title: Effects of oxygen inhalation on cardiac output, coronary blood flow and oxygen delivery in healthy individuals, assessed with MRI.
abstract: OBJECTIVE
  Oxygen (O2) is a cornerstone in the treatment of critically ill patients, and the guidelines prescribe 10-15 l of O2/min even to those who are initially normoxic. Studies using indirect or invasive methods suggest, however, that supplemental O2 may have negative cardiovascular effects. The aim of this study was to test the hypothesis, using noninvasive cardiac magnetic resonance imaging, that inhaled supplemental O2 decreases cardiac output (CO) and coronary blood flow in healthy individuals.
  
  
  METHODS
  Sixteen healthy individuals inhaled O2 at 1, 8 and 15 l/min through a standard reservoir bag mask. A 1.5 T magnetic resonance imaging scanner was used to measure stroke volume, CO and coronary sinus blood flow. Left ventricular (LV) perfusion was calculated as coronary sinus blood flow/LV mass.
  
  
  RESULTS
  The O2 response was dose-dependent. At 15 l of O2/min, blood partial pressure of O2 increased from an average 11.7 to 51.0 kPa with no significant changes in blood partial pressure of CO2 or arterial blood pressure. At the same dose, LV perfusion decreased by 23% (P=0.005) and CO decreased by 10% (P=0.003) owing to a decrease in heart rate (by 9%, P<0.002), with no significant changes in stroke volume or LV dimensions. Owing to the decreased CO and LV perfusion, systemic and coronary O2 delivery fell by 4 and 11% at 8 l of O2/min, despite the increased blood oxygen content.
  
  
  CONCLUSIONS
  Our data indicate that O2 administration decreases CO, LV perfusion and systemic and coronary O2 delivery in healthy individuals. Further research should address the effects of O2 therapy in normoxic patients.
authors.affiliation: aDepartments of Emergency Medicine bClinical Physiology, Skåne University Hospital, Lund, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bodetoft
authors.forename: Marcus
authors.initials: M
authors.lastname: Carlsson
authors.forename: Håkan
authors.initials: H
authors.lastname: Arheden
authors.forename: Ulf
authors.initials: U
authors.lastname: Ekelund
mesh_terms: D000328:Adult; D002302:Cardiac Output / Q000502:physiology*; D003326:Coronary Circulation / Q000502:physiology*; D005260:Female; D006352:Heart Ventricles; D006439:Hemodynamics; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000008:administration & dosage*; D010101:Oxygen Consumption; D012016:Reference Values; D013548:Sweden
chemical_list: D010100:Oxygen