Morphology and gelation of thermosensitive xyloglucan hydrogels.

Galactose modified xyloglucan is a thermally reversible hydrogel that is increasingly used in the biomedical field due to the ease of altering the gelation time and temperature by modifying the galactose removal ratio. However there is little information concerning the morphology and rheological properties of the hydrogel under physiological conditions. Differential scanning microcalorimetry (DSmicroC) showed the thermal gelation process to occur over a broad temperature range (5-50 degrees C). The rheological properties of the hydrogels were investigated as a function of concentration, temperature and ionic strength. The final elastic moduli of the hydrogels increased with increases in concentration. Isothermal rheology suggests that the gelation occurred in two distinct stages, which was influenced by the solution media. Scanning electron microscopy (SEM) was used to characterize the morphology of the xyloglucan which were thermally gelled at 37 degrees C. The resultant morphology was strongly dependent on the concentration of the hydrogel. Strong hydrogels were only obtained at 3 wt.% at 37 degrees C, and the morphology characterized by an open 3-dimensional network, comprised of thin membranes. It is proposed that the first stage of the isothermal gelation is the formation and growth of the thin membranes, followed by the formation of a three dimensional network.

Aerosol delivery and safety of recombinant human deoxyribonuclease in young children with cystic fibrosis: a bronchoscopic study. Pulmozyme Pediatric Broncoscopy Study Group.

The purpose of this study was to assess the delivery to the lungs and the short-term safety of recombinant human deoxyribonuclease (rhDNase, Pulmozyme) in children with cystic fibrosis younger than 5 years of age compared with older children. Patients between the ages of 3 months and 10 years had bronchoscopic examination with bronchoalveolar lavage (BAL) after administration of an aerosol dose of 2.5 mg of rhDNase. After recovery from the procedure, patients were discharged home for an additional 13 days of rhDNase therapy. During this time adverse events were recorded to assess short-term safety. A total of 98 patients were enrolled, 65 (66%) aged 3 months to 5 years and 33 (34%) aged 5 years to 10 years. Deoxyribonuclease concentrations in BAL fluid were variable (interquartile range, 752 to 3943 micrograms/mL epithelial lining fluid [ELF]) and did not depend on patient age, weight, or height or differ when delivered through a mouthpiece or mask. The median value for the BAL DNA concentration in the younger group was 432 micrograms/mL ELF compared with 703 micrograms/mL ELF in the older patients. This study demonstrates the value of bronchoscopy and BAL for assessing nebulized medication delivery in young children and shows that aerosolized medications can be delivered to and are present in comparable amounts in the lower airways of younger and older children. Exposure to rhDNase appears to be safe over 2 weeks in infants and young children with cystic fibrosis.

A cephalometric, tomographic, and dental cast evaluation of Fränkel therapy.

The purpose of this study was to evaluate the skeletal, dental, and condylar positional changes induced by Fränkel FR-2 therapy. The pre- and posttreatment cephalometric, tomographic, and dental cast records of 25 consecutively treated cases were evaluated. Results showed little Class II skeletal correction with no headgear-type restraining effect on the maxilla or mandibular growth stimulation noted. Significant amounts of maxillary incisor retraction and mandibular incisor proclination were observed. The maxillary intermolar width along with the mandibular intercanine and intermolar widths were significantly increased during treatment. No significant changes in condylar position were found during Fränkel therapy and only a small increase in mandibular plane angle was noted.

Quantitation of lactate by a kinetic method with an extended range of linearity and low dependence on experimental variables.

We report conditions and characteristics of a new kinetic method for measuring lactate. Using a multiple linear regression method, we fit data for absorbance and for rate of change of absorbance to a modified rate form of the Michaelis-Menten equation. The principal objective of the fitting process is to compute the total absorbance change, delta A infinity, that would be measured if the reaction were monitored from the point of mixing to equilibrium. For data collected at 1-s intervals from 5 to 200 s, the fitting process gives values of delta A infinity that vary linearly with lactate concentration from 10.6 to 180 mumol/L in the reaction cell after 150-fold dilution of samples. For a range of enzyme activities that produced a 20% change in the initial rate, the regression-kinetic treatment yielded results with no detectable systematic error. The mean within-day CV was 2.1% for an average concentration of 14.4 mmol/L; the day-to-day CV was 5.2% for 3.90 mmol/L. For 25 samples of canine plasma with lactate concentrations from 2 to 26 mmol/L, comparison of results obtained with the regression-kinetic method (y) with results obtained with a commercially available equilibrium method (x) gave a least-squares equation of y = 1.01x - 10 mumol/L.

A nonlinear regression-kinetic method for quantification of serum triglycerides.

We report a new kinetic approach to the quantification of triglycerides (triacylglycerols) in human sera. The new approach combines a commercially available enzyme-reagent system with a multiple-linear-regression data-processing method. Values of absorbance collected at 3-s intervals between 20 and 305 s are fitted to a pseudo-first-order model to compute the total change in absorbance expected if the reaction were to proceed to equilibrium. The computed absorbance change varies linearly with triglyceride concentration between 3 and 20 mumol/L (after 250-fold dilution of sample). The pooled relative standard deviation was 7.2% for 23 serum samples with triglyceride concentrations between 3 and 20 mumol/L. Comparison of kinetic (y) and equilibrium (x) absorbance changes for the 23 sera gave a least-squares equation of y = 0.994x + 0.00066, confirming good agreement between the methods. The temperature coefficient is less than 0.2% per degree Celsius.

Kinetic method having a linear range for substrate concentrations that exceed Michaelis-Menten constants.

We describe a new data-processing method for the kinetic quantification of substrates of enzyme-catalyzed reactions. Nonlinear regression is used to fit data for absorbance (A) and rate (dA/dt) vs time to the rate form of the Michaelis-Menten equation. Fitting parameters are the maximum velocity (Vmax), the Michaelis constant (Km), and the total absorbance change (delta A infinity) that would be observed if the reaction were monitored to completion. The method is evaluated with use of the uricase-catalyzed oxidation of uric acid, monitored at 293 nm, as a model reaction. Results for aqueous solutions demonstrate linear calibration plots for concentrations from well below to 3.5-fold the Michaelis constant, a zero temperature coefficient (36-38 degrees C), and near zero dependence on inhibitor (xanthine) concentrations that reduce the initial rate of 28% of its uninhibited value. Relative standard deviations (RSDs) vary from about 2 to 15%, depending on the data range (95-65% completion) used to process the data. For an 80% reaction data range, the pooled RSD was 6%. The sensitivity for uric acid is 1.15 x 10(4) L mol-1 cm-1 and the detection limit (95% confidence level) is 1.2 x 10(-6) mol/L.

Disturbances in atrial rhythm and conduction following the surgical creation of an atrial septal defect by the Blalock-Hanlon technique.

Disturbances in atrial conduction or rhythm, or both, were found in 16 of 27 patients undergoing the surgical creation of an atrial septal defect by the Blalock-Hanlon technique. These included P-wave aberrations of intra-atrial block and ectopic atrial rhythm, A-V rhythm, A-V dissociation, sinus bradycardia, atrial flutter, escape-capture bigeminy, and atrial premature beats. Some of these were transient and occurred within 2 weeks after surgery. It seems likely that tissue trauma engendered by the clamp and resection of the atrial septum with possible injury to the internodal conducting pathways may be the genesis of these early postoperative disturbances. Of the eight cases with transient disturbances, six occurred in this period. Later changes, such as intra-atrial block, sinus bradycardia, and atrial flutter, may be attributed to changes in atrial size secondary to the postoperative pathophysiology. Digitalis intoxication and congestive heart failure cannot be excluded as contributory factors in either the early or the late disturbances. It was not possible to correlate the incidence and nature of these disturbances with morbidity and mortality. In such severely ill, cyanotic infants, irregularities, however slight, may have altered cardiac function significantly and contributed to their deaths.