Regional pleural surface expansile forces in intact dogs by wick catheters

Hoffman and co-workers (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 55: 935-948, 1983) using a technique based on distances between percutaneously inserted X-ray opaque apical and basal lung-parenchymal markers (LPM) calibrated to known transpulmonary pressures in dogs studied without thoracotomy found that apical values measured in the head-up position were more negative than values measured simultaneously by liquid-filled catheters. This finding prompted comparison of pleural pressures (Ppl) measured simultaneously by apical and basal pairs of identical percutaneously inserted liquid-filled catheters, one open ended (OE) and the other wick tipped (WT). Simultaneously OE and WT values were always closely similar in dependent regions of the thorax and usually also in nondependent regions independent of body position and the orientation of the external segment of the wick relative to the catheter tip. However, in some instances in head-up dogs when the wick was extended distal to the catheter tip, apical WT values were 10-15 cm more negative than simultaneous OE measurements. The latter observations agree with the more negative values obtained previously by the LPM technique and support the possibility that apical expansile forces in head-up dogs may be greater than indicated by Ppl measured by liquid-filled catheters and considerably greater than indicated by usually accepted balloon techniques.

Repair of postinfarction ventricular septal defect in the elderly. Early and long-term results

We performed 13 operations on 12 elderly patients with ventricular septal defect (VSD) following myocardial infarction. All patients were older than 65 years (range 66 to 82 years) and six were over 70 years of age. Ten underwent operation, with counterpulsation support, within 3 weeks of development of the VSD. Among eight patients with anteriorly located VSDs, there were four survivors. Among four patients with inferior defects, three survived. Overall hospital survival was 58%. Hospital costs were no greater in the elderly than in younger patients. The seven long-term survivors were followed up for from 10 months to 7.5 years (mean 3.9 years). There was one sudden death at 7.5 years in a previously well man. Of the remaining six patients, five are in New York Heart Association Class I, and one is in Class II. One woman, now 84 years old, lives independently over 2 years after repair. Our experience with respect to management suggests that unless medical therapy results in continued improvement rather than stability alone, hemodynamic deterioration is inevitable, and survival for delayed repair is unlikely. Furthermore, undue delay frequently results in renal failure and severely compromises the chances for survival after repair in the acute state.

Early surgical treatment of severe electrical injury of bilateral upper extremities: a case report

A patient with both upper limbs injured by high-voltage current was treated by early wound débridement, segmental excision of the necrosed humerus of the left upper arm, internal screw fixation and vascularized skin free grafting on the right wrist. Functional recovery were satisfactory.

Heterogeneous catalysis by phospholipase A2: formulation of a kinetic description of surface effects

The kinetics of hydrolysis of aqueous dispersion of long-chain, saturated phosphatidylcholines (PC) catalysed by Crotalus atrox phospholipase A2 (PLA) have been analyzed, and a reaction mechanism proposed which takes surface effects into account. PLA is proposed to form an enzyme-substrate complex with surface substrate molecules, thereby undergoing a conformational change which exposes sites that interact with the lipid surface. After a hydrolytic event, the enzyme can either desorb from the surface (path 1), or diffuse along the surface to an adjacent substrate molecule (path 2). The path 1 dominated mechanism leads to Michaelis-Menton steady-state kinetics, and characterizes hydrolysis of gel phase PC. Evidence for saturation of the surface with PLA was obtained at high enzyme concentrations. The path 2 mechanism dominates when the desorption rate is very small; this mechanism describes hydrolysis of liquid crystalline phase PC and is characterized by an initial burst of hydrolysis followed by a very slow reaction. The velocities in these two phases of the reaction are independent of bulk PC concentration. When gel and liquid crystalline PC phases coexist, as in mixtures of dimyristoyl- and distearoyl-PC, the liquid crystalline phase is preferentially hydrolysed. Products of the reaction (lyso-PC and fatty acid) stimulated hydrolysis, apparently by stimulating desorption of PLA. The desorption rate constant appears to be a linear function of the surface concentrations of lyso-PC and fatty acid. The proposed model describes hydrolysis progress curves extremely well and is consistent with current ideas on the mechanism of catalysis by this enzyme.

Kinetics of hydrolysis of dispersions of saturated phosphatidylcholines by Crotalus atrox phospholipase A2

Dispersions of lamellar phase dipalmitoyl phosphatidylcholine (DDPC) and dimyristoyl phosphatidylcholine (DMPC) in 0.01 M CaCl2 were subjected to hydrolysis by phospholipase A2 (EC 3.1.1.4) from Crotalus atrox venom. The reaction was followed continuously by titrating the released fatty acids. For hydrolysis of gel phase phosphatides, the steady-state initial velocities were hyperbolic functions of bulk lipid concentrations. At the 'pre-transition' temperature (34 degrees C for DPPC, 15 degrees C for DMPC), there was a large increase in the Michaelis parameter Vmax but no change in the parameter Km. A model was devised to account for these observations, in which the enzyme desorbs from the lipid surface after hydrolysis. The desorption rate constant is postulated to increase above the pretransition temperature. For hydrolysis of liquid crystalline phosphatides, the reaction consisted of a short initial burst of hydrolysis, a long 'lag' period of very slow reaction, followed by a dramatic increase in the reaction rate. Addition of 10 mol% lysolecithin or fatty acid abolished the 'lag' period. It was postulated that the enzyme adsorbs irreversibly to the surface of the liquid crystalline phase. Reaction products are postulated to stimulate desorption of enzyme from the surface. Thus, temperature-dependent changes in the rate of hydrolysis of dispersed phosphatidylcholines are attributed to changes in the rate of desorption of the enzyme from the lipid surface.

T4 Bacteriophage-coded RNA polymerase subunit blocks host transcription and unfolds the host chromosome

T4 bacteriophage mutants selected for their ability to grow with cytosine in their DNA are defective in host transcriptional shutoff and host chromosome unfolding. The host RNA polymerase purifed from cells infected by such a mutant lacks a small T4-coded subunit.

Variable refractive index and birefringent waveguides by sputtering tantalum in O(2)-N(2) mixtures

Optical waveguides with losses <1 dB/cm at 632.8 nm have been prepared by sputtering tantalum in O(2)-N(2) mixtures. As the fraction of N(2) in the sputtering atmosphere increases, the refractive index of the guides exhibit a sharp maximum and then decreases to a much lower value, and the films become birefringent. Using an oxygen discharge, the indices at 632.8 nm for both TE and TM modes are 2.083 +/- 0.003, but the values are 1.850 and 1.877, respectively, for the highest fraction of nitrogen used. The indices have been measured at wavelengths down to 457.9 nm. For low fractions of N(2), the results are consistent with a decreasing film density and a constant molecular polarizability, but a number of effects, including the birefringence, are inconsistent with this picture. Waveguide structures, such as interconnects, branching waveguides, and layered directional couplers, have been demonstrated using films with different indices. The birefringence has also been verified by observation of interference between TE and TM modes simultaneously coupled into the guide.