Search

Atrial fibrillation (AF), the most common cardiac arrhythmia, is characterized by disorganized electrical activities that cause atrial quivering and uncoordinated contraction. AF significantly affects the quality of life for patients and increases the risk of stroke. Ultrasound ablation surgery has been proposed a decade ago as a treatment for AF. By focusing ultrasound energy at a narrow spot, rapid temperature rises along with tissue necrosis are generated. In this thesis, we investigated high-intensity focused ultrasound (HIFU), an ablation technology being used to eliminate arrhythmogenic foci for treatment of AF. During HIFU ablation, little is known regarding the detailed characteristics of cellular electrophysiological (EP) changes. The first part of the thesis aims to characterize EP changes during HIFU corresponding with temperature increases. Langendorff-perfused intact rabbit heart model stained with di-4-ANEPPS, a fluorescent dye sensitive to the membrane voltage changes, was used. Simultaneous optical mapping and infrared imaging were employed to measure epicardial EP and temperature during HIFU application. The results revealed the temperature-dependent spatiotemporal characteristics of HIFU-induced EP changes including changes of action potential (AP) amplitude, duration, and electrical activation. Temperature dosage criterion for generating irreversible tissue physical and AP changes were obtained. Intra-procedural imaging is important for guiding cardiac ablation for AF. However, it is difficult to obtain intra-procedural correlation of thermal lesion with AP changes in tissue transmural plane. The second part is to develop parametric ultrasound imaging techniques for transmural lesion and AP detection during ablation. Perfused canine ventricular wedge was used. Simultaneous optical mapping and high frequency ultrasound imaging of the same tissue trasnsmural plane were performed during HIFU. Tissue transmural EP changes were characterized and the AP changes were spatiotemporally correlated between optical and ultrasound images. The results show that parametric ultrasound imaging using cumulative extrema of ultrasound parameters (log-normal and Rayleigh) can detect HIFU lesions and surrounding AP amplitude changes. Overall, the information obtained from this thesis enhances our understanding of the EP mechanisms of HIFU ablation and can help promote the development of effective HIFU ablation strategies. Ultrasound parametric imaging provides a promising technique to identify lesion transmurality which is important in clinical ablations.

The study assessed the performance of a newly-built sustainable hospital by comparing the thermal comfort of its patients and staff, and the ambient thermal conditions with those of two other hospitals with less sophisticated designs. Additionally, a facility management perspective was used to understand the role hospital administrators had in contributing to sustainable design outcomes and document the unanticipated challenges and unintended consequences of operating the newly-built sustainable hospital. Data were collected through thermal environment equipment, a thermal comfort survey, and interviews with care providers, patients, and facility managers. The hypotheses were that the hospital with the modern and more sophisticated sustainable ventilation design features would have a higher level of thermal comfort and lower heat index in the naturally ventilated wards than hospitals without those features and that thermal comfort would be higher in air-conditioned wards than naturally ventilated wards. The results indicate that sophisticated sustainable hospital designs can improve the ambient thermal environment and occupant thermal comfort but not all those features were necessary. The study also suggests the need for adopting an integrated sustainable design strategy to prevent or mitigate some of the facility operation challenges encountered. Additionally, the study proposes for a shift in thermal comfort standards and green building rating tools to meet the unique thermal comfort needs of hospital users. ii