UBC Theses and Dissertations
The measurement and the monitoring of the central hemodynamics using non-invasive and minimally-invasive data Leung, Mande Tak Man
According to the World Health Organization (WHO), cardiovascular (CV) diseases are the number one cause of death globally, and are projected to remain the single leading cause of death by 2030. Central pulse pressure and several arterial stiffness indices, especially aortic pulse wave velocity (PWV), are among the strongest predictors of CV events, including stroke, myocardial infarction (heart attack) and angina (chest pain). Therefore, non-invasive methods for the assessment of the central pressure and central arterial stiffness are very important for the diagnosis of CV diseases at their early stage of development. In this thesis, non-invasive methods are developed to (i) measure the aortic PWV, and (ii) measure the aortic pressure waveform (APW). In the intensive care unit, cardiac output (CO) is an important measure of the adequacy of circulation among post-operative patients of cardiovascular diseases. Current methods of monitoring use the heart rate, peripheral blood pressure, and urine output as surrogates of CO, but these indices are inadequate. CO can be monitored directly using thermodilution but the procedure is highly invasive. In this thesis, a minimally-invasive method is developed to monitor the CO using the radial artery pressure waveform. The underlying algorithms of the methods developed in this thesis are interrelated. In this thesis, the arterial system is modeled as a single uniform lossless transmission line terminated by a complex load. Each measuring and monitoring task is a problem of identification, simulation or data acquisition. The measurement of the aortic PWV is formulated as an identification problem. The method developed in this thesis was shown to be able to differentiate a group of children with Marfan syndrome from the healthy children. The monitoring of CO is formulated as a problem of identification and simulation. The method developed in this thesis was applied to five post-surgical infants. It showed clinically acceptable agreement with the more established echocardiographic technique. The measurement of APW is a problem of data acquisition. A method was developed to estimate APW from the aortic distension waveform obtained using B-mode ultrasound. This method showed good agreement with carotid artery applanation tonometry when applied to nine healthy children.
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