Mechanical Properties of a Photopolymerizable Hydrogel for Intervertebral Disc Replacement.

We report on the modelling and experimental validation of a photopolymerizable hydrogel for a Nucleus Pulposus replacement.

Mechanical ventilation and clinical practice heterogeneity in intensive care units: a multicenter case-vignette study.

BACKGROUND: Observational studies on mechanical ventilation (MV) show practice variations across ICUs. We sought to determine, with a case-vignette study, the heterogeneity of processes of care in ICUs focusing on mechanical ventilation procedures, and whether organizational patterns or physician characteristics influence practice variations. METHODS: We conducted a cross-sectional multicenter study using the case-vignette methodology. Descriptive analyses were calculated for each organizational pattern and respondent characteristics. An Index of Qualitative Variation (IQV, from 0, no heterogeneity, to a maximum of 1) was calculated. RESULTS: Forty ICUs from France (N = 33) and Switzerland (N = 7) participated; 396 physicians answered our case-vignettes. There was major heterogeneity of management processes related to MV within and across centers (mean IQV per center 0.51, SD 0.09). We observed the lowest variability (mean IQV per question < 0.4) for questions related to intubation procedure, ventilation of acute respiratory distress syndrome and the use of the semirecumbent position. We observed a high variability (mean IQV per question > 0.6) for questions related to management of endotracheal tube or suctioning, management of sedation and analgesia, and respect of autonomy. Heterogeneity was independent of respondent characteristics and of the presence of written procedures. There was a correlation between the processes associated with the highest variability (mean IQV per question > 0.6) and the annual volume of ICU admission (r = 0.32 (0.01 to 0.58)) and MV (r = 0.38 (0.07 to 0.63)). Within ICUs there was a large heterogeneity regarding knowledge of a local written procedure. CONCLUSIONS: Large clinical practice variations were found among ICUs. High volume centers were more likely to have heterogeneous practices. The presence of a local written procedure or respondent characteristics did not influence practice variation.

The automatic selection of ventilation parameters during the initial phase of mechanical ventilation.

OBJECTIVE: To test a method that allows automatic set-up of the ventilator controls at the onset of ventilation. DESIGN: Prospective randomized crossover study. SETTING: ICUs in one adult and one children's hospital in Switzerland. PATIENTS: Thirty intubated stable, critically ill patients (20 adults and 10 children). INTERVENTIONS: The patients were ventilated during two 20-min periods using a modified Hamilton AMADEUS ventilator. During the control period the ventilator settings were chosen immediately prior to the study. During the other period individual settings were automatically determined by the ventilatior (AutoInit). MEASUREMENTS AND RESULTS: Pressure, flow, and instantaneous CO2 concentration were measured at the airway opening. From these measurements, series dead space (V(DS)), expiratory time constant (RC), tidal volume (VT, total respiratory frequency (f(tot), minute ventilation (MV), and maximal and mean airway pressure (Paw, max and Paw, mean) were calculated. Arterial blood gases were analyzed at the end of each period. Paw, max was significantly less with the AutoInit ventilator settings while f(tot) was significantly greater (P < 0.05). The other values were not statistically significant. CONCLUSIONS: The AutoInit ventilator settings, which were automatically derived, were acceptable for all patients for a period of 20 min and were not found to be inferior to the control ventilator settings. This makes the AutoInit method potentially useful as an automatic start-up procedure for mechanical ventilation.

In vivo loading increases mechanical properties of scaffold by affecting bone formation and bone resorption rates.

A successful bone tissue engineering strategy entails producing bone-scaffold constructs with adequate mechanical properties. Apart from the mechanical properties of the scaffold itself, the forming bone inside the scaffold also adds to the strength of the construct. In this study, we investigated the role of in vivo cyclic loading on mechanical properties of a bone scaffold. We implanted PLA/β-TCP scaffolds in the distal femur of six rats, applied external cyclic loading on the right leg, and kept the left leg as a control. We monitored bone formation at 7 time points over 35 weeks using time-lapsed micro-computed tomography (CT) imaging. The images were then used to construct micro-finite element models of bone-scaffold constructs, with which we estimated the stiffness for each sample at all time points. We found that loading increased the stiffness by 60% at 35 weeks. The increase of stiffness was correlated to an increase in bone volume fraction of 18% in the loaded scaffold compared to control scaffold. These changes in volume fraction and related stiffness in the bone scaffold are regulated by two independent processes, bone formation and bone resorption. Using time-lapsed micro-CT imaging and a newly-developed longitudinal image registration technique, we observed that mechanical stimulation increases the bone formation rate during 4-10 weeks, and decreases the bone resorption rate during 9-18 weeks post-operatively. For the first time, we report that in vivo cyclic loading increases mechanical properties of the scaffold by increasing the bone formation rate and decreasing the bone resorption rate.

Assistance circulatoire chronique: le point en 2013 [Long-term mechanical circulatory support: where do we stand in 2013?].

With the advent of new technologies, experience with long-term mechanical circulatory support (MCS) is rapidly growing. Candidates to MCS are selected based on concepts, strategies and classifications that are specific to this indication. As results drastically improve, supported by stronger scientific evidence, the trend is towards earlier implantation. An adequate pre-implant follow-up is mandatory in order to avoid missing the best window of opportunity for implantation. While on chronic support, the hemodynamic profile of patients with continuous-flow ventricular assist devices is unique and remarkably influenced by the hydration status. Optimal management of these patients from the pre-implant phase to the long-term support phase requires a multidisciplinary approach that is similar to that already long validated for organ transplantation.

Influence of the quality of nursing on the duration of weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease.

OBJECTIVE: To evaluate the influence of nursing on the duration of weaning from mechanical ventilation in patients with chronic obstructive pulmonary disease. DESIGN: Data were collected prospectively over a 1-yr period (study year) and compared with previously collected prospective data recorded in our chronic obstructive pulmonary disease database during a 5-yr period. SETTING: The medical intensive care unit (ICU) of a university hospital. PATIENTS: Eighty-seven patients with chronic obstructive pulmonary disease. Fifteen patients had chronic obstructive pulmonary disease that required mechanical ventilation for acute exacerbation of their disease (study year), and 72 were patients with chronic obstructive pulmonary disease from the previously collected data. INTERVENTIONS: The ICU course (duration of mechanical ventilation, mortality) was recorded, as well as several respiratory parameters (pulmonary function tests and arterial blood gases in stable conditions, and nutritional status), and they were compared with an "index of nursing." MEASUREMENTS AND MAIN RESULTS: We developed an "index of nursing", comparing the effective workforce of the nurses (number and qualifications) with the ideal workforce required by the number of patients and the severity of their diseases. A value of 1.0 represented a perfect match between the needed and the effectively present nurses, whereas a lesser value signified a diminished available workforce. This index was compared with the complications and duration of weaning from mechanical ventilation. During the first 5 yrs, the duration of mechanical ventilation increased progressively from 7.3 +/- 8.0 to 38.2 +/- 25.8 days (p = .006). A significant inverse correlation between the duration of mechanical ventilation and the nursing index (p = .025) was found. In the sixth comparative year, the number of nurses increased (nursing index = 1.05) and the duration of mechanical ventilation decreased to 9.9 +/- 13 days (p < .001, yr 5 vs. yr 6). CONCLUSIONS: The quality of nursing appears to be a measurable and critical factor in the weaning from mechanical ventilation of patients with chronic obstructive pulmonary disease. Below a threshold in the available workforce of ICU nurses, the weaning duration of patients with chronic obstructive pulmonary disease increases dramatically. Therefore, very close attention should be given to the education and number of ICU nurses.

Biomechanical characterization and in vitro mechanical injury of elderly human femoral head cartilage: comparison to adult bovine humeral head cartilage.

OBJECTIVES: In vitro mechanical injury of articular cartilage is useful to identify events associated with development of post-traumatic osteoarthritis (OA). To date, many in vitro injury models have used animal cartilage despite the greater clinical relevance of human cartilage. We aimed to characterize a new in vitro injury model using elderly human femoral head cartilage and compare its behavior to that of an existing model with adult bovine humeral head cartilage. DESIGN: Mechanical properties of human and bovine cartilage disks were characterized by elastic modulus and hydraulic permeability in radially confined axial compression, and by Young's modulus, Poisson's ratio, and direction-dependent radial strain in unconfined compression. Biochemical composition was assessed in terms of tissue water, solid, and glycosaminoglycan (GAG) contents. Responses to mechanical injury were assessed by observation of macroscopic superficial tissue cracks and histological measurements of cell viability following single injurious ramp loads at 7 or 70%/s strain rate to 3 or 14 MPa peak stress. RESULTS: Confined compression moduli and Young's moduli were greater in elderly human femoral cartilage vs adult bovine humeral cartilage whereas hydraulic permeability was less. Radial deformations of axially compressed explant disks were more anisotropic (direction-dependent) for the human cartilage. In both cartilage sources, tissue cracking and associated cell death during injurious loading was common for 14 MPa peak stress at both strain rates. CONCLUSION: Despite differences in mechanical properties, acute damage induced by injurious loading was similar in both elderly human femoral cartilage and adult bovine humeral cartilage, supporting the clinical relevance of animal-based cartilage injury models. However, inherent structural differences such as cell density may influence subsequent cell-mediated responses to injurious loading and affect the development of OA.

New record of Pterotaenia fasciata (Wiedemann) (Diptera, Ulidiidae) in Brazil, a probably mechanical vector of enteric bacteria

Pterotaenia fasciata is commonly recorded in rural areas in Argentina, but during a Diptera survey study developed in a reservoir which retains storm water from polluted canals in an urban area of Taboão da Serra municipality, SP, Brazil, we could capture P. fasciata adults. Enteric bacteria Escherichia coli T. Escherich, 1885 and Proteus sp. were isolated from P. fasciata collected in traps inside the reservoir and around it. Fecal coliforms and E. coli were found in the water of the reservoir. These records suggest that a high abundance of this species at urban areas with inadequate sewage canals should reveal these muscoid dipterans as mechanical vectors of enteric bacteria.

Running versus strength-based warm-up : acute effects on isometric knee extension function

This study investigated the influence of two warm-up protocols on neural and contractile parameters of knee extensors. A series of neuromuscular tests including voluntary and electrically evoked contractions were performed before and after running- (R (WU); slow running, athletic drills, and sprints) and strength-based (S (WU); bilateral 90 degrees back squats, Olympic lifting movements and reactivity exercises) warm ups (duration ~40 min) in ten-trained subjects. The estimated overall mechanical work was comparable between protocols. Maximal voluntary contraction torque (+15.6%; P < 0.01 and +10.9%; P < 0.05) and muscle activation (+10.9 and +12.9%; P < 0.05) increased to the same extent after R (WU) and S (WU), respectively. Both protocols caused a significant shortening of time to contract (-12.8 and -11.8% after R (WU) and S (WU); P < 0.05), while the other twitch parameters did not change significantly. Running- and strength-based warm ups induce similar increase in knee extensors force-generating capacity by improving the muscle activation. Both protocols have similar effects on M-wave and isometric twitch characteristics.

Explaining movements in the labor share

In this paper we study the evolution of the labor share in the OECD since 1970. We show it is essentially related to the capital-output ratio; that this relationship is shifted by factors like the price of imported materials or the skill mix; and that discrepancies between the marginal product of labor and the real wage (due to, e.g., product market power, union bargaining, and labor adjustment costs) cause departures from it. We provide estimates of the model with panel data on 14 industries and 14 countries for 1973-93 and use them to compute the evolution of the wage gap in Germany and the US.

Colonic movements in healthy subjects as monitored by a Magnet Tracking System.

The Magnet Tracking System (MTS) is a minimally-invasive technique of continuous evaluation of gastrointestinal motility. In this study, MTS was used to analyse colonic propulsive dynamics and compare the transit of a magnetic pill with that of standard radio-opaque markers. MTS monitors the progress in real time of a magnetic pill through the gut. Ten men and 10 women with regular daily bowel movements swallowed this pill and 10 radio-opaque markers at 8 pm. Five hours of recordings were conducted during 2 following mornings. Origin, direction, amplitude and velocity of movements were analysed relative to space-time plots of the pill trajectory. Abdominal radiographs were taken to compare the progress of both pill and markers. The magnetic pill lay idle for 90% of its sojourn in the colon; its total retrograde displacement accounted for only 20% of its overall movement. Analysis of these movements showed a bimodal distribution of velocities: around 1.5 and 50 cm min(-1), the latter being responsible for 2/3 of distance traversed. There were more movements overall and more mass movements in males. Net hourly forward progress was greater in the left than right colon, and greater in males. The position of the magnetic pill correlated well with the advancement of markers. MTS showed patterns and propulsion dynamics of colonic segments with as yet unmet precision. Detailed analysis of slow and fast patterns of colonic progress makes it possible to specify the motility of colonic segments, and any variability in gender. Such analysis opens up promising avenues in studies of motility disorders.

Protonation controls ASIC1a activity via coordinated movements in multiple domains.

Acid-sensing ion channels (ASICs) are neuronal Na(+)-conducting channels activated by extracellular acidification. ASICs are involved in pain sensation, expression of fear, and neurodegeneration after ischemic stroke. Functional ASICs are composed of three identical or homologous subunits, whose extracellular part has a handlike structure. Currently, it is unclear how protonation of residues in extracellular domains controls ASIC activity. Knowledge of these mechanisms would allow a rational development of drugs acting on ASICs. Protonation may induce conformational changes that control the position of the channel gate. We used voltage-clamp fluorometry with fluorophores attached to residues in different domains of ASIC1a to detect conformational changes. Comparison of the timing of fluorescence and current signals identified residues involved in movements that preceded desensitization and may therefore be associated with channel opening or early steps leading to desensitization. Other residues participated in movements intimately linked to desensitization and recovery from desensitization. Fluorescence signals of all mutants were detected at more alkaline pH than ionic currents. Their midpoint of pH dependence was close to that of steady-state desensitization, whereas the steepness of the pH fluorescence relationship was closer to that of current activation. A sequence of movements was observed upon acidification, and its backward movements during recovery from desensitization occurred in the reverse order, indicating that the individual steps are interdependent. Furthermore, the fluorescence signal of some labeled residues in the finger domain was strongly quenched by a Trp residue in the neighboring β-ball domain. Upon channel activation, their fluorescence intensity increased, indicating that the finger moved away from the β ball. This extensive analysis of activity-dependent conformational changes in ASICs sheds new light on the mechanisms by which protonation controls ASIC activity.

Morfogénesis del valle de Sant Miquel de Campmajor

A series of circumstances which converge in a little valley in the province of Girona, result in a peculiar type of morphogenetic evolution and a quite singular mechanical instability of its buttons. Very recent tectonic movements as well as dissolution phenomena of its subsoil due to pressurized underground water have played an important role in the morphogenesis. Such conditions have resulted in a fast morphological evolution which a progressive lowering of the valley floor as well as peculiar morphological features which favour the existence of numerous pits caused by sudden collapses distributed in altitude and time