Millions of Americans are fighting for their lives -- while sleeping. When they slumber, their airways collapse. The level of oxygen in their blood declines and the level of carbon dioxide rises.

They're being strangled.

Sensing danger, the brain rouses the sleepers enough to start gasping for air. The chest convulsively shudders, and they begin breathing again. They settle down.

And it happens again. And again. Up to 400 times a night.

The next day, they're bleary-eyed and unfocused. They put on weight, and are told to diet and exercise. But they're too tired to make the effort.

This is what it's like for those with severe obstructive sleep apnea, a condition that affects 6 million Americans, and a total of 20 million Americans to a lesser degree. When they should be revitalizing, their bodies are struggling against death.

"Imagine if I reached over and choked you several times throughout the hour," said Helen Kent, founder of Progressive Medical, a Carlsbad-based supplier of medical devices that treat sleep disorders.

Kent played a video of a sleeping man with obstructive sleep apnea to make her point. The overweight man periodically stopped breathing, then after several seconds resumed chest and belly heaving. It was easy to imagine him battling an unseen assailant trying to asphyxiate him. As far as his body was concerned, that's exactly what was happening.

Evidence grows

Previously thought of as side effects of illness, sleep disorders and lack of good sleep are now considered to be underlying causes or aggravators of the most lethal diseases. Surprisingly, modern medicine, usually so prolific at providing polysyllabic Latinate names, appears not to have a name for the constellation of diseases connected to poor sleep.

Apnea and other sleep disorders are connected to elevated risks from the top three killers: cardiovascular disease, stroke and cancer. These respectively account for 28, 22.7 and 6.4 percent of U.S. deaths in 2003, according to the Centers for Disease Control and Prevention. Sleep disorders and poor sleep are implicated in the fifth and sixth leading causes of deaths -- unintentional injuries and diabetes.

Sleep expert Dr. Delmer Henninger said recent studies in the New England Journal of Medicine established a solid case for connecting apnea and stroke.

"It confirms the link we've all suspected for many years. The evidence is pretty overwhelming," said Henninger, who operates a sleep lab in Murrieta. His typical patient, he says, is a male, over 40, overweight, who snores.

Sleep breathing disorders may contribute to heart failure, according to a study in the Feb. 10 issue of the journal Circulation. The Mayo Clinic study found that those with central sleep apnea were more likely to develop heart failure. Also, those with heart failure were more likely to have central sleep apnea.

Severe sleep-disordered breathing is associated with a twofold to fourfold increase in complex, abnormal heart rhythms in sleep, according to the Sleep Heart Health Study, in the April 15 issue of the American Journal of Respiratory and Critical Care Medicine.

Decreased libido and depression are also linked to sleep apnea. A 2002 study at the Technion-Israel Institute of Technology found that male patients with the disorder produced lower amounts of testosterone. This was the first scientific explanation given for the previously reported finding of lower libido.

A 2003 study at Stanford University School of Medicine found that people with depression were five times more likely to have a sleep-related breathing disorder as people without depression.

Many vehicle accidents are caused by weary drivers, many with sleep apnea, Kent said.

"It's not a fender-bender," he said. "These people are sleeping. Their foot is on the accelerator. They're going to hit the massive tree with no braking. They're going to go off the roadway, They're going to cream another car and kill people."

That grim view finds backing from a 2004 study by researchers at UCSD Medical Center. Nearly 1,000 lives could be saved and about $11 billion in automobile accident-related damage could be avoided if people with sleep apnea were treated, stated the study in the May 2004 issue of the journal Sleep.

Treatment

Drugs can help with some sleep disorders, at least for a time, Henninger said, but for conditions such as sleep apnea, "there's no pill." He divides treatment options into four categories: behavioral changes, an orthodontic device to keep the jaw and tongue from sliding back and blocking the airway, surgery, and a device to push air down the nose into the lungs.

Surgery is effective half the time, he said, most often working in children. Tissue that obstructs the airway, such as adenoid or tonsil tissue and the soft palate, is partially removed.

The last option, called Continuous Positive Airway Pressure, or CPAP, is "100 percent effective," Henninger said. The drawback is that some patients can't stand to wear the device, which may include a mask if patients are mouth-breathing. CPAP devices are made by Poway's ResMed, which has aggressively championed research into the linkage between sleep-disordered breathing and other diseases.

Follow-through is key to success, said Progressive Medical's Kent. Her company provides CPAP devices to patients under a doctor's care.

"We get the prescription just like a drug prescription from a doctor, then we provide the equipment," Kent said. The company tests patients to see how best to apply the device, and also frequently checks in with patients, even if they hear no complaint.

Bill Neff of Hemet is one of Progressive Medical's clients, as the company calls them. Neff has central sleep apnea, a condition in which the muscles that control breathing are weakened. Neff's condition is part of postpolio syndrome, an aftereffect of having contracted polio.

Neff had an unhappy introduction to assisted breathing while having surgery. He was given a CPAP mask with the pressure set too high: he could inhale, but had trouble exhaling. Much to his doctor's distress, Neff took off the mask. Out of the hospital, Neff had unsatisfactory experiences with equipment from two companies.

Progressive Medical fitted him with an intermittent air supply timed to his breathing rhythm. Air enters through two tubes attached to "pillows" that fit inside his nostrils.

"It doesn't even feel like it's on," Neff said. "I can sleep on my side, sleep on my back, anyway I want to."

Sleep tips

The need for sleep is deeply ingrained in mammals, as well as birds and fishes. At the alert end of the spectrum, giraffes can get by on a half-hour of sleep a day. Sloths do little except sleep, as much as 18 to 20 hours a day. Humans fall into the middle of this spectrum.

A lack of sleep impairs memory retention and immune system function, among other things. So researchers theorize that during sleep, the body strengthens those functions. The longer without sleep, the greater the need to sleep -- the human record for sleeplessness in a healthy person is 11 days.

But there is such a thing as sleeping too much. An editorial in the February 2004 issue of the journal Sleep pointed to studies showing increased mortality for those sleeping more than eight hours a day or fewer than 4.5 hours a day.

The ideal is to sleep regularly, in a predictable pattern, and to keep your body's circadian rhythm, or biological clock, in synch. Well-rested people are more productive and find it easier to practice other healthy habits.

Dr. John Cronin, a sleep specialist who is certified by the American Board of Sleep Medicine, suggests that people set a constant time for getting up in the morning, and fitting their sleep cycle around that time. Also, avoid caffeine in the late afternoon and drinking.

"The circadian rhythm is extremely powerful," Cronin said. "It's the system that governs jet lag. So believe it or not, when you don't pay attention to your circadian rhythms, you can almost exist in a state of mild jet lag, even though you're not traveling."

That's tough for teens, because their circadian rhythms are geared to a late-to-rise, late-to-bed cycle that early school hours disrupt.

"People have done some very elegant experiments where they've tried to delay school start times. And it actually has been shown to improve school performance, alertness and attendance," Cronin said. "The problem is how that fits into societal requirements of parental schedules, sports schedules after school, and it just doesn't fit in the way we'd like it to."

Contact staff writer Bradley J. Fikes at bfikes@nctimes.com or (760) 739-6641. Go to http://www.nctimes.com to comment on this story.

Diagnosis

Patients usually get referred to a sleep specialist like Henninger by their own primary care doctor. The patient complains of tiredness or being unable to sleep. Males typically seek help because their wives notice that they snore -- a major symptom of sleep problems -- or they otherwise can't sleep well.

Sometimes, patients will be referred to a sleep lab like that operated by Henninger in Murrieta. In San Diego County, Scripps Clinic operates one of the most prominent sleep labs at its Green Hospital in the Torrey Pines Mesa area. Patients stay the night and their sleep patterns observed.

The lab at the Green Hospital looks like a cross between a high-tech data center and a hotel. It has four rooms designed to look like hotel rooms, with beds, nightstands and paintings. The air temperature is kept a little on the chilly side. There are no clocks or television sets or telephones, although people can bring whatever they want.

After arriving, usually around 7:30 p.m, patients are attached to various instruments, to measure brain waves, chest and stomach movements, muscle tone, heart rhythm and oxygen level. Two techs are on hand to monitor the four patients, said John Cronin, MD., a sleep specialist who is certified by the American Board of Sleep Medicine.

Sleep apnea shows a telltale breathing pattern that you don't have to be a doctor to identify, Cronin said: The monitors that measure chest and stomach movement go flat, followed by large spikes in activity that slow down. Oxygen levels also drop, sometimes precipitously.

The stress of that oxygen deprivation takes a major toll on patients' bodies, Cronin said.

"I tell them it's kind of like going to Mt. Everest -- repeatedly -- going up and down, up and down."

Age makes the symptoms worse, because older people have less reserve capacity.

"A 20-year-old man may have very severe sleep apnea by oxygen level, but because he's got so much cardiac and lung reserve, he they make it through," Cronin said.

A related point: apnea is a chronic condition.

"You don't just have it for a year, and then it goes away," Cronin said.

Sleeping well

- Get up every day at the same time.

- Don't consume caffeine at night or in the late afternoon.

- Be moderate in alcohol consumption.

- If you snore, see a doctor. Snoring can be a sign of obstructive sleep apnea.

Stages of sleep

Sleep is divided into five stages, each of which is associated with a particular pattern of brain waves.

Stage 1, or drowsiness. The person becomes less aware of surroundings, but easily awakable. The person may experience visual or auditory hallucinations. Breathing becomes more regular.

Stage 2: Heart rate slows, body temperature decreases, and the person's awareness of surroundings drops off further. However, the person can still be easily aroused. Characteristic brain waves of sleep, such as "spindles," begin to be seen.

Stage 3 and 4. These states of deep sleep blend into each other. It's hard to awaken a person from these stages, especially Stage 4.

REM (Rapid Eye Movement) sleep: The period of sleep when most dreaming takes place. Brain waves show activity similar to wakefulness, although the person is not aware of surroundings. People can't voluntarily move while in REM sleep.

This paralysis can carry over for a short time upon awakening. This is called sleep paralysis and usually is normal. People are sometimes frightened when they awaken in this state and falsely sense the presence of danger. Some researchers believe reports of alien abductions or other paranormal experiences are in fact memories of this "hypnagogic" state.

Getting help

Information

National Sleep Foundation

http://www.sleepfoundation.org

National Institutes of Health

http://www.nhlbi.nih.gov/health/dci/Browse/Sleep.html

Mayo Clinic

http://www.mayoclinic.com/health/sleep/SL99999

Progressive Medical

http://www.hesnores.org

ResMed

http://tinyurl.com/nh8bv

Treatment and clinical trials

Sleep-certified specialists

American Board of Sleep Medicine

http://tinyurl.com/ps9vt

Palomar Pomerado Health

Sleep lab

555 E. Valley Parkway

Escondido (760) 739-3685

http://www.pph.org

Pacific Sleep Medicine Services

Seven locations in California

Oceanside (760) 721-9200

San Diego (858) 657-0550

http://www.sleepmedservices.com

Murrieta Sleep Center

25405 Hancock Ave. No. 203

Murrieta (951) 698-6629

West Coast Sleep Diagnostics

28991 Old Town Front St. No. 105

Temecula (951) 693-4678

Scripps Clinic Sleep Disorders Center

10666 N. Torrey Pines Road

La Jolla (858) 554-8845

http://tinyurl.com/lbm9r

Sleep Studies Center

Children's Hospital and Health Center

3020 Children's Way

San Diego, CA 92123

(800) 788-9029

http://www.chsd.org/1496.cfm

UCSD Medical Center

Sleep Medicine Center

200 W. Arbor Drive

San Diego, CA 92103

(619) 543-5713

http://tinyurl.com/nxnwc