My Quantified Self Experiment: Can Heart Rate Variability Be Useful In Predicting A CF Exacerbation?
There is a movement afoot. It goes by a few names; quantified self, biohacking, and biologging are a few. The quantified self website has a tagline which sums up the purpose of this movement quite well, “self knowledge through numbers.” By using technology, usually in the form of wearable tracking devices, data is acquired which allows the self-tracker to understand herself better.
A simple example is the popular Fitbit, which is a device worn somewhere on the body, depending on the model, that tracks steps taken over the course of the day. It’s fancier than a simple pedometer (the original self-tracker), in that it has a built in accelerometer, so the user can wirelessly sync to her computer dashboard and record sleep, calories expended, steps and miles walked, floors climbed, most active time of the day, and of course even connect with fellow fitbit friends. It’s really amazing what you can track these days.
My recent foray into self-tracking involves first-thing-in-the-morning measurement of my heart rate variability, or HRV. I learned about the value of this measurement through my obsessive thinking about and planning my latest “comeback.” After the third bout of pneumonia this year, I guess I needed more than the usual amount of motivation, and was looking into the latest and greatest fitness gear/technologic toys to spice up the process a bit.
HRV measurement is definitely not new, but using it to enhance one’s training is a relatively recent phenomenon. It’s been used for years in professional athlete circles, but easy to use cellphone apps for the masses are new. There are a few, but the one I chose is called “Bioforce.” Using a bluetooth enabled Polar heartrate monitor strap and this iPhone app, I’ve been watching my HRV steadily “improve” as I’ve slowly but surely increased my training intensity since rolling out of my room in the wheelchair (why do they have that rule?).
So what is HRV? In brief, there is a normal rhythm to the heartbeat that is a bit different from the constant “lub dub, lub dub, lub dub” that you might imagine. Your heart rate is under the control of your autonomic nervous system, which is a good thing or else you’d have to consciously contract your heart with every beat. The autonomic control of heart rate depends on a delicate balance between the sympathetic nervous system (think “fight or flight”) and the parasympathetic nervous system (think “rest and digest”). As you inhale, the sympathetic nervous system is more in control, and as you exhale, the parasympathetic nervous system prevails. As a result, when you inhale, heart rate speeds up just a smidge, and as you exhale, it slows down. So when a regular heart rate monitor says your HR is 75, that is just an average of what it is over a given time period. Really, it probably ranges from about 70 to 80, depending on your breath cycle.
Now it gets simpler. A given measurement of HRV is a reflection of your autonomic nervous system, the balance of sympathetic and parasympathetic input, in the moment. Increased parasympathetic function is associated with higher HRV and aerobic capacity and has been shown to correlate to increased life expectancy (in “normals,” i.e. they don’t have CF).
Why is this useful? Well, when the body is stressed, sympathetic system is more prominent. This is why your heart and breathing rate increase, why you stop digesting food, why blood shunts to your muscles to get ready to fight. It’s all automatic. When you are relaxed, parasympathetic control leads to the opposite effects. So HRV can reflect your body’s state of stress.
Elite athletes use this measurement to tell them if they are overtraining. This is why HRV apps for your phone have been created. A given daily measurement will let them know whether they should train hard that day, or take it easy because their sympathetic control is too high, warning them that they are approaching the overtrained state.
But HRV can also reflect the body’s state of inflammation, because there is a linkage between inflammation and the sympathetic nervous system. This is a bit complicated, because obviously you can have low grade inflammation and not have a flight or fight response. But remember, we are talking about measuring a fine balance here, and a significant inflammatory process (such as a CF exacerbation) could very well tip the balance a bit, and this could be picked up by a measure of HRV, especially if you are your own control. At least, this is my hypothesis.
So this is my N of 1 trial. Basically, N of 1 is a clinical trial in which a single patient is the entire trial. I am running my own case study. And N of 1 trials are what the quantified self movement is all about.
What have I learned so far? Well, for the first few days out of the hospital, my HRV was extremely low (green line is HRV, yellow line is heart rate, and blue is average). This makes sense, as I was stressed and my body was WAY stressed. Gradually, it has increased, with downward blips here and there:
The colors of the bars on the bottom of the graph have meaning if you are an elite athlete and basing your day’s training on your HRV. Green means go hard, amber means take it easy, and red means take a day off because your body is in the danger zone of too much sympathetic input.
Here is what I have learned so far: My HRV goes down (bad) if I drink any amount of alcohol the night before. This saddens me. It also goes down if I am dehydrated, which is likely related. As you can see, I am supposed to take today off from training, but my take away is that the second bottle of Fat Tire last night was a really bad idea.
Okay, so I know I’m a nerd. But I’m going to keep this up and watch what happens when I get sick the next time. Maybe I’ll have an early warning. We’ll see.
These types of experiments can be very enlightening. What would be really cool though would be if those of us with specific questions (CF related) could share with others our experiences, and get immediate feedback from others with similar questions. Do you think we could uncover some interesting results? Think of the surfers’ experiences leading to the development of hypertonic saline. More to follow!