title: Impact of intermittent apnea on myocardial tissue oxygenation--a study using oxygenation-sensitive cardiovascular magnetic resonance.
abstract: BACKGROUND
  Carbon dioxide (CO(2)) is a recognized vasodilator of myocardial blood vessels that leads to changes in myocardial oxygenation through the recruitment of the coronary flow reserve. Yet, it is unknown whether changes of carbon dioxide induced by breathing maneuvers can be used to modify coronary blood flow and thus myocardial oxygenation. Oxygenation-sensitive cardiovascular magnetic resonance (CMR) using the blood oxygen level-dependent (BOLD) effect allows for non-invasive monitoring of changes of myocardial tissue oxygenation. We hypothesized that mild hypercapnia induced by long breath-holds leads to changes in myocardial oxygenation that can be detected by oxygenation-sensitive CMR.
  
  
  RESULTS
  In nine anaesthetized and ventilated pigs, 60s breath-holds were induced. Left ventricular myocardial and blood pool oxygenation changes, as monitored by oxygenation-sensitive CMR using a T2*-weighted steady-state-free-precession (SSFP) sequence at 1.5T, were compared to changes of blood gas levels obtained immediately prior to and after the breath-hold. Long breath-holds resulted in an increase of paCO(2), accompanied by a decrease of paO(2) and pH. There was a significant decrease of blood pressure, while heart rate did not change. A decrease in the left ventricular blood pool oxygenation was observed, which was similar to drop in SaO(2). Oxygenation in the myocardial tissue however, was maintained throughout the period. Changes in myocardial oxygenation were strongly correlated with the change in paCO(2) during the breath-hold (r = 0.90, p = 0.010).
  
  
  CONCLUSIONS
  Despite a drop in blood oxygen levels, myocardial oxygenation is maintained throughout long breath-holds and is linearly correlated with the parallel increase of arterial CO(2), a known coronary vasodilator. Breathing maneuvers in combination with oxygenation-sensitive CMR may be useful as a diagnostic test for coronary artery function.
authors.affiliation: Stephenson Cardiovascular MR Centre at the Libin Cardiovascular Institute of Alberta, Department of Cardiac Sciences and Radiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Dominik P
authors.initials: DP
authors.lastname: Guensch
authors.forename: Kady
authors.initials: K
authors.lastname: Fischer
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Flewitt
authors.forename: Matthias G
authors.initials: MG
authors.lastname: Friedrich
mesh_terms: D000818:Animals; D001049:Apnea / Q000473:pathology*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000378:metabolism; D003326:Coronary Circulation; D003331:Coronary Vessels / Q000473:pathology* / Q000502:physiology; D006935:Hypercapnia / Q000473:pathology; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D055414:Myocardial Perfusion Imaging; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D010101:Oxygen Consumption; D013552:Swine
chemical_list: D002245:Carbon Dioxide