Abstract
In the previous study, the multi-element tonometry sensor-based noninvasive PWV measurement system was evaluated for its frequency response characteristics, and for its accuracy in pulse wave propagation time measurement in simulated circulatory system. Excellent results supported the use of this system in noninvasive measurement of PWV possibly from the carotid and femoral arteries. However, its accuracy has not been validated in an actual physiological system. Since the noninvasive pulse wave measurement is affected by the tissue between the sensor and the vessel, hold-down force applied to position the sensor, and physiological variables such as heart rate and blood pressure levels, further study was undertaken to quantify their effects upon pulse wave, hence PWV measurement. For the animal model, we used the common carotid artery of female goats whose body weight was close to average human size (60kg). The study was divided into two groups; in Group I the tonometric sensor was directly applied to the exposed left common carotid artery, while in Group II the sensor was applied over the skin and subcutaneous tissues covering the artery. As a control measurement, a 1.4F Millar catheter was inserted inside the carotid artery in the vicinity of the tonometric measurement site. Also, a 4F Millar catheter was inserted through a contra-lateral carotid artery and its tip was advanced to the root of the aorta for measurement of aortic pressure waveform. Both the Millar and tonometric measurements were referenced to the aortic waveform for computation of PWV. First, we changed the hold-down forces of the sensor applied to the artery. Second, systolic blood pressure levels were changed from 85 to 170mmHg by drugs. Third, heart rate was changed from 80 to 145 beats/minute by drugs and a pacemaker. The results showed an excellent correlation between the tonometric and Millar measurements with and without skin and subcutaneous tissues. The correlation coefficients between the Millar and tonometric methods for PWV measurements were 0.99 with and without skin and subcutaneous tissues. The bias ±2SD for the pulse transmission time between the two methods (the Millar minus tonometric) were -1.14±0.76ms for the exposed artery, while for the covered artery -0.87±0.56ms. These results confirmed that the arterial wall, subcutaneous tissue and skin do not affect the accuracy of pulse wave measurements under varying physiological conditions. It was thus concluded that the multi-element sensor could be used for effective and accurate noninvasive PWV measurement in vivo.
