Circadian Variation of Bronchial Caliber and Antigen-induced Late Asthmatic Response: Results

Circadian Variation of Bronchial Caliber and Antigen-induced Late Asthmatic Response: ResultsInformation describing each patient involved in the study is given in Figure 1 and Table 2. The FEV, immediately before the house-dust inhalation was within 10 percent of the value at the beginning of the study, at 10 am in the morning challenge, and at 6 pm in the evening challenge in each patient. The mean (±SD) CV of six FEV, values on the control day in the morning challenge was 4.2 ±3.4 percent versus 5.9 ± 5.2 percent in the evening challenge. The difference was insignificant. The mean (±SD) FEV, as percent of predicted immediately before the house-dust inhalation in the morning challenge was 91.7 ± 9.5 versus 94.2 ± 8.3 in the evening challenge. The difference was insignificant.
No IAR occurred following inhalation of either the diluent or the house-dust solution in all challenges. A LAR following the house-dust inhalation occurred in all challenges. The mean (±SD) maximum decrease in FEV, in the morning challenge was — 35.5 ± 13.1 percent versus —32.0 ±13.0 percent in the evening challenge. The difference was insignificant. The mean (± SD) time to onset of the LAR following the house-dust inhalation in the morning challenge was 11.3±3.0 h versus 6.0±2.2 h in the evening challenge (p<0.05). The lowest FEV, (maximum LAR) was at 10 pm in 2 patients and at 2 am in 4 in the morning challenge and was at 2 am in 3 and at 6 am in 3 in the evening challenge. The mean (± SD) clock hour of the lowest FEV, in the morning challenge was 00:40 ±02:06 am versus 04:00 ±02:12 am in the evening challenge (p<0.05). The FEV, at 2 am was lowest or within 10 percent of the lowest value in all challenges. The mean (± SD) time to occurrence of the lowest FEV, (maximum LAR) following the house-dust inhalation in the morning challenge was 14.7±2.1 h versus 10.0±2.2 h in the evening challenge (p<0.05).
The FEV, at 24 h after the house-dust inhalation recovered to within 10 percent of the baseline value in 2 patients in each challenge study (patients 1 and 5 and patients 5 and 6 in the morning and evening challenge studies, respectively) but did not in the other 4 patients.
In the present study the times to the onset of the LAR and the occurrence of maximum bronchial obstruction (maximum LAR) following the morning challenge were significantly later than those following the evening challenge, despite the same magnitude of obstruction, which is agreement with the results reported by Mohiuddin and Martin. Mechanisms related to an upward arm of the circadian variation of the bronchial caliber until early afternoon might delay the development of bronchial obstruction based on inflammation following the morning challenge.

Figure-1

Figure 1. Time course of FEV, after inhalation of diluent, (0.9 percent sodium chloride with 0.5 percent phenol) (m and e in the morning [at 10 am] and evening [at 6 pm] challenges, respectively) and after inhalation of house-dust solution (M and E in the morning [at 10 am] and evening [at 6 pm] challenges, respectively) in 6 children with stable asthma over 2 consecutive days. Open circles indicate FEV, as percent of predicted in the morning challenge study; closed circles indicate FEV, as percent of predicted in evening challenge study.

Table 2—Comparison of Results From Morning and Evening Challenge Studies

Data Patient
1 2 3 4 5 6
CV of FEV, (% of predicted) on control day, %
Morning 8.9 0.9 1.7 4.0 2.0 7.7
Evening 11.0 3.5 2.1 3.3 1.7 13.9
Magnitude of LAR, %
Morning -26 -39 -44 -24 -24 -56
Evening -29 -28 -34 -31 -15 -55
Onset of LAR afterinhalation, h
Morning 12 12 8 16 8 12
Evening 4 8 8 4 8 4
Clock hour of lowest FEV, as % of predicted*
Morning 22:00 02:00 02:00 02:00 22:00 02:00
Evening 02:00 06:00 06:00 02:00 06:00 02.ЧЮ
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