Abstract
In this paper, an indirect method of continuously measuring blood pressure is proposed. This method is based on the well-known relationship between arterial pressure and pulse wave velocity, that is, the arterial pressure can be estimated from the change of the pressure waveform.
In arteries, especially distal arteries such as the femoral artery, two obvious peaks are observed in the pressure waveforms. The systole causes the first one, and reflected waves at multiple sites in the arterial system cause the other one called the dicrotic wave. Taking the time interval between two peaks (Ta) and the pulse wave velocity into consideration, the most effective reflecting site is at or near the iliac artery, and Ta is the time the pulse wave takes to propagate between the aortic valve and this reflecting site.
It is well known that Young's modulus for a blood vessel increases in proportion to the arterial pressure and that this increase increases the pulse wave velocity. Therefore, Ta is inversely proportional to the arterial pressure, and so the change of arterial pressure can be calculated from the change of Ta.
Ta is determined from the autocorrelation function of the pressure waveform which is transcutaneously detected at the dorsal artery. In order to establish the relation between Ta and the arterial pressure, Ta is calibrated in corresponding pressure readings by the usual cuff method.
From results, we can see that the change of Ta is inversely proportional to the change of diastolic pressure. Therefore, the change of diastolic pressure can be estimated from the change of Ta within the measurement accuracy of about 5mmHg.
