commonly fed to horses. However, steaming of the MM hay reduced dustiness to levels comparable to the LM hay, whichwas considered an acceptable hay for horses. Additional research needs to determine acceptable levels of dust; until then, results from this study indicate that steaming represents a viable management strategy for reducing dustiness in hay containing elevated dust levels. Measuring gastrointestinal pH and pressure in cribbing and non-cribbing horses with a wireless gastrointestinal monitoring capsule C.A. McCall , P.J. Tyler , L.S. Riggs , and W.H. McElhenney 3 Department of Animal Sciences, Auburn University, Auburn, AL 36849, 2 Department of Electrical and Computer Engineering, Auburn University, Auburn, AL 36849, Department of Agricultural and Environmental Sciences, Tuskegee University, Tuskegee, AL 36088 Four mature geldings were used to evaluate differences in gastrointestinal pH and pressures in cribbing (n1⁄42) and non-cribbing horses (n1⁄42). Horses were maintained on pastures and brought into stalls 1 h prior to starting gastrointestinal monitoring. While on trial horses were given their usual concentrate ration and free-choice hayand water. A wireless gastrointestinal monitoring capsule (SmartPill Corp., Buffalo, New York 14203-1109), which recorded pH every 5 sec and pressure (mmHg) every 0.5 sec, was administered to each horse via nasogastric tube. A wireless receiver, enhanced to more easily capture capsule data signals through the horse’s bodymass, was attached to a flysheet worn by the horse. Data were recorded until the first of two outcomes occurred: 72 h passed or the capsule passed through the horse. One cribbing horse and one noncribbing horse were administered capsules on two separate occurrences to evaluate repeatability of measurements on different days. No discernible differences were found between days and these data were averaged to give one set of data points for each horse. A consistent pH change was used to determine capsule location within the gastrointestinal tract. Data were analyzed in a completely randomized design with treatments arranged as a 3X2 factorial with three gastrointestinal locations (stomach, small intestine, cecum/colon) and twobehavioral conditions (cribbing, noncribbing). Proc GLM analyses revealed no treatment differences (P>0.05) in pH or pressure in any gastrointestinal location for cribbing vs. non-cribbing horses. However, gastrointestinal locations did differ (P<0.005) in mean minimum pH (3.62 0.59, 6.77 0.46, and 6.13 0.46 for the stomach, small intestineandcecum/colon, respectively), median pH (4.47 0.53, 7.51 0.42 and 6.73 0.42 for the stomach small intestine and cecum/colon, respectively) and maximum pH (5.68 0.40, 7.98 0.32, 7.38 0.32 for the stomach, small intestine and cecum/colon, respectively) with the stomach consistently exhibiting lower pH values than the remainder of the tract. No significant differences were found between small intestinal pHmeasurements and that of the cecum/colon. No significant differences in pressure measurements were detected among the segments of the gastrointestinal tract. Because the gastrointestinal monitoring system was designed for human use, problems were encounteredwith its use in horses. Bodymass of these horses often prevented data capture, especially from the stomach and small intestine. Data capture was more successful in horses weighing under 500 kg. Also, on-board data receivers were not designed to withstand the punishment associated with equine use. Based on these results, a larger study is not warranted unless this system can be modified to accommodate a larger body mass.

The pressure effects of facemasks during noninvasive ventilation: a volunteer study

Noninvasive ventilation by facemask is commonly used for patients with respiratory failure. We evaluated the pressure exerted by two types of facemask on the faces of 12 healthy volunteers while they were being given different levels of continuous or bi-level positive airway pressure ventilation. The mean (SD) pressure recorded on the bridge of the nose was much higher than that on the cheek (nose: 65.8 (21.2) vs cheek 15.4 (7.2) mmHg, p < 0.0001). Progressive tightening of the harness and increasing of the volume of air in the facemask cushions increased the pressure on the bridge of the nose, and the effect of these two factors was additive. Some commercially available facemasks can produce substantial pressure on the bridge of the nose and this explains why pressure complications on the bridge of the nose are common during noninvasive ventilation.

Foot Pressure Measurement Differences Between Boys and Girls With Reference to Hallux Valgus Deformity and Hypermobility

Previous studies that compared foot pressures in boys and girls found that girls had greater peak pressures under the hallux than did boys. Only one of these studies considered plantar pressure measurements in children. The purpose of the study was to investigate the effect of gender on foot pressure measurements in children. This is a comparative study using the F-Scan pressure platform (F-Mat; Texscan Boston, MA) on a sample of children attending a podiatric clinic. Pressure measurements and temporal parameters were measured in 61 children between the ages of 5 and 16 years. Associations between joint hypermobility and hallux valgus angle also were investigated. Girls were found to have significantly greater peak pressure under the hallux, faster timing of heel contact to first metatarsal head loading, and a more medially placed center of pressure trajectory. No associations were found between these significant variables and hypermobility scores or hallux valgus angle. The results indicate that there are differences in pressure measurements between boys and girls, but the reasons for these remain unclear. Differences in pressure measurements in the feet of boys and girls may be useful in establishing the cause of foot pathologies for which a prevalence has been shown in boys or girls, such as hallux valgus deformity, which is known to be more frequent in females of all ages.

Direct Measurement of Intratracheal Pressure in Pediatric Respiratory Monitoring

We describe a method based on a Fabry-Perot interferometer at the tip of an optic fiber with a diameter of 0.25 mm for direct measurement of tracheal pressure in pediatric respiratory monitoring. The response time of the pressure transducer and its influence on the resistance of pediatric endotracheal tubes (internal diameter, 2.5 to 5 mm) during constant and dynamic flow at different ventilator settings in a lung model were measured. The transducer was positioned at -1.5 (inside), 0, and +1.5 cm (outside) relative to the tip of the endotracheal tube and compared with a reference pressure inside the trachea. The clinical application of the transducer was tested in five pediatric patients. The response time of the transducer was 1.3 ms. The influence of the fiberoptic transducer on tube resistance was negligible during constant flow in inspiratory and expiratory directions for all endotracheal tubes tested. There was no difference in pressure measurements with the transducer positioned at or 1.5 cm below or above the tip of the endotracheal tube during dynamic measurements. During clinical circumstances insertion of the fiberoptic transducer was easy, recordings were stable, and the safety of the patient was not jeopardized. The fiberoptic transducer provided a reliable and promising way of monitoring tracheal pressure in intubated pediatric patients. The presence of the probe did not interfere with either pressure-flow relationship or patient care and safety. The technique is proposed for monitoring of respiratory mechanics and calculation of changes in tube resistance caused by kinking and secretions.