Alexander Lin

Management of the second stage of labor in nulliparas with continuous epidural analgesia

OBJECTIVE To determine if waiting for a strong urge to push in nulliparas with continuous low-concentration epidural analgesia shortens the pushing duration in the second stage. METHODS Nulliparas with standardized patient-controlled epidural analgesia (0.0625% bupivacaine with fentanyl 2 μg/mL) were randomly assigned to pushing immediately upon complete cervical dilatation (n = 85) or waiting for a strong urge to push (n = 117). Urge to push and patient satisfaction were quantified on 100-mm visual analogue scales. Duration of pushing and total duration of the second stage were analyzed as survival time data. RESULTS Women who delayed pushing and those who pushed immediately were similar with respect to maternal characteristics. Women who delayed pushing had a stronger urge to push (P < .01) and a longer second stage (P < .05) than women who pushed immediately. There was no significant difference in the time spent pushing (median 57 versus 62 minutes, respectively) or the median level of patient satisfaction (80 mm for both groups). There were no significant differences in the overall rates of cesarean delivery (6% versus 12%, respectively), cesarean delivery during the second stage (2% in each group), spontaneous vaginal delivery (70% versus 69%, respectively), or neonatal or maternal morbidity. CONCLUSION In nulliparas with continuous low-concentration epidural analgesia, delaying pushing until a strong urge is felt does not reduce the duration of pushing in the second stage of labor.

Postoperative outcomes after robotic versus abdominal myomectomy.

Operative time was significantly longer with robotic myomectomy; however, patients experienced shortened lengths of hospital stay and less time before returning to work.

Liquid B2O3 up to 1700 K: x-ray diffraction and boroxol ring dissolution.

Using high energy x-ray diffraction, the structure factors of glassy and molten B2O3 were measured with high signal-to-noise, up to a temperature of T  =  1710(20) K. The observed systematic changes with T are shown to be consistent with the dissolution of hexagonal [B3O6] boroxol rings, which are abundant in the glass, whilst the high-T (>~1500 K) liquid can be more closely described as a random network structure based on [BO3] triangular building blocks. We therefore argue that diffraction data are in fact qualitatively sensitive to the presence of small rings, and support the existence of a continuous structural transition in molten B2O3, for which the temperature evolution of the 808 cm−1 Raman scattering band (boroxol breathing mode) has long stood as the most emphatic evidence. Our conclusions are supported by both first-principles and polarizable ion model molecular dynamics simulations which are capable of giving good account of the experimental data, so long as steps are taken to ensure a ring fraction similar to that expected from Raman spectroscopy. The mean thermal expansion of the B-O bond has been measured directly to be αBO  =  3.7(2)  ×  10−6 K−1, which accounts for a few percent of the bulk expansion just above the glass transition temperature, but accounts for greater than one third of the bulk expansion at temperatures in excess of 1673 K.

Grain Boundary Assisted Crevice Corrosion in CoCrMo Alloys

Cobalt chromium molybdenum alloys have been extensively used for biomedical implants, but are susceptible to grain boundary corrosion resulting from local chromium depletion, which is called sensitization. This work extended the understanding of chromium depleted zones in CoCrMo alloys and their role in corrosion to the nanoscale. Selected boundaries were analyzed from the millimeter to the nanometer scale in order to link the chemical composition and crystallographic structure to the observed local corrosion properties. The shape and severity of grain boundary corrosion crevices were measured, linked with the coincidence site lattice geometry. Additionally, direct high-resolution energy dispersive x-ray spectroscopy maps of chromium depleted zones at the grain boundaries were measured to completely characterize the grain boundary properties. Chromium depleted zones were found in 100% of corroded grain boundaries, yet were too small to follow classical models of sensitization. Nanoscale regions of chromiu...

Effects of Grain Boundary Misorientation and Chromium Segregation on Corrosion of CoCrMo Alloys

The influence of grain boundary interfacial energy on the structure of carbides and the local segregation of chromium were investigated at the nanoscale for coincident site lattice boundaries in a ...

Osseointegration of a 3D Printed Stemmed Titanium Dental Implant: A Pilot Study

In this pilot study, a 3D printed Grade V titanium dental implant with a novel dual-stemmed design was investigated for its biocompatibility in vivo. Both dual-stemmed (n = 12) and conventional stainless steel conical (n = 4) implants were inserted into the tibial metaphysis of New Zealand white rabbits for 3 and 12 weeks and then retrieved with the surrounding bone, fixed, dehydrated, and embedded into epoxy resin. The implants were analyzed using correlative histology, microcomputed tomography, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The histological presence of multinucleated osteoclasts and cuboidal osteoblasts revealed active bone remodeling in the stemmed implant starting at 3 weeks and by 12 weeks in the conventional implant. Bone-implant contact values indicated that the stemmed implants supported bone growth along the implant from the coronal crest at both 3- and 12-week time periods and showed bone growth into microporosities of the 3D printed surface after 12 weeks. In some cases, new bone formation was noted in between the stems of the device. Conventional implants showed mechanical interlocking but did have indications of stress cracking and bone debris. This study demonstrates the comparable biocompatibility of these 3D printed stemmed implants in rabbits up to 12 weeks.

Classifying the Severity of Grain Boundary Corrosion in CoCrMo Biomedical Implants

Cobalt-chromium-molybdenum (CoCrMo) alloys with the addition of carbon are popular for biomedical devices, specifically total hip replacements, due to their superior wear resistance, longer service duration and reduced inflammation resulting from such devices. In the mid-2000s, approximately 35% of the hip replacements in the US were metal-on-metal hip replacements based on CoCrMo alloys.[1] Despite its superior mechanical properties and wear resistance compared to metal-on-plastic or ceramics systems, CoCrMo is susceptible to corrosion due to tribological events such as joint movements and its constant exposure to corrosive body fluids.