Objective.

To assess at what age bronchial hyperresponsiveness (BHR) is acquired in children with asthma.

Background.

A relationship between BHR and infantile wheezing diseases has been reported. Infants with a genetic predisposition to atopy are more likely to wheeze with respiratory viral infection or bronchiolitis, and it is suspected that the continued BHR after the first attack of asthma may be induced or triggered by some viral infections. Also, recent studies have reported the existence of atopic and BHR-related genes. However, whether BHR is congenital or acquired after asthma attacks, and when BHR in children with asthma is established or acquired remain unclear.

Methods.

We performed methacholine inhalation challenge using a transcutaneous oxygen pressure (tcPO2) monitoring system in 205 children without asthma from 6 months to 6 years of age. During follow-up, 18 of these participants were diagnosed with asthma (group N-A). This group and 15 age-matched children without asthma (group N-N) were tested twice using methacholine inhalation challenge. For comparison, 39 age-matched atopic-type asthmatic children (group A-A) were also given the inhalation challenge twice. Methacholine inhalation challenge using a tcPO2 monitoring system was performed while the participants were asleep in the supine position. Sequential doses of inhaled methacholine delivered by oxygen mask were doubled until a 10% decrease in tcPO2 from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO2 (minimal dose of methacholine [Dmin]-PO2) was considered to represent BHR.

Results.

In groups N-N and A-A, there was no difference in Dmin-PO2 between the first and second challenge. However, the Dmin-PO2 in group N-A significantly decreased from the first challenge to the second challenge. There was no significant difference between the Dmin-PO2 in group N-N and the first Dmin-PO2 in group N-A; or between the Dmin-PO2in group A-A and the second Dmin-PO2 in group N-A.

Conclusions.

These data suggest that BHR in many infants with asthma is acquired after several asthma attacks.bronchial hyperresponsiveness, childhood asthma, methacholine inhalation challenge, transcutaneous oxygen pressure.

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