Overnight Heart Rate and CVHR Explained
What your pulse usually does while you sleep, what the CVHR number counts, and how to compare your overnight heart rate across nights.
Your oximeter records two things all night: blood oxygen and pulse. Most people only look at the oxygen. Here's what the pulse line adds.
What does your pulse usually do overnight?
- It drops as you fall asleep.
- It drifts lower into the small hours.
- It rises again towards morning.
Your own nights are the only useful comparison. Record a week, note your average and your lowest reading, and compare later nights against that.
What is CVHR?
CVHR stands for cyclic variation of heart rate. It's a repeating pattern: your pulse falls below its recent level, rises above it, then does the same again. On the chart it looks like a sawtooth.
Researchers described the pattern in 1984, in people with sleep apnea. A 2011 study by Hayano and colleagues built a method for counting it. That work used ECG recordings, not a ring's pulse reading. So use your CVHR to compare your own nights. It isn't a test for any condition.
How does PulseOxTracker count it?
A rise in pulse alone isn't counted, because rolling over produces one too. A cycle only counts when:
- Your pulse falls first, then rises.
- The rise is 10 to 60 seconds wide.
- At least three happen in a row, 20 to 120 seconds apart.
You get the result as cycles per minute. You also get the same count at three dip sizes, so you can see whether the figure depends on shallow dips. The heart rate and CVHR help page lists every rule.
Why look at pulse if you already have oxygen?
They're two readings of the same moment.
- An oxygen dip followed a few seconds later by a rise in pulse is one kind of event.
- A dip with a flat pulse next to it is more likely to be the sensor.
PulseOxTracker shows the share of pulse cycles that were followed by an oxygen dip.
What changes your overnight pulse?
Record 5 ordinary nights, change one thing, and compare. These posts cover four things you can test:
Tag the night with what you changed. Then compare two nights side by side. Not sure how many nights you need? Read how many nights to record.
To check one recording without an account, open it in the free session viewer. It works out CVHR in your browser.
When should you see a doctor?
See a doctor if, across several nights:
- You see a sawtooth in your pulse that lines up with oxygen dips.
- You also snore loudly, someone has heard you stop breathing or gasp, or you're exhausted during the day.
Bring a few weeks of recordings, not one night. Here's how to share them.
Not a medical device. Does not diagnose, treat or prevent any condition. Discuss results and changes with a clinician.
References
- Guilleminault C, Winkle R, Connolly S, Melvin K, Tilkian A. Cyclical variation of the heart rate in sleep apnoea syndrome. The Lancet. 1984;323(8369):126-131. doi:10.1016/S0140-6736(84)90062-X
- Hayano J, Watanabe E, Saito Y, et al. Screening for obstructive sleep apnea by cyclic variation of heart rate. Circulation: Arrhythmia and Electrophysiology. 2011;4(1):64-72. doi:10.1161/CIRCEP.110.958009