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AHI definition in SHHS

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jbehar +0 points · 2 months ago

Dear Mike/Stephanie,

I would like to know how the variable ahi_a0h3a was elaborated from the original scoring guidelines used in defining apneas and hypopneas in the SHHS. Do you have some pointer for me? Do you know of any publication that looked at re-scoring this dataset according to AHI2012 recommended rule and how far the AHI was from ahi_a0h3a?

Definition of ahi_a0h3a: https://sleepdata.org/datasets/shhs/variables/ahi_a0h3a

Definition of the rules used to score apneas and hypopneas: https://sleepdata.org/datasets/shhs/pages/mop/6-627-mop-scoring-respiratory-events.md

In particular the ahi_a0h3a hypopneas take a 3% SpO2 threshold for hypopneas whereas the original scoring guidelines use a 2% threshold.

Thank you, Joachim

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mrueschman +0 points · 2 months ago

Joachim,

I'm not aware of any projects/publications that looked to re-score parts of the SHHS dataset. The ahi_X variables, like ahi_a0h3a, were derived from the counts of apneas and hypopneas from the original scoring. These were created to mimic AHIs from other cohorts where we normally use "all apneas" and "hypopneas with >=X% oxygen desaturation" as the AHI numerator. The scoring software output counts of respiratory events that met different desaturation thresholds and with/without arousals factored in. You can see this by looking at the variables that comprise the ahi_a0h3a calculation.

Mike

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jbehar +0 points · 2 months ago

Hi Mike,

Thanks for the prompt feedback.

Ok so I understand from your response that the ahi_a0h3a follows the rules you defined here (https://sleepdata.org/datasets/shhs/pages/mop/6-627-mop-scoring-respiratory-events.md) but for a 3% desaturation threshold for the hypopneas (adjusted from the computer program to output this variable). Is that correct?

Did you elaborated this variable (ahi_a0h3a) as part of the original SHHS study or was it created at a later date by you/another research group?

Thanks again for your help, Joachim

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mrueschman +0 points · 2 months ago

We did create ahi_a0h3a at a later date. Prior to that, a variable like rdi3p was commonly used as the primary AHI indicator in SHHS, though this variable required that apneas also have an associated >=3% desaturation (like the hypopneas). The meaning of "RDI" has also shifted a bit over time, so the variable name and its approach for including apneas had become a bit antiquated.

Just to give you a sense of how the scoring program works and how the different AHIs are computed, here's another description. The study is scored once. You cited the rules about hypopneas requiring an associated >=2% desaturation. The scoring program (Profusion) would then give us different variables ("components" for AHI calculations) representing counts of specific event types at specific desaturation/arousal criteria. For instance, we might get something like the following in an individual sleep study.

  1. 50 total hypopneas (>=2% desaturation criteria as based on scoring manual)
  2. 40 hypopneas with >=3% desaturation (subset of #1)
  3. 25 hypopneas with >=4% desaturation (subset of #2)

Thus, if I want a "total AHI" (all hypopneas) I might use #1, if I want ahi_a0h3 I am going to use #2 (for the hypopnea component), and if I want ahi_a0h4 I am going to include #3.

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jbehar +0 points · 2 months ago

Thank you Mike. That's clear, Joachim

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