Oral Presentation 2014 International Biophysics Congress

Measuring the mechano-energetics of cardiac tissue (#218)

Andrew Taberner 1
  1. Auckland Bioengineerig Institute and Department of Engineering Science, The University of Auckland, Auckland, New Zealand

With each beat of the heart, its cells release calcium, which triggers force development and shortening, funded by expenditure of energy with its attendant heat liberation and oxygen consumption. We are developing new instruments to monitor all of these processes simultaneously, while subjecting isolated samples of heart tissue to contraction patterns that mimic the pressure-volume-time loops experienced by the heart with each beat. This demanding undertaking has required us to develop our own actuators, force transducers, heat sensors, and optical measurement systems, and to synchronise these in our new measurement device: The Cardiac Myometer. 

Our system can resolve the heat released by cardiac trabeculae at 37 °C, to a few nanoWatts1 . Muscle force and length are controlled and measured by a laser interferometer2 , while the muscle is scanned in the view of an optical microscope equipped with a Fura-2 calcium imaging system. Concurrently, trabecula geometry is monitored in 3D by an optical coherence tomograph3 , and sarcomere length distribution is imaged in real-time by transmission-microscopy4  and laser diffraction systems. O¬2 consumption will be measured using fluorescence-quenching techniques. 

Equipped with these capabilities, we have probed the mechano-energetics of failing hearts from rats with streptozotocin-induced diabetes. We found that the peak twitch stress and peak mechanical efficiency of diabetic trabeculae from these hearts was normal, despite prolonged twitch duration. We conclude that the compromised mechanical performance of the diabetic heart arises from a reduced period of diastolic filling which, as a consequence of the Frank-Starling mechanism, impairs the following beat - impairment that does not reflect either diminished mechanical performance or diminished efficiency of its tissues5 .

  1. Johnston CM, Han J-C, Ruddy BP, Nielsen PM, Taberner AJ. Examination of the Heat-Stress Relationship of Rat Cardiac Trabeculae using an Improved Muscle Calorimeter. 58th Annual meeting of the Biophysical Society 2014. Vol. 106, Page 773a.
  2. Taberner AJ, Han JC, Loiselle DS, Nielsen PM. An innovative work-loop calorimeter for in vitro measurement of the mechanics and energetics of working cardiac trabeculae. J Appl Physiol 2011, 111:1798-1803.
  3. Cheuk ML, Lippok N, Dixon AW, Ruddy BP, Vanholsbeeck F, Nielsen PMF, Taberner AJ. Optical Coherence Tomography Imaging of Cardiac Trabeculae. In: Proceedings of 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. Chicago, USA; 2014.
  4. Anderson AJ, Nielsen PMF, Taberner AJ. An investigation into the viability of image processing for the measurement of sarcomere length in isolated cardiac trabeculae. In: Proceedings of 34th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, San Diego, USA; 2012.
  5. Han JC, Tran K, Nielsen PM, Taberner AJ, Loiselle DS. Streptozotocin-induced diabetes prolongs twitch duration without affecting the energetics of isolated ventricular trabeculae. Cardiovasc Diabetol 2014, 13:79.