Monday, February 28, 2011

Blood Pressure

To most people, heart rate doesn’t seem like a terribly important number. That’s OK, because a far more important measure of your heart’s health is blood pressure—in fact, it’s the most reliable predictor of heart trouble to come.

Blood pressure is the force your blood exerts on the walls of your arteries. Many factors influence blood pressure, including your heart rate, the amount of blood in your body, and how thick that blood is. The most significant thing your blood pressure measures is the condition of your arteries. As they age, your arteries stiffen and swell, forcing your heart to pump harder to deliver blood to the far corners of your body. Most people find that their blood pressure creeps up as they grow older. It’s a matter of debate whether this is a natural consequence of an aging body, or the cumulative toll of a modern lifestyle.

Blood pressure can vary in different parts of your body, so doctors generally measure it in the main artery of your upper arm. A blood-pressure reading actually consists of two measurements. The systolic pressure is the force your heart exerts when it pushes blood out. The diastolic pressure is the force between heartbeats.

In the past, the medical community thought that diastolic pressure was the more important of the two, possibly because your blood vessels experience this level of pressure between heartbeats, which is most of the time. But recent research shows that systolic pressure is the best predictor of future ills. (It’s also possible that the difference between the two figures is even more significant, which means that a person with a high systolic pressure and a low diastolic pressure is at the greatest health risk of all.)

The following table outlines commonly observed blood-pressure ranges and what they mean. Although the best way to measure your blood pressure is with the high-quality equipment in a doctor’s office, you can perform an informal check with a free, automated machine at many drugstores. Slightly low blood pressure puts you at greater risk of fainting and dizziness, but it doesn’t raise any health concerns. (However, extremely low blood pressure—a.k.a. hypotension—may be the sign of an underlying disease.)

High blood pressure isn’t so forgiving. Called hypertension, it takes a slow and steady toll on your body, scarring your arteries and organs like a highpressure washing hose that’s set too high. Hypertension is insidious because it has no obvious symptoms until it’s far advanced, and by then it may already have damaged your heart, eyes, kidneys, and even your brain.

Now that you know the importance of tracking your blood pressure, the next question is this: What can you do if it’s outside the norm? If you already have hypertension, several lifestyle changes may help reduce your blood pressure. However, these steps are unlikely to reverse the condition completely. That means that once you make all the changes you can, you need to take careful blood-pressure readings and work with your doctor to choose the most suitable pressure-lowering drugs. And be warned: The cardiac unit of many a hospital is full of self medicating patients who tossed their drugs after adopting a “miracle diet” or a serious workout regimen, only to suffer devastating heart problems. A healthy lifestyle is an admirable thing, but it’s not likely to repair weakened arteries or roll back time.

If you’re in the warning zone, with a systolic blood pressure that’s nudged past 120 but still sits under the 140 mark, your prospects are better. By making the right changes, you can delay the onset of hypertension— perhaps indefinitely. Even if you eventually cross the dreaded threshold of hypertension, your hard work can keep you off blood-pressure medication for years before that point.

Source of Information :  Oreilly - Your Body Missing Manual

Thursday, February 24, 2011

Mind Control for the Heart

For the most part, your heart rate ratchets up and slows down on its own, without any conscious control on your part. However, an interesting technique called biofeedback can give you the ability to influence automatic body processes like heart rate. In a typical biofeedback session, a trainer hooks you up to specialized equipment that measures something you can’t ordinarily perceive, like brain activity, skin temperature, or muscle tension. The equipment then translates this information into something you can perceive, such as a tone that varies in pitch, a light that varies in brightness, or an image with shifting lines. You then follow a series of mental exercises until you eventually stumble on a technique that causes the right physical change and the corresponding auditory or visual signal. For example, a biofeedback session might measure the activity of a brain region known to influence heart rate. Through trial and error, you can learn how to slightly slow your rate using nothing more than mental power.

The ultimate goal of most biofeedback training is to give you the ability to consciously reduce your reaction to the stresses of ordinary life—for example, damping down a racing heart or a sudden spike in blood pressure—even without the help of the fancy biofeedback equipment. Despite its promise, however, biofeedback hasn’t yet graduated from an experimental curiosity to a truly therapeutic tool.

Source of Information : Oreilly - Your Body Missing Manual

Thursday, February 17, 2011

Heart Rate

When you relax, your heart beats about 60 to 80 times a minute. (On average, a man’s heart beats 70 times per minute and a woman’s beats 75 times per minute.) If you’re an athlete or a fitness geek, the training you do improves your heart’s efficiency and helps it pump more blood with each beat. As a result, your resting heart rate may drop as low as 40 to 60 beats per minute.

If you’re older and out of shape, your heart may be gradually weakening. To keep up with the demands of your body, it may beat faster, increasing your resting heart rate to closer to 100 beats per minute. A heart rate like this is a hallmark of poor fitness and a flashing danger sign of heart trouble ahead. Studies show that a high resting heart rate goes hand-in-hand with a higher risk of heart attack, especially later in life. That said, there’s a healthy amount of natural variation in each person’s heart rate. So even if yours clocks in at 60 beats per minute and your friend’s sets a quicker pace of 75 beats per minute, you can’t assume that your heart is the superior specimen.

Unless your heart rate seems unnaturally fast or unnaturally slow, you’re unlikely to give it much thought. Tracking your heart rate during exercise, however, is worthwhile, because it tells you how hard your heart is working. You can use this information to make sure you get the most out of your cardio workouts.

Source of Information :  Oreilly - Your Body Missing Manual

Monday, February 14, 2011

十大健腦食物 - 让孩子更聪明












Tuesday, February 8, 2011

Python Boom

Big snakes poised to change U.S. ecosystems BY MICHAEL TENNESEN

Brought to the U.S. as pets, Burmese pythons have made headlines with their uncontrolled spread in the Florida Everglades and willingness to challenge alligators for the position of top predator. A report released by the U.S. Geological Survey last fall delivered more bad news: two other constrictor species, also former pets, are thriving in the area, and six others could pose similar threats. Researchers fear that reproductive populations could spread and eat native animals into extinction.

The new interlopers—northern and southern African pythons, reticulated pythons, boa constrictors and four species of anacondas—have “ecological similarities,” explains Robert Reed, a USGS biologist and one of the authors of the report. “They are large invasive predators that native birds and mammals aren’t adapted to, and they are highly fecund, capable of producing up to 100 hatchlings in one nest.” They’re also big; some grow up to 20 feet and 200 pounds. They seize prey with their teeth and then wrap around the prey’s body, squeezing it to death.

Biologists first noticed the slithering invasion in the late 1990s. Snake numbers have risen dramatically: in 2000 two Burmese pythons were captured in the Everglades National Park; in 2008 the number captured hit 343. Biologists believe that tens of thousands now live in the park. Other constrictors have begun appearing beyond the Everglades: boa constrictors south of Miami and African pythons just west of the city.

Cryptic by nature, constrictors are extremely difficult to capture. “We know how they move and what they look like,” says USGS biologist Kristen Hart. “We had a radio-tagged snake in a fenced-off area the other day, right in the middle of six of us, and yet we couldn’t even see it. They are often underground or underwater or in a tree. They blend in so well here in the Everglades.”

When they move, however, they can move far. Relocated pythons have demonstrated a homing ability, returning up to 48 miles to the place where they were captured. Biologists worry that the reptiles may populate the Florida Keys, perhaps by riding on floating logs or even swimming the distance.

Without native predators, the snakes could really thrive. In fact, Burmese pythons may do better in Florida than in their home ranges in Southeast Asia, where jackals, monitor lizards, disease and parasites limit their numbers. “By the time they reach two years of age, not much can eat them in the Everglades,” Hart states. She describes one python she captured that “threw up four feet of an alligator.” Although biologists have recovered 10 alligators in python stomachs, for the most part the constrictors prey on small mammals and birds.

This predilection concerns Dave Hallac, chief of biological resources for the Everglades and Dry Tortugas. “We are going through this comprehensive restoration program here in the Everglades, trying to restore a number of wading and water-dependent birds, yet at the same time we have this big new predator in our midst.” Hallac and others do not want a repeat of what happened on the American island of Guam. There the nonnative brown tree snake invaded shortly after World War II and devastated native wildlife. Since the snake’s arrival, most likely as stowaways on cargo vessels, Guam has lost 10 of its 12 native forest bird species, most of its bats and about half of its lizards.

Given the number of constrictors imported to the U.S. as pets—Reed pegs the figure at just under one million—some species appear poised to take up permanent residence. (Florida law stipulates jail terms up to one year for anyone releasing a pet constrictor, which can grow from a 20-inch-long juvenile to an eight-foot-long monster in a year.) Still, wildlife biologists hope to keep the invasion contained. Although much of the southern U.S. offers a hospitable climate, the availability of prey, habitat and other factors will affect the snakes’ success.

Hart and others are working with different traps, transmitters and “Judas snakes”—radio-tagged pythons that lead them to other snakes—in an attempt to understand and control the creatures. She laments the fact that Florida didn’t take a more aggressive stance against these snakes years ago, when the reptiles were first sighted and might have been eradicated quickly. Says Hart: “We’ve gone beyond the point where they’re easily controllable.”

Source of Information :  Scientific American Magazine February 2010

Friday, February 4, 2011

Poisoned Shipments

Are strange, illicit sinkings making the Mediterranean toxic? BY MADHUSREE MUKERJEE

In October 2009 the government of Italy announced that a wreck discovered off the southwestern tip of the country is the Catania, a passenger vessel sunk during
World War I—and not the Cunski, a cargo ship loaded with radioactive waste, as alleged by district authorities from nearby Calabria. Few locals are reassured, says Michael Leonardi of the University of Calabria. He and others maintain that the putative Cunski is still out there and is just one of numerous ships full of poisonous garbage that a crime syndicate has scuttled in the Mediterranean Sea. Such a startling allegation, if true, would not only damage the tourism and fishing industries along this idyllic coast but also compromise the health of Mediterranean residents.

Processing and safely storing waste from the chemical, pharmaceutical and other industries can cost hundreds, even thousands, of dollars per ton—which makes illegal disposal highly profitable. According to the Italian environmental organization Legambiente, some waste shippers that have operational bases in southern Italy have been using the Mediterranean as a dump. While acknowledging that “no wreck has yet been found that contains toxic or radioactive waste,” physicist Massimo Scalia of the University of Rome, La Sapienza, who has chaired two parliamentary commissions on illegal waste disposal, argues that other evidence makes their existence “beyond reasonable doubt.”

Scalia contends that 39 ships were wrecked under questionable circumstances between 1979 and 1995 alone; in every case, he adds, the crew abandoned the ship long before it sank. An average of two ships per year suspiciously disappeared in the Mediterranean during the 1980s and early 1990s, according to Legambiente— and the number has increased to nine wrecks per year since 1995. Paolo Gerbaudo of the Italian daily il Manifesto, who is assisting investigations, has identified 74 suspect wrecks of which he regards 20 as being extremely suspicious. (The record extends until 2001.)

One notable example of a dubious wrecking is the Jolly Rosso, which washed up in December 1990 near the town of Amantea, after what investigators believe was a botched attempt to scuttle it. The cargo was offloaded and allegedly buried on land. In October 2009 an environmental ministry report noted that district authorities detected dangerous substances in a nearby river valley, including a buried concrete block containing mercury, cobalt, selenium and thallium at very high concentrations—and displaying substantial radioactivity indicative of synthetic radionuclides. Authorities also found marble granules mixed in with thousands of cubic meters of earth, which was contaminated with heavy metals and cesium 137, typically a waste product of nuclear reactors. The assemblage suggests that the Jolly Rosso’s cargo included radioactive waste, sealed in concrete and shielded from detection by marble dust (which absorbs radioactivity).

Significantly, the increase in the frequency of wrecking correlates with the progressive tightening of international dumping regulations. The first suspect sinking, in 1979, occurred the year after the Barcelona Convention, which restricts the disposal of pollutants in the Mediterranean Sea, came into force. Over the following decades other treaties expanded the regulations, culminating in a 1993 amendment to the London Dumping Convention that halted the ocean disposal of all radioactive waste and in a 1995 amendment to the Basel Convention that banned the deposition of the industrial world’s lethal excreta in developing countries. The laws ruined the ambitious plans of one firm, Oceanic Disposal Management, incorporated in the British Virgin Islands, to drop tens of thousands of cubic meters of radioactive waste into the seabed off the African coast. Andreas Bernstorff, who formerly headed a Greenpeace campaign against the trade in toxic waste, reports that the number of schemes to ship such garbage to Africa fell steeply at this time, to at most one attempt per year. The drop coincides with a sudden and ominous rise in the frequency with which ships in the Mediterranean perished.

Despite profound concern in southern Italy, efforts to find the wrecks and identify their cargo have been slow. The endeavor is expensive, Scalia notes, and requires “serious engagement by magistrates and politicians”—which, but for “a few honorable exceptions,” has been lacking. Fear of violence may also have hindered investigation. In 1994 Italian television journalist Ilaria Alpi and cameraman Miran Hrovatin were shot dead near Mogadishu, after they picked up the hazardous waste trail in Somalia, where political upheaval has kept the country from enforcing controls.

That African nation possibly holds clues to the kinds of health hazards Italians might face. “My committee heard from Somalians who said many people in that area had symptoms of poisoning and some died,” Scalia attests, referring to a stretch of highway along which Alpi and Hrovatin may have witnessed the offloading of toxic substances. The tsunami of December 2004 dredged up giant metal containers from the seabed and placed them on Somali beaches—proving that the country’s coastal waters had also received questionable trash. A United Nations report blamed fumes from these unidentified objects for internal hemorrhages and deaths of local people.

In April 2007 Calabrian authorities had temporarily halted fishing in waters off Cetraro (where the Cunski lies, according to a turncoat from the ’Ndrangheta mafia) because of dangerous levels of heavy metals in marine sediment. In the region around Amantea, mortality from cancer between 1992 and 2001 exceeded that in neighboring areas, a study found; just as worrisome, hospitalizations for certain malignancies have risen in recent years.

“Almost all the coastal regions of our country may be compromised,” warned 28 Italian legislators from opposition parties on October 1, in a parliamentary motion demanding that the sunken ships be located and their contents secured. Until investigators can salvage the truth about the shipwrecks, suspicion and anxiety will plague the Mediterranean shores.

Source of Information :  Scientific American Magazine February 2010