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Blood Pressure Analyzer

The Blood Pressure Analyzer extracts the systolic, diastolic and mean arterial blood pressures, as well as the pulse, from a continuous blood pressure signal, and calculates descriptive statistics for each epoch.


Table of contents
  1. Introduction
  2. User Corrections
  3. Settings
  4. Metrics
  5. Resampled Signals

Introduction

The Blood Pressure (BP) Analyzer performs standard epoch-based analyses on a BP signal. The module features automatic calibration event detection, pulse estimation, and user-correction of the systolic peak detection.

Blood Pressure Analyzer
Figure 1: The BP Analyzer GUI, showing the BP signals and the estimated pulse. Note the automatically detected calibration event around 1865 seconds.

User Corrections

The Blood Pressure Analyzer allows the user to define zones in which the systolic and diastolic landmarks are disregarded. The module also estimates the pulse, in BPM, using the detected systolic peaks. The pulse signal itself cannot be corrected, and is instead automatically filtered using MATLAB’s hampel filter (k = 10, nSigma = 4). Artifacts in the pulse signal must thus be corrected indirectly by inserting correction zones in the blood pressure signal.

When a noisy section is detected, the user can insert a correction zone by left-clicking in the graph and dragging the mouse. Once a section is selected, landmarks can either be disabled or enabled. It is advisable to select a segment that is as big as possible, maximizing the interval in which no peaks should be detected.

Blood Pressure analyzer artifact correction 1
Figure 2: A blood pressure plot showing some deviating waveforms around 1880 seconds.
Blood Pressure analyzer artifact correction 2
Figure 3: Once the noisy section is selected, systolic and diastolic peak detection can be enabled or disabled within that section.
Blood Pressure analyzer artifact correction 3
Figure 4: Disabling the peak detection within the previously selected section removes the deviation from the interpolated blood pressure signals.

Settings

The Blood Pressure Analyzer assumes that the unit of the BP signal is mmHg. If this is not the case, fill in an appropriate gain value (multiplier) to transform the raw signal into mmHg.

The toolbox automatically detects calibration segments in the raw signal, and removes them from the filtered signal. The user cannot modify the segments that were classified as calibration segments. In the case that the calibration fails, the user may tweak the sensitivity, or completely disable the calibration detection by setting the sensitivity to zero.

A calibration sensitivity values below have been found to work well:

  • BMEYE Nexfin:
    0.02 (default).

  • Finapres:
    0.02 (default).

  • BIOPAC NIBP100D (CNAP Monitor by CN systems):
    0.002.

The auto-generated list below shows the settings available in the Blood Pressure Analyzer module:

  • General Settings:
    Name, source and epoch settings for this PhysioAnalyzer.

    • Analyzer prefix (tag):
      The tag (name) of this PhysioAnalyzer. The tag must be unique and start with a letter, and may only contain alphanumeric characters.

    • Channel-number of signal:
      The channel number (index) of the signal to be analyzed.

    • Generate epochs from:
      Specifies how epochs are generated.

  • Preprocessing Settings
    Settings for processing the raw blood pressure signal. This module assumes that the signal is in mmHg, if it is not, fill in a multiplier to convert it (e.g. 100).

    • Gain (signal multiplier) [x]:
      The gain is the value with which the raw signal is multiplied before being further processed and analyzed.

    • Lowpass filter [Hz]:
      The low-pass filter and its cutoff frequency.

  • Calibration Detection Settings:
    The Toolbox automatically detects calibration segments in the raw signal, and cuts these parts out. The setting below determines the detection sensitivity (0.02 recommended).

    • Calibration detection sensitivity:
      The sensitivity of the automatic calibration detection.
  • Systolic Peak Detection:
    To increase robustness, the Toolbox automatically applies a minimum separation criteria to the detected Systolic peaks.

    • Minimum systolic-peak separation [s]:
      Systolic peaks must be this distance from each other.

Metrics

The auto-generated table belows lists all the metrics produced by the Blood Pressure Analyzer module.

Table 1: The metrics calculated by the Blood Pressure Analyzer module.

Variable: Unit: Description:
Min_Sys_BP mmHg The minimum systolic blood pressure, per epoch.
Max_Sys_BP mmHg The maximum systolic blood pressure, per epoch.
Mean_Sys_BP mmHg The mean systolic blood pressure, per epoch.
Count_of_Sys_Points - The number of systolic peaks detected inside the epoch.
Min_Dia_BP mmHg The minimum diastolic blood pressure, per epoch.
Max_Dia_BP mmHg The maximum diastolic blood pressure, per epoch.
Mean_Dia_BP mmHg The mean diastolic blood pressure, per epoch.
Count_of_Dia_Points - The number of diastolic valleys detected inside the epoch.
Min_MAP mmHg The minimum MAP (Mean Arterial Pressure), per epoch.
Max_MAP mmHg The maximum MAP (Mean Arterial Pressure), per epoch.
Mean_MAP mmHg The mean MAP (Mean Arterial Pressure), per epoch.
Mean_Pulse BPM The mean of the interpolated pulse, as estimated from the intervals between the systolic peaks, per epoch.
Pulse_Coverage % The percentage of the epoch for which there is (interpolated) pulse data.
Missing_Data % Percentage of missing data (either due to calibrations or user rejection), per epoch.

Resampled Signals

When exporting the resampled epoch signals, the Blood Pressure Analyzer resamples and extracts the filtered BP signal, the systolic BP signal, the diastolic BP signal, and the MAP signal.


© Copyright Leiden University, 2022.