Monthly Archives: September 2014

rMSSD – Finding the Right Metric

My question throughout these months of study has been around unnecessary distraction from an enjoyable life due to stressing out about things that did not merit the stress. My very first results were around surprising ways I was stressing myself out that on examination disappeared. Most of this work was self reported upsets. 

Once I started down the road to finding technology that could help me know when I was upset things became very complicated very fast. There are a large number of devices that claim to measure stress but my experience was that they were not consistently reading stress events. I highlight Heartmath in a lot of my work and it does provide a good baseline for relaxed coherence, but the technology is virtually unusable in all but quiet meditative session. For example, if you turn your head the readings will drop out to zero which is not very useful if you are meeting someone in a coffee shop. 

I have spent a lot of time with apps and Bluetooth heart rate belts. I built my knowledge reading academic papers and with off the shelf apps got to the point I have a good set of readings on stress events. The most complicated manual structure I devised was this:

  • take a reading with a Polar H7 heart rate sensor,
  • capture the output in SweetbeatLife app,
  • email the results to myself from the app,
  • download that associate file
  • import the data in that file to Kubios,
  • in Kubios cut the data into 30 second increments which meant three keystrokes repeated up to 120 times,
  • generate a pdf report that shows 11 different heart rate variability features,
  • enter the data from those features back into a spreadsheet (typically 660 entries),
  • manually tag whether I was clear headed or upset in a new column on the spreadsheet,
  • save that spreadsheet to CSV format,
  • copy a text version of that CSV format into the WEKA arff format,
  • use that arff formatted data to run an Artifical Neural Network in WEKA,
  • reword that WEKA data back into a prose form that said “this is how much I was upset or not”

I got pretty good results that were consistent with some academic papers I read and I had the satisfaction of learning a lot about HRV, and the process was not sustainable. I want to take readings while shooting shotguns and getting a foot massage, not spend all my time crunching data. 

To cut through that complexity and make the measuring and reading of data a small part of the experience I am settling on rMSSD as a single metric on which I am going to focus. Both the SweetBeatLIfe app and HeartRateLogger give a real time rMSSD reading and have that as an exportable feature. I can use Kubios to extract it from all the Heartmath work I have done. And I was pleased to read in an academic paper “SDNN/RMSSD as a Surrogate for LF/HF: A Revised Investigation” in Section 4.1 titled “The Epoch Aspect” that the rMSSD was a stable measurement when used in 10, 20, 30, 60, 120, 300 and 600 second readings. That means there has been some work done to support the fact that an rMSSD on 30 second increments can be reliable as long as I compare it to other 30 second increments. The study also indicates that rMSSD is a good proxy for the frequency based measurements that many of the apps use to indicate stress. 

So with my process of data collection vastly simplified I can work on refining and interpreting data given the various contexts I will be operating in. Administrative burden relieved I am off to the foot masseuse. 



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Doc’s Needle Better Than Dentist Drill

Finishing off my service provider stress-off I had the opportunity to take a reading while getting shots at the Doctor. I used the Polar H7, SweetBeat Life and Kubios to pull the data together. I was quite surprised to see that getting a needle stuck in me was not nearly as stressful at having the tooth drilled, and other then the moment of anticipation prior to the jab I was quite relaxed.


You can see at time had 2 I was anticipating the jab and the jab itself happened between 3 and 4. Afterward I was quite pleased when it was over. So looking across service providers my stress leader board looks like this:


When relaxed my average pNN50 was just a bit higher than getting a needle at the doctor. Doctors win gold, hairdressers win silver and dentists get a distant bronze. I use average pNN50 read at 30 second intervals to compare because the length of time I was in an anticipatory state and the time of treatment was different for each provider.

I can only speculate why the stress levels were not what I was expecting. I would have guessed a doctor’s jab would be nearer the dentists drill. Two factors may have influenced the readings, both related to mental state. First, the length of time was different for each. The doctor’s needle was very fast. The haircut had not pain, but it was 45 minutes long. And I was in the dentists chair for an hour during which 20 minutes was drilling. So mentally I was working on different time horizons.

Second, the certainty of outcome and context was different. In the doctors office my wife was with me, we were joking around and discussing our upcoming trip to Vietnam. We know the doctor and the atmosphere was quite convivial. The jab was going to be quick and done. So my relaxed state was consistent with those environmental factors. The haircut was with a long time and trusted provider and sadly I had to tell him at the end I was moving from London to San Francisco and would no longer be seeing him. So the readings tail off at the end where I said goodbye. Finally, the dentist was putting in a filling “to see how it goes” with the possibility that if they drilled and found the tooth in too bad a shape more detailed, longer and painful work was going to have necessary. So the anticipation in that chair was very high stakes.

Despite my calling this a description of the effect of the doctor and dentist, what we are actually seeing is the physiological output of my expectations. Where this journey has taken us is where it began. My interpretation of the situation fires my physiological stress. With the doctor, dentist and hairdresser I was sitting and they were using a sharp object to bring on some physical improvement. In each case my own interpretation of what was happening and what was about to happen triggered my reaction, so we continue to show that all stress has a powerful subjective element.