## 3 System Description
### Software  
The LabVIEW graphical programming language was used to develop the main routines included in the software part of the proposed prototype. In addition to the generation of the different pulse envelope profiles used for the evaluation of NIBP measurement parameters using the amplitude ratio and the maximum slope algorithms, the proposed NIBP simulator and analyzer also includes routines to perform the following tasks: static pressure tests, leak tests and algorithm-independent BP calibrations. There are also routines to record the measurement data, to generate arbitrary waveform pressure signals with specific pulse envelope parameters and to represent the pressure signals that are used for calibration purposes and the BP oscillometric pulses whose profile is selected according to the algorithm-selected BP parameter evaluation. As an example, Figure 8a,b represent two graphics contained in the panel of the developed software. Figure 8a represents the cuff pressure variation during the three phases of a BP measurement: the pressure inflation phase, which occurs between 0 and 5 s, the pressure deflation phase, which occurs between 5 and 35 s, and the pressure release phase, which occurs between 35 and 37 s. In this example, the maximum cuff pressure is equal 180 mmHg, obviously higher than the SBP used for simulation that is equal 150 mmHg, and the cuff pressure during the release is equal 50 mmHg, obviously lower than the DBP used for simulation that is equal 100 mmHg. Regarding Figure 8b, it represents the BP oscillometric pulse for a trapezoidal pulse envelope associated with a maximum pulse amplitude equal to 3 mmHg and an MAP equal to 120 mmHg. For the same example that was previously considered, the upper part of Figure 9 displays the graphical representation of the pressure peaks of the oscillometric signal, and the lower part of the figure represents the numerical values that were evaluated for different BP parameters, obtained after processing the previous signal. It can be easily confirmed that the evaluated parameters are very near the theoretical values used for the simulated cuff pressure signal. The main routines that were developed to generate the calibration signal are the following: synthesis of the complete BP signal, which includes the inflation pressure variation, the deflation pressure variation plus the small amplitude BP pulses, and the pressure variation of the measuring release phase. All timing and amplitude parameters of the synthesized cuff pressure curve, represented in Figure 2, can be adjusted by the user according to the purpose of the calibration to be performed. On the other hand, the main routines that were developed to acquire the BP signal are the following: signal filtering and outlier removal, extraction of the BP pulse envelope, either the fixed ratio algorithm or the derivative algorithm, and routines associated with signal display, data storage, and  
Figure 7: Hardware block diagram of a multiple pressure sensor calibration platform (DAQ—data acquisition board; EPPR—electro-pneumatic pressure regulator; A.S.—air supply; PCal—pressure calibrator; PS—pressure sensor; S—solenoid valve actuator). data transmission. It is also important to note that, regarding signal processing routines, particular attention must be paid to the usage of filters and other processing operators to minimize measurement errors caused by signal amplitude and phase distortions. Thus, for example, the smoothing of the oscillometric waveform was performed using the Savitzky-Golay filter [40] to ensure that the pulse shape remained preserved in terms of peak amplitudes, positions, widths and areas. Figure 8: Example of two graphics contained in the LabVIEW front panel: (**a**) cuff pressure variation during the three phases of BP measurement; (**b**) BP oscillometric pulse for a trapezoidal pulse envelope associated with a maximum pulse amplitude equal to 3 mmHg and an MAP equal to 120 mmHg.