Key Point

Circadian variations in lung function have been identified in a large group of patients with diagnosed or suspected obstructive lung disease.

SEATTLE—For some time it has been suspected that lung function may be among the biological processes known to fluctuate with the body’s circadian rhythms. A recent study has confirmed that suspicion.

“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,” reported Boris I. Medarov, MD, at the annual meeting of the American College of Chest Physicians in Seattle.¹ Dr. Medarov is a Pulmonary and Critical Care Medicine Fellow at Long Island Jewish Medical Center in New Hyde Park, New York.

His five-year study looked at the fluctuations in two lung function indicators—the FEV₁/FVC ratio and total lung capacity—between 8 am and 5 pm. Most of the 4,835 individuals in the study had previously been diagnosed with obstructive lung disease such as chronic bronchitis or emphysema, and some were being tested for lung disease.

“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,” Dr. Medarov related. It appeared to be lowest around noon, when it typically dropped by about 7%—in some cases dropping by as much as 15%.

While relatively small lung function variations such as these may not be significant in a healthy person, they could be, in patients with lung disease. Extubation and physical activity may be easier for such patients when timed to correspond with peak lung function. In addition, the need for bronchodilator therapy may be reduced if the treatment is administered when lung function is poorest rather than if it is given indiscriminately throughout the day, as is common.

ASTHMA EXPERIENCE

A 2003 study by researchers at the University of Wisconsin in Madison2 examined the circadian variability in lung function in patients with mild asthma. The investigators compared lung function and analyzed sputum eosinophils at 7 am and 4 pm.

An early-morning increase in total sputum leukocytes and eosinophils was observed. Furthermore, sputum eosinophils correlated with β-agonist reversibility.

Levels of interleukin-5 and eosinophil-derived neurotoxin were also significantly increased at 7 am compared with levels later in the day. The authors concluded that the circadian variablity in pulmonary function in asthma patients could possibly be related to changes in airway eosinophil recruitment.

One of Dr. Medarov’s next research objectives is to identify the specific mechanism behind the lung function changes he observed in his study. For instance, fluctuating hormone levels may be a factor. Further study will also be necessary to determine if it is possible to use relaxation techniques or biofeedback to enhance lung function by modifying its circadian variations.

—Timothy Begany

References
1. Medarov BI. Hour-to-hour variation of FEV₁/FVC. Presented at: annual meeting of the American College of Chest Physicians; October 26, 2004; Seattle, Wash.
2. Panzer SE, Dodge AM, Kelly EA, Jarjour NN. Circadian variation of sputum inflammatory cells in mild asthma. J Allergy Clin Immunol. 2003;111:308-312.

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