Background: The effects of breathing pattern and inspired air conditions on the volume and content of exhaled breath condensate (EBC) were investigated. Methods: Total exhaled water (TEW), EBC volume, pH, nitrite and protein concentrations were measured in three groups of 10 healthy subjects breathing into a condenser at different target minute ventilations (Vm), tidal volumes (Vt), and inspired air conditions. Results: The volumes of both TEW and EBC increased significantly with Vm. For Vm 7.5, 15 and 22.5 l/ min, mean (SD) EBC was 627 (258) ml, 1019 (313) ml, and 1358 (364) ml, respectively (p,0.001) and TEW was 1879 (378) ml, 2986 (496) ml, and 4679 (700) ml, respectively (p,0.001). TEW was significantly higher than EBC, reflecting a condenser efficiency of 40% at a target Vm of 7.5 l/min which reduced to 29% at Vm 22.5 l/min. Lower Vt gave less TEW than higher Vt (26.6 v 30.7 ml/l, mean difference 4.1 (95% CI 2.6 to 5.6), p,0.001) and a smaller EBC volume (4.3 v 7.6 ml/l, mean difference 3.4 (95% CI 2.3 to 4.5), p,0.001). Cooler and drier inspired air yielded less water vapour and less breath condensate than standard conditions (p,0.05). Changes in the breathing pattern had no effect on EBC protein and nitrite concentrations and pH. Conclusion: These results show that condensate volume can be increased by using high Vt and increased Vm without compromising the dilution of the sample.

Circassia Ltd (Oxford, UK) provided an unrestricted educational grant to support the meeting in Perth on 9 th October 2018 which formed the basis of this manuscript. Circassia was not present at the meeting and had no input into the preparation of the manuscript.

This study did not show additional benefit from 1.2g IV MgSO(4) when given as an adjunct to standard therapy for acute asthma.

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