New Eocene fossil data suggest climate models may underestimate future polar warming

Foraminifera, small single-celled marine organisms, form their shells in concert with the ocean's temperature and chemistry. Like tiny time capsules, they can reveal the climate conditions of millions of years ago.

A new international analysis of marine fossils shows that warming of the polar oceans during the Eocene, a greenhouse period that provides a glimpse of Earth's potential future climate, was greater than previously thought.

By studying the chemical composition of fossilized foraminifera, tiny single-celled animals that lived in shallow tropical waters, a team of researchers generated precise estimates of tropical sea surface temperatures and seawater chemistry during the Eocene Epoch, 56-34 million years ago. Using these data, researchers fine-tuned estimates from previous foram studies that captured polar conditions to show tropical oceans warmed substantially in the Eocene, but not as much as polar oceans.

Importantly, when modern climate models -- the same as those used in the United Nations' recent Intergovernmental Panel on Climate Change reports -- were run under Eocene conditions, many could not replicate these findings. Instead, the models consistently underestimated polar ocean warming in the Eocene.

This discrepancy may result from a gap in our understanding of the climate system or from what we know about the Eocene, said David Evans, the study's lead author and Leverhulme Research Fellow at the University of St Andrews' School of Earth and Environmental Sciences. If it does indeed relate to the climate system, it raises the possibility that predictions of future polar warming are also too low.

"Yes, the tropics are warming but nowhere near to the same degree as the polar regions," Evans said. "That's something we really need to be able to understand and replicate in climate models. The fact that many models are unable to do that at the moment is worrying."

The researchers published their findings this week in the Proceedings of the National Academy of Sciences.

Scientists frequently look to the Eocene to understand how the Earth responds to higher levels of carbon dioxide. During the Eocene, the concentration of carbon dioxide in the atmosphere was more than 560 parts per million, at least twice preindustrial levels, and the epoch kicked off with a global average temperature more than 8 degrees Celsius -- about 14 degrees Fahrenheit -- warmer than today, gradually cooling over the next 22 million years. These characteristics make the Eocene a good period on which to test our understanding of the climate system, said Laura Cotton, study co-author and curator of micropaleontology at the Florida Museum of Natural History.

One of the challenges has been accurately determining the difference between sea surface temperatures at the poles and the equator during the Eocene, with models predicting greater differences than data suggested.

The research team used large bottom-dwelling forams as "paleothermometers" to gain a more precise temperature reading. Forams have an exceptionally long fossil record, spanning more than 540 million years, and they are often well-preserved in ocean sediments. Most are small enough to fit into the eye of a needle -- Cotton describes them as "an amoeba with a shell" -- but they were so abundant during the Eocene that there are entire rocks composed of them.

"If you look at the pyramids, they're full of these tiny little lentil-like things -- those are forams," Cotton said. "The ancient Greeks thought the pyramids were made from the fossilized lentils of slaves, but it's just the limestone from one of these deposits that is absolutely filled with them."

Forams form their shells in concert with ocean temperatures and chemistry, acting as miniscule time capsules, each containing a precise record of the temperature and ocean chemistry during its lifetime. Their shells are primarily made of calcium, carbon and oxygen. Heavy isotopes of carbon and oxygen bond together as a foram makes its shell -- the cooler the temperature, the more they bond to each other.

By analyzing these clumped isotopes from fossil specimens found in India, Indonesia and Tanzania, the researchers could get an accurate reading of sea surface temperature across the tropics in the Eocene. They also lasered a small hole in each specimen to measure the amount of magnesium and calcium that vaporized, revealing the seawater chemistry.

They found that tropical sea surface temperature in the Eocene was about 6 degrees Celsius -- about 10 degrees Fahrenheit -- warmer than today.

"This was the first time we had samples that were good enough and this method was well-known enough that it could all come together," Cotton said.

The team then used their dataset from the tropics to back-calculate the temperature and chemistry of polar oceans, relying on previous studies of forams that captured the conditions of those regions.

With this correction factor in place, they investigated the degree to which polar oceans warmed more than the tropics, a feature of the climate system known as polar amplification. Their data showed that the difference between polar and equatorial sea surface temperatures in the Eocene was an estimated 20 degrees Celsius, about 36 degrees Fahrenheit. Today the difference is 28 degrees Celsius, indicating that polar regions are more sensitive to increases in atmospheric carbon dioxide than the tropics.

Troublingly, said Evans, when the team compared their data with various modern climate models under Eocene conditions, most models underestimated polar amplification by about 50 percent.

The two models that came closest to reproducing the team's data had one key aspect in common -- they modified the way they accounted for cloud formation and the longevity of clouds in the atmosphere, particularly in the polar regions.

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Astronomers produce first detailed images of surface of giant star

This is the giant star, ?1Gruis. Credit European Southern Observatory

An international team of astronomers has produced the first detailed images of the surface of a giant star outside our solar system, revealing a nearly circular, dust-free atmosphere with complex areas of moving material, known as convection cells or granules, according to a recent study.

The giant star, named π1Gruis, is one of the stars in the constellation Grus (Latin for the crane, a type of bird), which can be observed in the southern hemisphere. An evolved star in the last major phase of life, π1Gruis is 350 times larger than the Sun and resembles what our Sun will become at the end of its life in five billion years. Studying this star gives scientists insight about the future activity, characteristics and appearance of the Sun.

Convection, the transfer of heat due to the bulk movement of molecules within gases and liquids, plays a major role in astrophysical processes, such as energy transport, pulsation and winds. The Sun has about two million convective cells that are typically 2,000 kilometers across, but theorists believe giant and supergiant stars should only have a few large convective cells because of their low surface gravity. Determining the convection properties of most evolved and supergiant stars, such as the size of granules, has been challenging because their surfaces are frequently obscured by dust.

In this study, the researchers discovered the surface of the giant star π1Gruis had a complex convective pattern and the typical granule measured 1.2 x 10^11 meters horizontally or 27 percent of the diameter of the star. The findings are published in the journal Nature.

"This is the first time that we have such a giant star that is unambiguously imaged with that level of details," said Dr. Fabien Baron, assistant professor in the Department of Physics and Astronomy at Georgia State University. "The reason is there's a limit to the details we can see based on the size of the telescope used for the observations. For this paper, we used an interferometer. The light from several telescopes is combined to overcome the limit of each telescope, thus achieving a resolution equivalent to that of a much larger telescope."

The star π1Gruis was observed with the PIONIER instrument, which has four combined telescopes, in Chile in September 2014. Baron, who specializes in making images, used interferometric data, image reconstruction software and algorithms to compose images of the star's surface. Interferometry is relatively new to astronomy, and Georgia State's Center for High Angular Resolution Astronomy array was the first facility to use interferometry to image a star similar to the Sun in 2007.

This study was also the first to confirm theories about the characteristics of granules on giant stars.

"These images are important because the size and number of granules on the surface actually fit very well with models that predict what we should be seeing," Baron said. "That tells us that our models of stars are not far from reality. We're probably on the right track to understand these kinds of stars."

The detailed images also showed different colors on the star's surface, which correspond to varying temperatures. A star doesn't have the same surface temperature throughout, and its surface provides our only clues to understand its internals. As temperatures rise and fall, the hotter, more fluid areas become brighter colors (such as white) and the cooler, more dense areas become darker colors (such as red).

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New Caledonian crows extract prey faster with complex hooked tools

New Caledonian crow using a stick as a tool.

Biologists at the Universities of St Andrews and Edinburgh have discovered why some crows 'craft' elaborate hooked tools out of branched twigs.

The new study, published in Nature Ecology & Evolution today (22 January), explores why crows go the extra mile rather than using simple, unmodified sticks to extract prey -- it allows them to get at hidden food several times faster than if they used basic (non-hooked) tools.

New Caledonian crows are famous for their use of tools to winkle beetle grubs and other small prey out of hiding places. Although crows are capable of extracting food with straight twigs, in some areas they actively manufacture hooked stick tools before going hunting.

"It's a painstaking sequence of behaviours," explains lead author Dr James St Clair, from the School of Biology, University of St Andrews. "Crows seek out particular plant species, harvest a forked twig, and then -- firmly holding it underfoot -- carve, nibble and peel its tip, until it has a neat little hook."

Biologists have long assumed that there was some benefit to crows manufacturing hooked tools, but had no idea just how much better they might be. The Scottish team conducted experiments to record how long wild-caught crows took to extract food from a range of naturalistic tasks, using either hooked or non-hooked tool designs.

Depending on the task, they found that hooked tools were between two and ten times more efficient than non-hooked tools. "That's a huge difference!" says project leader, Professor Christian Rutz from the University of St Andrews. "Our results highlight that even relatively small changes to tool designs can significantly boost foraging performance."

These new findings help explain why New Caledonian crows have evolved such remarkable tool-making abilities: "In nature, getting food quickly means that birds have more time and energy for reproduction and steering clear of predators. It's really exciting that we were able to measure the benefits of these nifty crow tools," adds study co-author Professor Nick Colegrave from the University of Edinburgh's School of Biological Sciences.

Scientists still don't know how crows acquire the 'know-how' and make hooks; they may inherit the ability from their parents, or learn by observing experienced birds. Either way, because hooked-tool users will live longer and leave more offspring, the skill is expected to spread.

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First evidence of winds outside black holes throughout their mealtimes

Artistic rendition of strong winds disrupting the outer disc of material surrounding a stellar-mass black hole. The disk material (mostly in yellow) is first pulled from the outer parts of a nearby star (upper right-hand). The stellar-mass black hole sits at the center of the approximately 5 million kilometer disc, but it only consumes the material if and when it reaches the central 30 kilometers.

New research shows the first evidence of strong winds around black holes throughout bright outburst events when a black hole rapidly consumes mass.

The study, published in Nature, sheds new light on how mass transfers to black holes and how black holes can affect the environment around them. The research was conducted by an international team of researchers, led by scientists in the University of Alberta's Department of Physics.

Using data from three international space agencies spanning 20 years, the scientists used new statistical techniques to study outbursts from stellar-mass black hole X-ray binary systems. Their results show evidence of consistent and strong winds surrounding black holes throughout outbursts. Until now, strong winds had only been seen in limited parts of these events.

"Winds must blow away a large fraction of the matter a black hole could eat,'' described Bailey Tetarenko, PhD student and lead author on the study. "In one of our models, the winds removed 80 per cent of the black hole's potential meal."

Depending on their size, stellar-mass black holes have the capacity to consume everything within a 3 to 150 kilometre radius. "Not even light can escape from this close to a black hole," explained Gregory Sivakoff, associate professor of physics and co-author. Other, much larger black holes, called supermassive black holes, appear to have affected the formation of entire galaxies. "But even supermassive black holes are smaller than our solar system. While they are small, black holes can have surprisingly large effects," explained Sivakoff.

So, what exactly causes these winds in space? For now, it remains a mystery. "We think magnetic fields play a key role. But we'll need to do a great deal of future investigation to understand these winds," explained Craig Heinke, associate professor of physics and co-author.

"Strong disk winds traced throughout outbursts in black-hole X-ray binaries" will be published online January 22 in Nature, one of the world's top peer-reviewed scientific publications.

From Science Daily

Sea turtle crisis: Moisture, not just heat impacts sex of sea turtle hatchlings

A sea turtle hatchling emerges from an egg on a beach in Palm Beach County in southeast Florida. Since 2002, researchers have found that 97 to 100 percent of the hatchlings have been female.

Alarming results from a recent gender ratio study revealed that 99 percent of young green turtles from Australia's Northern Great Barrier Reef are female and that male sea turtles are disappearing. Closer to home, researchers from Florida Atlantic University have documented a similar trend in sea turtle hatchlings in southeast Florida. Since 2002, they have studied sea turtles in Palm Beach County and discovered that 97 to 100 percent of the hatchlings have been female.

Unlike humans, turtles and other reptiles like crocodiles who lay their eggs do not have sex chromosomes. In sea turtles, sex is determined by the nest's environment: warmer temperatures produce females and cooler temperatures produce males.

However, it is not just temperature that affects embryogenesis and the phenotype of the resulting hatchlings. Moisture changes the microclimate experienced by the eggs inside the nest and can significantly affect their development. Wetter substrates tend to produce more males and drier substrates tend to produce more females.

In a study published in Zoology, FAU researchers are the first to show why and how moisture conditions inside the nest affect the development and sex ratios of turtle embryos. They are the first to estimate sex ratios using a male-specific, transcriptional molecular marker Sox9, a marker of testis development in sea turtles and freshwater turtles.

The researchers found that the coolest and the wettest substrates produce 100 percent males compared to 42 percent males from the warmest and driest treatment. They also found that embryonic growth appears to be more sensitive to temperature at earlier stages of development and to moisture at later stages.

"During incubation, the turtle embryo grows inside the nest from a few cells to a fully formed and independent organism at hatching," said Jeanette Wyneken, Ph.D., author of the study and a professor of biological sciences in FAU's Charles E. Schmidt College of Science. "For proper development, embryos require an appropriate range of temperature, moisture, salinity, and respiratory gases."

Using their novel experimental design, Wyneken and study collaborators Sarah L. Milton, Ph.D., an associate professor of biological sciences at FAU, Itzel Sifuentes-Romero, Ph.D., a Fulbright postdoctoral fellow at FAU, and Boris M. Tezak, a Ph.D. candidate at FAU, found differences in developmental rates, egg mass and sex ratios. Results show that embryos developed slowly in cooler and wetter sand substrates while water uptake by the eggs was significantly greater on wetter substrates.

"We found that development differences were due to moisture interacting with temperature where increased water content of the sand resulted in temperatures that were 2 to 3 degrees Celsius lower than air temperatures," said Wyneken.

For the study, the researchers incubated eggs from the Trachemys scripta elegans, a semi-aquatic turtle, under different temperature and moisture regimes to study the effect of the two environmental factors on developmental rate, egg mass, embryo mass and length, and sex ratio. They monitored embryonic development until stage 22 when their sex is determined. Turtle embryonic development is divided into 27 stages. The pivotal temperature is the constant temperature (29 degrees Celsius or 84.2 degrees Fahrenheit) at which 50:50 sex ratio is expected. Sex ratio was based on expression levels of Sox9 and all data were tested for normality and for homogeneity before statistical analysis.

This laboratory study is consistent with field studies of freshwater turtles and sea turtles. Results of the study also are relevant when considering nesting phenology in the wild because conditions such as temperature and rainfall often vary depending across the nesting season.

"Our study demonstrates how moisture may change the incubation conditions inside nests by changing the temperature experienced by eggs, which affects development, growth and sex ratios," said Wyneken. "Furthermore, results of our study highlight the importance of including moisture conditions when predicting embryo growth and sex ratios and in developing proxies of embryonic development. Improving accuracy is particularly important when trying to assess the impact of climate change in species with temperature-dependent sex determination and other forms of environmental determination."

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Heat loss from the Earth triggers ice sheet slide towards the sea

Several glaciers flow into the area of Young Sound where researchers have shown that heat from the Earth's interior warms up the bottom water of the fjord.

Greenland's ice sheet is becoming smaller and smaller. The melting takes place with increased strength and at a speed that no models have previously predicted.

Today, in the journal Scientific Reports, researchers from the Arctic Research Centre, Aarhus University, and the Greenland Institute of Natural Resources present results that, for the first time, show that the deep bottom water of the north-eastern Greenland fjords is being warmed up by heat gradually lost from the Earth's interior. And the researchers point out that this heat loss triggers the sliding of glaciers from the ice sheet towards the sea.

Icelandic conditions

"North-East Greenland has several hot springs where the water becomes up to 60 degrees warm and, like Iceland, the area has abundant underground geothermal activity," explains Professor Soren Rysgaard, who headed the investigations.

For more than ten years, the researchers have measured the temperature and salinity in the fjord Young Sound, located at Daneborg, north of Scoresbysund, which has many hot springs, and south of the glacier Nioghalvfjerdsfjorden, which melts rapidly and is connected to the North-East Greenland Ice Stream (NEGIS).

By focusing on an isolated basin in the fjord with a depth range between 200 and 340 m, the researchers have measured how the deep water is heated over a ten-year period. Based on the extensive data, researchers have estimated that the loss of heat from the Earth's interior to the fjord is about 100 MW m-2. This corresponds to a 2 megawatt wind turbine sending electricity to a large heater at the bottom of the fjord all year round.

Heat from the Earth's interior -- an important influence

It is not easy to measure the geothermal heat flux -- heat emanating from the Earth's interior -- below a glacier, but within the area there are several large glaciers connected directly to the ice sheet. If the Earth releases heat to a fjord, heat also seeps up to the bottom part of the glaciers. This means that the glaciers melt from below and thus slide more easily over the terrain on which they sit when moving to the sea.

"It is a combination of higher temperatures in the air and the sea, precipitation from above, local dynamics of the ice sheet and heat loss from the Earth's interior that determines the mass loss from the Greenland ice sheet," explains Soren Rysgaard.

"There is no doubt that the heat from the Earth's interior affects the movement of the ice, and we expect that a similar heat seepage takes place below a major part of the ice cap in the north-eastern corner of Greenland," says Soren Rysgaard.

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A 'hot Jupiter' with unusual winds

Artist’s concept shows the gaseous exoplanet CoRoT-2b with a westward hot spot in orbit around its host star.

The hottest point on a gaseous planet near a distant star isn't where astrophysicists expected it to be -- a discovery that challenges scientists' understanding of the many planets of this type found in solar systems outside our own.

Unlike our familiar planet Jupiter, so-called hot Jupiters circle astonishingly close to their host star -- so close that it typically takes fewer than three days to complete an orbit. And one hemisphere of these planets always faces its host star, while the other faces permanently out into the dark.

Not surprisingly, the "day" side of the planets gets vastly hotter than the night side, and the hottest point of all tends to be the spot closest to the star. Astrophysicists theorize and observe that these planets also experience strong winds blowing eastward near their equators, which can sometimes displace the hot spot toward the east.

In the mysterious case of exoplanet CoRoT-2b, however, the hot spot turns out to lie in the opposite direction: west of center. A research team led by astronomers at McGill University's McGill Space Institute (MSI) and the Institute for research on exoplanets (iREx) in Montreal made the discovery using NASA's Spitzer Space Telescope. Their findings are reported Jan. 22 in the journal Nature Astronomy.

Wrong-way wind

"We've previously studied nine other hot Jupiter, giant planets orbiting super close to their star. In every case, they have had winds blowing to the east, as theory would predict," says McGill astronomer Nicolas Cowan, a co-author on the study and researcher at MSI and iREx. "But now, nature has thrown us a curveball. On this planet, the wind blows the wrong way. Since it's often the exceptions that prove the rule, we are hoping that studying this planet will help us understand what makes hot Jupiters tick."

CoRoT-2b, discovered a decade ago by a French-led space observatory mission, is 930 light years from Earth. While many other hot Jupiters have been detected in recent years, CoRoT-2b has continued to intrigue astronomers because of two factors: its inflated size and the puzzling spectrum of light emissions from its surface.

"Both of these factors suggest there is something unusual happening in the atmosphere of this hot Jupiter," says Lisa Dang, a McGill PhD student and lead author of the new study. By using Spitzer's Infrared Array Camera to observe the planet while it completed an orbit around its host star, the researchers were able to map the planet's surface brightness for the first time, revealing the westward hot spot.

New questions

The researchers offer three possible explanations for the unexpected discovery -- each of which raises new questions:

• The planet could be spinning so slowly that one rotation takes longer than a full orbit of its star; this could create winds blowing toward the west rather than the east -- but it would also undercut theories about planet-star gravitational interaction in such tight orbits.
• The planet's atmosphere could be interacting with the planet's magnetic field to modify its wind pattern; this could provide a rare opportunity to study an exoplanet's magnetic field.
• Large clouds covering the eastern side of the planet could make it appear darker than it would otherwise -- but this would undercut current models of atmospheric circulation on such planets.

"We'll need better data to shed light on the questions raised by our finding," Dang says. "Fortunately, the James Webb Space Telescope, scheduled to launch next year, should be capable of tackling this problem. Armed with a mirror that has 100 times the collecting power of Spitzer's, it should provide us with exquisite data like never before."

Scientists from the University of Michigan, the California Institute of Technology, Arizona State University, New York University Abu Dhabi, the University of California, Santa Cruz, and Pennsylvania State University also contributed to the study.

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The world's most powerful acoustic tractor beam could pave the way for levitating humans

Working principle of virtual vortices: intertwined short vortices of opposite directions are emitted to trap and stabilize the particle.

Acoustic tractor beams use the power of sound to hold particles in mid-air, and unlike magnetic levitation, they can grab most solids or liquids. For the first time University of Bristol engineers have shown it is possible to stably trap objects larger than the wavelength of sound in an acoustic tractor beam. This discovery opens the door to the manipulation of drug capsules or micro-surgical implements within the body. Container-less transportation of delicate larger samples is now also a possibility and could lead to levitating humans.

Researchers previously thought that acoustic tractor beams were fundamentally limited to levitating small objects as all the previous attempts to trap particles larger than the wavelength had been unstable, with objects spinning uncontrollably. This is because rotating sound field transfers some of its spinning motion to the objects causing them to orbit faster and faster until they are ejected.

The new approach, published in Physical Review Letters today [Monday 22 January], uses rapidly fluctuating acoustic vortices, which are similar to tornadoes of sound, made of a twister-like structure with loud sound surrounding a silent core.

The Bristol researchers discovered that the rate of rotation can be finely controlled by rapidly changing the twisting direction of the vortices, this stabilises the tractor beam. They were then able to increase the size of the silent core allowing it to hold larger objects. Working with ultrasonic waves at a pitch of 40kHz, a similar pitch to that which only bats can hear, the researchers held a two-centimetre polystyrene sphere in the tractor beam. This sphere measures over two acoustic wavelengths in size and is the largest yet trapped in a tractor beam. The research suggests that, in the future much larger objects could be levitated in this way.

Dr Asier Marzo, lead author on the paper from Bristol's Department of Mechanical Engineering, said: "Acoustic researchers had been frustrated by the size limit for years, so its satisfying to find a way to overcome it. I think it opens the door to many new applications."

Dr Mihai Caleap, Senior Research Associate, who developed the simulations, explained: "In the future, with more acoustic power it will be possible to hold even larger objects. This was only thought to be possible using lower pitches making the experiment audible and dangerous for humans."

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Challenging existing models of black holes

Chris Packham, associate professor of physics and astronomy at The University of Texas at San Antonio (UTSA), has collaborated on a new study that expands the scientific community's understanding of black holes in our galaxy and the magnetic fields that surround them.

"Dr. Packham's collaborative work on this study is a great example of the innovative research happening now in physics at UTSA. I'm excited to see what new research will result from these findings," said George Perry, dean of the UTSA College of Sciences and Semmes Foundation Distinguished University Chair in Neurobiology.

Packham and astronomers lead from the University of Florida observed the magnetic field of a black hole within our own galaxy from multiple wavelengths for the first time. The results, which were a collective effort among several researchers, are deeply enlightening about some of the most mysterious objects in space.

A black hole is a place in space where gravity pulls so strongly that even light cannot escape its grasp. Black holes usually form when a massive star explodes and the remnant core collapses under the force of intense gravity. As an example, if a star around 3 times more massive than our own Sun became a black hole, it would be roughly the size of San Antonio. The black hole Packham and his collaborators featured in their study, which was recently published in Science, contains about 10 times the mass of our own sun and is known as V404 Cygni.

"The Earth, like many planets and stars, has a magnetic field that sprouts out of the North Pole, circles the planet and goes back into the South Pole. It exists because the Earth has a hot, liquid iron rich core," said Packham. "That flow creates electric currents that create a magnetic field. A black hole has a magnetic field as it was created from the remnant of a star after the explosion."

As matter is broken down around a black hole, jets of electrons are launched by the magnetic field from either pole of the black hole at almost the speed of light. Astronomers have long been flummoxed by these jets.

These new and unique observations of the jets and estimates of magnetic field of V404 Cygni involved studying the body at several different wavelengths. These tests allowed the group to gain a much clearer understanding of the strength of its magnetic field. They discovered that magnetic fields are much weaker than previously understood, a puzzling finding that calls into question previous models of black hole components. The research shows a deep need for continued studies on some of the most mysterious entities in space.

"We need to understand black holes in general," Packham said. "If we go back to the very earliest point in our universe, just after the big bang, there seems to have always been a strong correlation between black holes and galaxies. It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked. Our results are surprising and one that we're still trying to puzzle out."

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'Explosive evolution' of techniques to restore blood flow to the brain

Recent decades have seen an "explosive evolution" of techniques to restore blood flow to areas of the brain endangered by stroke or clogged arteries, according to a report by Loyola Medicine neurologists and neurosurgeons.

Historically, the introduction of operating microscopes enabled surgeons to perform delicate microsurgeries to clear clogged arteries and remove blood clots that cause strokes. More recently, physicians have begun using minimally invasive endovascular techniques.

"The last 50 to 60 years have witnessed an explosive evolution of techniques geared at restoring blood flow to compromised regions of the brain, senior author Camilo R. Gomez, MD, and colleagues wrote in the Nov. 9, 2017 MedLink Neurology.

Endovascular techniques do not require invasive open surgery. The physician employs catheters (thin tubes) that are guided through blood vessels to the brain. From the tip of the catheter, the physician deploys stents or other devices to restore blood blow. (Endovascular means inside blood vessels.) These endovascular techniques have "amplified the dimensions of care for many patients whose therapeutic options were previously limited," the Loyola authors wrote.

Cerebral vascular insufficiency (not enough blood flow to the brain) increases the risk of stroke and is a major cause of neurologic death and disability worldwide. It is typically caused by atherosclerosis (buildup of fats, cholesterol and other substances that clog arteries that supply blood to the brain).

Techniques and procedures used to improve blood flow to the brain are similar to those used in heart procedures. They include bypass surgery, balloon angioplasty and stenting. One of the latest devices is called a stent retriever (also known as a stentriever). The device is a self-expanding mesh tube attached to a wire. The device is guided through blood vessels to a clot that is blocking blood flow to a part of the brain. The device pushes the blood clot against the wall of the blood vessel, immediately restoring blood flow. The stent retriever then is used to grab the clot, which is pulled out when the physician removes the catheter.

Dr. Gomez began performing neuroendovascular procedures more than 20 years ago, when the field was in its infancy. During that time, he said, there has been a tremendous improvement in both devices and techniques. "The chances a stroke patient will have a good outcome are two to three times better now than they were 10 to 15 years ago," Dr. Gomez said.

Modern endovascular techniques can, in effect, stop a stroke in its tracks by removing blockages. Patients with the largest blockages and most devastating strokes are deriving the greatest benefits, said Loyola neurosurgeon Joseph C. Serrone, MD, one of the co-authors of the paper. "Seven clinical trials have shown that endovascular techniques restore significant function in these patients," Dr. Serrone said.

In the past two decades, there have been tremendous advancements in the way ischemic strokes are treated, said Loyola neurosurgeon Matthew R. Reynolds, MD, PhD, also a co-author of the paper. "With the advent of mechanical thrombectomy (blood clot removal) and minimally-invasive techniques, patients who otherwise would be permanently disabled from stroke can often lead normal, productive lives," Dr. Reynolds said. "It's truly an exciting time to be an endovascular neurosurgeon."

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