Breathing manoeuvre-dependent changes in myocardial oxygenation in healthy humans.
OBJECTIVE
CO₂ is an intrinsic vasodilator for cerebral and myocardial blood vessels. Myocardial vasodilation without a parallel increase of the oxygen demand leads to changes in myocardial oxygenation. Because apnoea and hyperventilation modify blood CO₂, we hypothesized that voluntary breathing manoeuvres induce changes in myocardial oxygenation that can be measured by oxygenation-sensitive cardiovascular magnetic resonance (CMR).


RESULTS
Fourteen healthy volunteers were studied. Eight performed free long breath-hold as well as a 1- and 2-min hyperventilation, whereas six aquatic athletes were studied during a 60-s breath-hold and a free long breath-hold. Signal intensity (SI) changes in T₂*-weighted, steady-state free precession, gradient echo images at 1.5 T were monitored during breathing manoeuvres and compared with changes in capillary blood gases. Breath-holds lasted for 35, 58 and 117 s, and hyperventilation for 60 and 120 s. As expected, capillary pCO₂ decreased significantly during hyperventilation. Capillary pO₂ decreased significantly during the 117-s breath-hold. The breath-holds led to a SI decrease (deoxygenation) in the left ventricular blood pool, while the SI of the myocardium increased by 8.2% (P = 0.04), consistent with an increase in myocardial oxygenation. In contrast, hyperventilation for 120 s, however, resulted in a significant 7.5% decrease in myocardial SI/oxygenation (P = 0.02). Change in capillary pCO₂ was the only independently correlated variable predicting myocardial oxygenation changes during breathing manoeuvres (r = 0.58, P < 0.01).


CONCLUSIONS
In healthy individuals, breathing manoeuvres lead to changes in myocardial oxygenation, which appear to be mediated by CO₂. These changes can be monitored in vivo by oxygenation-sensitive CMR and thus, may have value as a diagnostic tool.
Stephenson Cardiovascular MR Centre, Libin Cardiovascular Institute of Alberta, Departments of Cardiac Sciences and Radiology, University of Calgary, Calgary, Alberta, Canada.
Dominik P
DP
Guensch
Kady
K
Fischer
Jacqueline A
JA
Flewitt
Janelle
J
Yu
Ryan
R
Lukic
Julian A
JA
Friedrich
Matthias G
MG
Friedrich
D000328:Adult; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000378:metabolism*; D003326:Coronary Circulation; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006985:Hyperventilation; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods; D008297:Male; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D010101:Oxygen Consumption; D012119:Respiration; D013177:Sports; D013550:Swimming
D002245:Carbon Dioxide
BOLD-sensitive MRI; T2*-weighted imaging; apnoea; carbon dioxide; hyperventilation; vasodilation