Lung function regulated by circadian rhythms

October 26, 2004

Circadian rhythms, the body's biological processes that repeat in 24-hour cycles, may have a significant effect on a person's lung function and, ultimately, help determine the best time of day for exercise and the administration of medications and medical procedures. In a new study presented at CHEST 2004, the 70th annual international scientific assembly of the American College of Chest Physicians (ACCP), lung function was found to have a natural circadian rhythm, where it is at its peak during the late afternoon hours and at its lowest around midday.

"Circadian rhythms regulate our biological cycles for sleep, activity level, metabolism, and many other processes through our body's exposure to sunlight and darkness," said Boris I. Medarov, MD, FCCP, Long Island Jewish Medical Center, New Hyde Park, NY. "Our study finds that lung function has its own rhythm that may govern how much energy we exert throughout the day and the best times to engage in certain activities."

The study investigated how lung function fluctuated throughout the working hours of 8:00 am and 5:00 pm. In a 5-year period, 4,835 patients underwent several breathing tests and were subdivided into nine groups based on the time of day the test was performed. Results of FEV1/FVC and total lung capacity testing were compared within nine time intervals. Results showed that patients' overall airway resistance was at its most prominent around 12:00 pm but reached its minimum between 4:00 to 5:00 pm, showing that lung function was at its best in the late afternoon.

"We often associate the end of the work day with being tired and less motivated for physical exertion; however, lung function seems to be at its best during this time. As a result, exercising or engaging in other physical activities in the late afternoon may help us to achieve optimal performance," said Dr. Medarov. Circadian rhythms of lung function may also have implications for the administration of asthma medications and the timing of medical procedures.

"Many patients with asthma and chronic obstructive pulmonary disease administer bronchodilators around the clock, when they actually may need less treatments and a different regimen that includes administering the medication at midday when their lung function is at its lowest," said Dr. Medarov. "It also may be better to extubate patients in the late afternoon when their lung function is at its best and breathing on their own is easier." Relaxation techniques or biofeedback may modify lung function circadian rhythms, helping to manage a person's low and high lung function throughout the day, added Dr. Medarov, but more studies need to be completed in this area.

"Circadian rhythms can greatly influence how patients with respiratory conditions respond to certain therapies," said Paul Kvale, MD, FCCP, President of the American College of Chest Physicians. "By knowing how the respiratory system naturally responds at different times during the day, health-care providers can adapt treatments and procedures to better fit patients' individual needs."
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CHEST 2004 is the 70th annual international scientific assembly of the American College of Chest Physicians, held October 23-28 in Seattle, WA. ACCP represents 16,000 members who provide clinical respiratory, critical care, sleep, and cardiothoracic patient care in the United States and throughout the world. The ACCP's mission is to promote the prevention and treatment of diseases of the chest through leadership, education, research, and communication. For more information about the ACCP, please visit the ACCP Web site at www.chestnet.org.

American College of Chest Physicians

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