Strain analysis of a chiral smectic-A elastomer.

We present a detailed analysis of the molecular packing of a strained liquid crystal elastomer composed of chiral mesogens in the smectic-A phase. X-ray diffraction patterns of the elastomer collected over a range of orientations with respect to the x-ray beam were used to reconstruct the three-dimensional scattering intensity as a function of tensile strain. We show that the smectic domain order is preserved in these strained elastomers. Changes in the intensity within a given scattering plane are due to reorientation, and not loss, of the molecular order in directions orthogonal to the applied strain. Incorporating the physical parameters of the elastomer, a nonlinear elastic model is presented to describe the rotation of the smectic-layered domains under strain, thus providing a fundamental analysis to the mechanical response of these unique materials.

Indomethacin therapy for patent ductus arteriosus in premature infants: efficacy of a dosing strategy based on a second-dose peak plasma indomethacin level and estimated plasma indomethacin levels.

The objective of this study was to determine the rate of patent ductus arteriosus (PDA) closure in premature infants using an adjustable indomethacin (INDO) dosing strategy, based on a second-dose peak plasma INDO level. We conducted a retrospective review of the medical records of premature infants that were treated with INDO for a PDA, had a second dose peak plasma NDO levels, and followed predetermined guidelines for INDO dosing adjustments, over a 4-year period (1995 to 1998). Of 103 infants treated with the adjustable INDO dosing strategy, 66 (64%) achieved PDA closure whereas 37 (36%) did not. No differences in the second-dose peak plasma INDO levels (830 +/- 339 versus 702 +/- 381 ng/mL), day of life treatment was started (4 +/- 3 versus 4 +/- 2 days), or the number of doses of INDO received (4 +/- 1 versus 5 +/- 2 dose) were observed between responders and nonresponders. However, fourth-dose peak plasma INDO levels, which were available from 38 of 66 (57%) of the responders and 20 of 37 (54%) of the nonresponders, were lower in nonresponders (1553 +/- 413 versus 1829 +/- 609 ng/mL, p < 0.05). Patient demographics, including birth weight and gestational age, were similar between these groups. Using an adjustable INDO dosing strategy, based on a second-dose peak plasma INDO level and estimated plasma levels, PDA closure rates of 64% can be achieved. Although a clear relationship between INDO plasma levels and PDA closure was evident form this study, the rate of PDA closure in our study was lower than has been observed in studies with serial plasma INDO level monitoring.

Necrotizing enterocolitis and gastrointestinal complications after indomethacin therapy and surgical ligation in premature infants with patent ductus arteriosus.

BACKGROUND: Indomethacin is the most frequently used pharmacological agent for closure of a patent ductus arteriosus (PDA) in premature infants. However, reports of complications, particularly, necrotizing enterocolitis (NEC) and isolated gastrointestinal perforation have generated concerns about the use of this medication. OBJECTIVES: A retrospective study to compare the incidence of NEC, NEC-related gastrointestinal complications and isolated gastrointestinal perforation among premature infants treated for a PDA with either, indomethacin alone (I), surgical ligation alone (L), or indomethacin followed by surgical ligation (I-L). METHODS: The medical records of 224 infants that underwent treatment, either pharmacological or surgical, for a PDA, confirmed by echocardiography, over a 4-year period (1995 to 1998) were analyzed. Treatment history and gastrointestinal complications were reviewed. RESULTS: Of the 224 infants, 108 (48.2%) were treated with I, 50 (22.3%) by L, 66 (29.5%) with I-L. The clinical characteristics of the three treatment groups were similar and no differences in the incidence of NEC were observed between groups. NEC occurred in 14 (13%) of the I group, seven (14%) of the L group, and eight (12%) of the I-L group. The rate of NEC related gastrointestinal complications and isolated gastrointestinal perforation were also similar among groups. CONCLUSION: In this large retrospective study, indomethacin treatment for a significant PDA in premature infants was not associated with a greater risk for NEC or NEC-related gastrointestinal complications than surgical ligation.