Internal Clock Governs Lungs, Too

Findings could help doctors schedule procedures

WEDNESDAY, Oct. 27, 2004 (HealthDayNews) -- Do your lungs know what time it is?

New research suggests they do indeed, and their daily rhythms could provide insight into the best periods of the day for everything from exercise to medical procedures.

A study of pulmonary patients during office hours found their lungs lost power around lunchtime but were at their best from 4 p.m. to 5 p.m. While researchers still need to better understand the rhythms of the lungs, the findings "might have some practical applications," said study author Dr. Boris Medarov, a lung specialist at Long Island Jewish Medical Center.

From blood pressure to heart rate to hormone levels, many bodily measurements fluctuate during a 24-hour cycle, known as a circadian rhythm. That's why people generally feel sleepy at the same time each day instead of, say, 10 a.m. on Tuesdays and 11 p.m. on Wednesdays.

Researchers have suspected the lungs also operate on a circadian rhythm, and doctors often ask patients to come in at the same times of the day for lung testing. "Our classical understanding was that people with limited [lung] functions, obstructive lung disease and asthma have their lowest [air] flow rates in the early morning hours," Medarov said. "That's the worst time for them."

Asthma patients, for example, tend to get worse around 6 a.m. and breathe their best at 2 p.m., he said.

In the new study, Medarov examined the results of lung-function tests given to more than 4,000 patients during office hours of 8 a.m. to 5 p.m. Most clearly had serious lung diseases such as chronic bronchitis and emphysema, but some were sent for testing to diagnose their illness.

Medarov was expected to release the findings Oct. 26 at the American College of Chest Physicians annual convention in Seattle.

The test showed that lung function typically dropped by about 7 percent -- in some cases as much as 15 percent -- around noon. But the lungs of the patients worked at their best around 4 and 5 p.m.

A difference of 7 percent isn't much to a healthy person, but it could make a lot of difference to someone who's seriously ill and facing a medical procedure, Medarov said. "Often, we face decisions about when to extubate, when to take a person off a ventilator in our intensive-care units," he said. "A lot of those are people with obstructive lung disease. It looks like these results may be the most pertinent with those people."

It's possible that being in the intensive care unit (ICU) may disrupt the daily rhythms, said Dr. Tom Stibolt, a lung specialist with the Kaiser Permanente Health Plan in Portland, Ore. "Even if this variation persists, it is hard to know how relevant it is in a process such as extubation in the ICU, but it is great for speculation," he said.

The next step in research is to look into what may cause changes in lung function during the day. Hormones are one possible suspect, Medarov said, "but I still don't really have the answer to that."

More information

Learn more about circadian rhythms from Wikipedia.com.

SOURCES: Boris Medarov, M.D., pulmonary and critical fellow, Long Island Jewish Medical Center, New Hyde Park, N.Y.; Tom Stibolt, M.D., senior physician, pulmonology critical care, Kaiser Permanente Health Plan, Portland, Ore.; Oct. 26, 2004, presentation, American College of Chest Physicians annual convention, Seattle
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