UBC Faculty Research and Publications

Changes in left ventricular function and coronary blood flow velocity during isocapnic hypoxia: A cardiac… Foster, Glen E; Deng, Zixin; Boulet, Lindsey M; Mehta, Puja K; Wei, Janet; Fan, Zhaoyang; Dharmakumar, Rohan; Noel, C; Merz, Bairey; Li, Debiao; Nelson, Michael D Jan 27, 2016

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POSTER PRESENTATION Open AccessChanges in left ventricular function and coronaryblood flow velocity during isocapnic hypoxia:A cardiac magnetic resonance imaging studyGlen E Foster1*, Zixin Deng2, Lindsey M Boulet1, Puja K Mehta3, Janet Wei3, Zhaoyang Fan2, Rohan Dharmakumar2,C Noel1, Bairey Merz3, Debiao Li2, Michael D Nelson2,3From 19th Annual SCMR Scientific SessionsLos Angeles, CA, USA. 27-30 January 2016BackgroundCardiac stress testing is the standard of care for diag-nosing ischemic heart disease. Traditional stress testinginvolves physical or pharmacological stress to inducehyperemia and/or increase myocardial oxygen demand.Physical stress is not possible in 100% of cases however,and pharmacological stress carries rare but serious risk.We asked whether acute isocapnic hypoxia could be uti-lized as an alternative cardiovascular stress test.MethodsEight healthy male volunteers (31 + 4 yrs) were exposedto isocapnic hypoxia using a dynamic end-tidal forcingsystem. Left ventricular function and coronary arteryblood flow velocity were measured by MRI (3T, Sie-mens). The end-tidal partial pressure of oxygen wasmaintained at 43 ± 0.3 mmHg, while the end-tidal par-tial pressure of carbon dioxide was controlled at baselinelevels. Left ventricular ejection fraction was assessedusing a free-breathing cine sequence (TE/TR = 1.08/46.74 ms; in-plane spatial resolution = 2.5 × 2.5 mm2;slice thickness = 8 mm). Coronary blood flow velocitywas measured in the left anterior descending (LAD), leftcircumflex (LCX), and left main (LM) coronary arteriesusing a free-breathing, navigator-gated, Cartesian 2Dphase-contrast (PC)-MRI sequence (temporal resolution= 26.4 ms; in-plane spatial resolution = 0.88 × 0.88mm2; slice thickness = 7 mm; VENC = 40-80 cm/s inz-direction). Coronary cross-sectional area was assessedin 3 of 8 subjects (all in the left anterior descending cor-onary artery, LAD), using a 2D balanced steady-statefree precession sequence (ECG-triggered and navigatorgated; acquisition only in the quiescent phase; in-plane spa-tial resolution = 0.85 × 0.85 mm2; slice thickness = 7 mm).ResultsDuring hypoxia arterial oxyhemoglobin saturation wasreduced to 79 ± 1% and heart rate and systolic pressureincreased by 47% and 4%, respectively (all P < 0.05).Hypoxia increased left ventricular ejection fraction from 66+ 1 to 74 + 1% (p< 0.01) and rate pressure product from7057 + 639 to 10340 + 801 mmHg/beat/min (P < 0.01).Mean coronary flow velocity increased significantly inseven of the eight subjects (5 LAD, increasing from 17.9 +2.1 to 25.6 + 1.2 cm/s; 1 LCX, increasing from 20.1 to 38.8cm/s; and 1 LM, increasing from 18.6 to 40.0 cm/s). Poorimage quality prevented analysis of coronary flow velocityin 1 subject. The change in coronary flow velocity was pro-portional to the change in myocardial oxygen demand (P =0.26). Coronary cross-sectional area was measured in threesubjects and found to remain constant (22.3 + 4.5 vs. 22.4+ 5.3 mm2, p = ns, baseline vs. hypoxia, respectively).ConclusionsThis is the first MRI study to simultaneously evaluatecardiac function and coronary blood flow in response toacute isocapnic hypoxia using dynamic end-tidal forcing.The results support the use of hypoxia as a unique cardi-ovascular stress test. Further investigation is required todetermine the feasibility and efficacy of its use in targetedpatient populations.Authors’ details1Center for Heart, Lung, and Vascular Health, University of British Columbia,Kelowna, BC, Canada. 2Biomedical Imaging Research Institute, Cedars-Sinai1Center for Heart, Lung, and Vascular Health, University of British Columbia,Kelowna, BC, CanadaFull list of author information is available at the end of the articleFoster et al. Journal of Cardiovascular MagneticResonance 2016, 18(Suppl 1):P126http://www.jcmr-online.com/content/18/S1/P126© 2016 Foster et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided theoriginal work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Medical Center, Los Angeles, CA, USA. 3Heart Institute, Cedars-Sinai MedicalCenter, Los Angeles, CA, USA.Published: 27 January 2016doi:10.1186/1532-429X-18-S1-P126Cite this article as: Foster et al.: Changes in left ventricular function andcoronary blood flow velocity during isocapnic hypoxia: A cardiacmagnetic resonance imaging study. Journal of Cardiovascular MagneticResonance 2016 18(Suppl 1):P126.Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submitFoster et al. Journal of Cardiovascular MagneticResonance 2016, 18(Suppl 1):P126http://www.jcmr-online.com/content/18/S1/P126Page 2 of 2

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