Measuring exhaled hydrogen sulphide (eH2S) levels in asthma

Background: Hydrogen sulfide (H₂S) has an important role in cell signalling and inflammation and levels in sputum are increased in asthma, as a marker of neutrophilic inflammation and chronic airflow obstruction (JACI 2013; 131: 232). Aim: To set-up an on-line measurement of eH₂S and investigate the usefulness of measuring eH₂S in asthmatics. Method: 11 healthy volunteers and 21 stable asthmatics were recruited. 18 patients with severe asthma attended during exacerbations. Patients exhaled into a Flex-foil plus breath gas collection bag. The collected breath was sampled using a H₂S UV fluorescent machine (Model T101 ,Cal-Bay Control Inc). Results: Preliminary studies showed that poor dental hygiene affected eH₂S levels and this was therefore accounted for. In 21 asthma subjects, mean eH2S was 3.6±0.6 ppb (range: 1.3 - 12.8 ppb) and in 11 normal subjects, 3.2±0.5 ppb. 18 patients with severe asthma (taking >1000mcg fluticasone propionate or equivalent daily) of whom 12 were on maintenance oral steroids, attended during and after an exacerbation. Exacerbations led to increases in ACQ (2.08 vs 3.62, p=0.0008), decreased FEV₁ (2.04 vs 1.77L, p = 0.007) and elevation of blood eosinophils (0.26 to 0.34 (10^9/L), p = 0.341), blood neutrophils (6.79 to 8.22 (10^9/L), p = 0.037), CRP (4.6 to 7.6 (mg/L) p = 0.275) and exhaled Nitric Oxide (eNO) (37.9 to 58.0 ppb, p= 0.0004). ). eH₂S decreased (from 6.0 ± 1.1 ppb to 3.0 ± 0.3 ppb, p=0.05) at exacerbation and then rose at recovery (to 4.6 ± 0.8 ppb, p=0.08). eH2S did not correlate with eNO or any other biomarkers. Conclusions: eH2S levels may be useful in monitoring control of asthma. H2S may play a role in asthmatic inflammation. (This study was supported by NIHR BRU).