Hematologist v/s Pathologist

CBI arrests two Chandigarh doctors for admissions racket

The Central Bureau of Investigation (CBI) Tuesday arrested two doctors of the prestigious Post-Graduate Institute of Medical Education and Research (PGIMER) here after the lid was blown off an organised admissions racket at the premier health institute.

CBI officials here said that the doctors, Amit Musale and Sujay Sonawane, were pursuing a post-graduation course at the PGIMER. The doctors had obtained admission to the course, one of the most sought after in the country, on the basis of impersonation and manipulation during the admission process.

PG seat for sale in Prestigious medical colleges

PG seats for sale in prestigious medical colleges like PGI chandigarh  and ??AIIMS,

read here

UPDATE- Pathology labs run by DMLT technicians banned by Gujarat Highcourt

Complete high court judgment now available at following link




High Court Judgement

Pathology labs run by DMLT technicians banned by Gujarat Highcourt

Gujarat high court has banned all pathology laboratories run by DMLT technicians.

For details in Gujarat Samachar pl. click below Gujarat Samachar

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Diagnostic Lymph Node Pathology

     Diagnostic Lymph Node Pathology is a comprehensive and generously illustrated guide, making it the ideal practical reference book. The international team of highly regarded haematopathologists write in an authoritative and accessible style with an emphasis on morphological evaluation as well as immunohistochemistry. The book clearly and logically presents the criteria for differential diagnosis with illustrations of both classical and less well-known features of each disease process. This will prove to be an essential guide for all surgical pathologists and haematopathologists involved in interpreting lymph node biopsies and will be an invaluable learning text for histopathologists in training. 

Drinking water before meals helps dieting, says study

Drinking water before meals can help people to lose weight, says a US study.

Scientists from Virginia found that slimmers can lose an average of 5lb extra if they drink two glasses of water three times a day before meals.

They tested the theory on 48 older adults, split into two groups, over 12 weeks.

While drinking water can make you feel full on zero calories, say researchers, too much water can also lead to serious health problems.

The researchers presented their findings at the National Meeting of the American Chemical Society in Boston.

All adults who took part in the study were aged 55 to 75.

The first group followed a low-calorie diet but did not drink any extra water before meals.

The second group followed the low-calorie diet but also drank two glasses of water before each meal.

VIolance against Doctors of Surat

            On the 9th of August, The medical fraternity of Surat was witness to this in human Act of Violence at a local Hospital. A pregnant patient was admitted with high grade fever. She was seriously ill when brought to the hospital. The gravity of the situation was explained to the relatives and needed signatures were taken from the husband. She succumbed to her illness by evening with a Probable diagnosis of Swine flu. She was ill for the past 4 days, but brought to the hospital on this very day. The relatives took away the body and later after a few hours at 11PM, a mob of 70-80 people came and ransacked the Hospital ICCU, beating the Doctors, nurses and watchman. The pregnant nurse had a premature delivery(7th month) after that and the doctor has a fractured rib. The Entire staff of that Hospital is scared to treat serious patients now.

Biodisc - fraud of the century

Introduction:
One of the leading magazine from Gujarat, India (Chitralekha), has published cover story about Biodisc. According to them Water that come into contact with biodisc become structured and organised, which appear crystalised!!!! Wow now you can change the physical properties of water!!! This water can do miracle, and treat almost anything!!!

At last they say the cost of biodisc (Rs. 17,750 for 1, Rs. 31400 for 2), which can be purchased by phone number given by them or someone linked with qnet.

Analysis:
Being a doctor, thing like this is difficult to digest, so I did some googling. One of the pioneer of this energized water theory is Dr. Masaru Emoto. In 2003, James Randi publicly offered Emoto one million dollars if his results can be reproduced in a double-blind study. No need to say that no one has won one million dollar from James Randi till date.
Gary Greenberg commented on Emoto's work:

"As a scientist, I was astonished. It didn’t surprise me that I couldn’t find any scientific experiments [Emoto] has performed or any peer-reviewed journal articles that have been published describing controlled studies of Emoto’s work. A further search revealed that Emoto’s degree was from the Open International University in India, where an M.D. degree costs $500 and a Ph.D. costs $350, no classes or tests required."

Kristopher Setchfield has researched on Emoto's work and concluded, "After the lengthy review of Emoto’s research methods and results, I have come to believe that Dr. Emoto is offering pseudoscience to the masses in the guise of defensible research."

Here is the disclairmer by amezcua, the company selling biodisc,

"Disclaimer

Your use of this website constitutes your acceptance to the terms of this Disclaimer.

No Warranty to Accuracy The information provided by us on this website is on an "as is" basis and is for general, indicative purposes only. We do not give any express or implied warranty as to the accuracy of the information contained in this website. As such, we will not be liable for any errors in, omissions from, or mis-statements or misrepresentations concerning any such information and will not have or accept any liability, obligation or responsibility whatsoever for any loss or damage, including without limitation, consequential loss or damage arising from or in respect of any use or misuse of or reliance on the information delivered in this website. We expressly disclaim any guarantee or warranty of promised future income or earning. Any claim of earning or earning potential should be treated as an opinion only and you shall not rely on it unless you have verified its accuracy. We shall not be held liable to and shall not accept any liability, obligation or responsibility whatsoever for any loss or damage arising from your reliance on such claims. You do so at your own risk."

In the end, it's really an outright fraud! It's like selling hamburgers that can heal your stomach problem!

Pathology undergraduate lectures POWERPOINT

Very good lecture powerpoint presentation are available at following sites

http://www.medicalschoolpathology.com/PPTs.htm
http://dentalstudentpathology.homestead.com/lectures.html

for other subjects look here

http://medicalppt.blogspot.com/search/label/PATHOLOGY

Compression-only CPR found effective

Chest compressions alone are as effective in rescuing victims of heart attacks as conventional cardiopulmonary resuscitation that combines compressions with forced breathing, researchers said Wednesday.

Studies in Washington and Sweden confirm the growing idea that the breathing component of CPR is necessary only for children and those who have suffered drowning or who have respiratory problems. Recent guidelines based on these and earlier studies may overcome some of the fears of bystanders who are reluctant to initiate CPR because of the danger of infectious diseases.

"These studies reinforce the message that the American Heart Assn. has been promoting since 2008," said Dr. Michael Sayre, a professor of emergency medicine at Ohio State University in Columbus and a spokesman for the heart association. "When you encounter a person who has collapsed suddenly, the best thing to do is to call 911 and then push hard and fast on their chest. It's simple, and something anyone can do even if they don't have any training."

Williams Hematology, Eighth Edition

The landmark hematology reference -- now in full color

Edition after edition, Williams Hematology has guided generations of clinicians, biomedical researchers, and trainees in many disciplines through the origins, pathophysiological mechanisms, and management of benign and malignant disorders of blood cells and coagulation proteins. The book begins with the evaluation of the patient and progresses to the molecular and cellular underpinnings of normal and pathological hematology. Subsequent sections present disorders of the erythrocyte, granulocytes and monocytes, lymphocytes and plasma cells, malignant myeloid and lymphoid diseases, hemostasis and thrombosis, and transfusion medicine.

Featuring a brand-new full-color presentation, the Eighth Edition of Williams Hematology is extensively revised to reflect the latest views of experts in the field. Two new chapters examine the importance of genomics in hematology and cell therapy for tissue replacement, whereas other chapters have been revised to incorporate the newest clinical approaches to the leukemias and lymphomas, and the application of targeted therapy in the treatment of hematologic disorders.

'People become immune to coffee boost', experts believe

Using coffee for a pick-me-up may be pointless if you drink it all the time, researchers believe.

Experts say they have discovered that people who drink a lot of caffeine develop a tolerance to its stimulatory effects.

While caffeine can give people a buzz, raising alertness, the effect only works in those unused to the drink, they tell Neuropsychopharmacology journal.

They base their assumptions on the results of an experiment that they carried out on 379 volunteers.

Cold turkey

To put coffee to the test, the scientists from the UK and Germany asked all of the trial participants to abstain from the beverage for 16 hours.

Blood group diets - a new way to fitness

After hitting the gym, doing yoga and jogging, people are now trying blood group-based diets as experts say the secret to a fit body may be hidden in the blood type.

These diets are popular in the West and they are finding a foothold in India where some fitness experts are recommending them.

Explaining how such diets work, Ekta Tandon, Delhi-based nutritionist and dietician at dailydiet.in, says a chemical reaction occurs between your blood and foods as they are digested.

"Lectins, a diverse and abundant protein found in food, may be incompatible with your blood group and adverse side effects may occur. So I would recommend that one can follow a blood group diet along with the normal food in order to give all the nutrients to the body," Tandon told IANS.

World's Smallest, Lightest Telemedicine Microscope

Researchers at The California NanoSystems Institute at UCLA (CNSI) have developed a tiny telemedicine microscope for imaging blood samples or other fluids, testing water quality or other public health need in resource-limited settings.

From the press release:

Slightly wider than a US quarter and weighing just 46 grams, the lensless microscope is a self-

Beware If your girlfriend loves chocolate

Research in Archives of Internal Medicine shows those who eat at least a bar every week are more glum than those who only eat chocolate now and again.

Many believe chocolate has the power to lift mood, and the US team say this may be true, although scientific proof for this is lacking.

But they say they cannot rule out that chocolate may be a cause rather than the cure for being depressed.

New Studies Eat Into Diet Math

How many calories must a dieter cut to lose a pound?

The answer most dietitians have long provided is 3,500. But recent studies indicate that calories can't be converted into weight through a simple formula.

The result is that the 3,500-calorie rule of thumb gets things very wrong over the long term, and has led health analysts astray. Much bigger dietary changes are needed to gain or shed pounds than the formula suggests.

Consider the chocolate-chip-cookie fan who adds one 60-calorie cookie to his daily diet. By the old math, that cookie would add up to six pounds in a year, 60 pounds in a decade and hundreds of pounds in a lifetime.

But new research—based on studies of volunteers whose calorie consumption is observed in laboratory settings, rather than often-unreliable food diaries—suggests that the body's self-regulatory mechanisms tamp down the effects of changes in diet or behavior.

Eccrine Spiradenoma - Images

There were multiple nodules like this, in this case

Two type of cells, dark ones in periphery, light ones in centre. Cells are arranged around small lumina containing eosinophilic material.

Well circumscribed and not attached to epidermis

Eosinophilic material prominent here.

Cystic changes are seen in some (degenerative or ancient changes)

Lymphocytic infilteration is common in this tumor.

Case - ?lipid storage

Male 12 year, presented with severe anemia, moderate splenomegaly, moderate hepatomegaly, PS shows microcytic hypochromic anemia (Hb 3.5), with rouleaux formation, platelet low normal, total count appear low normal with neutrophils 70%. BM examination done 3 days after first BT given on the day of admission. cilincally ??acute leukemia. On bone marrow, there was mild erythroid hyperplasia, prominent toxic granulation in neutrophilic precursors. No significant number of blasts. Megakaryocytes appear within normal limits. Now after almost ruling out acute leukemia, second clinical possibility remains is of ?lipid storage or ?some chronic infection. I am posting few pictures here, does it suggest any storage disorder or just arteffects. Kindly give your opinions. I feel it is some chronic infection, but not sure. MP negative by slide and card. Kindly give your comments. Will try to post more pictures soon.

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Sudden Sniffing Death Syndrome

At age 12, most kids are concerned with finding a ride to the movies and making it through middle school. Ashley Upchurch was younger -- 11 -- when she became addicted to inhaling air dusters as a way to get high. 

"It was a cheap high, it was instant, and it was intense," Upchurch, now 17 and sober for over two years, said today in a Washington D.C. seminar about the danger inhalants pose to children. 

New data released today by the Substance Abuse and Mental Health Services Administration (SAMHSA) indicates that 12-year-old kids are more likely to get high from common, legal household substances including aerosol computer cleaners, air fresheners, hair spray or shoe polish than use cigarettes or marijuana. 

Stem Cells May Provide Vaccine For Colon Cancer

Immunology experts in the US and China have discovered human stem cells that "fool" the immune system may provide a vaccination for colon cancer.

The study was led by Dr. Bei Liu and Dr. Zihai Li in collaboration with stem cell expert Dr. Renhe Xu at the University of Connecticut Stem Cell Institute and is to be published in the journal Stem Cells.

The study builds on an old notion that immunizing with embryonic materials might produce anti-tumor responses, but this has only been shown in animal studies.

AIDS virus can hide in bone marrow

The virus that causes AIDS can hide in the bone marrow, avoiding drugs and later awakening to cause illness, according to new research that could point the way toward better treatments for the disease.

Finding that hide-out is a first step, but years of research lie ahead.

Dr. Kathleen Collins of the University of Michigan and her colleagues report in this week's edition of the journal Nature Medicine that the HIV virus can infect long-lived bone marrow cells that eventually convert into blood cells.

The virus is dormant in the bone marrow cells, she said, but when those progenitor cells develop into blood cells, it can be reactivated and cause renewed infection. The virus kills the new blood cells and then moves on to infect other cells, said.

Gut Bacteria May Spur Obesity, Research Suggests

Intestinal bacteria may contribute to obesity and metabolic syndrome, a new study in mice suggests.

"It has been assumed that the obesity epidemic in the developed world is driven by an increasingly sedentary lifestyle and the abundance of low-cost, high-calorie foods. However, our results suggest that excess caloric consumption is not only a result of undisciplined eating but that intestinal bacteria contribute to changes in appetite and metabolism," senior study author Andrew Gewirtz, an associate professor of pathology and laboratory medicine at Emory University School of Medicine, said in a university news release.

Tuberculosis, Fourth Edition: The Essentials

Edited by Dr. Mario C. Raviglione, Director of the World Health Organization’s(WHO) Stop TB Department, the Fourth Edition presents key updates on recent discoveries and studies in tuberculosis (TB) detection, treatment, and prevention, to give pulmonologists, infectious disease specialists, and research scientists the tools they need to provide better patient care and develop new paths of TB research.

Sternberg's Diagnostic Surgical Pathology

This is fourth edition of Sternberg's diagnostic surgical pathology, published in 2004. Does not require a introduction. Fifth edition has been published in last quarter of 2009.

Peanut allergies tackled in largest ever trial

Cambridge University researchers will give increasing doses of peanut flour to 104 British children, up to the equivalent of five nuts a day.

Twenty out of 23 sufferers in an earlier study became able to eat more than 30 peanuts safely.

The new £1m three-year trial could lead to a widely available treatment.

About one in 50 young people in the UK suffers from peanut allergies which can cause breathing problems, itching and, in severe cases, a potentially fatal inflammatory reaction called anaphylaxis.

A year later, woman told she's not HIV+

Till last January, 23-year-old Batashi and husband Tarak, 26, of Serampore were the quintessential happy couple. They had married for love and were expecting their first child. Then a routine blood test brought their world crashing down. Batashi was inexplicably diagnosed HIV positive at Kolkata's School of Tropical Medicine (STM). A test on Tarak proved negative.

What followed was worse than nightmare for Batashi. Her in-laws ostracized her and her husband accused her of straying. Tarak would have kicked her out had a little compassion for the woman he had once loved not lurked in one corner of his heart.

5,000 more post-grad medical seats

India will now produce 5,000 more specialized doctors every year. The Cabinet Committee on Economic Affairs (CCEA) on Thursday approved health ministry's proposal to add more postgraduate seats in 148 state government medical colleges.

The Rs 1,350 crore scheme will see a cost sharing ratio of 75:25 between the Centre and states. Though still far short of the numbers needed, the decision is being viewed as a positive step for a country that has a shortfall of six lakh doctors, 10 lakh nurses and two lakh dental surgeons.

Ironically, Indian doctors who have migrated to the developed world form nearly 5% of the medical workforce of their respective countries.

An eye opener from neuropathology blog - "Should Football Be Illegal?"

       Dr. Brian recently posted this article on his blog, I found the post so interesting that I am replicating the post entirely.

"Two neuropathologists are prominently spotlighted in an article by Malcolm Gladwell in the October 19 issue of The New Yorker. The article explores a provocative question raised by autopsy results on football players: namely, should football be illegal? Featured are Dr. Ann McKee (pictured), neuropathologist at the Veterans Hospital in Bedford, Massachusetts and Dr. Bennet Omalu, forensic neuropathologist and San Joaquin Valley (CA) chief medical examiner. Drs. McKee and Omalu have done some interesting autopsy work which suggests that the tau-positive chronic traumatic encephalopathy suffered by football players is much more common, even among high school players, than previously realized. As an example, McKee provides photomicrographs from a case of an 18-year-old high school football player and says: "He's got all this tau. This is frontal and this is insular.... This is completely inappropriate. You don't see tau like this in an 18-year-old. You don't see tau like this in a fifty year old."

Tests show King Tut died from malaria

There has been speculation about the fate of the boy king, who died sometime around 1324 BC probably at age 19, since the 1922 discovery of his intact tomb in Egypt's Valley of Kings.

Tests performed on 16 royal mummies found four, including Tut, had contracted a severe form of malaria that likely cut short Tut's reign -- ruling out murder or some other sickness.

Scientists from Egypt, Germany and elsewhere, including Zahi Hawass of Egypt's Supreme Council of Antiquities, compiled results from genetic and radiological testing performed on the mummies between 2007 and 2009. The results clarify details about the 155-year-long 18th Dynasty that included Tutankhamen, who inherited the throne at age 11.

Analysis: Chocolate may reduce stroke risk

Just in time for Valentine's Day, research out this week suggests eating chocolate may have a positive impact on stroke. Don't go buying too many heart boxes just yet, though, say the study authors.

A new analysis, which involved a review of three prior studies, suggests eating about a bar of chocolate a week can help cut the risk of stroke and lower the risk of death after a stroke. But the evidence is still limited, says study author, neurologist Gustavo Saposnik at St. Michael's Hospital, University of Toronto.

"This is something that requires further investigation," Saposnik says.

Child Obesity Risks Death at Early Age, Study Finds

A rare study that tracked thousands of children through adulthood found the heaviest youngsters were more than twice as likely as the thinnest to die prematurely, before age 55, of illness or a self-inflicted injury.

Youngsters with a condition called pre-diabetes were at almost double the risk of dying before 55, and those with high blood pressure were at some increased risk. But obesity was the factor most closely associated with an early death, researchers said.

Three Simple Steps to Healthy Weight in Children

To curb the childhood-obesity epidemic, health experts have long urged parents to make healthy changes to their family's lifestyle — such as eating nutritiously, reducing TV time, exercising and getting a good night's sleep.

Individually, these behaviors have been linked to a lower risk of obesity in kids, but researchers at Ohio State University were interested in learning whether their effect might be cumulative — that is, whether families who adopted not just one but two or more of these behaviors could reduce their children's risk of obesity even further.

Study links sugary soft drinks to pancreas cancer

People who drink two or more sweetened soft drinks a week have a much higher risk of pancreatic cancer, an unusual but deadly cancer, researchers reported on Monday.

People who drank mostly fruit juice instead of sodas did not have the same risk, the study of 60,000 people in Singapore found.

Sugar may be to blame but people who drink sweetened sodas regularly often have other poor health habits, said Mark Pereira of the University of Minnesota, who led the study.

"The high levels of sugar in soft drinks may be increasing the level of insulin in the body, which we think contributes to pancreatic cancer cell growth," Pereira said in a statement.

Promising Blood test For Pancreatic Cancer Detection

Scientists state that they have been successful in developing a blood test which could detect pancreatic cancer early on in its more treatable stages.

The test employs an antibody that functions as a heat-detecting projectile that homes in and attaches to cells which bear PAM4 protein which is found vastly in pancreatic cancer cases.

The researchers stated that this protein is pancreatic cancer-specific and is atypically present in healthy tissues or in other types of cancers.

India to turn out over 145,000 rural doctors

With people-doctor ratio six times lower in rural India in comparison to cities, the central government on Thursday said it will produce 145,000 rural doctors through a truncated medical course designed after the Chinese "barefoot doctors".
"The proposal envisages training persons from rural areas on the basis of merit to equip him or her to primarily, I underline, primarily to work in 145,000 sub centres," Health Minister Ghulam Nabi Azad said here.

Iron deficiency V/S thal minor V/S chronic disease anemia

A variety of equations have been proposed to distinguish the microcytic anemia of iron deficiency from that of thalassemia minor.

These formulas may not be applicable:

(1) if the patient has been treated with iron;

(2) if the patient has been treated with blood transfusions;

(3) if both iron deficiency and thalassemia minor coexist in the same patient

(4) in some patients with polycythemia vera who develop iron deficiency (England-Fraser formula)

Some of the formulas do not account for a gray, intermediate region where it is not possible to differentiate between the two conditions reliably.

Mentzer Formula

How One Woman's Cells Changed Medicine

               In a microbiology lab at New York's Columbia University, Professor Vincent Racaniello experiments with some cells that have led to some of the greatest medical breakthroughs of the last hundred years. But these are no ordinary cells.

Henrietta Lacks, circa 1950.

(Courtesy of PNAS.org)

They're called, HeLa. And they were first used in research that led to the Polio vaccine, as well as helping to develop medicines to fight cancer, the flu and Parkinson's disease, and in the research that led to gene mapping and cloning. They were used to test the effects of atomic radiation and sent into outer space.

Overweight elderly 'live longer'

Moderately overweight elderly people may live longer than those of normal weight, an Australian study suggests.

But being very overweight or being underweight shortened lives.

The report, which was published in the Journal of the American Geriatric Society, said dieting may not be beneficial in this age group.

But the study of 9,200 over-70s also found that regardless of weight, sedentary lifestyles shortened lives, particularly for women.

The study by the University of Western Australia set out to find out what level of body mass index (BMI) was associated with the lowest risk of death in the elderly.

Concerns have been raised about encouraging apparently overweight older people to lose weight Professor Leon Flicker, University of Western Australia

For younger people, there is a well established health risk from being overweight or obese.

Overweight best

The team tracked the number of deaths over 10 years among volunteers who were aged 70 - 75 at the start of the study.

It found that those with a BMI which classed them as overweight not only had the lowest overall risk of dying, they also had the lowest risk of dying from specific diseases: cardiovascular disease, cancer and chronic respiratory disease.

The overall death rate among the obese group was similar to that among those of normal weight.

But those who were very obese had a greater risk of dying during the 10 year period.

Lead researcher, Professor Leon Flicker said: "Concerns have been raised about encouraging apparently overweight older people to lose weight.

"Our study suggests that those people who survive to age 70 in reasonable health have a different set of risks and benefits associated with the amount of body fat to younger people."

The conclusion of this study, that being overweight may be less harmful for elderly people, corroborates the findings of previous research.

Staying still

Sedentary lifestyles shortened lives across all weight groups, doubling the risk of mortality for women over the period studied, and increasing it by 25% for men.

Physical exercise "really matters", said Professor Flicker.

As well as helping to build muscle mass, it has broader health benefits for elderly people, he said.

The authors believe BMI may give a poor reflection of fatty mass in elderly people.

"It may be time to review the BMI classification for older adults," says Professor Flicker.

Professor Kay-Tee Khaw from Cambridge University agreed, noting that optimal weight appears to be higher in older age groups.

"This is important since under-nutrition is an important problem in older people.

"Waist circumference, which assesses abdominal obesity, appears to be a better indicator of health consequences of obesity" she said.

Smokers With Lung Cancer: Not Too Late to Quit

Smokers with lung cancer who have asked "Why quit now, I'm already sick?" may find new motivation in this answer: Doing so could double their odds of survival over five years.

A report published online in BMJ suggests that people who give up smoking after being diagnosed with early-stage lung cancer live longer than patients who continue the habit.

The findings underscore the importance of the notion that it is never too late to quit smoking.

Lung cancer is the most common cause of cancer death, according to the American Lung Association. And smoking causes most cases of lung cancer.

Medical evidence has repeatedly shown that as soon as a person quits smoking the body begins to repair the damage done by tobacco-smoke-related chemicals, and it's been theorized that continued smoking can influence the behavior of lung tumors. But until now it was not clear if ending the smoking habit after being diagnosed with lung cancer had any impact on a patient's survival.

Researchers at the University of Birmingham in England reviewed the results of 10 studies that evaluated how smoking cessation after lung cancer diagnosis affected a patient's prognosis. The review included patients with both non-small-cell and small-cell forms of lung cancer.

Among their findings:

• Patients with early-stage lung cancer who continued to smoke had a "substantially higher risk of death" than those who quit after their diagnosis. The increased death risk appeared to be due to the cancer spreading.
• The five-year survival rate for the quitters was 64%-70% compared with 29%-33% for those who continued to smoke.
• The continued smokers were also more likely to have their cancer return than those who quit.

The researchers say their findings suggest that smoking-cessation programs may benefit patients with early-stage lung cancer, but they add that more research is needed.

Catching up on lost sleep a dangerous illusion

The study followed participants who each took up residence for 38 days at Brigham and Women's Hospital in Boston.

The study looked at three things: the number of consecutive hours awake, the number of days or weeks of chronic sleep reduction, and what time it was in the person's day. "How those three factors combine determine how well we perform at any moment," says Cohen.

"It's very hard to cheat the sleep system. You will pay a price sooner or later," says David Dinges, a professor of sleep studies at the University of Pennsylvania school of medicine. This research suggests "it takes longer to recover from sleep debts than has been believed in the past."

This study shows for the first time in humans that sleep regulation is actually composed of at least two separate processes acting on different time scales. The short-term process causes performance to decline with each hour awake, and this process can be rapidly overcome with one extended sleep episode.

The long-term process builds over weeks of too-little sleep. It causes a faster decline in performance for each hour a person is awake, particularly during the biological late night, the equivalent of 3 a.m. to 7 a.m. It is unknown how many nights of good sleep it takes to recover from this longer-term component.

This work in humans parallels work in animals showing more than one mechanism that promotes sleepiness in the context of reduced sleep hours. The sleep-inducing chemical adenosine appears to increase with hours spent awake. Recently a second mechanism, which is affected by long-term sleep deprivation, has been found. In this, the number of receptors in the brain for adenosine increase as long-term sleep deficit becomes bigger.

In effect, the brain becomes sensitized to the effects of adenosine, and the same number of hours awake has a bigger impact on performance.

"Sleep appears to be a crucial process, and evolutionary mechanisms have evolved so that more than one mechanism kicks in to promote sleepiness," says Cohen.