Monday, March 29, 2021

Polar H10 ECG tracing - a short how to guide

Question: Why bother with looking at ECG tracings?

Answers (click on each to expand): 

Differentiate noise from cardiac arrhythmia

Optimize signal for most precise heart rate variability measurements

Getting a more accurate DFA a1 measurement

Recognize early signs of atrial fibrillation

Distinguish atrial from ventricular arrhythmia

Using Kubios Premium for ECG derived respiratory rate

Exercise intensity thresholds using ECG derived respiratory rate 

 

Multiple previous posts in this blog have examined the Movesense Medical module and HR plus in terms of single lead ECG devices.  At a relatively moderate cost, they are able to provide accurate HRV and rhythm analysis using the premium version of Kubios software.  However, what if you just had a Polar H10 and wanted to see what your ECG rhythm looked like - could you do it? 

Here is what the output looks like on an S21:


Pretty cool!

Requirements: Polar H10, spreadsheet program like Excel (for a long session), Polar Sensor Logger App for android

Shortcomings: Kubios free will not process the data, sample rate is only 130 Hz - probably adequate for DFA a1 precision, but not ideal.

Instructions:

  • Install the Polar Sensor app, wear the H10 HRM
  • Open the app, choose your device, pick ECG as the output type, hit start.

 

  • To see the above graph, scroll to the right under graphs and it should show.  
  • When you press "stop" you can save the file to your storage to view in Excel.
  • Locate the file and open it with a spreadsheet program.
  • Just plot time x voltage:

How does it look in Kubios (premium):

  • An APC is easily spotted in this strip of mine
  • Seems reasonable for rhythm - APC, VPC, etc


And the waveform:

  • Not great.

Is it Kubios' fault? No.  Here is a view in the android app, magnified:

 
 
  • You can only get so much resolution out of this low sample rate.

 For a similar app designed for the iPhone, please see this


 

Comments:

  • Yes, we can get a rhythm strip from a Polar H10 with just an android/iOS app.
  • Detecting severe arrhythmia's should not be too difficult for those familiar with reading these tracings.
  • To get either HRV or aberrant beat detection, you still need Kubios premium.
  • For those who think they are having abnormal beats and don't have a medical background, YMMV.

Heart rate variability during dynamic exercise

 


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Friday, March 26, 2021

DFA a1 problems during running - why?

 Low DFA a1 while running - a possible fix? 

I have previously noted DFA a1 decline associated with poor Movesense ECG waveform and have had multiple "complaints" of DFA a1 reading too low at easy intensity levels during certain forms of exercise in certain people.  The most common example being running. The scenario is usually as follows :

"My DFA a1 drops while running at trivial effort, way below what it should be and much different than with similar heart rates when biking."

My guess was that some type of core/trunk/diaphragm electro mechanical interaction was distorting the ECG waveform, making the peak of the R wave less able to be measured precisely. Since DFA a1 is an index of correlation properties and fractal patterns, a loss of true R peak timing will result in an artificial reduction in the complexity of these patterns.  Kind of like a dirty fingerprint on your camera lens - a loss of detail occurs and the picture is not going to be sharp. But perhaps the answer is from a different type of interference.

Why would running give us a distorted R peak?  Here is a clever and informative view of  chest wall motion during running:


As you can see there is quite a bit of motion and sensor bounce going on.  Whether this is part of the issue is unclear, but it does make one wonder.  In addition, the volume is rapidly changing, which could lead to variation in the ECG signal.

 

The question is what happens if we reduce the "pounding"?  Would the DFA a1 measurement normalize to where it should?

Thanks to a blog reader who kindly did some tests, we have some confirmation that this might be true.

He did a series of intensity ramps under three conditions, all using the same HRM (H10)

  • Bike
  • Stepper/elliptical
  • Running on a treadmill

What I have done is simply plotted the heart rate and DFA a1 over the course of the intensity ranges.  Normally, if your DFA a1 is in a .75 range cycling at a HR of 150 for example, we would expect similar behavior while running with the same HR.

  • The Run test in red clearly shows the early DFA a1 drop at low HR.
  • The green (stepper) and black (cycle) show similar and more realistic DFA a1 behavior.
  • The stepper/elliptical machine is using similar motor kinetics as the run, just without the impact.

 

His HRVT on the bike:


  •  The HRVT HR is about 146 bpm - a very reasonable figure with good R correlation


Comments

  • Early DFA a1 decline when running with a typical HRM chest belt occurs is a subset of individuals.  However, most do not have this issue. 
  • It is not an issue on the bike.
  • In this case, simply decreasing the ground force impact totally eliminated the effect.
  • It seems to be due to some sort of electromechanical interference related to impact.  Since there is no significant impact on the bike or elliptical stepper, the effect on DFA a1 does not occur.
  • Can this be compensated for?  I can't say, but the HRM designers and engineers may be able to adjust their algorithms to eliminate some of this.  The first step (no pun intended) is to confirm that the phenomena exists (done), why it happens (maybe) then hopefully find the solution.
  • In the meantime, trust the bike results but an alternate solution is using an elliptical trainer, stepper, staircase as workarounds.


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Tuesday, March 23, 2021

DFA a1 stability over longer exercise times

In the last post we saw how DFA a1 can be a marker of "fatigue" after intense short bouts of effort.  Since it represents a marker of "organismic demand" and autonomic balance, typical values for a given level of power will be altered post HIT.  On the other hand, what about behavior over the course of longer durations of mild to moderate intensity?  With this question in mind, we are going to examine two examples in this post looking at DFA a1 behavior over the course of a 2 hour easy pace cycling ride and one just below the AeT.  The questions are:

  • Does DFA a1 "drift" during a constant power effort below the AeT (aerobic threshold) over 1 to 2 hours?
  • Does the HRVT (AeT related DFA a1 threshold) change after 1 to 2 hours of "just below" AeT cycling?

 

The first example is from a friend who is a former (very) elite athlete who is still active in cycling and running sports.  His usual AeT by HRVT was about 210w.  He did a double ramp test, each separated by 2 hours of easy riding at 140 watts (2w/kg). The ramp consisted of 5 x 6min at 100w, 130w, 160w, 190w and 220w. He used a Polar H10 with nearly no artifacts. 

Here is how the entire session looked up to the second ramp:

Ramp comparison:

Because the ramps were not the usual incremental type I use, I decided to simply superimpose the ramps on top of each other.  In addition, this athlete had improved their fitness and instead of the usual HRVT being about 210-220w, it is now higher, and not totally captured on the tracing.

DFA a1 on Pre and Post ramp:


Heart rate on each ramp:




Conclusions:

  • There was no significant alteration in HRVT dynamics from Pre to Post 2 hour cycling ramps.  
  • There was noticeable HR "drift".
  • DFA a1 during the 2 hours was in the highly correlated range (above 1), consistent with very easy effort.
  • From this example it appears that the 2 hours of easy cycling did not impact either the HRVT nor the ability of DFA a1 to gauge intensity status.
  • DFA a1 stability was in the face of some cardiac drift.

 

Example 2

The next set of data comes from me.  I'm about 25 years older and recreational level - so a good cross section comparison.  What I did was a 20 min warmup, then first ramp (incremental, 5w/min, good cooling, Polar H10 with <2% artifact, Kubios time varying analysis). Immediately after the first ramp, I cycled at just under my AeT (5-15w) for one hour.  This was about 30 watts above my typical "easy" days, but I was curious to see if pushing the limits would be an issue on the second ramp.  

After the hour, a second ramp was done, identical method to the first.

Comments:

  • DFA a1 was both above and below the .75 for the hour of "just below" AeT riding.
  • There did not appear to be major cardiac drift (red is HR) despite stable power.
  • Histogram of DFA a1 during that 1 hour at just under AeT is below
  • Although some of the time was spent below .75, the bulk was not.
  • This is important to note as some users of this method have worried about variation in the DFA a1 during a relatively stable power session - the fact is variation is normal, but the average was well above .75.  The official mean was .89 in this example.

 

Ramp comparisons (Pre and Post the 1 hour):

Ramp overlays (as I did above):

DFA a1:

  • The early parts of the ramps were a bit different since the second was preceded by the "just under" AeT 1 hour, but the DFA a1 later on looks remarkably similar.

Was there any HR drift?

  • Except for the first few minutes (as noted), there was no noticeable cardiac drift.

 

HRVT in each ramp:

Heart rate at HRVT:

Power at HRVT (calculated from the time:power relationship)

Observations:

  • Both the HR and power at HRVT were about the same during each ramp before and after 1 hour of cycling just under the AeT. 
  • This was even in the face of some of that hour session having DFA a1 dip below .75 on occasion.
  • There was no cardiac drift (good fan and cool room).


Summary:

  • It appear that 2 hours of continuous cycling well under the AeT does not lead to a change in DFA a1 behavior and does not alter the HRVT.
  • It also seems that 1 hour of continuous cycling just under the AeT does not alter the HRVT or the DFA a1 relationship to power.
  • DFA a1 behavior appears to be independent of HR drift (first example had it, second did not).
  • On a practical basis, one can be reassured that DFA a1 values over longer time spans still accurately reflect the exercise intensity as long as HIT was not performed. Even prolonged cycling at an intensity a few watts below the AeT did not seem to affect the HRVT after 1 hour.
  • Of course, longer time frames (>2 hours) may entail a very different set of results.  
  • Finally, for enforcement of a low intensity session, real time monitoring of DFA a1 appears to be a promising aide to endurance exercise training.



Heart rate variability during dynamic exercise


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