Dr. Kevin Tracey

It's an interesting hypothesis.

It's very hard to study, but it's very interesting.

So if you can't measure it, and heart rate is confounded by all kinds of things like activity and stress and other things, so what else can... Well, you can measure heart rate variability.

Now, heart rate variability...

The problem with measuring heart rate variability comes down to a very simple understanding of what it is.

It's a statistical analysis using things like Fourier transformations of individual bits of data, which are the amounts of time between individual heartbeats.

So you're looking at the summation of the individual heartbeats as a statistical phenomenon.

And the reasoning is that when the vagus nerve fires, it prolongs the time to the next heartbeat.

So you get a longer duration between heartbeats.

And because the vagus nerve fires intermittently,

then the more vagus nerve activity you have, then the more variability you will have in the instantaneous heartbeats.

That's the fundamental principle of the relationship of the vagus nerve to heart variability.

And in opposition to this, you have the sympathetic input to the heart accelerating heartbeat, which is also going to be dependent on activity and your state of mind and stress and whatever else is going on.

So what you do with this information, and here's where it gets up to now, it's easy.

Up to now, it's easy.

What you do with this information is subjected to algorithms.

You know, you have an algorithm on your watch.

You have an algorithm on your wearable.

You have an algorithm on your arm, in your bed, you said.

We don't know what all these algorithms are.