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Can CO2 drive Hypopnea? - Printable Version

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Can CO2 drive Hypopnea? - Arik - 02-14-2020


Can CO2 leftovers in the mask drive Hypopnea as they drive Centrals? Is this phenomena typical to FF masks or can happen with any mask?

See attached screenshot with few Hypopneas that look to me somewhat similar to the CO2 driven Centrals in Fred's explanation in a previous post.


RE: Can CO2 drive Hypopnea? - bonjour - 02-14-2020

There is a thing called Central Hypopneas that is (shouldn't be) an optional parameter for PSG to evaluate for. None of our CPAPs evaluate for it.
A complete stoppage is easy to check for, there is no flow.
Hypopneas are a partial blockage or reduction in flow. The rule says 50 to 80% reduction in comparison to normal. What is normal? The obvious way is to take a moving average. Obviously if this average contains disturbed breathing the average is flawed.

This also applies at the 80 to 99% reduced breathing Apneas

Why all the above, because I believe the hypopneas criteria was met earlier than the flags and more often.

You have identified Central Hypopneas which you identified by spotting the typical cyclical breathing pattern of CO2 near the apneic threshold.

In a normally functional mask, any mask, the venting should be sufficient to prevent this. Should the vents be compromised in any way, such as condensation build up, which will increase CO2 in the mask and subsequently rebreathed. Note this CO2 buildup does not cause centrals, it treats them, at least where the CO2 apneic threshold is in play.

It is low levels of CO2 in the blood that suppresses our drive to breathe, not high levels as you suggest in your OP.

Seeing this pattern I recommend reducing the efficiency of your device to reduce the amount of CO2 being flushed from your system. This is best done by reducing EPR or PS or Flex depending on machine by 1

RE: Can CO2 drive Hypopnea? - Arik - 02-14-2020

Thanks, Fred, for the fast response.

Not sure I understand why it is low levels of CO2 in the blood that suppresses our drive to breathe, not high levels.

For this specific case, I was trying ResMed F30 for few days as a potential replacement for my FF Dreamware. It turned out that it increased my AHI by far (from less than 1 to 3-5), creating Centrals and Hypopneas that were not with the Dreamware. So I returned it back and trying now Amara View. 


RE: Can CO2 drive Hypopnea? - Sleeprider - 02-14-2020

Your body uses CO2 to drive respiration (not oxygen). Look up the terms "hypercapnea" and "hypocapnea". As CO2 levels rise in the blood stream, inferring poor ventilation, chemical changes occur that increase the respiratory drive. Similarly, if CO2 levels drop, inferring a high rate of ventilation, the respiratory drive decreases. EPR increases respiratory ventilation exchange. As the pressure difference between inhale and exhale increase (also called pressure support), the lungs more efficiently exchange CO2, reducing CO2 in the blood stream. This decreases the respiratory drive in some people, and may result in hypopnea or central apnea as the need to breathe is diminished. By reducing EPR or pressure support, the "flushing" effect of the additional ventilation is reduced, so CO2 remains better balanced. This will reduce H and CA events in sensitive individuals.

RE: Can CO2 drive Hypopnea? - SarcasticDave94 - 02-14-2020

FWIW my 2 cents on "why it is low levels of CO2 in the blood that suppresses our drive to breathe, not high levels". Our brain is looking for a low level of CO2 to trigger the breathing mechanism to fill the lungs with oxygen laden air and expelling waste air laden with CO2. The low level trigger status is likened to the low fuel light in our cars. The low fuel light is turned on only when fuel level is low enough to illuminate it.

Our CPAP machines blow air in forcing out more CO2 than our brain perceives as normal. Since the low CO2 signal is delayed, we'd get a Central Apnea/CA as a result.