Chest, Vol 102, 771-774, Copyright © 1992 by American College of Chest Physicians

ARTICLES

The amplitude of circadian FEV1 variation suitable for phase determination by cosinor analysis in stable asthmatic children

S Kondo
Children's Asthmatic Center, Kawasaki City Ida Hospital, Japan.

To elucidate the criterion for amplitude of circadian FEV1 variation suitable for phase analysis, six FEV1 measurements within a day were made on 346 days in 125 stable asthmatic children aged 8 to 12 years. Since coefficient of variation (CV) of FEV1 within a day in nonasthmatic children in our laboratory is less than 5 percent, circadian FEV1 variations were divided into CV greater than or equal to 5 percent and CV less than 5 percent groups. Forty-two (12 percent) variations with significant fit of cosinor rhythm were CV greater than or equal to 5 percent. Troughs in 32 (76 percent) variations of the 42 were distributed between 12 PM and 6 AM, and the deviation was highly significant against a uniform distribution (p less than 0.001). This was consistent with nocturnal asthma. Thirty-five (10 percent) variations with significant fit of cosinor rhythm were CV less than 5 percent. Troughs in 12 (34 percent) variations of the 35 were distributed between 12 PM and 6 AM, and the deviation from a uniform distribution was nonsignificant. These suggest that 5 percent or more of CV of FEV1 may be clinically suitable for analysis of circadian FEV1 variation.