Joon-Hock Yeo | PubMed Health

PubMed2006

Ventriculo-aortic junction in human root. A geometric approach.

With advances in tissue engineering and improvement of surgical techniques, stentless biological valves and valve-sparing procedures have become alternatives to traditional aortic valve replacement with stented bioprostheses or mechanical valves. New surgical techniques preserve the advantages of native valves but require better understanding of the anatomical structure of the aortic root. Silicone rubber was injected in fresh aortic roots of nine human cadavers under the physiological closing pressure of 80 mmHg. The casts reproduced every detail of the aortic root anatomy and were used to digitize 27 leaflet attachment lines (LALs) of the aortic valves. LALs were normalized and described with a mathematical model. LALs were found to follow a pattern with the right coronary being the largest followed by the non-coronary and then the left coronary. During diastole, the aortic valve LAL can be described by an intersection between a created tube and an extruded parabolic surface. This geometrical definition of the LAL during end diastole gives a better understanding of the aortic root anatomy and could be useful for heart valve design and improvement of aortic valve reconstruction technique.

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PubMed2004

Progress on the development of the MediWatch ambulatory blood pressure monitor and related devices.

The MediWatch is a wrist-mounted noninvasive blood pressure monitor designed to capture the radial pulse waveform using arterial tonometry and yield blood pressure measurements when the waveform is calibrated. An early prototype of this monitor uses a pulse-sensing system with a cylindrical plunger to applanate the radial artery. This prototype was evaluated against simulated blood pressure generated by a pneumatic pressure-pulse generator. The simulation-based results show that the prototype gave accurate pressure measurements when the MediWatch waveforms were calibrated against the simulator's pressure, indicating that the pulse-sensing system was able to measure force accurately. The prototype was clinically evaluated against intra-arterial pressure on post-open heart surgery patients. The results show that, under stationary conditions, for short periods of time and when the MediWatch waveforms were calibrated against the intra-arterial pressure, the prototype gave measurements that satisfy some of the statistical criteria of the 1993 Association for the Advancement of Medical Instrumentation standard, the 1993 British Hypertension Society protocol and the 2002 European Society of Hypertension protocol. These clinical results indicate that, under the stated test conditions, the prototype was able to accurately track changes in the patients' systolic and diastolic pressures. The MediWatch is being developed into an ambulatory device that provides a macroscopic view of the patient's blood pressure through measurement at preprogrammed intervals over 24 h, as well as a microscopic view of the patient's pressure through the pulse waveform captured during each measurement cycle. The design features of the MediWatch are being adapted for other applications that require the arterial pulse waveform, calibrated beat-to-beat blood pressure or both. An improved MediWatch prototype has been developed that provides memory storage for measurement data and functions as an integral part of a Web-based system that allows measurement data to be accessed over the Internet. A pulse-wave analyser has been developed that allows the radial pulse waveform to be captured, calibrated and viewed in real time on a personal computer. A continuous noninvasive blood pressure monitoring system based on arterial tonometry is being developed for use as an alternative to the arterial line in invasive blood pressure monitoring.

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