3. Data Analysis

HRV for ECG data. Specifically, R-R variability found out by Time Domain Measures of Root Mean Square of Successive Differences (RMSSD), Frequency Domain Measure of Low Frequency (LF) by High Frequency (HF) Power Spectrum or Sympathetic-Vagal Balance measure. Follow the SPR guidelines at https://sprweb.org/page/Guidelines_Papers to make sure that the particular measure you are interested can be meaningful with the way data collection was done. Typically rest data for 5 minutes will be ok for both LF/HF and RMSSD calculations. Typical RMSDD can be found in https://elitehrv.com/normal-heart-rate-variability-age-gender. Typical LF/HF should be <1 in at least healthy controls. This is because LF representing sympathetic should be less than HF representing parasympathetic.  

Basic summary measure extraction

This provides intensity measures (i.e. on the y-axis) for each channel. Check units. For example, beats per minute is probably not what you need for ECG because you receive means in mV, i.e. the vertical dimension of the signal). CAUTION: this has limited use, i.e. make sure the measure you are looking for can be provided using this tool.

• Select focus area using the selection tool
• Click on the graph elements button (- and + in top bar) and select “Focus Area Bar” and “Focus Areas”
• In the Measurement area, select measures of interest
  • Optional: Click triangle->Dual Row x 3 , e.g.
  • Mean
  • Median
  • Standard Deviation
  • Freq
  • BPM
  • P-P
• Ctrl+K copies the measurements to the clipboard (alternatively Edit->Clipboard ->Copy Measurement)
• Copy to Excel
• As long as “SC” is selected besides the measurement options, clicking on another channel will change the values to that channel

QT interval:

• Longer with lower heart rate, shorter with higher heart rate
• Includes QRS complex, ST segment, T-wave
  • Beginning of QRS: repolarization, relaxation Until end of T wave
• Ventricular contraction
• How fast the ventricles are repolarized (QT interval=repolarization time; baseline, ~440-460ms)
• T-wave: ventricular repolarization; positive waveform (negative in an AVR and biphasic if ?)
• >500ms or <340ms abnormal
• If T-wave ends before the halfway point between two R’s (R-R interval), the QT interval/heart rate can be considered normal
• QTc is corrected QT, including QT for heart rate (RR interval in seconds); normal ~0.5sec (500ms)
• U-wave rare but possible after T-wave (peaks in same direction) -> included in the QT interval if present à if consistent, it is a marker for abnormalities
• ST segment: baseline point after S (called the J point) until onset of T-wave: brief interval between depolarization and repolarization
• PR interval: atrial depolarization

1. You can click on generate log RSA to get logarithmic values.

If a large number of inhales and/or exhales is missing, place flag markers (flag button) on EITHER peaks or troughs on the respiration channel (i.e. start with one of the two).

Now we replace the flags with respiration markers.

• Analysis ->find cycle 
  • Select “Events”
  • Start event: Flag (if you have flags on multiple channels, also select channel)
  • End event: Flag
  • Uncheck “Match pairs of events only”
• Go to the selection tab
  • Left edge: Time of “Starting event” type in the box -0.15 (don’t forget the minus)
  • Right edge: “Ending event” 0.15
  • do like + and - 0.09 for missing T peak since these waves are shorter in duration
• Go to the output tab
  • Check box “Output events”
  • Event 1:
    • For Inspirations select minimum (the trough)
    • For Expirations, select maximum (the peak)
  • Select channel 2 respiration
  • Output type: whether inspire or expire start
  • Output channel: channel 2 respiration
• Hit “Find all cycles” on bottom (if asked, select move cursor to origin): this turns all flags into inhale or exhale markers

Next we have to remove the flags that are now superimposed on the new markers.

• Open the event palette, either
  • By right-clicking on any marker, then select “edit marker” ->this opens the event palette
  • Alternatively, click on the +/- symbol in the event palette bar and select event palette
• In the bottom part, click “clear” (NOT clear all!)
  • In the box, select the channel (i.e. channel 2 for respiration), the type of marker you want to remove (Type → Notes-> Flag) and click ok

Export respiration data into an excel spreadsheet

Analysis ->Find cycle

• Select “Events”
• Start event: Inspire start
• End event: expire start
• Output tab: Check box: “Save measurements into excel spreadsheet file”
• Click “find all in focus areas” if you have multiple focus areas, from the dropdown menu select “single spreadsheet”
• Box pops up, say yes

Then repeat the same process for:

• Start event: Inspire start
• End event: expire start

https://www.biopac.com/events/acqknowledge-webinar-find-cycle/