Definition of OAHI in the SHHS variable

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[-] Winda NG +0 points · 3 months ago

Hi Mrueschman

In the dataset, OAHI was defined as OAHI = 60 * ( hrembp4 + hrop4 + hnrbp4 + hnrop4 + oarbp + oarop + oanbp + oanop ) / slpprdp

This includes hypopneas at 4% desaturation index and apneas at any level of desaturation.

I am confused, should the apneas be at 4% as well? or was there a specific reason?

Best Winda

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[-] mrueschman +1 point · 3 months ago

Hey Winda,

The AHI has been calculated a bunch of different ways, as you've probably noticed. In SHHS, something like RDI4P includes obstructive apneas, central apneas, and hypopneas, yet all the events require a >=4% desaturation.

For OAHI and other, newer variables (like the ICSD-3 set of AHI variables), the trend seems to be toward using "all apneas regardless of desaturation" (obstructive or central or both depending on the index of interest), instead of using a consistent desaturation requirement across both apneas and hypopneas.

I think the Medicare AHI definition and current AASM guidelines use this sort of approach.

Hope that helps!

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[-] Winda NG +0 points · 3 months ago

Great, thanks Mrueschman, that definitely helps.

So If I want to use current definitions, the more appropriate variables would be OAHI and AHI (ahi_a0h4)? I looked at RDI4P, it doesn't seem to include RERA.

Best Winda

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[-] mrueschman +0 points · 3 months ago

Winda,

I believe the answer is "Yes", but I am going to ask another member of the NSRR team to comment on "current definitions".

Thanks!

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[-] DanMobley +0 points · 3 months ago

Hi Winda,

Your comment about the more appropriate variables is correct. The OAHI and ahi_a0h4 variables would give3 all apneas regardless of desaturation and hypopnea events with at least a 4% desaturation. The rdi4p variable uses only events with a 4% desaturation. Regarding RERAs, those events were not scored when this study was performed. Hope this helps.

Dan

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[-] Winda NG +0 points · 3 months ago

Thanks Mrueschman and Dan, much appreciated!

Best Winda

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[-] Winda NG +0 points · 3 months ago

Hi again Mrueschman

I wonder why for oahi at baseline, n is equal to 5,106; but for ahi_a0h4 at baseline, n is equal to 5,804? Shouldn't they have the same "n"?

Sorry to trouble you! W

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[-] Winda NG +0 points · 3 months ago

Also, how was the apnea defined? I think current guideline is at least 90% reduction of airflow for 10s... But not sure about the shhs dataset. Is it "airflow drop to 25% of baseline, for at least 10s"?

Thanks Winda

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[-] mrueschman +1 point · 3 months ago

Winda,

The Ns are different on those variables because "oahi" had some sort of filtering applied to it based upon the quality of the sleep study signals (e.g. oximqual). "ahi_a0h4" did not have any filtering applied. I don't know the exact set of filters used on the older variables. "ahi_a0h4" was created more recently.

The scoring rules are laid out in the Manual of Procedures. Here's a page that describes respiratory event scoring: https://sleepdata.org/datasets/shhs/pages/mop/6-627-mop-scoring-respiratory-events.md

Let us know if you can't find sufficient description in those documentation pages.

Mike

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[-] Winda NG +0 points · 3 months ago

Hi Mike

Thanks for clarifying. The only difference between oahi and ahi_a0h4 seems to be the filtering, and it makes sense to me to include the filtering. Do you know if there's a similar RDI/AHI variable with the filtering applied?

Best Winda

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[-] mrueschman +1 point · 3 months ago

"oahi" only contains obstructive apneas, while "ahi_a0h4" contains both obstructive and central apneas.

These two variables are very similar, save for the filtering:

https://sleepdata.org/datasets/shhs/variables/oahi https://sleepdata.org/datasets/shhs/variables/ahi_o0h4 (I notice the calculation incorrectly lists the 3% variables, but the values appear correct)

Variables like "oai0p" and "cai0p" also have filtering. The primary AHI/RDI variables used in SHHS1, like "rdi3p", do not appear to always have filtering present.

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[-] Winda NG +0 points · 3 months ago

Hi Mike

The mop file is very useful, thank you. I think I now understand what the filtering is for. Some notes below for others to check!

**Arousals in REM unreliable: when EMG is artifactual or absent during all or REM portion of the study.

Respiratory events/RDI unreliable: when due to the technical quality of the respiratory signals, distinctions between hypopneas and normal breaths are equivocal in over 20 % of scored events ; also when the quality of the oximetry signal raises doubts about actual magnitude of desaturation linked with over 20 % of respiratory events (unstable baseline).

Apnea/hypopnea unreliable – when airflow signal is artifactual or absent for over 20 % of scored respiratory events.**

I am not sure which variables were used for filtering; but it seems like this filter "airqual >2" was used for OAHI

Thanks again Mike! Now I can address the reviewer's comments!

Best Winda

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[-] mrueschman +0 points · 3 months ago

Glad this helped!

Based on my experience from other, older datasets, filtering based on "airqual" sounds logical.

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[-] Winda NG +0 points · 3 months ago

Many thanks =)

W

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