Viscosimetric squeeze flow of suspensions

The rheology of particle suspensions has been extensively explored in the case of a simple shear flow, but less in other flow configurations which are also important in practice. Here we investigate the behavior of a suspension in a squeeze flow, which we revisit using local pressure measurements to deduce the effective viscosity. The flow is generated by approaching a moving disk to a fixed wall at constant velocity in the low Reynolds number limit. We measure the evolution of the pressure field at the wall and deduce the effective viscosity from the radial pressure drop. After validation of our device using a Newtonian fluid, we measure the effective viscosity of a suspension for different squeezing speeds and volume fractions of particles. We find results in agreement with the Maron-Pierce law, an empirical expression for the viscosity of suspensions that was established for simple shear flows. We prove that this method to determine viscosity remains valid in the limit of large gap width. This makes it possible to study the rheology of suspensions within this limit and therefore suspensions composed of large particles, in contrast to Couette flow cells which require small gaps.

Rheology of granular rafts

Rheology of macroscopic particle-laden interfaces, called "granular rafts," has been experimentally studied in the simple shear configuration. The shear-stress relation obtained from a classical rheometer exhibits the same behavior as a Bingham fluid, and the viscosity diverges with the surface fraction according to evolutions similar to 2D suspensions. The velocity field of the particles that constitute the granular raft has been measured in the stationary state. These measurements reveal nonlocal rheology similar to dry granular materials. Close to the walls of the rheometer cell, one can observe regions of large local shear rate while in the middle of the cell a quasistatic zone exists. This flowing region, characteristic of granular matter, is described in the framework of an extended kinetic theory showing the evolution of the velocity profile with the imposed shear stress. Measuring the probability density functions of the instantaneous local shear rate, we provide evidence of a balance between positive and negative instantaneous local shear rate. This behavior is the signature of a quasistatic region inside the granular raft.

Successive reintrusions in a granular medium

We measure and analyze the drag force experienced by a rigid rod that penetrates vertically into a granular medium and partially withdraws before sinking again. The drag during the successive reintrusions is observed to be significantly smaller than the force experienced in the first run. Two force regimes are evidenced depending on how the reintrusion depth compares with the withdrawal distance Δ. These two regimes are characterized by a force curve of positive and negative curvature and are separated by an inflection point, which is characterized experimentally. We approach the difference between the first intrusion and the following reintrusions by considering a modification in the stress field of the granular material after the partial extraction of the rod. A theoretical model for the stress modification is proposed and allows to rationalize all the experiments realized for different withdrawal distances Δ. This framework introduces a crossover length λ above which the stress modification in the granular medium is maintained and that is shown to depend linearly on Δ. Finally, the model provides a prediction for the location of the inflection points in reasonable agreement with observations.

Added-mass force in dry granular matter

From two-dimensional (2D) numerical simulations of the motion of a circular intruder into a dry granular packing, we provide evidence for a specific force term in the case of unsteady motion in addition to the force corresponding to a steady motion. We show that this additional term is proportional to the acceleration of the intruder relative to the grains as the added-mass force known for simple fluids. This force term corresponds to a variation in the kinetic energy of the surrounding flow and is characterized by a coefficient C_{AM} which is intrinsically linked to the nature of the granular media. An analytical calculation of the added-mass coefficient C_{AM} is developed based on the specific velocity field known for 2D granular flow around a cylinder. The theoretical value is shown to depend on the grain-cylinder size ratio, in good agreement with the measurements from our unsteady simulations.

Nationwide survey on training and device utilization during tracheal intubation in French intensive care units

Background

Intubation is a lifesaving procedure that is often performed in intensive care unit (ICU) patients, but leads to serious adverse events in 20–40% of cases. Recent trials aimed to provide guidance about which medications, devices, and modalities maximize patient safety. Videolaryngoscopes are being offered in an increasing range of options and used in broadening indications (from difficult to unremarkable intubation). The objective of this study was to describe intubation practices and device availability in French ICUs.

Materials and methods

We conducted an online nationwide survey by emailing an anonymous 26-item questionnaire to physicians in French ICUs. A single questionnaire was sent to either the head or the intubation expert at each ICU.

Results

Of 257 ICUs, 180 (70%) returned the completed questionnaire. The results showed that 43% of intubators were not fully proficient in intubation; among them, 18.8% had no intubation training or had received only basic training (lectures and observation at the bedside). Among the participating ICUs, 94.4% had a difficult intubation trolley, 74.5% an intubation protocol, 92.2% a capnography device (used routinely to check tube position in 69.3% of ICUs having the device), 91.6% a laryngeal mask, 97.2% front-of-neck access capabilities, and 76.6% a videolaryngoscope. In case of difficult intubation, 85.6% of ICUs used a bougie (154/180) and 7.8% switched to a videolaryngoscope (14/180). Use of a videolaryngoscope was reserved for difficult intubation in 84% of ICUs (154/180). Having a videolaryngoscope was significantly associated with having an intubation protocol (P = 0.043) and using capnography (P = 0.02). Airtraq^® was the most often used videolaryngoscope (39.3%), followed by McGrath^®Mac (36.9%) then by Glidescope^® (14.5%).

Conclusion

Nearly half the intubators in French ICUs are not fully proficient with OTI. Access to modern training methods such as simulation is inadequate. Most ICUs own a videolaryngoscope, but reserve it for difficult intubations.

Hysteresis of the drag force of an intruder moving into a granular medium

We numerically investigate the force-displacement relation of a moving intruder initially at rest into a granular medium. Our model granular medium is composed of one layer of coplanar polydisperse spheres subjected to a gravity field. The interactions between the grains are modelled by Hertzian contacts to which a viscous damping is applied. Moving it horizontally and with alternating positive and negative velocity, we recover a hysteresis of the force-displacement curve. Considering that the flow is plastic as the yield strength has been reached, we describe the transient part of the flow around the intruder. We show that the drag stress increases as its distance to an ultimate drag stress [Formula: see text] with a typical deformation [Formula: see text]: the drag stress-strains curve appears to exponentially decay as it saturates to this ultimate drag stress. This protocol of deformation highlights that the deformation of the grains is negligible compared to the deformation of the packing, i.e. related to the irreversible displacements of grains allowing the intruder to pass through. Simultaneously, the lift force is constant on average during the displacement of the intruder. We then give the different scaling laws of the yield strength, this ultimate drag stress, the characteristic deformation of the packing and the lift stress. Finally, we recover the complete hysteresis cycle of the drag force around the intruder.

Severe atypical pneumonia in critically ill patients: a retrospective multicenter study

BACKGROUND

Chlamydophila pneumoniae (CP) and Mycoplasma pneumoniae (MP) patients could require intensive care unit (ICU) admission for acute respiratory failure.

METHODS

Adults admitted between 2000 and 2015 to 20 French ICUs with proven atypical pneumonia were retrospectively described. Patients with MP were compared to Streptococcus pneumoniae (SP) pneumonia patients admitted to ICUs.

RESULTS

A total of 104 patients were included, 71 men and 33 women, with a median age of 56 [44-67] years. MP was the causative agent for 76 (73%) patients and CP for 28 (27%) patients. Co-infection was documented for 18 patients (viruses for 8 [47%] patients). Median number of involved quadrants on chest X-ray was 2 [1-4], with alveolar opacities (n = 61, 75%), interstitial opacities (n = 32, 40%). Extra-pulmonary manifestations were present in 34 (33%) patients. Mechanical ventilation was required for 75 (72%) patients and vasopressors for 41 (39%) patients. ICU length of stay was 16.5 [9.5-30.5] days, and 11 (11%) patients died in the ICU. Compared with SP patients, MP patients had more extensive interstitial pneumonia, fewer pleural effusion, and a lower mortality rate [6 (8%) vs. 17 (22%), p = 0.013]. According MCA analysis, some characteristics at admission could discriminate MP and SP. MP was more often associated with hemolytic anemia, abdominal manifestations, and extensive chest radiograph abnormalities. SP-P was associated with shock, confusion, focal crackles, and focal consolidation.

CONCLUSION

In this descriptive study of atypical bacterial pneumonia requiring ICU admission, mortality was 11%. The comparison with SP pneumonia identified clinical, laboratory, and radiographic features that may suggest MP or CP pneumonia.

Buckling of a rod penetrating into granular media

We investigate experimentally the possible buckling of a thin rod when penetrating downwards into a granular packing. When its bottom end reaches a specific depth, the rod may start buckling provided that the embrace is not enough to stop that phenomenon. The critical rod depth z_{c} at buckling is observed to scale with the rod length L either as 1/L or 1/L^{2}. These two scalings are shown to arise from the two resistant force terms that come into play during the rod penetration: a pressure force at the bottom of the rod that increases linearly with depth and a frictional force on the rod side that increases quadratically with depth. At the buckling point, the destabilizing force corresponds to the expected value given from conventional Euler's critical load for a rod bottom end considered as fixed in the granular clutch. Finally, we draw a buckling-nonbuckling phase diagram in a parameter space given by the rod aspect ratio and a rod-to-grain stress ratio.

Drag force in a cold or hot granular medium

We measure experimentally and analyze the resisting force exerted by a bidimensional packing of small disks on a larger intruder disk dragged horizontally at constant velocity V_{0}. Depending on the vibration level of the packing that leads to a granular "cold" or "hot" packing, two force regimes are observed. At low vibration level ("cold" granular medium), the drag force F does not depend on V_{0}, whereas for high vibrations ("hot" granular medium), the drag force increases linearly with V_{0}. Both regimes can be understood by the balance of two "granular temperatures" that can be defined in the system: a bulk temperature T_{b} imposed by the external vibration to the overall packing and a local temperature T_{0} induced by the own motion of the intruder disk in its vicinity. All experimental data obtained for different sizes and velocities of the intruder disk are shown to be governed by the temperature ratio T_{0}/T_{b}. A critical velocity V_{0c}, above which the system switches from "hot" to "cold," can be obtained in this frame. Finally, we discuss how these two "viscous" regimes should be followed by an inertial regime where the drag force F should increase as V_{0}^{2} at high enough velocity values, for V_{0} greater than a critical value V_{0i} corresponding to high enough Reynolds or Froude number.

[A case of mediastinum actinomycosis by Aggregatibacter actinomycetemcomitans]

The actinomycosis is a suppurative infection due to an anaerobic and microaerophillic bacteria called actinomyces. Only few case reports are described for the mediastinal locations of this rare entity. We report a new case of inflammatory pseudotumor in the mediastinum due to Aggregatibacte actinomycetemcomitans revealed by hemoptysis. The mediastinoscopy procedure with biopsy was needed to confirm the definitive bacteriological diagnosis by a positive culture. During the postoperative course, a cutaneous fistula was found which had a favourable evolution after appropriate antibiotherapy. Through this case report, the authors insist upon the importance of considering the diagnosis of mediastinal actinomycosis when facing non-specfic mediastinal mass symptoms and also about the interest of systematic bacterioscopic examination and histopathologic examination on nodes' biopsies to avoid to be lost on pathology of mediastinal tumor or tuberculosis. In practise, we caution the non-expert during biopsies because of this lesion's invasive characteristic especially in the confined space of the mediastinum.

Experimental Evidence of the Gardner Phase in a Granular Glass

Analyzing the dynamics of a vibrated bidimensional packing of bidisperse granular disks below jamming, we provide evidence of a Gardner phase deep into the glass phase. To do so, we perform several compression cycles within a given realization of the same glass and show that the particles select different average vibrational positions at each cycle, while the neighborhood structure remains unchanged. The separation between the cages obtained for different compression cycles plateaus with an increasing packing fraction, while the mean square displacement steadily decreases. This phenomenology is strikingly similar to that reported in recent numerical observations when entering the Gardner phase, for a mean-field model of glass as well as for hard spheres in finite dimension. We also characterize the distribution of the cage order parameters. Here we note several differences from the numerical results, which could be attributed to activated processes and cage heterogeneities.

Clustering and flow around a sphere moving into a grain cloud

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains far from any boundaries and without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size. The key point is that the upstream cluster size increases with the initial solid fraction [Formula: see text] but the cluster packing fraction takes an about constant value independent of [Formula: see text]. Although the upstream cluster size around the moving sphere diverges when [Formula: see text] approaches a critical value, the drag force exerted by the grains on the sphere does not. The detailed analysis of the local strain rate and local stress fields made in the non-parallel granular flow inside the cluster allows us to extract the local invariants of the two tensors: dilation rate, shear rate, pressure and shear stress. Despite different spatial variations of these invariants, the local friction coefficient μ appears to depend only on the local inertial number I as well as the local solid fraction, which means that a local rheology does exist in the present non-parallel flow. The key point is that the spatial variations of I inside the cluster do not depend on the sphere velocity and explore only a small range around the value one.

Local rheological measurements in the granular flow around an intruder

The rheological properties of granular matter within a two-dimensional flow around a moving disk is investigated experimentally. Using a combination of photoelastic and standard tessellation techniques, the strain and stress tensors are estimated at the grain scale in the time-averaged flow field around a large disk pulled at constant velocity in an assembly of smaller disks. On the one hand, one observes inhomogeneous shear rate and strongly localized shear stress and pressure fields. On the other hand, a significant dilation rate, which has the same magnitude as the shear strain rate, is reported. Significant deviations are observed with local rheology that justify the need of searching for a nonlocal rheology.

Cardiac troponin-I on diagnosis predicts early death and refractoriness in acquired thrombotic thrombocytopenic purpura. Experience of the French Thrombotic Microangiopathies Reference Center

BACKGROUND

Cardiac involvement is a major cause of mortality in patients with thrombotic thrombocytopenic purpura (TTP). However, diagnosis remains underestimated and delayed, owing to subclinical injuries. Cardiac troponin-I measurement (cTnI) on admission could improve the early diagnosis of cardiac involvement and have prognostic value.

OBJECTIVES

To assess the predictive value of cTnI in patients with TTP for death or refractoriness.

PATIENTS/METHODS

The study involved a prospective cohort of adult TTP patients with acquired severe ADAMTS-13 deficiency (< 10%) and included in the registry of the French Reference Center for Thrombotic Microangiopathies. Centralized cTnI measurements were performed on frozen serum on admission.

RESULTS

Between January 2003 and December 2011, 133 patients with TTP (mean age, 48 ± 17 years) had available cTnI measurements on admission. Thirty-two patients (24%) had clinical and/or electrocardiogram features. Nineteen (14.3%) had cardiac symptoms, mainly congestive heart failure and myocardial infarction. Electrocardiogram changes, mainly repolarization disorders, were present in 13 cases. An increased cTnI level (> 0.1 μg L(-1) ) was present in 78 patients (59%), of whom 46 (59%) had no clinical cardiac involvement. The main outcomes were death (25%) and refractoriness (17%). Age (P = 0.02) and cTnI level (P = 0.002) showed the greatest impact on survival. A cTnI level of > 0.25 μg L(-1) was the only independent factor in predicting death (odds ratio [OR] 2.87; 95% confidence interval [CI] 1.13-7.22; P = 0.024) and/or refractoriness (OR 3.03; 95% CI 1.27-7.3; P = 0.01).

CONCLUSIONS

A CTnI level of > 0.25 μg L(-1) at presentation in patients with TTP appears to be an independent factor associated with a three-fold increase in the risk of death or refractoriness. Therefore, cTnI level should be considered as a prognostic indicator in patients diagnosed with TTP.

Shear modulus and dilatancy softening in granular packings above jamming

We investigate experimentally the mechanical response to shear of a monolayer of bidisperse frictional grains across the jamming transition. We inflate an intruder inside the packing and use photoelasticity and tracking techniques to measure the induced shear strain and stresses at the grain scale. We quantify experimentally the constitutive relations for strain amplitudes as low as 10(-3) and for a range of packing fractions within 2% variation around the jamming transition. At the transition strong nonlinear effects set in: both the shear modulus and the dilatancy shear soften at small strain until a critical strain is reached where effective linearity is recovered. The scaling of the critical strain and the associated critical stresses on the distance to jamming are extracted. We check that the constitutive laws, together with mechanical equilibrium, correctly predict to the observed stress and strain profiles. These profiles exhibit a spatial crossover between an effective linear regime close to the inflater and the truly nonlinear regime away from it. The crossover length diverges at the jamming transition.

Diagnostic contribution from pulmonary biopsies in hematology patients with acute respiratory failure from undetermined etiology

BACKGROUND

In about 20% of patients with malignancies with acute respiratory failure (ARF), no etiology can be determined, whatever the diagnostic strategy used. Lung biopsy could then be a precious diagnostic tool leading to therapeutic adaptations and increasing chances for cure. The aim of this study was to assess the diagnostic contribution of lung biopsy in patients for whom a complete diagnosis strategy failed to identify ARF etiology.

METHODS

All hematology patients admitted for ARF to our ICU between 1995 and 2011, and for whom lung biopsy was performed were included in the study. Lung biopsies were surgical, CT guided, or post-mortem. Histological findings were compared to prebiopsy diagnosis and classified into specific or non-specific diagnosis. Therapeutic impact (or Goldman-class in post-mortem biopsies) was also recorded.

RESULTS

Among the 1440 hematology patients with ARF managed during the study period, 21 (1%) biopsies were performed, including 10 post-mortem biopsies. Histological diagnoses were specific in 10 biopsies, non specific in 8 biopsies and lung parenchyma was normal in three patients. In 8/11 (72.7%) alive patients, lung biopsy had lead to therapeutic modifications, including treatment implementation in 5 patients and treatment withdrawal in 3 patients. One out of 10 (10%) patients had minor complications. For the 10 dead patients, only one Goldman-type 1 error was found.

CONCLUSION

Diagnostic lung biopsy is rarely needed in hematology patients with ARF. But, it has a 73% therapeutic impact and has overall no major complications. Contribution from post-mortem biopsies seems less relevant.

Airway transplantation: a challenge for regenerative medicine

After more than 50 years of research, airway transplantation remains a major challenge in the fields of thoracic surgery and regenerative medicine. Five principal types of tracheobronchial substitutes, including synthetic prostheses, bioprostheses, allografts, autografts and bioengineered conduits have been evaluated experimentally in numerous studies. However, none of these works have provided a standardized technique for the replacement of the airways. More recently, few clinical attempts have offered encouraging results with ex vivo or stem cell-based engineered airways and tracheal allografts implanted after heterotopic revascularization. In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction. In vivo regeneration of epithelium and cartilage were demonstrated in animal models. This led to the first human applications using cryopreserved aortic allografts that present key advantages because they are available in tissue banks and do not require immunosuppressive therapy. Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

Experimental velocity fields and forces for a cylinder penetrating into a granular medium

We present here a detailed granular flow characterization together with force measurements for the quasi-bidimensional situation of a horizontal cylinder penetrating vertically at a constant velocity in dry granular matter between two parallel glass walls. In the velocity range studied here, the drag force on the cylinder does not depend on the velocity V(0) and is mainly proportional to the cylinder diameter d. While the force on the cylinder increases with its penetration depth, the granular velocity profile around the cylinder is found to be stationary with fluctuations around a mean value leading to the granular temperature profile. Both mean velocity profile and temperature profile exhibit strong localization near the cylinder. The mean flow perturbation induced by the cylinder decreases exponentially away from the cylinder on a characteristic length λ that is mainly governed by the cylinder diameter for a large enough cylinder/grain size ratio d/d(g): λ~d/4+2d(g). The granular temperature exhibits a constant plateau value T(0) in a thin layer close to the cylinder of extension δ(T(0))~λ/2 and decays exponentially far away with a characteristic length λ(T) of a few grain diameters (λ(T)~3d(g)). The granular temperature plateau T(0) that scales as V(0)(2)d(g)/d is created by the flow itself from the balance between the "granular heat" production by the shear rate V(0)/λ over δ(T(0)) close to the cylinder and the granular dissipation far away.

Tracheal regeneration: evidence of bone marrow mesenchymal stem cell involvement

OBJECTIVES

Recent advances in airway transplantation have shown the ability of ex vivo or in vivo tracheal regeneration with bioengineered conduits or biological substitutes, respectively. Previously, we established a process of in vivo-guided tracheal regeneration using vascular allografts as a biological scaffold. We theorized that tracheal healing was the consequence of a mixed phenomenon associating tracheal contraction and regeneration. The aim of the present study was to determine the role that bone marrow stem cells play in that regenerative process.

METHODS

Three groups of 12 rabbits underwent a gender-mismatched aortic graft transplantation after tracheal resection. The first group received no cells (control group), the second group had previously received autologous green fluorescent protein-labeled mesenchymal stem cell transplantation, and the third group received 3 labeled mesenchymal stem cell injections on postoperative days 0, 10, and 21.

RESULTS

The clinical results were impaired by stent complications (obstruction or migration), but no anastomotic leakage, dehiscence, or stenosis was observed. The rabbits were killed, and the trachea was excised for analysis at 1 to 18 months after tracheal replacement. In all 3 groups, microscopic examination showed an integrated aortic graft lined by metaplastic epithelium. By 12 months, immature cartilage was detected among disorganized elastic fibers. Positive SRY gene detection served as evidence for engraftment of cells derived from the male recipient. EF-green fluorescent protein detection showed bone marrow-derived mesenchymal stem cell involvement.

CONCLUSIONS

The results of the present study imply a role for bone marrow stem cells in tracheal regeneration after aortic allografting. Studies are necessary to identify the local and systemic factors stimulating that regenerative process.

[Surgical lung biopsy: Indications and therapeutic implications]

Surgical biopsy of lung parenchyma can be used to establish a diagnosis in interstitial lung disease both of acute and chronic presentation. The present article summarizes the current indications, the therapeutic implications, the different surgical techniques and postoperative complications of the procedure. Common controversies and problems related to surgical lung biopsy are also presented.

[The lung]

Lung transplantation is still the only curative treatment for end-stage pulmonary diseases. The results remain poor, however, because of the limited availability of lung donors, chronic rejection, and complications related to immunosuppressive therapy. The use of a bioartificial lung generated from autologous cells could offer a solution. We have demonstrated that in vivo epithelial and cartilage regeneration of the airways is feasible with the use of an aortic tissue matrix. Other studies show that in vitro and in vivo airway regeneration, respectively, can be obtained by using bio-engineering and heterotopic allograft implantation. A more complex challenge is the creation of an artificial lung Indeed, this would require the use of an elastic matrix that can promote regeneration of the different lung components (airways, alveoli, vessels) over a large surface area, thus allowing ventilation, blood perfusion and gas exchanges. Recent studies have demonstrated the possibility of in vitro and in vivo regeneration of lung tissue from autologous cells, and especially stem cells. This emerging research field is currently dominated by the use of decellularized lung matrices and autologous epithelial and endothelial cells. Implantation of such a recellularized matrix in animals has proved the feasibility of a functional bio-artificial lung. The first human transplantation of a bio-artificial lung should be possible within 10-20 years.

Dexamethasone in patients with acute lung injury from acute monocytic leukaemia

The use of steroids is not required in myeloid malignancies and remains controversial in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). We sought to evaluate dexamethasone in patients with ALI/ARDS caused by acute monocytic leukaemia (AML FAB-M5) via either leukostasis or leukaemic infiltration. Dexamethasone (10 mg every 6 h until neutropenia) was added to chemotherapy and intensive care unit (ICU) management in 20 consecutive patients between 2005 and 2008, whose data were compared with those from 20 historical controls (1994-2002). ICU mortality was the primary criterion. We also compared respiratory deterioration rates, need for ventilation and nosocomial infections. 17 (85%) patients had hyperleukocytosis, 19 (95%) had leukaemic masses, and all 20 had severe pancytopenia. All patients presented with respiratory symptoms and pulmonary infiltrates prior to AML FAB-M5 diagnosis. Compared with historical controls, dexamethasone-treated patients had a significantly lower ICU mortality rate (20% versus 50%; p = 0.04) and a trend for less respiratory deterioration (50% versus 80%; p = 0.07). There were no significant increases in the rates of infections with dexamethasone. In conclusion, in patients with ALI/ARDS related to AML FAB-M5, adding dexamethasone to conventional chemotherapy seemed effective and safe. These results warrant a controlled trial of dexamethasone versus placebo in AML FAB-M5 patients with noninfectious pulmonary infiltrates.

Dense granular flow around a penetrating object: experiment and hydrodynamic model

We present in this Letter experimental results on the bidimensional flow field around a cylinder penetrating into dense granular matter, together with drag force measurements. A hydrodynamic model based on extended kinetic theory for dense granular flow reproduces well the flow localization close to the cylinder and the corresponding scalings of the drag force, which is found to not depend on velocity, but linearly on the pressure and on the cylinder diameter and weakly on the grain size. Such a regime is found to be valid at a low enough "granular" Reynolds number.

Tracheal replacement with cryopreserved allogenic aorta

BACKGROUND

Radical resection of primary tracheal tumors may be challenging when more than one-half of the tracheal length is concerned. The present study evaluated the use of cryopreserved aortic allografts (CAAs) to replace long tracheal segments.

METHODS

Sixteen adult minipigs underwent tracheal replacement with a CAA. A silicone stent was used to splint the CAA for the first 12 months. Animals were followed-up using bronchoscopic evaluation and killed at predetermined times, for a period up to 18 months long.

RESULTS

Intense inflammation and progressive disappearance of typical histologic structures of the aorta were seen within the first 3 months. All animals studied for more than 3 months showed progressive transformation of the graft into a chimerical conduit sharing aortic and tracheal histologic patterns (eg, islands of disorganized elastic fibers/mature respiratory ciliated epithelium, respiratory glands, islets of cartilage). Stent removal was attempted after 12 months in 10 animals, and critical tracheal stenosis was found in six animals and moderate asymptomatic stenosis in four. Clinical course in these latter animals was uneventful until they were killed at 15 to 18 months. In situ hybridization showed that collagen2a1 mRNA was expressed in the cartilage islets at 1 year. Polymerase chain reaction analysis of the SRY gene demonstrated that the newly formed cartilage cells derived from the host.

CONCLUSIONS

CAA may be considered as a valuable tracheal substitute for patients with extensive tracheal tumors. Prolonged stenting will be probably mandatory for the clinical application of the procedure in humans.

Tracheal replacement with cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts

BACKGROUND

Seven years of experimental research provided a valuable tracheal substitute, the aortic allograft, which can promote the regeneration of epithelium and cartilage. In human application, both fresh and preserved aortic allografts could be used. The optimal method of aortic allograft preservation remains to be evaluated. This study assessed the use of cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts as tracheal substitutes.

METHODS

Twenty-two sheep underwent tracheal replacement using cryopreserved (n = 10), decellularized (n = 7) or glutaraldehyde-treated (n = 5) allografts, supported by a temporary stent to prevent airway collapse. Aortic segments were retrieved at regular intervals up to 12 months after implantation to analyze the regenerative process.

RESULTS

All animals survived the operation. Major complications such as infection, stent migration, or obstruction were predominantly encountered in the decellularized group. The lack of major inflammatory response within the aortic graft observed in the glutaraldehyde group was associated with the absence of tracheal regeneration. Histologic examinations showed a progressive transformation of the aorta into a tracheal tissue comprising respiratory epithelium and cartilage only in the cryopreserved group.

CONCLUSIONS

This study demonstrated that regeneration of a functional tissue could be obtained after tracheal replacement with a cryopreserved aortic allograft. The regenerative process followed the same pattern as previously described for fresh allografts. Cryopreserved aortic allografts present major advantages: availability in tissue banks, permanent storage, and no need for immunosuppression. This offers a new field of perspectives for clinical application in patients with extensive tracheal cancer.

Carinal Replacement With an Aortic Allograft

BACKGROUND

Carinal replacement after extensive resection remains a tremendous challenge in thoracic surgery. In previous studies, we demonstrated that an aortic graft could be a valuable tracheal substitute. The goal of this new study was to evaluate the reconstruction of the carina using a stent supported bifurcated aortic allograft.

METHODS

In 15 sheep the replacement of the tracheobronchial bifurcation with an aortic allograft was performed under cardiopulmonary bypass. A temporary stent prevented airway collapse. No immunosuppression was used. Aortic segments were retrieved at regular intervals up to 24 months after implantation.

RESULTS

All animals survived the initial aortic allograft operation. Six animals died postoperatively (1 of graft necrosis, 2 of pneumonia, and 3 of bronchial fistula). The remaining 9 animals were in good condition until they were euthanized. Stent removal was tolerated after 9 months in 3 animals. Progressive transformation of the arterial graft initially into extensive inflammatory tissue, and after 3 to 6 months into a tracheal tissue comprising a well-differentiated epithelium and cartilage was confirmed by histology.

CONCLUSIONS

This study showed that regeneration of a functional tissue can be obtained after replacement of the carina with an aortic allograft. The origin and mechanisms of this regenerative process remains to be discovered. These results represent an important hope for the reconstruction of the carina after extensive resection, especially for cancer lesions. In human application, the systemic use of omentoplasty or myoplasty should further reduce its risk of complication.

Tracheal regeneration following tracheal replacement with an allogenic aorta

BACKGROUND

Tracheal replacement remains an unsolved surgical problem. Attempts to use tracheal substitutes have failed to achieve reliable results. In this study, tracheal regeneration was obtained after tracheal replacement with an allogenic aorta.

METHODS

Twenty female sheep underwent a 8-cm tracheal replacement with a fresh aortic allograft. In the six last animals, aortic grafts came from male sheep. A stent prevented airway collapse. No immunosuppressive therapy was used. Aortic segments were retrieved at regular intervals up to 16 months. A polymerase chain reaction for the SRY gene was performed in specimens with aortic grafts from male sheep.

RESULTS

All animals but one survived the operation without complications. Clearly identified between the suture lines, the aortic segments were completely transformed into a tracheal structure. Histology showed initially an inflammatory reaction with proliferation of a squamous epithelium followed by mucociliary epithelium and newly formed cartilage rings. SRY gene was not found in newly formed cartilage rings showing that the regeneration originated from recipient cells.

CONCLUSIONS

This study presents a new type of tissue regeneration and brings hopes to the treatment of extensive tracheal lesions.

Early and long-term results of lung resection for non-small-cell lung cancer in patients with severe ventilatory impairment

OBJECTIVE

To study clinical characteristics, surgical treatment modalities, early and long-term outcome of patients with severe ventilatory impairment undergoing lung resection for NSCLC.

METHODS

We performed a retrospective review of clinical records of all patients with severe chronic ventilatory impairment (FEV1 and/or FVC< or =50% of predicted values) operated on for NSCLC in a 21-year period (1983-2003).

RESULTS

One hundred and six patients were operated on. Mean FEV1 and FVC were 40% (range 23-50%) and 69% (17-117%), respectively. An obstructive pattern was observed in 87 cases (82%). Extent of maximal exeresis was based on the assessment of predicted post-operative FEV1 (ppoFEV1). Major resections were contraindicated if ppoFEV1 was lower than 30%. Sixteen pneumonectomies, 73 lobectomies and 17 sublobar resections were carried out. Pathologic stages were I, II, IIIA and IIIB in 58, 26, 18 and 4 cases, respectively. Resection was complete in 104 patients. Operative mortality and morbidity were 8.5% (n=9) and 70% (n=74), respectively. Twenty-two patients needed prolonged (>48 h) mechanical ventilation. Overall mean ppoFEV1 loss was 9.1% (0-34%). If ppoFEV1 loss was >15%, the morbidity rate was 100%. Mean PaCO2 and ppoFEV1 loss were higher among patients who died (41 mmHg versus 37 mmHg, P=0.02 and 13.2% versus 8.5%, P=0.025, respectively) as compared with operative survivors. Among patients with PaCO2>39 mmHg and ppoFEV1 loss>15% (n=9), mortality rate was 33%. Overall 1-year and 5-year survival rates were 82 and 33%, respectively. Respiratory failure was the cause of late death in 2 patients. Among patients available at follow-up (n=85), respiratory function was considered subjectively improved, stable and worsened in 6 (7%), 62 (73%) and 17 (20%) cases, respectively. Eleven patients needed continuous oxygen therapy.

CONCLUSIONS

Lung resection should not be denied a priori in patients with severe ventilatory impairment. Evaluation of predicted post-operative function often allows major resections, which are functionally economic, at the price of a high operative morbidity. Operative mortality, long-term survival and respiratory function are acceptable in the absence of a valid therapeutic alternative.

Long-term evaluation of the replacement of the trachea with an autologous aortic graft

BACKGROUND

Tracheal reconstruction after extensive resection remains a challenge in thoracic surgery. The goal of this experimental study was to analyze the long-term evolution of tracheal replacement using an autologous aortic graft.

METHODS

In 21 sheep, a 5-cm segment of the cervical trachea was replaced by a segment of the descending thoracic aorta that was reconstructed to a prosthetic graft. Because of the airway collapse reported in a previous series, a permanent (n = 13) or temporary (n = 8) stent was systematically placed in the lumen of the graft. Clinical, bronchoscopic, and histologic examinations were performed up to 3 years after implantation.

RESULTS

All animals survived the operation with no paraplegia. In the group with a permanent stent, three complications occurred: one stent displacement, one laryngeal edema, and one infection. Stent removal was tolerated after 6 months in the group with a temporary stent. Histologic examination showed a progressive transformation of the arterial segment into first extensive inflammatory tissue with a squamous epithelium, and after 6 to 36 months well-differentiated tracheal tissue including a continuous mucociliary epithelium and regular rings of newly formed cartilage.

CONCLUSIONS

An autologous aortic graft used as a substitute for extensive tracheal replacement in sheep remained functional for periods up to 3 years. The progressive transformation of the graft into a structure resembling tracheal tissue seems to be a key factor in long-term patency. The mechanism of this regenerative process and the possibility of using arterial homografts, which would make clinical application easier, remain to be evaluated.

[Old Monteggia lesions in children. Apropos of 14 cases]

Fourteen patients between the ages of 3.5 years and 11 years, with an old Monteggia lesion were managed in the Orthopaedics department between 1968 and 1997. Dislocation of the radial head was not diagnosed at the time of the initial trauma in 9 out of 14 cases and the diagnosis was made an average of 14 months after the trauma (range: 5 weeks to 84 months). Twelve of the 14 patients underwent surgical reduction of chronic dislocation of the radial head, mostly associated with proximal ulnar osteotomy and/or a procedure on the extensor retinaculum. The mean follow-up is 4 years 9 months. There were 66% excellent and good results, 25% of moderate results and 9% of poor results. Due to the difficulty of surgery of neglected lesions, the authors report their experience and emphasize the importance of the initial diagnosis.

The theatre: an effective tool for health promotion

In Africa and in North America, in both rural and urban settings, theatre can be an effective means of health promotion. Projects on women's health, care for patients with mental disorders, and AIDS prevention show the usefulness of this medium for community action programmes.

[The territorial dimension of Quebec's international immigration]

"This paper is devoted to the spatial distribution of Quebec's international immigrants, and to the main territorial stakes related to this type of migration. After analysing international immigration as a flow (distribution of the cohorts of immigrants who entered Quebec during a given period) as well as a stock (distribution of all immigrants surviving in Quebec and their redistribution through internal migration), a critical analysis of the territorial stakes as defined by various agents (active at different levels) is proposed." (SUMMARY IN ENG)