Apple watch and Hear Rate Variability

Before spouting off on this (and making a complete fool of myself), I wanted to ask a question about Apple Watch Series 9 and how they determine a value for heart rate variability.

My impression is that the watch measures the interval (in milliseconds) between each heart beat over some time period (anyone know the time period?), then calculates the mean or average interval. Subsequently the change (or deviation) from each individual interval is compared to the mean and this results in the ability to display a standard deviation for the entirety of the time period.

Using this method enables the quantification of (say) a chaotic R-R during the period of observation.

DoI have this correct, or am I am misunderstanding something?

The HRV time periods can be found on your iPhone. Open health. Go to summary. Heart rate variability. Scroll down. Open show all data. You will see a daily list and the HRV for the day. Open a date. There will be a list of the time the watch took your HRV, how long it took and the result.



Edited 1 time(s). Last edit at 03/27/2024 10:32PM by JakeS.

Thanks Jake, that exactly what I wanted, how to navigate to the details for each HRV.
So what I learned was that the observation period is ~60 seconds.
Looking further, I see a table of BPM at various times, for example:
So I'm assuming that the time associated with each BPM data is the time at which a QRS occurred (because the time are not equally spaced), and that the BPM reported is the calculated value of beats per minute. for the preceding R-R interval.

(why the left hand column is not in milliseconds, which is what we want to see, who knows. but it's easy enough to covert BPM (measured beat to beat) to R-R interval in milliseconds).

Is my understanding of this data make sense to you?

Thanks for your help,

Quote
Searching9

(why the left hand column is not in milliseconds, which is what we want to see, who knows. but it's easy enough to covert BPM (measured beat to beat) to R-R interval in milliseconds).

Unless you have a different version HRV in ms. is available. You opened up (your screen shot) only one set of data that is available. A similar table for HRV is also there.

To get a similar HRV table open summary and then HRV scroll down to the bottom. There are two options on the bottom.

1. Show all Data - open this up it will give you the table in ms. Open a date. The times HRV was taken, how long taken for (usually one minute), and the rate are all listed.
2. Show all Beat-to-beat Measurements. This is the table you included in your post.

The other way to see your HRV throughout the day is to go to summary. Open HRV. HRV graph. Top of the graph set it to daily. The graph for the current date will be there. If you touch the data points it will indicate the HRV. If you set the graph to week, month, 6m, or year and touch a data point it will only give the average.

All the graphs in your iPhone lets you touch the data points to get the results.



Edited 4 time(s). Last edit at 03/28/2024 01:27PM by JakeS.

Not on the AW, but I use a Polar H10 chest strap and the HRV Logger app for recording to get an effectively infinite (many hours) recording of beat to beat data in ms. The only downside is I have to download the data after recording to view the whole series on an ancient Polar Windows program, where visually windowing on various pieces of the data are very fast & easy. The HRV Logger app, in its display shows averaged data in real time, which is useful but not as useful as being able to see each beat. During the episode I can simultaneously view each beat (in BPM form) with the HRV4training app which will do this for up to 5 minutes at a time before I have to reset and start over. I do this as my afib tends to convert to what I assume is flutter (very stable rate at high rates). I've learned that I need to get the rhythm from flutter back to afib for it to convert to NSR (with PIP flecainide on board).

For a more reliable HRV measurement, you want to manually activate a HRV reading, as opposed to just relying on Apple's averaging formula.
Here's how.

1) First thing in the morning -- or per whatever HRV protocol you subscribe to -- press digital crown and find the "Mindfulness App".

2) Now press "Breathe 3 minutes". (You can follow the breathing prompt or not, but after 3 minutes the Watch will now manually take an HRV reading.

3) Go into Apple Health on your Iphone and open "show all data" under the HRV section. You will now see your HRV corresponding to the time of the measurement you just took.

This way you can control the time and conditions of an HRV reading, which might be more helpful than how Apple does it automatically.

Jim

Very useful tip, I'll try it out
Thanks