Dominique Touchard

NéoGanesh: a working system for the automated control of assisted ventilation in ICUs.

Automating the control of therapy administered to a patient requires systems which integrate the knowledge of experienced physicians. This paper describes NéoGanesh, a knowledge-based system which controls, in closed-loop, the mechanical assistance provided to patients hospitalized in intensive care units. We report on how new advances in knowledge representation techniques have been used to model medical expertise. The clinical evaluation shows that such a system relieves the medical staff of routine tasks, improves patient care, and efficiently supports medical decisions regarding weaning. To be able to work in closed-loop and to be tested in real medical situations, NéoGanesh deals with a voluntarily limited problem. However, embedded in a powerful distributed environment, it is intended to support future extensions and refinements and to support reuse of knowledge bases.

Dissecting streptavidin-biotin interaction with a laminar flow chamber.

A laminar flow chamber was used to study single molecule interactions between biotinylated surfaces and streptavidin-coated spheres subjected to a hydrodynamic drag lower than a piconewton. Spheres were tracked with 20 ms and 40 nm resolution. They displayed multiple arrests lasting between a few tens of milliseconds and several minutes or more. Analysis of about 500,000 positions revealed that streptavidin-biotin interaction was multiphasic: transient bound states displayed a rupture frequency of 5.3 s(-1) and a rate of transition toward a more stable configuration of 1.3 s(-1). These parameters did not display any significant change when the force exerted on bonds varied between 3.5 and 11 pN. However, the apparent rate of streptavidin-biotin association exhibited about 10-fold decrease when the wall shear rate was increased from 7 to 22 s(-1), which supports the existence of an energy barrier opposing the formation of the transient binding state. It is concluded that a laminar flow chamber can yield new and useful information on the formation of molecular bonds, and especially on the structure of the external part of the energy landscape of ligand-receptor complexes.

Airway Occlusion Pressure to Titrate Positive End-expiratory Pressure in Patients with Dynamic Hyperinflation

Background Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P0.1t), could help to indicate the effects of PEEP on the work of breathing (WOB). Methods Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support. Results PEEP 5 significantly reduced intrinsic PEEP (mean ± SD, 5.2 ± 2.4 cm H2O at PEEP 0 to 3.6 ± 1.9 at PEEP 5;P < 0.001), WOB per min (12.6 ± 6.7 J/min to 9.1 ± 5.9 J/min;P = 0.003), WOB per liter (1.2 ± 0.4 J/l to 0.8 ± 0.4 J/l;P < 0.001), pressure time product of the diaphragm (216 ± 86 cm H2O · s−1 · min−1 to 155 ± 179 cm H2O · s−1 · min−1;P = 0.001) and P0.1t (3.3 ± 1.5 cm H2O to 2.3 ± 1.4 cm H2O;P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P0.1t (2.5 ± 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end-expiratory lung volume. Significant correlations were found between WOB per min and P0.1t at the three levels of PEEP (P < 0.001), and between the changes in P0.1tversus the changes in WOB per min (P < 0.005), indicating that P0.1t and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%. Conclusion These results show that P0.1t may help to assess the effects of PEEP in patients with intrinsic PEEP.

Cell Membrane Alignment along Adhesive Surfaces: Contribution of Active and Passive Cell Processes

Cell adhesion requires nanometer scale membrane alignment to allow contact between adhesion receptors. Little quantitative information is presently available on this important biological process. Here we present an interference reflection microscopic study of the initial interaction between monocytic THP-1 cells and adhesive surfaces, with concomitant determination of cell deformability, using micropipette aspiration, and adhesiveness, using a laminar flow assay. We report that 1), during the first few minutes after contact, cells form irregular-shaped interaction zones reaching approximately 100 micro m(2) with a margin extension velocity of 0.01-0.02 micro m/s. This happens before the overall cell deformations usually defined as spreading. 2), These interference reflection microscopic-detected zones represent bona fide adhesion inasmuch as cells are not released by hydrodynamic forces. 3), Alignment is markedly decreased but not abolished by microfilament blockade with cytochalasin or even cell fixation with paraformaldehyde. 4), In contrast, exposing cells to hypotonic medium increased the rate of contact extension. 5), Contacts formed in presence of cytochalasin, after paraformaldehyde fixation or in hypotonic medium, were much more regular-shaped than controls and their extension matched cell deformability. 6), None of the aforementioned treatments altered adhesiveness to the surface. It is concluded that adhesive forces and passive membrane deformations are sufficient to generate initial cell alignment to adhesive surfaces, and this process is accelerated by spontaneous cytoskeletally-driven membrane motion.

Impairment of hepatic glutathione S-transferase activity as a cause of reduced biliary sulfobromophthalein excretion in clofibrate-treated rats

Administration of clofibrate reduced the maximal excretion rate of bile sulfobromophthalein (BSP) in rats but left that of phenol-3,6-dibromophthalein (DBSP) unchanged. This decrease in liver transport of BSP was due to reduced bile excretion of conjugated BSP. Hepatic uptake and storage of this dye were not impaired. Liver glutathione S-transferase activity in vitro, measured with BSP, 1,2-dichloro-4-nitrobenzene (DCNB) or 1-chloro-2, 4-dinitrobenzene (CDNB) was significantly reduced. This alteration in liver conjugating activity was probably not related to a modification of the hepatic GSH pool, since the GSH level was unchanged or only increased slightly after clofibrate treatment. Detection of this inhibition required at least two daily doses of clofibrate. Inhibition was dose-related and lasted for several days after cessation of the drug. In clofibrate-treated rats, Lineweaver-Burk plots showed a reduced Vmax for both the BSP and GSH substrates. These results suggest that clofibrate decreases hepatobiliary transport of BSP by lowering glutathione S-transferase activity in the liver.

Inhibition of liver glutathione S-transferase activity in rats by hypolipidemic drugs related or unrelated to clofibrate

The effects of in vivo administration of six hypolipidemic drugs on rat liver glutathione S-transferase activity were compared. This activity was measured with sulfobromophthalein (BSP), 1,2-dichloro-4-nitrobenzene (DCNB) or 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. Except for the nicotinic acid derivative ethanolamine oxiniacate, all the compounds tested significantly reduced it, whether or not they were related to clofibrate. The hepatic glutathione concentration either remained unchanged or only increased slightly after treatment with the various drugs. When measured, the maximal excretion rate of bile BSP dropped significantly, but not that of phenol-3,6-dibromophthalein (DBSP). Hepatic dye uptake and storage were not impaired. These results show that hypolipidemic drugs of the peroxisome proliferator type inhibit rat liver glutathione S-transferase activity and may reduce transport of anions conjugated with glutathione before excretion.

Early contacts between T lymphocytes and activating surfaces

Cells continually probe their environment to adapt their behaviour. A current challenge is to determine how they analyse nearby surfaces and how they process information to take decisions. We addressed this problem by monitoring human T lymphocyte attachment to surfaces coated with activating anti-CD3 or control anti-HLA antibodies. Interference reflection microscopy allowed us to monitor cell-to-surface apposition with a few nanometre vertical resolution during the first minutes following contact. We found that (i) when a cell fell on a surface, contact extension was preceded by a lag of several tens of seconds. (ii) During this lag, vertical membrane undulations seemed to generate transient contacts with underlying surfaces. (iii) After the lag period, the contact area started increasing linearly with a rate of about 1.5 µm(2) s(-1) on activating surfaces and about 0.2 µm(2) s(-1) on control surfaces. (iv) Concomitantly with lateral surface extension, the apparent distance between cell membranes and surfaces steadily decreased. These results are consistent with the hypothesis that the cell decision to spread rapidly on activating surfaces resulted from the integration of information yielded by transient contacts with these surfaces generated by membrane undulations during a period of about 1 min.

A new method for rapid detection of T lymphocyte decision to proliferate after encountering activating surfaces

A critical step of the adaptive response is the detection of foreign peptides on antigen presenting cells by T lymphocytes. It is a major challenge for a T lymphocyte to detect the presence of a few tens of cognate ligands or less on the membrane of a cell exposing millions of protein molecules. Detection is followed by the cell decision to undergo full or partial activation or even to start an inhibitory program. While the measurement of cell proliferation or cytokine synthesis is accepted as a reliable means of monitoring T lymphocyte activation, this requires hours or days to complete, which is a significant drawback to relate decision to particular signaling events or to assess lymphocyte reactivity in patients. Here we show that the contact area formed between T lymphocytes and potentially activating surfaces is exquisitely correlated to the proliferative response measured with the standard CFSE technique. Correlation is even better than the Erk activation that was reported as a digital reporter of cell activation. The simple and accurate method of assessing lymphocyte-to-surface contact extension that we describe might be very useful both to monitor lymphocyte reactivity for clinical purposes and to identify early steps of lymphocyte activation.

Deficient induction of sulfobromophthalein conjugating activity by phenobarbital in hamster liver

Administration of phenobarbital, a known inducer of glutathione S-transferase activity in rat liver, failed to stimulate sulfobromophthalein (BSP) conjugation by liver cytosol in hamsters. The latter displayed poor ability to conjugate this substrate, despite very high glutathione-conjugating activity with the broad-spectrum substrate 1-chloro-2,4-dinitrobenzene (CDNB). Of the six substrates tested, in this species, 1,2-epoxy-3-(4-nitrophenoxy)propane (ENPP) was the only one whose conjugation was greatly enhanced by phenobarbital (+172%). Nevertheless, hamsters proved as responsive to phenobarbital induction as rats, since it increased their relative liver weight and microsomal enzyme activity. The deficient induction of liver BSP-conjugating activity observed with phenobarbital is consistent with the finding that it did not affect the hepatic transport of this substrate in hamsters.