The study hypothesises that the variability in relief of air hunger with inhaled furosemide that is reported in previous studies can be explained by the breathing pattern adopted during the inhalation and the droplet size in the aerosol, both of which would influence the site of deposition of the aerosol in the lungs

Recent studies suggest that inhaling furosemide as a mist reduces air hunger in healthy volunteers in whom air hunger is induced experimentally in the lab. However, how much reduction varies among individuals. It is not known if the way the mist is breathed (slow/deep or fast/shallow) or the size of the droplets in the mist (large or small) can explain the variation in relief. Both of these factors can influence the site of deposition of the aerosol in the lungs

In this study the relief of air hunger (induced by hypercapnia and constrained ventilation) will be compared when furosemide is inhaled quickly or slowly, and when the mist has large or small droplets. 20 healthy volunteers will be recruited. After a practice session, the 'air hunger' test will be performed before and after 4ml of a 10mg/ml solution of furosemide (40mg). This will be repeated on 4 separate test days using a different method of inhaling the furosemide on each day.

Inclusion Criteria:

- Healthy volunteers aged 18 and over

Exclusion Criteria:

• On any medication, including herbal medication (other than mild analgesics, vitamins and mineral supplements or, for females, oral contraceptives), whether prescribed or over-the-counter, in the two weeks prior to test sessions involving administration of furosemide or saline.
• Female participants who are pregnant, lactating or planning pregnancy over the course of trial
• A medical history of heart, kidney or liver disease/electrolyte disturbances/ immunosuppression/frequent fainting episodes/COPD/nasal polyps/Addison's/acute porphyria/significant prostatic symptoms/acute gout attack/life expectancy <6months or history of allergic reaction to furosemide and/or any of the other ingredients of furosemide or amiloride, sulfonamides or sulphonamide derivatives, such as sulfadiazine or co-trimoxazole
• Any other significant disease or disorder which, in the opinion of the Investigator, may either put the participants at risk because of participation in the trial, or may influence the result of the trial, or the participant's ability to participate in the trial.
• Have participated in another research trial involving an investigational product in the past 4 weeks.

Participants will not know which droplet size they will be receiving on any one test day