Thanks b_jim for having started this thread. I think it will be very useful, since the current Rutgers study on POIS is using Heart Rate Variability as one of its main measurement, and HRV is not very well known, so we will all benefit from discussing about it.
I totally agree with what you wrote in your reply to my post - it is just that your post explain one level of complexity further than the basic information I have shared :-) . You have included the frequency bands notion. I have reply to your question thinking you were new to the HRV concept, but you are obviously not. You're too quick and too smart, B_jim ;-) And I must say that I have worked with these concepts and my software more than 10 years ago, and didn't remember all the details. But, considering the current Rutgers study going on, and its use of HRV, it is a good time for me to review what I have learned back then. So I took the time to re-read about HRV, and following is the results of my refreshed understanding of it.
Great videos you are linking to ( For those not familiar with French, you can find similar info in English given on a more recent HeartMath device at
https://www.youtube.com/watch?v=h9SbrQ1AwiQ , beginning at 10:35, to 13:35 ). Those videos of Dr Servan-Scheiber - who, sadly, past away in 2011 - are very well done. And , hey, the software that is used in those videos is exactly the one I bought in 2004 - the Freeze-Framer software, of the HeartMath Institute ! I got out my old box form the shelves, and saw have paid $250, back then, for this kit ( software, sensor, and documentation). I have the exact same screens with my Freeze-Framer than what we see in those videos, including the Power Spectral Graph, with the 3 colored zones. Only my sensor is different, mine is a finger sensor. These videos are from 2007, so HeartMath may have developed this better sensor by then. Nowadays, HeartMath products have evolved a lot more, as seen in the English video - they now have small, portable units, but they still kept the same kind of tools and display, like the Power Spectrum Graph.
In general, the Power Spectrum Analysis of HRV uses 3 bands. The frequencies associated with these 3 bands are the very low frequencies (VLF) from 0.0033 to 0.04 Hz ( red/dark zone on the left), low frequencies (LF) from 0.04 to 0.15 Hz ( yellow zone in the center), and high frequency (HF) from 0.15 to 0.4 Hz ( pink zone on the right). This seems to be the better consensus in trying to define the influence zone of the sympathetic system at one end, the parasympathetic system at the other end, and the balancing zone of the two, in the middle.
Having the different frequency bands in mind, I should have been more precise in my answer and have said that
what we want, if we are looking for an optimal state of balance of the two branches of the autonomic system ( coherence state), is a higher HRV in the range of the 0,1 Hz, which is the center of the yellow zone that Dr Servan-Schreiber is pointing at at 01:15 of the first video you have linked to (
http://www.dailymotion.com/video/x34d7v_coherence-cardiaque-2-demonstration_news ). When using HeartMath products, the goal is to obtain, on the Power Spectrum Graph, a bell-curved group of bars, centered on the 0.10 value. This is what is termed a "cardiac coherence" state by HeartMath. I say "when using HeartMath products", because, there are many other devices for HRV measurements, and there are many way to do the mathematical analysis of the data and to present them on graphs. The current Rutgers study may measure and analyze it in another way, but in the end, the results lead to similar conclusions. So, for being clear with everybody, you probably will not hear of the same particular indicators from the Rutgers team ( like the 3 color zones, the Power Spectrum Graph - there are other ways to evaluate HRV). Information about the various way to analyze HRV data can be found at
https://en.wikipedia.org/wiki/Heart_rate_variability#HRV_analysis . For now, I do not know what method is used in the current POIS study. They may even use a method where there is no frequency bands implied, like with SDNN and SDANN ( see the wikipedia article on HRV for details) However, if you understand the concept of HRV, you will be able to understand what the results mean.
It is important to note that the coherence state is not a relaxation state - it is all relative to where you come from. When looking at the Power Spectrum Graph, the left, dark zone, is the sympathetic tone. Dr Servan-Schreiber says in the video that if your bars are centered there, you are in a state of anxiety , which he links to too much adrenaline and cortisol, too much stress. The pink zone at the right is the parasympathetic zone, and Dr Servan-Schreiber tells that if you are centered there, you are depressed ( parasympathetic is the vagal tone side, and in a simplify view, the "brake pedal" of the autonomic nervous system). So, the coherence concept is to have a right balance between the two sides of the autonomic nervous system. On the graph, that means being centered in the center of the yellow zone, at 0,1 Hz. As most people in our modern civilization are too stressed ( on the left side of the graph), the coherence state is obtained through being more relaxed. Becoming even more relaxed, the maximum of HRV can get centered at 0,2 Hz. If someone shows maximum HRV higher on the spectrum, farther on the right side, let's say at approx 3.5 Hz ( I suppose), Dr Servan-Schreiber says it is a sign of being depressed. Also, it is possible, for somebody not centered in the middle, LF frequencies, to show higher HRV in both left and right zones, meaning it is possible to be both anxious and depressed at the same time ( I think we can relate to date, when in POIS acute phase).
In HeartMath own terms: " There are three colored regions - the VLF (very low frequency) dark colored region on the left shows sympathetic activation. The LF (low frequency) region in the light colored middle is sometimes called the "baroreceptor region" which reflects the blood pressure control mechanisms between the heart and the brain. When in a coherent mode this indicates a synchronization of the sympathetic and the parasympathetic branches of the autonomic nervous system. The HF (high frequency) region on the right indicates parasympathetic activity. As you shift towards high coherence, the bars will focus around 0.1 Hz in this region and can get very high in amplitude.
Most people initially will have a large peak to the left in the VLF region due to sympathetic activity. A peak around .2 Hz to the right in the parasympathetic region can appear when the user is in relaxation mode." (found at
https://www.heartmath.com/support/knowledgebase/?article=kA180000000XbWdCAK&t=%28Power%29+Spectrum+Average )
Going back to the Rutgers study interim report:
Hi All,
Demo and Daveman just received the public portion of Dr. Komisaruk's interim report from NORD. Here it is --
"A preliminary interpretation of our current data is that POIS symptoms are accompanied by a lowered heart rate and heart rate variability (HRV), and that vagal stimulation may produce a beneficial effect on POIS symptoms (increased heart rate and HRV) as a 're-bound' from the vagal stimulation. These are very preliminary findings and continued research with additional participants is underway, to assess the reliability of these findings."
Stef
I think we can assume that the lowered HRV found by the research team in POIS subjects is either the LF HRV, the low frequency HRV ( the middle zone, the yellow zone in the videos), or it is an overall mesure of HRV that do not imply the division in different frequency bands, like the SDNN analysis method. I have read in a recent review (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4111661/ , see table 1 in this article ) that the more frequently used method for analizing HRV are SDNN, SDANN and SDANN index, and those methods give only one value for HRV, they do not divide HRV values in different bands. So, "lower HRV", in most studies, seems to mean a lower overall variability in heart rate, all frequencies confounded. In this context, a lower HRV still means to me a lower adaptability of the autonomous system, implying a lower balance between the vagal/parasympathetic tone and the sympathetic tone.
The interim report mentions a lower heart rate, so we can suppose that the peak band where the frequencies are their HRV maximum has moved toward the HF band ( higher frequencies ), but that is pure speculations from my part, because it is not specified in the interim report, and we know that POIS can cause both anxiety and depressed feelings, so it is not clear. And if they have used a SDNN method, all that can be deducted is that in POIS state, a low HRV is an indicator of less physiological resiliency and behavioral flexibility, and can reflect an decreased ability to adapt effectively to stress and environmental demands. Well, in my case, I really do feel that way when in POIS - very low capacity to adapt to anything in my environment, as any challenge, as little as it is, becomes overwhelming and frustrating, at the physical and the emotional level ( in my case, the cognitive/mental abilities are spared)
While reviewing for myself all that is linked to HRV, its measurement and clinical interpretation, I have found this blog, well written, and that gives a good overall explanation:
http://www.brainhealthhacks.com/2008/08/07/heart-rate-variability-health-predictor-and-what-you-can-do-about-it/ , and a follow-up at
http://www.brainhealthhacks.com/2008/09/30/heart-rate-variability-and-your-brain-an-update/ .
I still find this HRV subject very useful and interesting. It has helped me back in 2004, and from a twist in history, it comes back now in 2015, on this POIS forum :-) .
Sorry for the long post, but HRV is not a simple subject to talk about.
