September 2, 2008, Volume 55, No. 2
New Method of Managing Risk in Pregnancy
An alternative method for obstetric care has led to lower neonatal intensive care unit (NICU) admission rates, higher uncomplicated vaginal birth (UVB) rates, and a lower mean Adverse Outcome Index (AOI) score, according to a new study from the Penn School of Medicine and published in the June issue of the American Journal of Obstetrics and Gynecology.
The alternative method is known as Active Management of Risk in Pregnancy at Term, or AMOR-IPAT, for short. AMOR-IPAT uses “risk-based preventative labor induction to ensure that each pregnant woman enters labor at a gestational age that maximizes her chance for vaginal delivery,” said lead researcher, Dr. James M. Nicholson, assistant professor of family medicine and community health at Penn.
“Over the past decade, the rates of cesarean delivery have climbed above 30%,” said Dr. Nicholson. “Cesarean delivery, when compared with vaginal delivery, is associated with higher rates of postpartum hemorrhage, major postpartum infection and hospital readmission,” he added.
The study included 270 women who were recruited when they were between 32 and 37 and a half weeks into their pregnancy. Women who remained undelivered at 37 weeks and 4 days of gestation were randomized to either AMOR-IPAT or usual care.
Risk factors for the AMOR-IPAT exposed group were identified and categorized as either interfering with placental growth or accelerating fetal growth. Each of these factors is associated with a published odds ratio for cesarean delivery, which, in turn, is used to determine the optimal time of delivery. If a woman in the exposed group did not experience spontaneous labor as she approached the end of this time frame, preventative labor induction was scheduled. In the AMOR-IPAT group, the greater the number and severity of risk factors, the earlier preventative labor induction was offered within the term period (38–41 weeks of gestation).
The findings of this study suggest that the AMOR-IPAT approach to obstetric risk lead to healthier babies and better birth outcomes for mothers. In addition, the results challenge the current belief that a greater use of labor induction necessarily leads to higher rates of cesarean delivery.
Why Are Diamonds Slippery?
Engineers and physicists have long studied diamonds because even though the material is hard it slips and slides with remarkably low friction, making it an ideal material or coating for seals, high performance tools and high-tech moving parts.
Dr. Robert Carpick, associate professor of mechanical engineering and applied mechanics at SEAS, and his group, led a collaboration with researchers from Argonne National Laboratories, the University of Wisconsin-Madison and the University of Florida, to determine what makes diamond films slippery. The study, funded by the US Air Force and US Department of Energy, was published in the June issue of Physical Review Letters.
The Penn experiments, the first study of diamond friction convincingly supported by spectroscopy, looked at two of the main hypotheses posited for years as to why diamonds demonstrate such low friction and wear properties. Using a highly specialized technique know as photoelectron emission microscopy, or PEEM, the study reveals that this slippery behavior comes from passivation of atomic bonds at the diamond surface that were broken during sliding and not from the diamond turning into its more stable form, graphite. The bonds are passivated by dissociative adsorption of water molecules from the surrounding environment. The researchers also found that friction increases dramatically if there is not enough water vapor in the environment.
Some previous explanations for the source of diamond’s super low friction and wear assumed that the friction between sliding diamond surfaces imparted energy to the material, converting diamond into graphite, itself a lubricating material. However, until this study no detailed spectroscopic tests had ever been performed to determine the legitimacy of this hypothesis. The PEEM instrument, part of the Advanced Light Source at Lawrence Berkeley National Laboratory, allowed the group to image and identify the chemical changes on the diamond surface that occurred during the sliding experiment.
The team tested a thin film form of diamond known as ultrananocrystalline diamond and found super low friction (a friction coefficient ~0.01, which is more slippery than typical ice) and low wear, even in extremely dry conditions, (relative humidity ~1.0%). Using a microtribometer, a precise friction tester, and X-ray photoelectron emission microscopy, a spatially resolved X-ray spectroscopy technique, they examined wear tracks produced by sliding ultrananocrystalline diamond surfaces together at different relative humidities and loads. They found no detectable formation of graphite and just a small amount of carbon re-bonded from diamond to amorphous carbon. However, oxygen was present on the worn part of the surface, indicating that bonds broken during sliding were eventually passivated by the water molecules in the environment.
Already used in industry as a mechanical seal coating to reduce wear and improve performance and also as a super-hard coating for high-performance cutting tools, this work could help lead to increased use of diamond films in machines and devices to increase service life, prevent wear of parts and save energy wasted by friction.
High-Tech Relief for Peripheral Arterial Disease
Researchers at the School of Medicine are the first in the Philadelphia region to begin using an innovative new drug-eluting stent to treat patients with peripheral arterial disease (PAD), the clogging and hardening of arteries that supply blood to the legs and feet. Afflicting ten million Americans, the disease is common among patients with diabetes and those who smoke, but studies show that only 25 percent of patients with the disease are undergoing treatment—which doctors say is essential, since PAD can cause debilitating leg pain that makes it difficult to walk and even lead to amputations.
“We know that earlier diagnosis and interventions saves limbs,” says Dr. Jeffrey Carpenter, professor of vascular surgery, who is the principal investigator for the Zilver PTX Drug-Eluting Stent trial site at Penn.
The Zilver stent, modeled on the same devices used to prop open blocked coronary arteries, is the first of its kind used to treat blockages in the major artery in the thigh. The stent is designed to provide both a mechanical and a chemical treatment for the blocked artery—placed through a minimally invasive catheter in the groin, the stent pops open like a scaffold inside the artery, and its paclitaxel drug coating aims to keep additional plaques from accumulating. This Phase II trial will test the effectiveness of that combination at keeping arteries open over time.
It’s hoped that the device will help restore patients’ function, decrease pain and eliminate the need for more invasive treatment such as bypass surgery. The trial will enroll 420 patients worldwide, about 80 at Penn. Participants will be randomized into two groups, one to receive the Zilver PTX Stent (manufactured by Cook Medical) and one to receive balloon angioplasty, a more traditional treatment for the disease. The safety phase of the trial, which was completed in 2006, involved 60 patients, none of whom showed breakage of the stent or major complications similar to angioplasty.
From Canada to the Caribbean: Tree Leaves Control Own Temperature
The temperature inside a healthy, photosynthesizing tree leaf is affected less by outside environmental temperature than originally believed, according to researchers in the School of Arts & Sciences.
Surveying 39 tree species ranging in location from subtropical to boreal climates, researchers found a nearly constant temperature in tree leaves. These findings provide new understanding of how tree branches and leaves maintain a homeostatic temperature considered ideal for photosynthesis and suggests that plant physiology and ecology are important factors to consider as biologists tap trees to investigate climate change.
Tree photosynthesis, according to the study, occurs when leaf temperatures are about 21°C. This homeostasis of leaf temperature means that in colder climates leaf temperatures are elevated and in warmer climates tree leaves cool to reach optimal conditions for photosynthesis. Therefore, methods that assume leaf temperature is fixed to ambient air require new consideration.
“It is not surprising to think that a polar bear in northern Canada and a black bear in Florida have the same internal body temperature,” Dr. Brent Helliker, professor of biology, said. “They are endothermic mammals like us, and they generate their own heat. However, to think that a black spruce in Canada and a Caribbean pine in Puerto Rico have the same average leaf temperature is quite astonishing, particularly since trees are most definitely not endothermic. Our research suggests that they use a combination of purely physical phenomena—like the cooling from water evaporation or the warming caused by packing a lot of leaves together—to maintain what looks like leaf-temperature homeostasis.”
The study, funded by the department of biology and the Mellon Foundation, presents a new hypothesis for why certain trees grow in certain climates and provides a new theory for how and why trees in the north will suffer from global warming, by overheating due to the mechanisms they have evolved to keep their leaves warm.Weather-forecasting models rely on accurate estimates of surface-water evaporation, much of which comes from tree leaves. Knowing the temperature of these leaves is crucial to an accurate prediction of future climate scenarios.
The research, published in Nature, contradicts the longstanding assumption that temperature and relative humidity in an actively photosynthesizing leaf are coupled to ambient air conditions. The assumption in all of these studies was that tree leaf temperatures were equal to ambient temperatures. Another finding was that across such a large area and across so many types of tree that the leaves seemed to be operating at the same temperature, probably a result of natural selection acting to maintain optimal temperature for photosynthesis in the face of widely varying ambient climates.