njit-etd2003-081 - New Jersey Institute of Technology

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4.2.3 Power Spectrum Analysis of Blood Pressure Variability
The power spectrum of the blood pressure (BP) signal was also obtained from a VI
written in LabVIEW. Again, the physiological signals were read from the same
spreadsheet data file (Read From Spreadsheet File.vi). Each of the raw ECG and blood
pressure signals was independently analyzed and displayed on the control panel.
Similar to the raw ECG signal, the raw blood pressure signal passed through a
high-pass filter (HP_FILT.vi) and successively into a peak detection block (Search
BP.vi). The filtered BP array was then analyzed for the detection of each systolic peak.
Unlike the peak detection block for the ECG signal, the location of each consecutive
peak of the blood pressure signal was not directly detected, but rather it was the peak
amplitude of the systolic blood pressure waveform, which was of importance. It was the
detection of the amplitude of each peak that indicates the peak location. Detection of the
BP peak location was dependent upon the maximum amplitude of the peak, i.e. the y-
axis. The first maximum value of amplitude that occurred in the peak was detected.
This value was interpolated over the interval until the next successive peak amplitude
was detected. The BP IBI was then interpolated to generate the IIBI. Each peak
amplitude value was interpolated over the period of time between each successive peak
amplitude detection. For example, if the first peak in succession has an amplitude of
1.135, the next detected peak has an amplitude of 0.850, and there was a period of 200
points between the two detected peaks, then the value of the first detected peak, or
1.135, was interpolated over the 200 points so that each point possesses this amplitude
until the next detection at 0.850. The resulting array then underwent a series of analyses
and mathematical calculations, similar to the heart rate IIBI, to graphically display the