By preventing the pauses in breathing that disrupt sleep and cause severe daytime sleepiness, the CPAP treatment helped her feel more alert and less tired, with extra energy to get through the day.

The only problem was that it irritated her nose. Nasal dryness and congestion are common side effects of the treatment, according to Dr. Patrick Strollo, director of the University of Pittsburgh Medical Center Sleep Medicine Center.

Once she added a humidifier to her CPAP unit, however, Ms. Bates, 63, of Cleveland, found that the added moisture made the treatment more comfortable.

"When I first started, I didn't use a humidifier and it was very annoying to my nose," she said. "Now that I use a humidifier it makes a big difference."

The original CPAP humidifiers used cold, "passover" humidification to reduce nasal dryness and congestion. Newer models now use heated humidification to provide patients with an extra measure of comfort. Some CPAP models come with the humidifier "integrated" into the unit, while others are compatible with attachable humidifiers.

The American Academy of Sleep Medicine recommends the use of heated humidification to improve the utilization of CPAP therapy, according to practice parameters published in the March 1 issue of the journal Sleep.

Strollo says that the need for humidification is a natural result of CPAP therapy and one of the best developments since CPAP was first introduced in 1981.

"With positive pressure therapy you're blowing air through the nose," he said. "When you blow air over a surface, it dries out. The nose is the humidifier for the body; by adding humidification to the CPAP system, you can offset the drying effect. That's been one of the major breakthroughs over the past 20 years."

Dr. Nancy Collop, medical director of the Johns Hopkins Hospital Sleep Disorders Center in Baltimore, sees humidification as one of a number of positive developments that have improved a treatment that was already highly effective.

"I think it's always been a good therapy," she said. "I do think there are some patients who clearly benefit from the newer modifications over the last 10 years, such as newer masks and head systems and humidification."

Collop said that sleep apnea patients should work closely with their sleep doctor when beginning CPAP treatment. Sleep specialist can help patients with side effects such as nasal congestion, which will boost the effectiveness of the therapy and help patients maintain a long-term commitment to it.

"In the critical period around the diagnosis when the treatment is initiated," she said, "if the sleep physician is involved and engaged, they can help the patient work through any problems with CPAP, along with the other staff at the clinic."