A numerical investigation on the visco-plastic response of structures to different pulse loading shapes

The time varying intensity character of a load applied to a structure poses many difficulties in analysis. A remedy to this situation is to substitute a complex pulse shape by a rectangular equivalent one. It has been shown by others that this procedure works well for perfectly plastic elementary structures. This paper applies the concept of equivalent pulse to more complex structures. Special attention is given to the material behavior, which is allowed to be strain rate and strain hardening sensitive. Thanks to the explicit finite element solution, it is shown in this article that blast loads applied to complex structures made of real materials can be substituted by equivalent rectangular loads with both responses being practically the same. (c) 2007 Elsevier Ltd. All rights reserved.

Effects of carbon dioxide feeding rate and light intensity on the fed-batch pulse-feeding cultivation of Spirulina platensis in helical photobioreactor

The behavior of S. platensis was investigated in this study through fed-batch pulse-feeding cultures performed at different carbon dioxide feeding rates (F = 0.44-1.03 g L-1 d(-1)) and photosynthetic photon flux density (PPFD = 80-250 mu mol photons m(-2) s(-1)) in a bench-scale helical photobioreactor. To achieve this purpose, an inorganic medium lacking the carbon source was enriched by gaseous carbon dioxide from a cylinder. The maximum cell concentration achieved was 12.8 g L-1 at PPFD = 166 mu mol photons m(-2) s(-1) and F= 0.44 g L-1 d(-1) of CO2. At PPFD = 80 and 125 mu mol photons m(-2) s(-1), the carbon utilization efficiency (CUE) reached maximum values of 50 and 69%, respectively, after about 20 days, and then it decreased, thus highlighting a photolimitation effect. At PPFD = 166 mu mol photons m(-2) s(-1), CUE was >= 90% between 20 and 50 days. The photosynthetic efficiency reached its maximum value (9.4%) at PPFD = 125 mu mol photons m(-2) s(-1). The photoinhibition threshold appeared to strongly depend on the feeding rate: at high PPFD, an increase in the amount of fed CO2 delayed the inhibitory effect on biomass growth, whereas at low PPFD, excess CO2 addition caused the microalga to stop growing. (c) 2007 Elsevier B.V. All rights reserved.

Correlation between macular and retinal nerve fibre layer Fourier-domain OCT measurements and visual field loss in chiasmal compression

Purpose The aim of this study was to test the correlation between Fourier-domain (FD) optical coherence tomography (OCT) macular and retinal nerve fibre layer (RNFL) thickness and visual field (VF) loss on standard automated perimetry (SAP) in chiasmal compression. Methods A total of 35 eyes with permanent temporal VF defects and 35 controls underwent SAP and FD-OCT (3D OCT-1000; Topcon Corp.) examinations. Macular thickness measurements were averaged for the central area and for each quadrant and half of that area, whereas RNFL thickness was determined for six sectors around the optic disc. VF loss was estimated in six sectors of the VF and in the central 16 test points in the VF. The correlation between VF loss and OCT measurements was tested with Spearman`s correlation coefficients and with linear regression analysis. Results Macular and RNFL thickness parameters correlated strongly with SAP VF loss. Correlations were generally stronger between VF loss and quadrantic or hemianopic macular thickness than with sectoral RNFL thickness. For the macular parameters, we observed the strongest correlation between macular thickness in the inferonasal quadrant and VF loss in the superior temporal central quadrant (rho=0.78; P<0.001) whereas for the RNFL parameters the strongest correlation was observed between the superonasal optic disc sector and the central temporal VF defect (rho=0.60; P<0.001).

Online monitoring of pulse pressure variation to guide fluid therapy after cardiac surgery

BACKGROUND: The arterial pulse pressure variation induced by mechanical ventilation (Delta PP) has been shown to be a predictor of fluid responsiveness. Until now, Delta PP has had to be calculated offline (from a computer recording or a paper printing of the arterial pressure curve), or to be derived from specific cardiac output monitors, limiting the widespread use of this parameter. Recently, a method has been developed for the automatic calculation and real-time monitoring of Delta PP using standard bedside monitors. Whether this method is to predict reliable predictor of fluid responsiveness remains to be determined. METHODS: We conducted a prospective clinical study in 59 mechanically ventilated patients in the postoperative period of cardiac surgery. Patients studied were considered at low risk for complications related to fluid administration (pulmonary artery occlusion pressure <20 mm Hg, left ventricular ejection fraction >= 40%). All patients were instrumented with an arterial line and a pulmonary artery catheter. Cardiac filling pressures and cardiac output were measured before and after intravascular fluid administration (20 mL/kg of lactated Ringer`s solution over 20 min), whereas Delta PP was automatically calculated and continuously monitored. RESULTS: Fluid administration increased cardiac output by at least 15% in 39 patients (66% = responders). Before fluid administration, responders and nonresponders were comparable with regard to right atrial and pulmonary artery occlusion pressures. In contrast, Delta PP was significantly greater in responders than in nonresponders, (17% +/- 3% vs 9% +/- 2%, P < 0.001). The Delta PP cut-off value of 12% allowed identification of responders with a sensitivity of 97% and a specificity of 95%. CONCLUSION: Automatic real-time monitoring of Delta PP is possible using a standard bedside rnonitor and was found to be a reliable method to predict fluid responsiveness after cardiac surgery. Additional studies are needed to determine if this technique can be used to avoid the complications of fluid administration in high-risk patients.

Arterial pulse pressure variation predicting fluid responsiveness in critically ill patients (Retracted article. See vol. 31, pg. 542, 2009)

In critically ill patients, it is important to predict which patients will have their systemic blood flow increased in response to volume expansion to avoid undesired hypovolemia and fluid overloading. Static parameters such as the central venous pressure, the pulmonary arterial occlusion pressure, and the left ventricular end-diastolic dimension cannot accurately discriminate between responders and nonresponders to a fluid challenge. In this regard, respiratory-induced changes in arterial pulse pressure have been demonstrated to accurately predict preload responsiveness in mechanically ventilated patients. Some experimental and clinical studies confirm the usefulness of arterial pulse pressure as a useful tool to guide fluid therapy in critically ill patients.

A Comparison Between Pulse Pressure Variation and Right End Diastolic Volume Index as Guides to Resuscitation in a Model of Hemorrhagic Shock in Pigs

Background: Different hemodynamic parameters including static indicators of cardiac preload as right ventricular end-diastolic volume index (RVEDVI) and dynamic parameters as pulse pressure variation (PPV) have been used in the decision-making process regarding volume expansion in critically ill patients. The objective of this study was to compare fluid resuscitation guided by either PPV or RVEDVI after experimentally induced hemorrhagic shock. Methods: Twenty-six anesthetized and mechanically ventilated pigs were allocated into control (group I), PPV (group II), or RVEDVI (group III) group. Hemorrhagic shock was induced by blood withdrawal to target mean arterial pressure of 40 mm Hg, maintained for 60 minutes. Parameters were measured at baseline, time of shock, 60 minutes after shock, immediately after resuscitation with hydroxyethyl starch 6% (130/0.4), 1 hour and 2 hours thereafter. The endpoint of fluid resuscitation was determined as the baseline values of PPV and RVEDVI. Statistical analysis of data was based on analysis of variance for repeated measures followed by the Bonferroni test (p < 0.05). Results: Volume and time to resuscitation were higher in group III than in group II (group III = 1,305 +/- 331 mL and group II = 965 +/- 245 mL, p < 0.05; and group III = 24.8 +/- 4.7 minutes and group II = 8.8 +/- 1.3 minutes, p < 0.05, respectively). All static and dynamic parameters and biomarkers of tissue oxygenation were affected by hemorrhagic shock and nearly all parameters were restored after resuscitation in both groups. Conclusion: In the proposed model of hemorrhagic shock, resuscitation to the established endpoints was achieved within a smaller amount of time and with less volume when guided by PPV than when guided by pulmonary artery catheter-derived RVEDVI.

Lack of Circadian Variation of Pulse Wave Velocity Measurements in Healthy Volunteers

Arterial stiffness is an independent marker of cardiovascular events. Pulse wave velocity (PWV) is a validated method to detect arterial stiffness that can be influenced by several factors including age and blood pressure. However, it is not clear whether PWV could be influenced by circadian variations. In the present study, the authors measured blood pressure and carotid-femoral PWV measurements in 15 young healthy volunteers in 4 distinct periods: 8 am, noon, 4 pm, and 8 pm. No significant variations of systolic (P=.92), mean (P=.77), and diastolic (P=.66) blood pressure among 8 am (113 +/- 15, 84 +/- 8, 69 +/- 6 mm Hg), noon (114 +/- 13, 83 +/- 8, 68 +/- 6 mm Hg), 4 pm (114 +/- 13, 85 +/- 8, 70 +/- 7 mm Hg), and 8 pm (113 +/- 7, 83 +/- 10, 68 +/- 7 mm Hg), respectively, were observed. Similarly, carotid-femoral PWV did not change among the periods (8 am: 7.6 +/- 1.4 m/s, noon: 7.4 +/- 1.1 m/s, 4 pm: 7.6 +/- 1.0 m/s, 8 pm, 7.6 +/- 1.3 m/s; P=.85). Considering all measurements, mean blood pressure significantly correlated with PWV (r=.31; P=.016). In young healthy volunteers, there is no significant circadian variation of carotid-femoral PWV. These findings support the concept that it does not appear mandatory to perform PWV measurements at exactly the same period of the day. J Clin Hypertens (Greenwich). 2011;13:19-22. (c) 2010 Wiley Periodicals, Inc.

Relationship between Optical Coherence Tomography, Pattern Electroretinogram and Automated Perimetry in Eyes with Temporal Hemianopia from Chiasmal Compression

PURPOSE. To evaluate the relationship between pattern electroretinogram (PERG) amplitude, macular and retinal nerve fiber layer (RNFL) thickness by optical coherence tomography (OCT), and visual field (VF) loss on standard automated perimetry (SAP) in eyes with temporal hemianopia from chiasmal compression. METHODS. Forty-one eyes from 41 patients with permanent temporal VF defects from chiasmal compression and 41 healthy subjects underwent transient full-field and hemifield (temporal or nasal) stimulation PERG, SAP and time domain-OCT macular and RNFL thickness measurements. Comparisons were made using Student`s t-test. Deviation from normal VF sensitivity for the central 18 of VF was expressed in 1/Lambert units. Correlations between measurements were verified by linear regression analysis. RESULTS. PERG and OCT measurements were significantly lower in eyes with temporal hemianopia than in normal eyes. A significant correlation was found between VF sensitivity loss and fullfield or nasal, but not temporal, hemifield PERG amplitude. Likewise a significant correlation was found between VF sensitivity loss and most OCT parameters. No significant correlation was observed between OCT and PERG parameters, except for nasal hemifield amplitude. A significant correlation was observed between several macular and RNFL thickness parameters. CONCLUSIONS. In patients with chiasmal compression, PERG amplitude and OCT thickness measurements were significant related to VF loss, but not to each other. OCT and PERG quantify neuronal loss differently, but both technologies are useful in understanding structure-function relationship in patients with chiasmal compression. (ClinicalTrials.gov number, NCT00553761.) (Invest Ophthalmol Vis Sci. 2009; 50: 3535-3541) DOI:10.1167/iovs.08-3093

Comparative study of pressure- and volume-controlled ventilation on pulse pressure variation in a model of hypovolaemia in rabbits

Background and objective: Dynamic indices represented by systolic pressure variation and pulse pressure variation have been demonstrated to be more accurate than filling pressures in predicting fluid responsiveness. However, the literature is scarce concerning the impact of different ventilatory modes on these indices. We hypothesized that systolic pressure variation or pulse pressure variation could be affected differently by volume-controlled ventilation and pressure-controlled ventilation in an experimental model, during normovolaemia and hypovolaemia. Method: Thirty-two anaesthetized rabbits were randomly allocated into four groups according to ventilatory modality and volaemic status where G1-ConPCV was the pressure-controlled ventilation control group, G2-HemPCV was associated with haemorrhage, G3-ConVCV was the volume-controlled ventilation control group and G4-HemVCV was associated with haemorrhage. In the haemorrhage groups, blood was removed in two stages: 15% of the estimated blood volume withdrawal at M1, and, 30 min later, an additional 15% at M2. Data were submitted to analysis of variance for repeated measures; a value of P < 0.05 was considered to be statistically significant. Results: At MO (baseline), no significant differences were observed among groups. At M1, dynamic parameters differed significantly among the control and hypovolaemic groups (P < 0.05) but not between ventilation modes. However, when 30% of the estimated blood volume was removed (M2), dynamic parameters became significantly higher in animals under volume-controlled ventilation when compared with those under pressure-controlled ventilation. Conclusions: Under normovolaemia and moderate haemorrhage, dynamic parameters were not influenced by either ventilatory modalities. However, in the second stage of haemorrhage (30%), animals in volume-controlled ventilation presented higher values of systolic pressure variation and pulse pressure variation when compared with those submitted to pressure-controlled ventilation.

Differential expression of osteoblast and osteoclast chemmoatractants in compression and tension sides during orthodontic movement

Orthodontic tooth movement is achieved by the remodeling of alveolar bone in response to mechanical loading, and is supposed to be mediated by several host mediators, such as chemokines. In this study we investigated the pattern of mRNAs expression encoding for osteoblast and osteoclast related chemokines, and further correlated them with the profile of bone remodeling markers in palatal and buccal sides of tooth under orthodontic force, where tensile (T) and compressive (C) forces, respectively, predominate. Real-time PCR was performed with periodontal ligament mRNA from samples of T and C sides of human teeth submitted to rapid maxillary expansion, while periodontal ligament of normal teeth were used as controls. Results showed that both T and C sides exhibited significant higher expression of all targets when compared to controls. Comparing C and T sides, C side exhibited higher expression of MCP-1/CCL2, MIP-1 alpha/CCL3 and RANKL, while T side presented higher expression of OCN. The expression of RANTES/CCL5 and SDF-1/CXCL12 was similar in C and T sides. Our data demonstrate a differential expression of chemokines in compressed and stretched PDL during orthodontic tooth movement, suggesting that chemokines pattern may contribute to the differential bone remodeling in response to orthodontic force through the establishment of distinct microenvironments in compression and tension sides. (C) 2008 Elsevier Ltd. All rights reserved.

Lower Extremities Magnetic Resonance Angiography With Blood Pressure Cuff Compression: Quantitative Dynamic Analysis

Purpose: To quantitatively evaluate changes induced by the application of a femoral blood-pressure cuff (BPC) on run-off magnetic resonance angiography (MRA). which is a method generally previously proposed to reduce venous contamination in the leg. Materials and Methods: This study was Health Insurance Portability and Accountability Act (HIPAA)- and Institutional Review Board (IRB)-compliant, We used time-resolved gradient-echo gadolinium (Gd)-enhanced MRA to measure BPC effects on arterial, venous, and soft-tissue enhancement. Seven healthy volunteers (six men) were studied with the BPC applied at the mid-femoral level unilaterally using a 1.5T MR system after intravenous injection of Gd-BOPTA. Different statistical tools were used such as the Wilcoxon signed rank test and a cubic smoothing spline fit. Results: We found that BPC application induces delayed venous filling (as previously described), but also induces significant decreases in arterial inflow, arterial enhancement, vascular-soft tissue contrast, and delayed peak enhancement (which have not been previously measured). Conclusion: The potential benefits from using a BPC for run-off MRA must be balanced against the potential pitfalls, elucidated by our findings.

Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of 3-Hole 4.5 mm locking compression plate and 3-hole 4.5 mm narrow dynamic compression plate, with two transarticular 5.5 mm cortex screws

Objectives To compare the biomechanical characteristics of 2 arthrodesis techniques for the equine proximal interphalangeal joint (PIP) using either a 3-hole 4.5 mm locking compression plate (LCP) or 3-hole 4.5 mm narrow dynamic compression plate (DCP), both with 2 transarticular 5.5 mm cortex screws. Study Design Experimental. Sample Population Cadaveric adult equine forelimbs (*n=6 pairs). Methods For each forelimb pair, 1 limb was randomly assigned to 1 of 2 treatment groups and the contralateral limb by default to the other treatment group. Construct stiffness, gap formation across the PIP joint, and rotation about the PIP joint were determined for each construct before cyclic axial loading and after each of four, 5000 cycle loading regimens. After the 20,000 cycle axial loading regimen, each construct was loaded to failure. Results There were no significant differences in construct stiffness, gap formation, or sagittal plane rotation between the LCP and DCP treatment groups at any of the measured time points. Conclusion Biomechanically, fixation of the equine PIP joint with a 3-hole 4.5 mm LCP is equivalent to fixation with a 3-hole 4.5 mm narrow DCP under the test conditions used.

The influence of erbium:yttrium-aluminum-garnet laser ablation with variable pulse width on morphology and microleakage of composite restorations

The objective of this study was to evaluate the influence of various pulse widths with different energy parameters of erbium:yttrium-aluminum-garnet (Er:YAG) laser (2.94 mu m) on the morphology and microleakage of cavities restored with composite resin. Identically sized class V cavities were prepared on the buccal surfaces of 54 bovine teeth by high-speed drill (n = 6, control, group 1) and prepared by Er:YAG laser (Fidelis 320A, Fotona, Slovenia) with irradiation parameters of 350 mJ/ 4 Hz or 400 mJ/2 Hz and pulse width: group 2, very short pulse (VSP); group 3, short pulse (SP); group 4, long pulse (LP); group 5, very long pulse (VLP). All cavities were filled with composite resin (Z-250-3 M), stored at 37A degrees C in distilled water, polished after 24 h, and thermally stressed (700 cycles/5-55A degrees C). The teeth were impermeabilized, immersed in 50% silver nitrate solution for 8 h, sectioned longitudinally, and exposed to Photoflood light for 10 min to reveal the stain. The leakage was evaluated under stereomicroscope by three different examiners, in a double-blind fashion, and scored (0-3). The results were analyzed by Kruskal-Wallis test (P > 0.05) and showed that there was no significant differences between the groups tested. Under scanning electron microscopy (SEM) the morphology of the cavities prepared by laser showed irregular enamel margins and dentin internal walls, and a more conservative pattern than that of conventional cavities. The different power settings and pulse widths of Er:YAG laser in cavity preparation had no influence on microleakage of composite resin restorations.

Pulp Vitality in Patients with Intraoral and Oropharyngeal Malignant Tumors Undergoing Radiation Therapy Assessed by Pulse Oximetry

Introduction: The aim of this study was to evaluate pulp oxygenation levels (%SpO(2)) in patients with malignant intraoral and oropharyngeal tumors treated by radiotherapy (RT). Methods: Pulp oxygenation levels were measured by pulse oximetry. Twenty patients were selected, and two teeth of each participant (n = 40) were analyzed, regardless of the quadrant and the area irradiated, at four different time points: TP1, before RI; TP2, at the beginning of RI with radiation doses between 30 and 35 Gy; TP3, at the end of RI with radiation dose! between 60 and 70 Gy; and TP4, 4 to 5 months after the beginning of cancer treatment. Results: Mean %SpO(2) at the different time points were 93% (TP1), 83% (TP2), 77% (TP3), and 85% (TP4). The Student`s t test showed statistically significant differences between TP1 and TP2 (P < .01), TP3 (P <.01), and TP4 (P <.01). TP3 was also statistically significantly different when compared with TP2 (P <.01) and TP4 (P <.01). No statistically significant difference could be observed between TP2 and TP4. Conclusion`s: Because the mean %SpO(2) before RI was greater than during and after therapy and values obtained 4 to 5 months after the beginning of RI were close to the initiation of RI, pulp tissue may be able to regain normal blood flow after RT. If the changes in the microcirculation of the dental pulp were indeed transitory, preventive endodontic treatment or extraction in patients who are currently undergoing or recently received RI and who show negative signs of pulp sensitivity may rot be necessary for pulpal reasons. (J Endod 2011;37:1197-1200)

Determination of pulp vitality in vivo with pulse oximetry

Aim To evaluate the use of pulse oximetry as a test for pulp vitality, by comparing in the same patient, the levels of oxygen saturation of the index finger and of the maxillary central incisor and canine teeth without clinically detectable pulp inflammation. Methodology Seventeen male and female patients aged between 26 and 38 years participated and a total of 32 maxillary central incisor and 32 canine teeth were analysed. Selection criteria required the teeth to have healthy crowns, or with restorations no more than 2 mm in diameter and no clinical and radiographical signs or symptoms of pulp or periapical inflammatory changes. The negative control group consisted of 10 root filled teeth. Measurements were first taken from the index finger of patients. Their teeth were then subjected to a thermal test with refrigerant gas and then to a vitality test with pulse oximetry. Data were analysed by Pearson`s and paired t-tests. Results There were no significant statistical correlations between blood oxygen levels in the index finger and in the teeth of the patient (P > 0.05). There was a statistically significant difference in the oxygen levels between the two tooth groups studied and the index finger (P <= 0.002). Mean oxygen values in the index finger of patients were 95% (SD = 1.6), oxygen values in the maxillary central incisor were 91.29% (SD = 2.61) and mean oxygen values in maxillary canine were 90.69% (SD = 2.71). Conclusion The method determined consistently the level of blood oxygen saturation of the pulp in maxillary central incisor and canine teeth and can therefore be used for pulp vitality testing. Further studies are required to assess the effectiveness and validity of pulse oximetry in determining pulp vitality in traumatized teeth.