Abstract
The success of cardiac surgery essentially depends on tissue preservation. To optimize this latter, a myocardial protection is applied thanks to a hypothermic cardioplegia that confers a marked protective effect to the heart under ischemia. Despite these technical developments, cardiac surgery still presents risks and complications are sometimes of an unknown nature. However, no operational real-time monitoring of myocardial tissue exists. Among the metrics that could be analyzed, the temperature change measurement may be a relevant indicator. The objective of the present thesis is therefore to establish a thermal monitoring system of the heart in a way to evaluate the quality of the cardioplegia perfusion during cardiovascular surgery.Among the non-invasive thermal monitoring methods implantable in the operating room, the ultrasonic thermometry and infrared thermography caught our attention. In the first stages of the study, a direct method of ultrasonic thermometry based on the echo tracking is performed on in-vitro samples with 2.25 MHz ultrasonic sensor in a temperature range between 10 to 30°C. The ultrasonic characterization of the heart muscle and the laboratory experiments brought to the forth an environmental complexity requiring prior calibration that may be difficult to implement in operational conditions. However, the technique has a satisfactory measurement accuracy for temperature variations of less than 10°C.An adjustment model is then proposed to identify the in-depth warming trend of the heart thanks to the surface temperature measurement performed by thermal infrared camera and the medium thickness estimated by ultrasound. The model is validated by finite element simulations and experiments realized on ghosts and in-vitro heart samples.Finally, the device is experimented on in-vivo animal models while hypothermic cardioplegia were conducted. Conclusive results were obtained on the heart thermal monitoring. In particular, the surface temperatures acquired by infrared thermography and the thickness estimation of the ventricular walls by ultrasound allowed an estimation of the myocardial-warming trend.This feasibility study has demonstrated the possibility of heart thermal monitoring, noninvasively and appropriate in real time. After specific adaptation, this device could be implemented during cardiovascular interventions and provide a valuable indicator for the surgeons about the efficacy of myocardial protection.