Two variants of occupational asthma separable by exhaled breath nitric oxide level.
Exhaled nitric oxide (FE(NO)) has been used as a marker of asthmatic inflammation in non-occupational asthma, but some asthmatics have a normal FE(NO). In this study we investigated whether, normal FE(NO) variants have less reactivity in methacholine challenge and smaller peak expiratory flow (PEF) responses than high FE(NO) variants in a group of occupational asthmatics.


METHODS
We measured FE(NO) and PD(20) in methacholine challenge in 60 workers currently exposed to occupational agents, who were referred consecutively to a specialist occupational lung disease clinic and whose serial PEF records confirmed occupational asthma. Bronchial responsiveness (PD(20) in methacholine challenge) and the degree of PEF change to occupational exposures, (measured by calculating diurnal variation and the area between curves score of the serial PEF record in Oasys), were compared between those with normal and raised FE(NO). Potential confounding factors such as smoking, atopy and inhaled corticosteroid use were adjusted for.


RESULTS
There was a significant correlation between FE(NO) and bronchial hyper-responsiveness in methacholine challenge (p = 0.011), after controlling for confounders. Reactivity to methacholine was significantly lower in the normal FE(NO) group compared to the raised FE(NO) group (p = 0.035). The two FE(NO) variants did not differ significantly according to the causal agent, the magnitude of the response in PEF to the asthmagen at work, or diurnal variation.


CONCLUSIONS
Occupational asthma patients present as two different variants based on FE(NO). The group with normal FE(NO) have less reactivity in methacholine challenge, while the PEF changes in relation to work are similar.
Occupational Lung Disease Unit, Birmingham Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS, UK. vicky.c.moore@heartofengland.nhs.uk
Vicky C
VC
Moore
Wasif
W
Anees
Maritta S
MS
Jaakkola
Cedd B S G
CB
Burge
Alastair S
AS
Robertson
P Sherwood
PS
Burge
D000328:Adult; D001249:Asthma / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D045853:Exhalation; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology*; D006801:Humans; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D009784:Occupational Diseases / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D016273:Occupational Exposure / Q000009:adverse effects*; D011446:Prospective Studies
D009569:Nitric Oxide