Cross-sectional area of the murine aorta linearly increases with increasing core body temperature

<p><b>Purpose:</b> The cardiovascular (CV) system plays a vital role in thermoregulation. To date, the response of core vasculature to increasing core temperature has not been adequately studied <i>in vivo</i>. Our objective was to non-invasively quantify the arterial response in murine models due to increases in body temperature, with a focus on core vessels of the torso and investigate whether responses were dependent on sex or age.</p> <p><b>Methods:</b> Male and female, adult and aged mice were anaesthetised and underwent magnetic resonance imaging (MRI). Data were acquired from the circle of Willis (CoW), heart, infrarenal aorta and peripheral arteries at core temperatures of 35, 36, 37 and 38 °C (±0.2 °C).</p> <p><b>Results:</b> Vessels in the CoW did not change. Ejection fraction decreased and cardiac output (CO) increased with increasing temperature in adult female mice. Cross-sectional area of the aorta increased significantly and linearly with temperature for all groups, but at a diminished rate for aged animals (<i>p</i> < 0.01; male and female: adult, 0.019 and 0.024 mm<sup>2</sup>/°C; aged, 0.017 and 0.011 mm<sup>2</sup>/°C). Aged male mice had a diminished response in the periphery (% increase in femoral artery area from 35 to 38 °C, male and female: adult, 67 and 65%; aged, 0.1 and 57%).</p> <p><b>Conclusion:</b> Previously unidentified increases in aortic area due to increasing core temperature are biologically important because they may affect conductive and convective heat transfer. Leveraging non-invasive methodology to quantify sex and age dependent vascular responses due to increasing core temperature could be combined with bioheat modelling in order to improve understanding of thermoregulation.</p>