Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB022

Poster Communications

Clinical ECG-gated MRI investigation of intracardiac shunting physiology in the red footed tortoise (Chelonoidis carbonarius).

C. J. Williams1, E. M. Greunz2, S. Ringgaard3, K. Hansen4, M. F. Bertelsen2, T. Wang1,5

1. Bioscience, Aarhus University, Aarhus, Denmark. 2. Centre for Zoo and Wild Animal Health, Copenhagen Zoo, Copenhagen, Denmark. 3. Department of Clinical Medicine - the MR research centre, Aarhus University, Aarhus, Denmark. 4. Forensic Medicine, Aarhus University, Aarhus, Denmark. 5. Aarhus Institute for Advanced Studies, Aarhus University, Aarhus, Denmark.

Modern imaging techniques enable non-invasive blood flow measurement, providing opportunities for sophisticated investigation of intracardiac shunting in reptiles. In chelonians, flow is under autonomic control; increased parasympathetic tone causes pulmonary vasculature constriction and increased resistance, consequently increasing systemic flow (Qsys) via intracardiac shunting in the undivided chelonian ventricle1. Flow determination previously required surgical implantation of probes2. Here, a clinical 1.5 Tesla MRI system with ECG-gating allowed non-invasive visualisation of the entire cardiac cycle and repeatable cross-sectional flow measurements in the major systemic and pulmonary (Qpul) arteries of five anaesthetised red-footed tortoises (isoflurane 5% in oxygen). The waveforms of flow resemble measurements in chelonians via Transonic probes, showing early peaks in Qpul related to the pulmonary circulation's greater distensibility and lower diastolic pressures. Flow measurements (mean±SD) are used to address changing shunt pattern via application of 1 mg/kg atropine in a crossover design. Shunt direction reversed from 0.24 ± 0.07 ((Qpul/Qsys) saline) to 1.25 ± 0.38 (atropine), as total Qpul quintupled to 2.98 ± 0.35 ml/sec (atropine vs saline Student's T test p<0.01), while total Qsys was unchanged (2.58 ± 0.58 ml/sec saline, 2.51 ± 0.54 ml/sec atropine). Left and right Qpul did not significantly differ from one another under saline or atropine conditions (Student t test: p=0.25, 0.45 respectively) and while variable right aortic branching hampered determination, Qsys was 3.32 ± 0.27 times left aortic flow under saline, 2.97 ± 0.65 after atropine. This MRI application holds potential for further understanding the complex cardiovascular systems of ectothermic vertebrates.

Where applicable, experiments conform with Society ethical requirements