[How to increase availability of grafts in lung transplantion: ex vivo lung reconditioning - cardiac death donors - high emergency list]. / Comment élargir l'accès aux greffons : ex vivo reconditionnement - Donneurs décédés par arrêt cardiaque - Super-urgence pulmonaire (SU).

Lung transplantation has become an established treatment for end-stage pulmonary failure refractory to medical management. However, the scarcity of lung grafts and the growing number of candidates has led to an increase in deaths among patients on waiting lists. Despite improvements in donor management, organ preservation, and the use of marginal and cardiac death donors, only about 20% of candidate lungs are currently being transplanted. A new ex vivo "reconditioning" technique is opening up new perspectives. Indeed, a significant number of rejected lungs can now be retrieved and transplanted with acceptable results. Given the longer storage times provided by this technique, transplantation can be programmed, with better surgical efficiency. A new mobile organ-care machine is currently under evaluation. In near future, a pilot laboratory will be created and dedicated to ex vivo reconditionning of all lung grafts before transplantation and grafts will be sent to lung transplant centers after immunologic cross-matching.

An unexpected plasma cholinesterase activity rebound after challenge with a high dose of the nerve agent VX.

Organophosphorus chemical warfare agents (nerve agents) are to be feared in military operations as well as in terrorist attacks. Among them, VX (O-ethyl-S-[2-(diisopropylamino)ethyl] methylphosphonothioate) is a low volatility liquid that represents a percutaneous as well as an inhalation hazard if aerosolized. It is a potent irreversible cholinesterase (ChE) inhibitor that causes severe signs and symptoms, including respiratory dysfunction that stems from different mechanisms. VX-induced pulmonary oedema was previously reported in dogs but mechanisms involved are not well understood, and its clinical significance remains to be assessed. An experimental model was thus developed to study VX-induced cardiovascular changes and pulmonary oedema in isoflurane-anaesthetized swine. In the course of this study, we observed a fast and unexpected rebound of plasma ChE activity following inhibition provoked by the intravenous injection of 6 and 12 microg kg(-1) of VX. In whole blood ChE activity, the rebound could stay unnoticed. Further investigations showed that the rebound of plasma esterase activity was neither related to spontaneous reactivation of ChE nor to VX-induced increase in paraoxonase/carboxylesterase activities. A bias in Ellman assay, haemoconcentration or severe liver cytolysis were also ruled out. All in all, these results suggest that the rebound was likely due to the release of butyrylcholinesterase into the blood stream from ChE producing organs. Nature of the organ(s) and mechanisms involved in enzyme release will need further investigations as it may represent a mechanism of defence, i.e. VX scavenging, that could advantageously be exploited.

Traveling wave ultrasonic motor: coupling effects in free stator.

Generally a stator of traveling wave ultrasonic motor (TWUM) consists of piezoelectric transducers (annular plate or rods) coupled by the way of a metallic ring. These transducers divided into halves are excited independently by two electrical signals with different phases of about 90 degrees. So an elastic traveling wave propagates along the circumference of the ring and a rotor pressed on this vibrating surface is then driven by the stator via contact forces. Many difficulties appear in developing TWUM because the contact between the stator and the rotor via a frictional material is very important. However that may be, the first stage consists in obtaining a vibrating stator with optimum characteristics with two symmetrical phases. The aim of this paper is to discuss some coupling effects in a free stator through an enhanced equivalent circuit model. A simple experimental method based on impedance measurements is performed to estimate the coupling characteristics at a low driving voltage. This paper reports results obtained with the free stator of the well known piezoelectric ultrasonic motor "USR60" by Shinsei Co. Ltd. Since the stator behaves as an elastic body, interactions between the two electrical inputs might be described by the introduction of a coupling oscillator. The comparison of experimental and theoretical results leads to validate the new equivalent circuit of the free stator. The presence of coupling impedance could imply a change of electrical supply condition to optimize the TWUM efficiency. The effects of unbalanced features for each electrical input and the applicability of the proposed model to actual operating condition are discussed in the paper.

Characterization of the mechanical nonlinear behavior of piezoelectric ceramics.

A characterization of the nonlinear behavior with high signal excitation in piezoceramic resonators was carried out. The behavior of power devices working at resonance, in which high strains are involved, is explained. A theoretical model previously described is used to explain the motional impedance variation proportional to the square of the motional current. This impedance increase DeltaZ is independent of the frequency and explains: the nonlinear elasticity that produces the A-F effect, the nonlinear mechanical losses that increase greatly close to the resonance, and the hysteresis phenomenon produced with frequency sweeps. Different methods for measuring the mechanical nonlinear coefficients of piezoceramics with high signal excitation are presented. An experimental method is proposed to measure the mechanical loss tangent and the compliance variations as a function of the mean square strain in the piezoceramic. This consists in measuring the maximum admittance and the series resonance frequency for downward frequencies. At this jumping point, the phase angle remains zero whatever the amplitude of the excitation. Two main coefficients characterizing the material mechanical nonlinearity are deduced. Experimental measurements were carried out to compare the nonlinearity of different ceramic materials in longitudinal and transverse mode.

A piezomotor using longitudinal actuators.

A new travelling wave type ultrasonic motor has been developed which uses longitudinal piezoelectric actuators to generate a progressive wave on the surface of a metallic ring. The rotor, which moves through frictional force, is pressed on this elastic plate. This paper deals with the motor construction and its characteristics. Theoretical modelling and experimental performances obtained with the motor prototypes are reported. A maximum of 0.8 Nm and a no-load rotation speed of 120 rpm have been obtained with a double rotor prototype. The results indicate that this piezomotor is proved to operate successfully at a mechanical output power of 4 W.

[Prediction of respiratory complications after surgery of the abdominal aorta]. / Prédiction des complications respiratoires après chirurgie de l'aorte abdominale.

The most frequent type of complication in patients undergoing aortic surgery is respiratory. Preoperative lung function (PFT) and arterial blood gas measurement (ABG) are often carried out to assess the risk more precisely. The aim of the present retrospective study was to determine which value of lung function test could identify patients who developed such complications. "Receiver Operating Characteristic" (ROC) curves and the area beneath the curve for the diagnosis of respiratory complications were calculated for each variable of PFT and ABG. The greatest Youden index for each variable was chosen as indicative pulmonary function criterion of increased risk of pulmonary complications. One hundred and ninety-five patients (age: 65 +/- 10 years) were included. Respiratory complications occurred in 15% of patients. Respiratory complications increased from 12% if the vital capacity (VC) was > or = 77% of the predicted value to 35% if the VC was < 77% (P = 0.002), and from 10% if the FEV1 was > 76% to 34% if the FEV1 was > or = 76% (P = 0.0005). A decreased PaO2 or increased PaCO2 was not correlated with an increased incidence of respiratory complications. Length of stay in ICU or in hospital were increased when VC or FEV1 were low. Frequency of pulmonary complications was 9% in patients without PFT abnormalities, 16% in patients with either diminished VC or FEV1 and 35% in patients with both lowered VC and FEV1. However, all the areas under the ROC curves were < 0.7 and the sensitivity of the different variables was low. It is concluded that routine preoperative PFT and ABG cannot predict respiratory complications after abdominal aortic surgery.