The uptake and excretion of N2O, enflurane, halothane, and ... Subjects breathed a constant,inspired mixture containing trace concentrations of all 4 gases.
www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve& db=PubMed&dopt=Abstract&list_uids=565161

Pharmacokinetic models are used to evaluate the inhalation uptake, distribution, metabolism, and excretion of vapors and gases by humans.
www.radiation-scott.org/deposition/Gases.htm