title: A simple breathing circuit allowing precise control of inspiratory gases for experimental respiratory manipulations.
abstract: BACKGROUND
  Respiratory manipulations modulating blood flow and oxygenation levels have become an important component of modern functional MRI applications. Manipulations often consist of temporarily switching inspired fractions of CO2 and O2; and have typically been performed using simple oxygen masks intended for applications in respiratory therapy. However, precise control of inspired gas composition is difficult using this type of mask due to entrainment of room air and resultant dilution of inspired gases. We aimed at developing a gas delivery apparatus allowing improved control over the fractional concentration of inspired gases, to be used in brain fMRI studies.
  
  
  RESULTS
  The breathing circuit we have conceived allowed well controlled step changes in FiO2 and FiCO2, at moderate flow rates achievable on standard clinical flow regulators. In a two run test inside the scanner we demonstrate that tightly controlled simple gas switching manipulations can afford good intra-subject reproducibility of induced hyperoxia/hypercapnia responses. Although our approach requires a non-vented mask fitting closely to the subject's face, the circuit ensures a continuous supply of breathable air even if the supply of medical gases is interrupted, and is easily removable in case of an emergency. The apparatus we propose is also compact and MRI compatible, allowing subject placement in confined spaces such as an MRI scanner for brain examinations.
  
  
  CONCLUSIONS
  We have reported a new approach for the controlled administration of medical gases, and describe an implementation of the breathing circuit that is MRI compatible and uses commercially available parts. The resultant apparatus allows simple, safe and precise manipulations of FiO2 and FiCO2.
authors.affiliation: Institut de génie biomédical, Département de physiologie, Université de Montréal, C,P, 6128, Succursale Centre-ville, Montréal, Québec H3C 3J7, Canada. felipe.tancredi@umontreal.ca.
authors.forename: Felipe B
authors.initials: FB
authors.lastname: Tancredi
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lajoie
authors.forename: Richard D
authors.initials: RD
authors.lastname: Hoge
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D005740:Gases / Q000032:analysis*; D018496:Hyperoxia / Q000503:physiopathology; D010100:Oxygen / Q000378:metabolism; D015203:Reproducibility of Results; D012119:Respiration; D012121:Respiration, Artificial
chemical_list: D005740:Gases; D002245:Carbon Dioxide; D010100:Oxygen
references.citation: Stroke. 2008 Jul;39(7):2021-8
references.pmid: 18451352
references.citation: J Appl Physiol Respir Environ Exerc Physiol. 1982 May;52(5):1353-7
references.pmid: 6807948
references.citation: Resuscitation. 2003 Apr;57(1):69-72
references.pmid: 12668302
references.citation: J Physiol. 2007 Jun 15;581(Pt 3):1207-19
references.pmid: 17446225
references.citation: J Cereb Blood Flow Metab. 2007 Aug;27(8):1521-32
references.pmid: 17406659
references.citation: J Appl Physiol (1985). 2000 May;88(5):1597-600
references.pmid: 10797118
references.citation: PLoS One. 2012;7(11):e47443
references.pmid: 23139743
references.citation: Neuroimage. 2010 May 15;51(1):274-9
references.pmid: 20056163
references.citation: Neurobiol Aging. 2013 May;34(5):1469-85
references.pmid: 23218565
references.citation: J Magn Reson Imaging. 2010 Nov;32(5):1068-75
references.pmid: 21031510
references.citation: Magn Reson Med. 2011 May;65(5):1278-86
references.pmid: 21500256
references.citation: J Cereb Blood Flow Metab. 2013 Jul;33(7):1066-74
references.pmid: 23571282
references.citation: NMR Biomed. 2009 Aug;22(7):779-86
references.pmid: 19388006
references.citation: Magn Reson Med. 2009 Feb;61(2):391-8
references.pmid: 19165902
references.citation: Neuroimage. 2012 Mar;60(1):582-91
references.pmid: 22209811
references.citation: Radiology. 2013 Feb;266(2):592-8
references.pmid: 23204541
references.citation: Magn Reson Med. 2010 Sep;64(3):749-56
references.pmid: 20648687
references.citation: Neuroimage. 2012 Apr 2;60(2):1212-25
references.pmid: 22227047
references.citation: Hum Brain Mapp. 2009 Apr;30(4):1120-32
references.pmid: 18465743