## 2 Oscillometric Blood Pressure Estimation Algorithms  
The oscillometric BP measurement technique is based on the measurement values obtained from a pressure transducer that is connected to the arm cuff. The pressure oscillation peaks around the mean arterial pressure (MAP) are processed by proprietary algorithms, yielding the systolic and diastolic pressures. The most popular empirical algorithms used to evaluate BP values from ABPMDs are the maximum amplitude, derivative, and fixed ratio algorithms [18,19]. The maximum amplitude algorithm estimates mean BP as the external pressure at which the BP oscillogram has a peak value [20,21]. Then, using interpolating algorithms, such as polynomial or spline interpolation algorithms, the fixed ratio algorithm estimates each diastolic BP and systolic BP reading as the external pressure at which the BP oscillogram is at some fraction of its peak value [22]. Another algorithm that is also commonly used is the derivative algorithm, which estimates diastolic BP and systolic BP as the external pressures at which the oscillogram interpolated peak curve has its maximum and minimum slopes, respectively [23,24]. It is important to underline that these algorithms are proprietary [25,26] and are not commonly divulgated by ABPMD manufacturers. Figure 1 includes a graphical representation of the key values that are used to evaluate the systolic and diastolic BP values based on the BP oscillogram peak envelope. Thus, to implement an algorithm-independent calibrator of ABPMDs, three specific pulse envelope profiles are considered, namely, the triangular, the trapezoidal and the parabolic pulse envelope profiles. Basically, the objective of each one of the envelope profiles is to create a reference profile that generates a similar measurement of the BP parameters independently of the specific algorithm used in the ABPMD under test. Taking as an example the sphygmo  
Figure 1: Graphical representation of the key values involved in the fixed ratio and maximum slope algorithms (MAP—mean arterial pressure; S\({}_{\rm H}\)— systolic pressure obtained by using the fixed ratio algorithm; D\({}_{\rm H}\)—diastolic pressure obtained by using the fixed ratio algorithm; S\({}_{\rm M}\)—systolic pressure obtained by using the maximum slope algorithm; D\({}_{\rm H}\)—diastolic pressure obtained by using the maximum slope algorithm; H\({}_{\rm MAP}\)—oscillometric pulse envelope amplitude associated with mean arterial blood pressure; H\({}_{\rm S}\)—oscillometric pulse envelope amplitude associated with systolic blood pressure; H\({}_{\rm D}\)—oscillometric pulse envelope amplitude associated with diastolic blood pressure; S\({}_{\rm coef}\)—systolic coefficient used in the fixed ratio algorithm; D\({}_{\rm coef}\)—diastolic coefficient used in the fixed ratio algorithm). manometer pressure curve represented in Figure 2, the variables that are used to synthesize the different envelope profiles are as follows: PM, maximum cuff pressure (mmHg); Pm, minimum cuff pressure (mmHg) during the deflation phase; dT, duration of the deflation phase (s); SBP, systolic blood pressure (mmHg); DBP, diastolic blood pressure (mmHg); MAP, mean arterial blood pressure (mmHg); HBR, heart beat rate (b.p.m. ); amp, amplitude of the pressure pulses (mmHg); and SR, sampling rate (S/s). In the same figure, dT represents the duration of the deflation phase, d_up represents the duration of the inflation phase and d_down represents the duration of the release phase, which are the three pressure variation phases associated with the cuff pressure curve. Figure 2: Synthesized cuff pressure curve (PM = 200 mmHg; Pm = 50 mmHg; MAP = 100 mmHg; dT = 30 s; d_up = 5 s; d_down = 5 s; amp = 6 mmHg). As an example, Figure 3 represents a triangular pulse envelope associated with the following set of simulation parameters: dT = 30 s; SBP = 120 mmHg; DBP = 80 mmHg; MAP = 100 mmHg; HBR = 90 b.p.m. and amp = 6 mmHg.