Sleep 7.4 Cardiopulmonary Coupling and Sleep Apnea Detection

Learn how cardiopulmonary coupling (CPC) helps detect and classify sleep apnea, with highlights from key validation studies.

Video Breakdown:

00:00 CPC and Apnea Detection

01:17 Sympathetic Activity in Apnea

02:02 Differentiating Obstructive vs Central Apnea

03:09 Correlation & Validation Studies

04:00 FDA-Cleared CPC Methods

Now I wanna talk a little bit about the CPC and apnea and hypopnea index. And this was, I think, Robert Thomas and his group recognized that people with sleep apnea had definitely, greater preponderance of this low frequency coupling here.
And with those individuals with complex sleep apnea, particularly a central sleep apnea component, you had this very stable periodic metronomic oscillation in both the respiration heart rate changes. And so we thought, oh, there may be a way to use this cardiopulmonary coupling to then differentiate or even assess for the presence of sleep apnea or complex sleep apnea.
And so this was the publication that came out in 2007, again, by the same group. And the last part when I was talking about the sleep stages was on the left side here. But now when it came to apnea detection, there was a different algorithm used altogether. In this case, this is where the low frequency coupling has a much greater component compared to the high frequency components.
So the ratio is greater than 30, which you notice in the CAP is, the ratio is like 0.5, so there's a marked difference here. The apnea hypopnea is characterized with a much greater sympathetic nervous activity. So this is a marker for general apnea or hypopnea, and he called it elevated LFC.
And then because central Apnea has much more of this metronomic stable oscillation, he was able to categorize the low frequency range where there's a consistent frequency for lasting for five windows, and that he called it the narrow band, ELFC. So this is a summary of what comes out for the CPC cycle.
So high frequency associated with stable sleep, low frequency, very low frequency I didn't talk about, but that's correlated with REM and wakefulness. But then in order to differentiate for obstructive sleep apnea, central sleep apnea, he had this broadband definition, ELFCBB, for broadband. This indicates obstructive sleep apnea, sympathetic surges, respiratory effort, etc. And this narrow band, which corresponds with central sleep apnea, and this often physiologically, is related to the chemo reflex hypersensitivity. I will talk about this in the future talks when I talk about sleep apnea. Now, this is a report, an example of this where, this CPC is used for detecting sleep apnea.
And again, in this individual, you see no high frequency blink. You see a lot of unstable sleep as demarcated by this elevated LFC. But then you could see the broadband component, it's hard to read here, but this is fragmentation. And you can see that this is, associated with obstructive sleep apnea.
And then the one that has to do with periodicity or the narrow band, which talks about the narrow band that you see with central sleep apnea is revealed here as well. And it turns out this method using the CPC method, either EKG or PPG, is actually really good and does pretty well against a PSG-based
determination of Apnea hypopnea index. So AHI of 3% here. So this is a study published in 2021. This used an Apple study cohort of about 833 individuals, and this is, uh, a comparison of the PSG-based AHI and the CPC-based AHI and you can see that the correlation is really strong with a Pearson correlation of 0.972 and an RSC, with an AUC of about 0.98 or nine six, which is really strong.
So this indicates that cardiopulmonary coupling does a pretty good job of detecting sleep apnea, at least when using the PSG as a gold standard. And this has been used by SleepImage and there's a ring based methodology, and a publication done by 2023, which again shows a pretty good correlation with a Spearman correlation about 0.9. This is FDA cleared for diagnosing sleep apnea and managing sleep disordered breathing.

Course episodes

Sleep 7.1 Understanding Cardiopulmonary Coupling in Sleep Studies

Sleep 7.2 Cardiopulmonary Coupling: Sleep Staging Classifications

Sleep 7.3 High vs. Low Frequency Coupling in Cardiopulmonary Physiology

Sleep 7.4 Cardiopulmonary Coupling and Sleep Apnea Detection

Sleep 7.5 Traditional vs. Modern CPC Methodology

Sleep 7.6 Cardiopulmonary Coupling in Sleep: Strengths, Limitations & Future