Fig. 6
From: Systolic blood pressure estimation method using electrocardiogram RRI data
Flowchart for calculating GTs of LTM and STM. In the residual function diagrams of LTM and STM (1), USR and LSR were set, the best approximation curve expressed with a quartic function was created (2)(3), and GTs were calculated via the double tangent. In cases where the function cannot be created, recalculation is conducted by changing the frequency ranges for analysis (5). In a spectrum diagram of a double logarithmic graph, curves having large approximate errors tend to occur on the ends of the low frequency side and the high frequency side. In cases where the three points at the end are linked with a parabola, the errors are small, but when a parabola is drawn with two points, errors occur. If two points are linked with a straight line, errors are few. Accordingly, in the end parts on the low frequency side, frequencies for analysis are extended to the two frequencies of 0.009 Hz (L1) and 0.012 Hz (L2), while in the end parts on the high frequency side, frequencies for analysis are extended to the two frequencies of 0.064 Hz (U1) and 0.08 Hz (U2). The analysis is conducted in the order of subscripts. Incidentally, L is an abbreviation of Lower, which means frequencies on the low frequency side, and U is an abbreviation of Upper, appertaining to frequencies on the high frequency side. Successively, in the frequency ranges of LSR and USR, a linear function is created (4) via the least squares method. The differential coefficient which the linear function has corresponds to GTs n1 and n2 expressed in Fig. 4. The agreement of the signs of these GTs with those of LSR and USR obtained from the approximation function was checked
