Gas permeability: a new quantitative method to assess endodontic leakage

Abstract Aim: The aim of this study was to evaluate a new endodontic leakage measurement method. Materials and methods: Permeability was assessed measuring the gas flow passing through the root. Positive and negative tests were carried out to assess the validity of the method. We used glass capillaries for calibration (diameters of 15, 30, 40, 50 and 75 mum). The applicability of the method was assessed with human teeth using three sealing methods: GuttaFlow (GF) and a single cone; Pulp Canal Sealer (PCS) and a single cone; PCS and system B. Results: This method demonstrated to be highly reproducible as the standard deviation was approximately 1% on average with glass capillaries. Significantly higher leakage (p<0.05) was recorded for endodontic treatment with GF and single cone compared to PCS and single cone and PCS with system B. Conclusion: Gas permeability is quantitative, sensitive, non-destructive and reproducible and seems appropriate for endodontic tests. It would participate in the indirect comprehension of leakage phenomena.     

Wall thickness referenced to myocardial volume: a new noninvasive framework for cardiac mechanics.

Dimensional variables measured for study of left ventricular mechanics are subject to errors arising from difficulty in determining zero-stress dimensions for use as a reference. Based on a method validated for measurements within individuals, we have devised an approach that facilitates comparison between individuals while minimizing random scatter. We define an exact mathematical index of strain, ln(h(0)/h), using wall thickness (h) referenced to extrapolated wall thickness at zero-luminal volume (h(0)). Noninvasive data from rabbits, pigs, and humans all yielded highly similar myocardial stress, ln(h(0)/h), and work values. The stress-ln(h(0)/h) relationship during afterload variation was constant among individual pigs with a twofold variation in ventricular mass. Stress-ln(h(0)/h) data from our analysis displayed lower scatter than either pressure-volume data normalized to myocardial mass or stress-ln(h(0)/h) data referenced to end-diastolic dimensions. A Frank-Starling-like curve with high correlation (r(2) = 0.96) was constructed from single points from different pigs, suggesting a low level of size and intersubject scatter. This method offers high precision for noninvasive characterization of ventricular and myocardial mechanics and for comparisons between subjects and between species.     

Expiratory muscle contribution to tidal volume in head-up dogs

A change from the supine to the head-up posture in anesthetized dogs elicits increased phasic expiratory activation of the rib cage and abdominal expiratory muscles. However, when this postural change is produced over a 4- to 5-s period, there is an initial apnea during which all the muscles are silent. In the present studies, we have taken advantage of this initial silence to determine functional residual capacity (FRC) and measure the subsequent change in end-expiratory lung volume. Eight animals were studied, and in all of them end-expiratory lung volume in the head-up posture decreased relative to FRC [329 +/- 70 (SE) ml]. Because this decrease also represents the increase in lung volume as a result of expiratory muscle relaxation at the end of the expiratory pause, it can be used to determine the expiratory muscle contribution to tidal volume (VT). The average contribution was 62 +/- 6% VT. After denervation of the rib cage expiratory muscles, the reduction in end-expiratory lung volume still amounted to 273 +/- 84 ml (49 +/- 10% VT). Thus, in head-up dogs, about two-thirds of VT result from the action of the expiratory muscles, and most of it (83%) is due to the action of the abdominal rather than the rib cage expiratory muscles.     

High-frequency oscillatory ventilation in neonatal RDS: initial volume optimization and respiratory mechanics

To determine whetherinitial lung volume optimization influences respiratory mechanics,which could indicate the achievement of optimal volume, we studied 17 premature infants with respiratory distress syndrome (RDS) assisted byhigh-frequency oscillatory ventilation. The continuous distendingpressure (CDP) was increased stepwise from 6-8 cmH₂Oup to optimal CDP (OCDP), i.e., that allowing good oxygenation with thelowest inspired O₂ fraction. Respiratory systemcompliance (Crs) and resistance were concomitantlymeasured. Mean OCDP was 16.5 ± 1.2 cmH₂O. InspiredO₂ fraction could be reduced from an initial level of 0.73 ± 0.17 to 0.33 ± 0.07. However, Crs (0.45 ± 0.14ml · cmH₂O¹ · kg¹at starting CDP point) remained unchanged through lung volume optimization but appeared inversely related to OCDP. Similarly, respiratory system resistance was not affected. We conclude that thereis a marked dissociation between oxygenation improvement and Crsprofile during the initial phase of lung recruitment by earlyhigh-frequency oscillatory ventilation in infants with RDS. Thusoptimal lung volume cannot be defined by serial Crs measurement. At themost, low initial Crs suggests that higher CDP will be needed.

     

Chest wall and respiratory system mechanics in cats: effects of flow and volume

The effects of inspiratory flow rate and inflation volume on the resistive properties of the chest wall were investigated in six anesthetized paralyzed cats by use of the technique of rapid airway occlusion during constant flow inflation. This allowed measurement of the intrinsic resistance (Rw,min) and overall dynamic inspiratory impedance (Rw,max), which includes the additional pressure losses due to time constant inequalities within the chest wall tissues and/or stress adaptation. These results, together with our previous data pertaining to the lung (Kochi et al., J. Appl. Physiol. 64: 441-450, 1988), allowed us to determine Rmin and Rmax of the total respiratory system (rs). We observed that 1) Rw,max and Rrs,max exhibited marked frequency dependence; 2) Rw,min was independent of flow (V) and inspired volume (delta V), whereas Rrs,min increased linearly with V and decreased with increasing delta V; 3) Rw,max decreased with increasing V, whereas Rrs,max exhibited a minimum value at a flow rate substantially higher than the resting range of V; 4) both Rw,max and Rrs,max increased with increasing delta V. We conclude that during resting breathing, flow resistance of the chest wall and total respiratory system, as conventionally measured, includes a significant component reflecting time constant inequalities and/or stress adaptation phenomena.     

Umbilical cord clamping and preterm infants: a randomised trial.

OBJECTIVE--To investigate the clinical effects of regulating umbilical cord clamping in preterm infants. DESIGN--A prospective randomised study. SETTING--The Queen Mother''s Hospital, Glasgow. SUBJECTS--36 vaginally delivered infants over 27 and under 33 weeks'' gestation. INTERVENTION--Holding the infant 20 cm below the introitus for 30 seconds before clamping the umbilical cord ("regulated" group, 17 patients), or conventional management ("random" group, 19 patients). MAIN OUTCOME MEASURES--Initial packed cell volume, peak serum bilirubin concentrations, red cell transfusion requirements, and respiratory impairment (assessed by ventilatory requirements, arterial-alveolar oxygen tension ratio over the first day in ventilated infants, and duration of dependence on supplemental oxygen). RESULTS--There were statistically significant differences between the two groups in mean initial packed cell volume (regulated group 0.564, random group 0.509) and median red cell transfusion requirements (regulated group zero, random group 23 ml/kg). 13 infants from each group underwent mechanical ventilation and showed significant differences in mean minimum arterial-alveolar oxygen tension ratio on the first day (regulated group 0.42, random group 0.22) and in median duration of dependence on supplemental oxygen (regulated group three days, random group 10 days). Differences in final outcome measures such as duration of supplemental oxygen dependence and red cell transfusion requirements were mediated primarily through arterial-alveolar oxygen tension ratio and also packed cell volume. CONCLUSIONS--This intervention at preterm deliveries produces clinical and economic benefits.     

The respiratory change in preejection period: a new method to predict fluid responsiveness.

The accuracy and clinical utility of preload indexes as bedside indicators of fluid responsiveness in patients after cardiac surgery is controversial. This study evaluates whether respiratory changes (Delta) in the preejection period (PEP; DeltaPEP) predict fluid responsiveness in mechanically ventilated patients. Sixteen postcoronary artery bypass surgery patients, deeply sedated under mechanical ventilation, were enrolled. PEP was defined as the time interval between the beginning of the Q wave on the electrocardiogram and the upstroke of the radial arterial pressure. DeltaPEP (%) was defined as the difference between expiratory and inspiratory PEP measured over one respiratory cycle. We also measured cardiac output, stroke volume index, right atrial pressure, pulmonary arterial occlusion pressure, respiratory change in pulse pressure, systolic pressure variation, and the Deltadown component of SPV. Data were measured without positive end-expiratory pressure (PEEP) and after application of a PEEP of 10 cmH2O (PEEP10). When PEEP10 induced a decrease of >15% in mean arterial pressure value, then measurements were re-performed before and after volume expansion. Volume loading was done in eight patients. Right atrial pressure and pulmonary arterial occlusion pressure before volume expansion did not correlate with the change in stroke volume index after the fluid challenge. Systolic pressure variation, DeltaPEP, Deltadown, and change in pulse pressure before volume expansion correlated with stroke volume index change after fluid challenge (r2 = 0.52, 0.57, 0.68, and 0.83, respectively). In deeply sedated, mechanically ventilated patients after cardiac surgery, DeltaPEP, a new method, can be used to predict fluid responsiveness and hemodynamic response to PEEP10.     

基于系统演化视角的可持续性评价方法

可持续发展水平的衡量是可持续发展研究的重要内容,它可以为政府的可持续发展决策提供重要的科学依据。现有的可持续性评价方法可分为指标列举法、流量分析法和系统分析法。前两类方法应用广泛,但理论基础较为薄弱,在指标的选取、标准化和赋权等方面存在一定的缺陷。基于系统运行机理的系统分析法尚不多见,但能弥补前两种方法的部分不足,Ulanowicz于2009年提出的演化模型是此类方法的代表。该模型从系统演化角度出发,以网络流为研究对象,以信息论为手段,指出系统的可持续性是系统上升性(效率)和恢复力平衡的结果,并提出了可持续性评价指标R。回顾了现有研究方法的优缺点。介绍了从演化视角分析可持续性的原理和数学模型,可持续发展的阈值范围以及该方法的应用案例。总结了该方法的应用步骤及尚需解决的问题。     

Evaluation of an accelerometer to assess knee mechanics during a drop landing

Non-contact anterior cruciate ligament (ACL) injuries account for 70% of all ACL injuries, and can lead to missed time from activity for athletes and a predisposition for knee osteoarthritis. Prior research has shown that athletes who land in a stiff manner, with larger internal knee adduction and extension moments, are at greater risk for an ACL injury. A three-dimensional accelerometer placed at the tibial tuberosity may prove to be a low-cost means of assessing these risk factors. The primary purpose of this study was to compare tibial accelerations during drop landings with kinematic and kinetic risk factors for ACL injury measured with three-dimensional motion capture. The secondary purpose of this study was to compare these measures between soft and stiff landings. Participants were instructed to land bilaterally in preferred, soft, and stiff manners. Peak knee flexion decreased significantly from soft to stiff landings. Peak internal knee extension moment, peak anterior/posterior knee acceleration, and peak medial knee acceleration all increased significantly from soft to stiff landings. No associations were found between landing condition and either frontal plane knee angle at maximum vertical ground reaction force or peak internal knee adduction moment. Significant positive associations between kinetics and accelerations were found only in the sagittal plane. As such, while a three-dimensional accelerometer could discern between soft and stiff landings in both planes, it may be better suited to predict kinetic risk factors in the sagittal plane.     

The evolution of function: a new method to assess the phylogenetic value of ribosomal sensitivity to antibiotics.

Thirty-five archaeal, bacterial and eukaryotic translational systems have been proved against forty different protein synthesis inhibitors with diverse domain and functional specificities. The inhibition curves generated in every ribosome-antibiotic combination had previously shown interesting similarities among organisms belonging to the same phylogenetic group. This opened the possibility of using such functional information for developing evolutionary studies. A new mathematical method based on the main data components analysis has been developed to extract most of the information contained in the inhibition curves. The phenograms obtained closely resemble those generated by the small ribosomal subunit rRNA sequence comparison and such functional clustering is also congruent when a particular subset of organisms and/or antibiotics is used. These results prove the phylogenetic value of our functional analysis and suggest that the ribosome represents an interesting intersection between genotypic and phenotypic (functional) information stored in organisms.     

A new method to assess air pollution using lichens as bioindicators

Lichens are increasingly used worldwide as air quality biomonitors because they are efficient, easy and cheap, but validation studies of the methodology are scarce. Three foliose lichen biomonitoring methods were compared by field tests (in the tropical urban habitat of San José, Costa Rica) and laboratory simulations: (1) the 100 uniform squares template traditionally used in North America, (2) the European 200 uniform points template and (3) a new computer-generated random points template (10 x 20 cm) in two versions: 100 points and 50 points. Repeated measurement by the same observer causes a variation of 2-14% and the templates' error is 0.2-11%. We recommend the 100 random point template (applied to four sides of trunk) for ecological studies and the 50 random points template (applied to side with greatest lichen cover) for biomonitoring because it reduces time and costs by nearly 50% but still has acceptable reliability values.     

Bacterial clearance rate and a new differential hemocyte staining method to assess immunostimulant activity in shrimp

New methods were developed to assess immunostimulant efficacy in the black tiger shrimp Penaeus monodon. Test shrimp were fed with 2 or 4 % yeast extract (YE)-coated feed while controls were fed non-coated feed. After 4 wk of feeding, individual shrimp were assessed for total hemocyte counts (THC), the number of granular hemocytes (GH) and rate of bacterial clearance. For hemocyte counts, formalin-fixed hemolymph was stained with 1.2 % Rose Bengal in 50 % ethanol for 20 min at room temperature. Some of this mixture was used for THC with a hemocytometer while some was smeared on a microscope slide and left to dry before counterstaining with hematoxylin for GH counts. By this technique, high quality smears were obtained for accurate differential counts. Bacterial clearance assays were used to assess the sum effect of humoral and cellular defense mechanisms. Vibrio harveyi was injected intramuscularly at 1 x 10(8) cells per shrimp and hemolymph was collected in anticoagulant at 0, 15, 30 and 60 min post-injection for quadruplicate drop counts (20 microl) on TCBS agar. Total hemocyte counts for shrimp fed with 4 % YE were significantly higher (p < 0.05) than those for shrimp fed with non-coated feed. The percentage of granular cells and the rates of bacterial clearance for the YE-fed shrimp were higher than those for shrimp fed the control diet. These 2 methods provide a simple and rapid comparison of shrimp groups for differences in anti-bacterial defense capacity.     

Effect of changes in lung volume on respiratory system compliance in newborn infants

Total respiratory system compliance (Crs) at volumes above the tidal volume (VT) was studied by use of the expiratory volume clamping (EVC) technique in 10 healthy sleeping unsedated newborn infants. Flow was measured with a pneumotachograph attached to a face mask and integrated to yield volume. Volume changes were confirmed by respiratory inductance plethysmography. Crs measured by EVC was compared with Crs during tidal breathing determined by the passive flow-volume (PFV) technique. Volume increases of approximately 75% VT were achieved with three to eight inspiratory efforts during expiratory occlusions. Crs above VT was consistently greater than during tidal breathing (P less than 0.0005). This increase in Crs likely reflects recruitment of lung units that are closed or atelectatic in the VT range. Within the VT range, Crs measured by PFV was compared with that obtained by the multiple-occlusion method (MO). PFV yielded greater values of Crs than MO (P less than 0.01). This may be due to braking of expiratory airflow after the release of an occlusion or nonlinearity of Crs. Thus both volume recruitment and airflow retardation may affect the measurement of Crs in unsedated newborn infants.     

Effects of early dexamethasone therapy on pulmonary fibrogenic mediators and respiratory mechanics in preterm infants

Corticosteroid administration may prevent chronic lung disease in premature newborns, perhaps by modulating the synthesis of various cytokines, including those involved in fibrogenic processes. This study analyses the levels of three fibrogenic cytokines, namely vascular endothelial growth factor, transforming growth factor-beta 1 and basic fibroblast growth factor in tracheobronchial aspirate fluids collected from 20 premature newborns randomly assigned to the early dexamethasone group or to the control group. Furthermore, pulmonary function tests were performed on days 0 and 2 following the start of therapy. The results show that early corticosteroid administration reduces transforming growth factor-beta 1 and basic fibroblast growth factor levels, and abolishes the spontaneous vascular endothelial growth factor increase observed in untreated patients, concomitantly with significant improvement of dynamic lung compliance and shorter duration of the intubation period in the treated group of patients. Significant correlations were observed between the levels of transforming growth factor-beta 1 and vascular endothelial growth factor, indicating that the production of both these cytokines is coordinated. Finally, transforming growth factor-beta 1 ratios (day 2/day 0), representing early variations of the cytokine levels, were significantly different between treated and untreated subjects and correlated with the dynamic lung compliance ratios and the extubation day, suggesting that the downmodulation of some fibrogenic mediators may be involved in the mode of action of dexamethasone.