A New Approach for Non-Invasive Continuous Arterial Blood Pressure Measurement in Human

The need for continuous noninvasive arterial blood pressure (ABP) monitoring from an artery closer to the heart (i.e. the ascending aorta) has led to the research and development work presented in this thesis. Clinical applications of continuous ABP waveform include assessments of cardiac function, cerebral autoregulation, autonomic function, arterial elasticity, physiological measurements in aerospace research, and also monitoring in anaesthesia and critical care. The superficial temporal artery (STA) was chosen as the measurement site and the measurement technique was the arterial volume clamping with photoplethysmography (PPG). The optoelectronic circuitry to measure PPG is contained in a specially designed probe placed over the STA and kept in place with a lightweight aluminium head frame. The complete prototype device (STAbp) also includes original designs for the pneumatic, electronic, signal processing, control and display sub-systems. A self-calibration feature that regularly updates the PPG reference level (Setpt) was also included to ensure accurate continuous ABP recording. The performance of the STAbp was compared against the Finapres®. Five parameters were evaluated: resting ABP (agreement, signal bandwidth, frequency response and magnitude squared coherence, and assessment of drift) and ABP dynamic change during isometric handgrip exercise. The agreement of resting ABP gave bias (SD) of -23.1 (15.05), -10.8 (13.83) and -12.4 (12.93) mmHg for systolic, mean (MAP) and diastolic pressures respectively. Further investigations were carried out to understand factors that can affect the accuracy of ABP measurements, notably the sensitivity of ABP to perturbation of the Setpt. Also, differences between the external compressing pressure at the PPG peak pulsation amplitude and the MAP were found to be normally distributed with mean (SD) of -4.7 (5.63) mmHg. In conclusion, it is demonstrated that the new STAbp device has great potential as a new tool for a wide range of clinical and research applications which require continuous ABP waveforms.