Test of 20 similar intensive care ventilators in daily use conditions--evaluation of accuracy and performances

Infrequent control, aging of components, may compromise the accuracy of ICU ventilators. In order to assess the reliability of ventilators during their clinical use, we bench tested a group of 20 CPU1 ventilators (Ohmeda) sampled at random in several ICU units. We found major leaks in 5 ventilators, attributable to the disposable tubings used in these systems. Mean error in expired tidal volume and corresponding standard deviation (precision) were greater than 100 ml in two. Positive end expiratory pressure measurement comprised a mean error higher than 2 cm H2O in 40% of the ventilators tested. The valve opening pressure threshold was correlated to the inspiratory flow (r = 0.81) contrary to the valve opening delay (average 138 +/- 40 ms). These two parameters did not correlate with the age of the ventilator. Our study addresses the need for periodic control of ventilator performance in order to minimize the risks of errors and malfunctions.

[A study of 11 ventilators for anesthesia: laboratory testing]

Eleven anaesthesia ventilators were instrumentally tested under various conditions. They included: Excel and Modulus II Plus (Ohmeda); 710 and Servo anaesthesia circle 985 (Siemens); Jollytronic (Soxil) and Elsa (Engström); SA2 and Cicero (Dräger); ABT 4,300 (Kontron); Monnal A and the prototype Alys (Taema). The test circuit comprised a two compartment model lung, a pneumotachograph, a pressure gauge in the "airway". The volume was calculated as the integral of flow rate. Each machine was calibrated by the firms' technicians. Before each test, the pneumotachograph was calibrated using a 11 air syringe and the pressure gauge with a 5 cm water column. Each machine ventilated the model lung for 30 min before starting the tests. There were five tests: 1) reliability of the machine's spirometer, 2) reliability of the ventilation rate, 3) reliability of pressure measurements, 4) effect of increasing fresh gas flow on spirometry, 5) effect of increasing downstream resistances. In usual simulated ventilatory conditions, all the machines accurately delivered the setted ventilation and spirometric measurements were with minimal error only. Several ventilators (SA2, Excel, 710, Elsa, ABT 4,300) did not succeed in maintaining their performances when compliance was strongly decreased or resistance of the test lung notably increased. Resistance in the circuit during simulated spontaneous ventilation was < 3.6 cmH2O.l-1.s-1. Increasing fresh gas flow raised the minute volume delivered in six ventilators. It is concluded that, during extreme ventilatory conditions, the inspired volume must be adjusted so as to maintain the inspired tidal volume. However, ventilators which increase inspiratory time in response to an increased mechanical load cannot be adjusted by this way.

Selection of high-level abamectin resistance from field-collected house flies, Musca domestica

Abamectin is a novel, highly promising insecticide with activity against many pests. To determine if resistance to abamectin could occur, we collected house flies from several New York dairies and selected them in the laboratory. Resistance developed rapidly and to a high level (36 or greater than 60,000-fold, depending upon test technique and/or adjuvant) that could not be overcome by the synergists piperonyl butoxide or S,S,S-tributylphosphorotrithioate. There was no increase in (cross)resistance to crotoxyphos, dichlorvos, dimethoate, tetrachlorvinphos, permethrin, dieldrin or lindane following abamectin selection. Our results suggest the potential for abamectin resistance is high, at least in house flies, and that the judicious use of abamectin will be needed to prolong its usefulness as an insecticide.

Demonstration of immuno-bound alkaline phosphatase by a direct lead method. Optimization of reaction parameters by microdensitometry using computer-aided image processing

Antigens labelled by the immunohistochemical alkaline phosphatase anti-alkaline phosphatase (APAAP) method can be visualized by a lead capture technique. Optimal conditions of the reaction, evaluated by microdensitometry using computer-aided image processing, are described.

[Analysis of failures of spinal anesthesia as a function of practice development in a university hospital]

This study is a retrospective analysis of 303 consecutive spinal anaesthesia performed in orthopaedic patients of a University Hospital between January and December 1990. Failure of spinal anaesthesia was defined as the requirement for general anaesthesia to perform surgery. The parameters studied as possible risk factors of failure were patients demographics, local anaesthetic agents and solutions and techniques of spinal anaesthesia (single injection versus continuous spinal anaesthesia). Failures were related to inadequate or incomplete extension of sensory blockade or to difficulties to perform spinal injection. Continuous spinal anaesthesia was performed in 209 patients mostly with 0.5% isobaric bupivacaine, while 94 patients received a single injection of either hyperbaric 0.5% tetracaine with adrenaline or 0.5% bupivacaine or 5% lidocaine. Failures occurred in 6.3% of the cases but were significantly less frequent with continuous spinal anaesthesia (4.8%) than with the conventional technique (9.6%). The incidence of failure was higher with hyperbaric tetracaine (11.1%) confirming its poor reliability. Inadequate extension of the anaesthetic block was the main cause of failure whatever the spinal anaesthetic technique. These results point out the reliability of continuous spinal anaesthesia but problems may occasionally occur due to spinal catheter misplacement.

[Experimental study of glucosylated low density lipoprotein metabolism and atherosclerosis]

The effect of LDL glucosylation on its pathway was assessed. Human serum LDL was isolated by density gradient ultracentrifugation and its purity was identified by polyacrylamide gel electrophoresis. LDL was radioiodinated with 125I by iodine monochloride. LDL radioreceptor assay was performed and intracellular total cholesterol was determined in cultured human fibroblasts. Maximal binding affinity (Bmax) of LDL receptor was 47 ng LDL/mg cell protein, Km was 9.4 micrograms/ml. The receptor mediated binding, internalization and degradation of glucosylated LDL were significantly decreased compared with control LDL, but total cholesterol content of cultured fibroblasts incubated with glucosylated LDL was significantly higher than those incubated with control LDL. The results suggested that glucosylation of LDL might be an important mechanism for the high incidence of disturbed lipid metabolism and atherosclerosis in diabetic patients.

Site-directed mutagenesis of recombinant rat DNA polymerase beta: involvement of arginine-183 in primer recognition

By site-directed mutagenesis using synthetic oligonucleotides, amino acid residues 181Phe-Arg-Arg183 of recombinant rat DNA polymerase beta were replaced by other amino acids to clarify the roles of these residues in the DNA synthesizing reaction. Replacement of Phe-181 by alanine reduced the enzyme activity only 30%. Replacement of Arg-182 by alanine and glutamine resulted in reduction of the activity by about 67% and 95%, respectively. The Arg-182----Gln replacement increased the binding strength to single-stranded DNA but did not significantly change the Km's for the primer and dTTP, suggesting that Arg-182 is involved in modulation of binding to the template rather than to the primer or deoxyribonucleoside triphosphate. Replacement of Arg-183 by Gln resulted in reduction of the activity by about 95%, and this change, although causing little change in binding strength to single-stranded DNA, resulted in a 3-4-fold increase in the Km's for the primer and deoxyribonucleoside triphosphate. A more dramatic change was observed when Arg-183 was replaced by Ala, which resulted in a 99.98% reduction of enzyme activity. Although the Km for deoxyribonucleoside triphosphate of this mutant enzyme was hardly changed, that for the primer increased 159-fold. Therefore, it is concluded that Arg-183 occupies an important part of the primer recognition site of DNA polymerase beta.

Dynamic injection of the digital flexor tendon sheaths

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[Opening of a foramen ovale during liver transplantation. The value of transesophageal echocardiography]

A case is reported of a foramen ovale becoming patent during orthotopic liver transplantation (OLT). The patient had a hepatoma secondary to post-hepatitis cirrhosis. Monitoring included transesophageal echocardiography (TEE). A veno-venous shunt between the right femoral, portal and left axillary veins was used so as to maintain the venous return during portal and caval clamping. The patient's haemodynamic state remained quite stable throughout this period, and no vasoactive drug was required. Five min after graft reperfusion, pulmonary arterial pressure increased suddenly (mean PAP: 27 mmHg). TEE revealed paradoxical movements of the atrial septum. Colour coded Doppler ultrasound showed blood flowing from the right to the left atrium through a patent foramen ovale. Fifteen min later, mean PAP decreased (18 mmHg) and TEE no longer showed any flow between the two atria. Several studies have reported transient pulmonary hypertension after unclamping when the donor liver is reperfused. This could induce right ventricular failure, with transient inversion of the atrial pressure gradient, which, in turn, could result in a right-to-left shunt through a patent foramen ovale. TEE can monitor regional and overall left ventricular function as well as the atrial septum. This technique might therefore to be useful for cardiac monitoring during OLT.

Physiology of the retrocalcaneal bursa

To clarify the function of the retrocalcaneal bursa the hindfoot was studied by magnetic resonance imaging at various positions of the ankle joint. In normal individuals a tongue-like extension of the retromalleolar fat pad entered the bursa during plantar flexion as the angle between Achilles tendon and calcaneus widened. The reverse occurred in dorsiflexion. In contrast, in a patient with spondyloarthritis and retrocalcaneal bursitis excessive cavitary fluid prevented the intrusion of the fat pad. The sliding motion of the fat pad in and out of the bursa during ankle motion allows a more caudal, advantageous insertion of the Achilles tendon into the calcaneus.

Conformity analysis for communication protocols

In this paper we propose a methodology for conformity analysis of communication protocols. By conformity analysis it is meant to demonstrate that a protocol does indeed provide the service for which it is intended. We specify both a protocol and its service by a CSP (Communicating Sequential Processes) based language. To perform the conformity analysis we develop a transformation system to extract from a CSP process the communication sequences that may arise during its execution, and to express these sequences in terms of behavior expressions in CCS (Calculus of Communicating Systems). By performing algebraic manipulations and the equivalence proof on these expressions, we can show that the external behavior of a protocol conforms to its intended service. A version of the Alternating Bit Protocol is used to demonstrate the feasibility of the methodology.

In vivo and in vitro tyrosine sulfation of a membrane glycoprotein

A431 cells incorporate 35SO4 into a protein of Mr 61,000 (P61). We examined sulfation of P61 by cells (in vivo) and by a cell-free system (in vitro) which requires only addition of A431 cell membranes and a 3'-phosphoadenosine 5'-phospho[35S]sulfate-generating system prepared from Krebs ascites cells. Sulfate is found exclusively in the form of tyrosine SO4 by two-dimensional high voltage electrophoresis following Pronase digestion. Endoglycosidase F digestion reduces the Mr by 2,000 but does not release the sulfate, indicating that P61 is a glycoprotein but that sulfate is not incorporated into the carbohydrate. Sulfated P61 is not found in the medium from cultured cells and remains associated with the membrane fraction following cell lysis. Treatment of membranes with 0.4 M NaCl, 0.3 M KCl, 15 mM EDTA, or pH 11.0 does not release sulfated P61. P61 is solubilized by Triton X-114 treatment of membranes and partitions into the detergent phase upon warming. Based on these characteristics, we conclude that P61 is an integral membrane protein. Trypsin digestion experiments with intact cells suggest that sulfated P61 is predominantly located in the plasma membrane. This is the first example of an integral membrane protein which is sulfated on tyrosine. The properties of the sulfation reaction are distinct from those reported for secreted proteins and are consistent with the possibility that this modification occurs at the plasma membrane rather than in the Golgi.

Electrophoretic mobility and agglutinability of red blood cells: a "new" polymorphism in mice

A quantitative method has been developed to determine agglutinability of mouse red blood cells. Tests with different inbred strains of mice revealed only two phenotypes. The same inbred strains were tested with the cytopherometer to determine the electrophoretic mobility of the corresponding red cells. Again, two phenotypes were uncovered, and faster mobility was found in the red cells that had higher agglutinability. The genetic control of this character is autosomal and codominant, and segregates independently of H-2 and coat color.