Evaluation of bronchial hyperresponsiveness by monitoring of transcutaneous oxygen tension and arterial oxygen saturation during methacholine challenge in asthmatic children.
BACKGROUND
Bronchial hyperresponsiveness (BHR) is a key feature of asthma, but the measurement of BHR is hampered by the fact that most tests of airway caliber are difficult to conduct at a young age. Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen pressure (tcPO2) and pulse oximetry. Evaluating BHR by monitoring tcPO2 instead of respiratory resistance (Rrs) has been used over a wide age range in childhood.


OBJECTIVE
To investigate whether there is a consistent relationship between changes in arterial oxygen saturation (SaO2) and respiratory resistance (Rrs) similar to the relationship between tcPO2 and Rrs during methacholine challenge in young children and to assess the usefulness of SaO2 as a parameter for the indirect measurement of BHR.


METHODS
We performed methacholine inhalation challenge by monitoring SaO2, tcPO2 and Rrs in 37 asthmatic children 5 to 7 years of age. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. We recorded the cumulative dose of methacholine (Dmin) at the inflection point of tcPO2 (Dmin-tcPO2), SaO2 (Dmin-SaO2), and Rrs(Dmin-Rrs).


RESULTS
The mean value of Dmin-Rrs was 4.27 +/- 2.02 units, the mean value of Dmin-tcPO2 was 4.48 +/- 2.01 units, and the mean value of Dmin-SaO2 was 4.57 +/- 0.20 units. Inhalation of increasing doses of methacholine raised Rrs curvilinearly and depressed tcPO2 and SaO2. There were no significant differences between any of the parameters. There were significant relationships between Dmin-tcPO2 and Dmin-Rrs (r = 0.914, p < 0.001) and between Dmin-SaO2 and Dmin-Rrs (r = 0.905, p < 0.001) and a relationship between Dmin-tcPO2 and Dmin-SaO2 (r = 0.949, p < 0.001).


CONCLUSIONS
We concluded that measurement of SaO2 and/or tcPO2 during methacholine inhalation challenge may be used to assess bronchial hyperresponsiveness. This study showed that both SaO2 and tcPO2 monitoring are safe, useful, and tolerable for use in children who are too young to cooperate with lung function tests.
Wang
Junying
J
Department of Pediatrics and Developmental Medicine, Gunma University, Graduate School of Medicine, Gunma, Japan.
Mochizuki
Hiroyuki
H
Muramatsu
Reiko
R
Arakawa
Hirokazu
H
Tokuyama
Kenichi
K
Morikawa
Akihiro
A
D001249:Asthma / Q000097:blood*; D001785:Blood Gas Monitoring, Transcutaneous; D016535:Bronchial Hyperreactivity / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D010100:Oxygen / Q000097:blood*
D016210:Methacholine Chloride; D010100:Oxygen