Day: 05/19/2012

Laxative-Free CT Colonography: Still Not Good Enough.

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The positive predictive value was low — particularly for polyps smaller than 10 mm.

Several studies, including a randomized controlled trial from the Netherlands (JW Gastroenterol Jan 6 2012), have now reported the performance of laxative-free computed tomographic colonography (CTC). In the current industry-supported, prospective study, investigators evaluate the performance of laxative-free CTC followed by colonoscopy in 605 adults aged 50 to 85 undergoing screening or surveillance exams. As usual, the CTC was performed after several doses of contrast ingestion, and colonoscopy was performed blinded to the results of the CTC.

Per-patient sensitivity and specificity of laxative-free CTC for polyps 10 mm in size were 91% and 85%, respectively. Sensitivity fell dramatically for lower size thresholds. For adenomas 8 mm, the sensitivity of CTC was 70% (vs. 88% for optical colonoscopy), and the positive predictive value of CTC was 26%. For adenomas or cancer 6 mm, the sensitivity of CTC was 59%, and the positive predictive value was 42%. For a confirmed polyp of any histology, the sensitivity of CTC was 59% for those 8 mm and 47% for those 6 mm.

Comment: Most experts will conclude from these results that computed tomographic colonography is not adequate as a substitute for colonoscopy. Patients typically want to know whether they have polyps in the 6–9 mm range, and if so, they want them removed. With an 85% specificity for polyps 10 mm, substantial portions of the screening population will need colonoscopy with each pass of CTC. With these low positive predictive values, many patients and their doctors will want repeat CTC to determine if a lesion is actually present when one cannot be found during colonoscopy. The test probably has adequate performance for patients who refuse to use bowel preparation for colonoscopy, but patients should be warned about the substantial chance of a false-positive result that will require colonoscopy anyway, the need to repeat the test in 5 years rather than 10 years even if the test is negative, and the persisting concerns about radiation risk and incidental extracolonic findings.

Source: Journal Watch Gastroenterology

Every black hole contains a new universe: A physicist presents a solution to present-day cosmic mysteries.

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Our universe may exist inside a black hole. This may sound strange, but it could actually be the best explanation of how the universe began, and what we observe today. It’s a theory that has been explored over the past few decades by a small group of physicists including myself. 

Successful as it is, there are notable unsolved questions with the standard big bang theory, which suggests that the universe began as a seemingly impossible “singularity,” an infinitely small point containing an infinitely high concentration of matter, expanding in size to what we observe today. The theory of inflation, a super-fast expansion of space proposed in recent decades, fills in many important details, such as why slight lumps in the concentration of matter in the early universe coalesced into large celestial bodies such as galaxies and clusters of galaxies.

But these theories leave major questions unresolved. For example: What started the big bang? What caused inflation to end? What is the source of the mysterious dark energy that is apparently causing the universe to speed up its expansion?

The idea that our universe is entirely contained within a black hole provides answers to these problems and many more. It eliminates the notion of physically impossible singularities in our universe. And it draws upon two central theories in physics.

The first is general relativity, the modern theory of gravity. It describes the universe at the largest scales. Any event in the universe occurs as a point in space and time, or spacetime. A massive object such as the Sun distorts or “curves” spacetime, like a bowling ball sitting on a canvas. The Sun’s gravitational dent alters the motion of Earth and the other planets orbiting it. The sun’s pull of the planets appears to us as the force of gravity.

The second is quantum mechanics, which describes the universe at the smallest scales, such as the level of the atom. However, quantum mechanics and general relativity are currently separate theories; physicists have been striving to combine the two successfully into a single theory of “quantum gravity” to adequately describe important phenomena, including the behavior of subatomic particles in black holes.

A 1960s adaptation of general relativity, called the Einstein-Cartan-Sciama-Kibble theory of gravity, takes into account effects from quantum mechanics. It not only provides a step towards quantum gravity but also leads to an alternative picture of the universe. This variation of general relativity incorporates an important quantum property known as spin. Particles such as atoms and electrons possess spin, or the internal angular momentum that is analogous to a skater spinning on ice.

 

In this picture, spins in particles interact with spacetime and endow it with a property called “torsion.” To understand torsion, imagine spacetime not as a two-dimensional canvas, but as a flexible, one-dimensional rod. Bending the rod corresponds to curving spacetime, and twisting the rod corresponds to spacetime torsion. If a rod is thin, you can bend it, but it’s hard to see if it’s twisted or not.

Spacetime torsion would only be significant, let alone noticeable, in the early universe or in black holes. In these extreme environments, spacetime torsion would manifest itself as a repulsive force that counters the attractive gravitational force coming from spacetime curvature. As in the standard version of general relativity, very massive stars end up collapsing into black holes: regions of space from which nothing, not even light, can escape.

Here is how torsion would play out in the beginning moments of our universe inside a black hole. Initially, gravitational attraction between particles would overcome torsion’s repulsive forces, serving to collapse matter into a smaller region of space. But eventually torsion would become very strong and prevent matter from compressing into a point of infinite density. Nonetheless, matter would still be packed together in a highly dense state. The immensely high gravitational energy in this densely packed state would cause an intense production of particles, since energy can be converted into matter. This process would further increase the mass inside the black hole.

The increasing numbers of particles with spin would result in higher levels of spacetime torsion. The repulsive torsion would stop the collapse and would create a “big bounce” like a compressed beach ball that snaps outward. The rapid recoil after such a big bounce could be what has led to our expanding universe. The result of this recoil matches observations of the universe’s shape, geometry, and distribution of mass.

In turn, the torsion mechanism suggests an astonishing scenario: every black hole would produce a new, baby universe inside. If that is true, then the first matter in our universe came from somewhere else. So our own universe could be the interior of a black hole existing in another universe. Just as we cannot see what is going on inside black holes in the cosmos, any observers in the parent universe could not see what is going on in ours.

The motion of matter through the black hole’s boundary, called an “event horizon,” would only happen in one direction, providing a direction of time that we perceive as moving forward. The arrow of time in our universe would therefore be inherited, through torsion, from the parent universe.

Torsion could also explain the observed imbalance between matter and antimatter in the universe. Because of torsion, matter would decay into familiar electrons and quarks, and antimatter would decay into “dark matter,” a mysterious invisible form of matter that appears to account for a majority of matter in the universe.

Finally, torsion could be the source of “dark energy,” a mysterious form of energy that permeates all of space and increases the rate of expansion of the universe. Geometry with torsion naturally produces a “cosmological constant,” a sort of added-on outward force which is the simplest way to explain dark energy. Thus, the observed accelerating expansion of the universe may end up being the strongest evidence for torsion.

Torsion therefore provides a theoretical foundation for a scenario in which the interior of every black hole becomes a new universe. It also appears as a remedy to several major problems of current theory of gravity and cosmology. Physicists still need to combine the Einstein-Cartan-Sciama-Kibble theory fully with quantum mechanics into a quantum theory of gravity. While resolving some major questions, it raises new ones of its own. For example, what do we know about the parent universe and the black hole inside which our own universe resides? How many layers of parent universes would we have? How can we test that our universe lives in a black hole?

The last question can potentially be investigated: since all stars and thus black holes rotate, our universe would have inherited the parent black hole’s axis of rotation as a “preferred direction.” There is some recently reported evidence from surveys of over 15,000 galaxies that in one hemisphere of the universe more spiral galaxies are “left-handed,” or rotating clockwise, while in the other hemisphere more are “right-handed,” or rotating counterclockwise. In any case, I believe that including torsion in geometry of spacetime is a right step towards a successful theory of cosmology.

Source: Inside Science News Service

 

This Is Your Brain On Sugar: Study in Rats Shows High-Fructose Diet Sabotages Learning, Memory.

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Attention, college students cramming between midterms and finals: Binging on soda and sweets for as little as six weeks may make you stupid.

A new UCLA rat study is the first to show how a diet steadily high in fructose slows the brain, hampering memory and learning — and how omega-3 fatty acids can counteract the disruption. The peer-reviewed Journal of Physiology publishes the findings in its May 15 edition.

“Our findings illustrate that what you eat affects how you think,” said Fernando Gomez-Pinilla, a professor of neurosurgery at the David Geffen School of Medicine at UCLA and a professor of integrative biology and physiology in the UCLA College of Letters and Science. “Eating a high-fructose diet over the long term alters your brain’s ability to learn and remember information. But adding omega-3 fatty acids to your meals can help minimize the damage.”

While earlier research has revealed how fructose harms the body through its role in diabetes, obesity and fatty liver, this study is the first to uncover how the sweetener influences the brain.

The UCLA team zeroed in on high-fructose corn syrup, an inexpensive liquid six times sweeter than cane sugar, that is commonly added to processed foods, including soft drinks, condiments, applesauce and baby food. The average American consumes more than 40 pounds of high-fructose corn syrup per year, according to the U.S. Department of Agriculture. “We’re not talking about naturally occurring fructose in fruits, which also contain important antioxidants,” explained Gomez-Pinilla, who is also a member of UCLA’s Brain Research Institute and Brain Injury Research Center. “We’re concerned about high-fructose corn syrup that is added to manufactured food products as a sweetener and preservative.”

Gomez-Pinilla and study co-author Rahul Agrawal, a UCLA visiting postdoctoral fellow from India, studied two groups of rats that each consumed a fructose solution as drinking water for six weeks. The second group also received omega-3 fatty acids in the form of flaxseed oil and docosahexaenoic acid (DHA), which protects against damage to the synapses — the chemical connections between brain cells that enable memory and learning.

“DHA is essential for synaptic function — brain cells’ ability to transmit signals to one another,” Gomez-Pinilla said. “This is the mechanism that makes learning and memory possible. Our bodies can’t produce enough DHA, so it must be supplemented through our diet.”

The animals were fed standard rat chow and trained on a maze twice daily for five days before starting the experimental diet. The UCLA team tested how well the rats were able to navigate the maze, which contained numerous holes but only one exit. The scientists placed visual landmarks in the maze to help the rats learn and remember the way.

Six weeks later, the researchers tested the rats’ ability to recall the route and escape the maze. What they saw surprised them.

“The second group of rats navigated the maze much faster than the rats that did not receive omega-3 fatty acids,” Gomez-Pinilla said. “The DHA-deprived animals were slower, and their brains showed a decline in synaptic activity. Their brain cells had trouble signaling each other, disrupting the rats’ ability to think clearly and recall the route they’d learned six weeks earlier.”

The DHA-deprived rats also developed signs of resistance to insulin, a hormone that controls blood sugar and regulates synaptic function in the brain. A closer look at the rats’ brain tissue suggested that insulin had lost much of its power to influence the brain cells.

“Because insulin can penetrate the blood-brain barrier, the hormone may signal neurons to trigger reactions that disrupt learning and cause memory loss,” Gomez-Pinilla said.

He suspects that fructose is the culprit behind the DHA-deficient rats’ brain dysfunction. Eating too much fructose could block insulin’s ability to regulate how cells use and store sugar for the energy required for processing thoughts and emotions.

“Insulin is important in the body for controlling blood sugar, but it may play a different role in the brain, where insulin appears to disturb memory and learning,” he said. “Our study shows that a high-fructose diet harms the brain as well as the body. This is something new.”

Gomez-Pinilla, a native of Chile and an exercise enthusiast who practices what he preaches, advises people to keep fructose intake to a minimum and swap sugary desserts for fresh berries and Greek yogurt, which he keeps within arm’s reach in a small refrigerator in his office. An occasional bar of dark chocolate that hasn’t been processed with a lot of extra sweetener is fine too, he said.

Still planning to throw caution to the wind and indulge in a hot-fudge sundae? Then also eat foods rich in omega-3 fatty acids, like salmon, walnuts and flaxseeds, or take a daily DHA capsule. Gomez-Pinilla recommends one gram of DHA per day.

“Our findings suggest that consuming DHA regularly protects the brain against fructose’s harmful effects,” said Gomez-Pinilla. “It’s like saving money in the bank. You want to build a reserve for your brain to tap when it requires extra fuel to fight off future diseases.”

The UCLA study was funded by the National Institute of Neurological Disorders and Stroke. Gomez-Pinilla’s lab will next examine the role of diet in recovery from brain trauma.

Source: Science daily