Morning-to-evening variation in exercise-induced bronchospasm.
BACKGROUND
Exercise is one of the most common triggers of asthmatic symptoms. Many factors, including hyperventilation, determine the prevalence and severity of exercise-induced bronchospasm (EIB). However, the influence of time of day has not been adequately described.


OBJECTIVE
We sought to compare morning and evening EIB and minute ventilation during exercise (VE).


METHODS
Twenty-two patients with stable asthma and 12 control subjects underwent exercise challenge at 7 am and 6 pm. The time of the first challenge was randomly assigned; the second challenge was performed within 1 week of the first. The primary outcomes were EIB intensity (maximum fall in FEV(1)) and VE.


RESULTS
The asthma group exhibited lower EIB values in the morning: 14.8% +/- 3.7% at 7 am vs 21.4% +/- 4.2% at 6 pm (P =.004)-ie, 0.37 +/- 0.09 L vs 0.53 +/- 0.10 L, respectively (P =.002). VE was higher at 7 am (55.4 +/- 4.7 L/min) than at 6 pm (52.4 +/- 4.3 L/min; P =.03). Baseline FEV(1) increased from 2.33 +/- 0.13 L (morning) to 2.49 +/- 0.15 L (evening; P =.04), and a significant correlation between baseline FEV(1) and EIB was found in the evening (r = +0.5; P =.049) but not in the morning. Post-exercise FEV(1) was similar at 7 am (1.96 +/- 0.13 L) and 6 pm (1.97 +/- 0.14 L). For the control group, no changes were detected in FEV(1) fall or VE.


CONCLUSIONS
Baseline airway caliber contributes to the mechanisms of the morning-to-evening EIB enhancement.
Vianna
Elcio O
EO
Department of Medicine, University of São Paulo Medical School at Ribeirão Preto, Av. Bandeirantes, 3900 Ribeirão Preto--SP 14048 900, Brazil.
Boaventura
Luiz C
LC
Terra-Filho
João
J
Nakama
Gilberto Y
GY
Martinez
José A B
JA
Martin
Richard J
RJ
D000203:Activities of Daily Living; D000328:Adult; D001250:Asthma, Exercise-Induced / Q000503:physiopathology*; D001986:Bronchial Spasm / Q000503:physiopathology; D005080:Exercise Test; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D013997:Time Factors