Effect of position on the mechanical interaction between the rib cage and abdomen in preterm infants.

To determine the influence of body position on chest wall and pulmonary function, we studied the ventilatory, pulmonary mechanics, and thoracoabdominal motion profiles in 20 preterm infants recovering from respiratory disease who were positioned in both the supine and prone position. Thoracoabdominal motion was assessed from measurements of relative rib cage and abdominal movement and the calculated phase angle (an index of thoracoabdominal synchrony) of the rib and abdomen Lissajous figures. The ventilatory and pulmonary function profiles were assessed from simultaneous measurements of transpulmonary pressure, airflow, and tidal volume. The infants were studied in quiet sleep, and the order of positioning was randomized across patients. The results demonstrated no significant difference in ventilatory and pulmonary function measurements as a function of position. In contrast, there was a significant reduction (-49%) in the phase angle of the Lissajous figures and an increase (+66%) in rib cage motion in prone compared with the supine position. In addition, the degree of improvement in phase angle in the prone position was correlated to the severity of asynchrony in the supine position. We speculate that the improvement in thoracoabdominal synchrony in the prone position is related to alterations of chest wall mechanics and respiratory muscle tone mediated by a posturally related shift in the area of apposition of the diaphragm to the anterior inner rib cage wall and increase in passive tension of the muscles of the rib cage. This study suggests that the mechanical advantage associated with prone positioning may confer a useful alternative breathing pattern to the preterm infant in whom elevated respiratory work loads and respiratory musculoskeletal immaturity may predispose to respiratory failure.     

Properties of β-Lactamase from Pseudomonas syringae

Pseudomonas syringae isolate BR2R produces tabtoxin, a β-lactam-containing antibiotic, and the causative agent of wildfire disease of green bean (Phaseolus vulgaris). β-Lactamase production has been suggested as the mechanism that protects P. syringae from tabtoxin. We sought to determine whether the organism produces β-lactamase and whether the enzyme plays a role in protection from this antibiotic. P. syringae and mutants defective in tabtoxin production and resistance produce β-lactamase. Three distinct β-lactamases with molecular weights of 41,000 were identified. The isoelectric points of the proteins were 6.1, 6.8, and 9.2. The enzymes preferentially hydrolyze cephalosporin. This investigation demonstrates that the organism produces multiple β-lactamases and describes characteristics of the proteins.     

A cumulative impact management plan for a forested wetland watershed in the Mississippi River Floodplain

A management plan using a watershed-scale approach was devised to limit loss of wetland functions in the one million ha Tensas Basin, Louisiana, U.S.A. Proposals to develop wetland areas are evaluated for their potential to affect the structure and function of the landscape as a whole. The plan required two prior steps. First, we assessed the structural and functional status of the landscape through time. Second, using the assessment, we formulated a set of environmental goals. The assessment indicated that the landscape is severely degraded; of the original forest, 85% has been lost, and the deforestation has negatively affected water quality and biota. Specific goals were devised to conserve remaining wetland resources and to restore functional integrity to the basin as a whole. On the basis of these two prior steps and principles of landscape ecology and conservation biology, we devised a plan that would establish two large tracts of bottomland forest (BLF) totaling 102 000 and 63 000 ha. These tracts would be established by reforesting about 1000 ha of corridors, primarily along streams, linking existing forest patches. In addition, set-back levees and man-made diversions would be incorporated to restore natural flooding to certain areas of remaining BLF. Existing wetlands would be prioritized on the basis of size and density of patches and placed in one of three management categories. Implementation of such a plan is possible under the present regulatory authority of U.S. federal government programs administered by regulatory agencies responsible for wetland protection.From a paper presented at the Third International Wetlands Conference, 19–23 September 1988, University of Rennes, France.     

The effect of cyclosporine A on bile secretion in dogs

Cyclosporine A is reported to cause cholestasis, but the evidence is confounded by anesthesia and surgery used in acute experiments. To better investigate the effect of cyclosporine on the liver, bile output was directly measured in three cholecystectomized dogs by cannulating the common duct through a chronic duodenal fistula. Control studies were done 1 month after surgery. Cyclosporine in oral doses of 5, 15, and 50 mg.kg-1.d-1 was then given for consecutive 1-week periods. Twice during each study period, bile output was measured for 5 h in fasted, awake animals: 3 h to establish basal conditions, followed by 2 h of taurocholate infusions at 1 and then 2 mumols.kg-1.min-1. Under basal conditions, bile flow rose with each dose of cyclosporine, increasing 63, 127, and 179% above control with cyclosporine 5, 15, and 50 mg.kg-1,d-1, respectively. Bile flow increased similarly during taurocholic acid stimulation. Cyclosporine had no effect on bile salt or bilirubin secretion. In this chronic dog model isolated from other causes of cholestasis, cyclosporine did not induce cholestasis but rather caused a dose-related choleresis without any change in bile salt secretion.