05-03-2018, 06:27 PM
Expiry Pressure Relief - Does it really work?
Some time ago I initiated a thread called Can EPR use cause Central Apnea Events? In that thread I asked for comments on another thread in another forum titled Not Understand EPR Setting. I got some feedback from posters here that if I can summarize briefly would be that in some individuals EPR can cause an increase in CA events, but in others it offers some advantages.
With some personal experience and some further research I have started to question the value of EPR in treating apena in general. I tried two treatment methods over a period of several days. I found that to get similar AHI results my 95% IPAP pressure had to be about 2.5 cm higher when I used 3 cm of EPR. In other words the IPAP therapy pressure to control apnea increased almost one for one by the amount of EPR used. Said another way, apnea events were controlled by EPAP pressure not IPAP. I then have wondered if my experience was unique or if it reflected that of the typical apnea sufferer. I found one very interesting article written by two sleep specialists from the University of Southern Florida Sleep Apnea Treatment Unit. They concluded somewhat surprisingly that the point in the inspiration and expiration cycle where apnea was most likely to occur was near the very end of the expiration cycle, and that if anything pressure should be maintained higher during expiration compared to inspiration. They even suggested that therapy could be improved if BiPAP machines would allow setting a negative pressure support, rather than a positive pressure support. I take this as a validation to my own conclusion that the EPAP pressure is the one that is most important in treating apnea, not the IPAP. And with a ResMed APAP the only way you can compensate for EPR use is to allow a higher IPAP therapy pressure. In other words the price you pay for EPR is increased IPAP pressure. In any case here is a link to the article. Warning. It is a bit of a tough read...
Expiratory and Inspiratory Positive Airway Pressures in Obstructive Sleep Apnea: How Much Pressure is Necessary? A Different Point of View
With respect to EPR and pressure causing increased central apnea, I'm having trouble finding a way to justify that this is a significant effect. Why? Well lets take the case of using EPR first. Lets say that by using an EPR of 3 cm you empty the lungs to a level 3 cm lower in pressure, and to compensate for that you pressurize the lungs to a level 3 cm higher. That adds about 6 cm of pressure effect oxygen which is said to be the cause of the centrals. However this needs to be put into context. Atmospheric pressure at sea level in our CPAP units of cm of water is about 1030 cm. 6 cm in comparison is an increase of about 0.1%. Not very much. And as another comparison when we go from a low pressure weather condition to a high pressure condition this is an increase of about 35 cm pressure. If 6 cm is significant, then changes in weather should have an effect that is about 6 times worse. And then there is the issue of traveling from say Denver Colorado to sea level. This is a pressure increase of about 155 cm of water. This should have a huge effect in increasing centrals. I recently traveled to an area about 1300 feet lower than where we live. I had the best AHI's I have ever had. There was a large reduction in centrals, no increase.
The same argument could be made for simply running higher pressure such as 20 cm vs 14 cm. 6 cm is just as insignificant as the 6 cm one could attribute to EPR. Bottom line is that I am having a hard time accepting that in the small pressures involved in CPAP that it really can have that big of an effect on oxygen levels and central apnea. That said, I do know that it is at least claimed that titration tests for treatment pressure frequently report increased centrals with increased pressure. I wonder if it is possible that due to the short duration of a titration test ( an hour or so at each pressure?), what is seen is a transient increase, that is not sustained when the pressure is used for days, months, and years?
So, my answer to the question of whether or not EPR works, my thoughts are: No, it doesn't really help with treatment, and it results in a requirement to increase treatment pressure almost one for one for the amount of EPR that you select. You pay for using EPR with an increased mask pressure and the effects that can have on leaks and comfort. And on the other hand, I find it hard to believe that it has any significant detrimental effects on central apnea frequency.
Comments?
With some personal experience and some further research I have started to question the value of EPR in treating apena in general. I tried two treatment methods over a period of several days. I found that to get similar AHI results my 95% IPAP pressure had to be about 2.5 cm higher when I used 3 cm of EPR. In other words the IPAP therapy pressure to control apnea increased almost one for one by the amount of EPR used. Said another way, apnea events were controlled by EPAP pressure not IPAP. I then have wondered if my experience was unique or if it reflected that of the typical apnea sufferer. I found one very interesting article written by two sleep specialists from the University of Southern Florida Sleep Apnea Treatment Unit. They concluded somewhat surprisingly that the point in the inspiration and expiration cycle where apnea was most likely to occur was near the very end of the expiration cycle, and that if anything pressure should be maintained higher during expiration compared to inspiration. They even suggested that therapy could be improved if BiPAP machines would allow setting a negative pressure support, rather than a positive pressure support. I take this as a validation to my own conclusion that the EPAP pressure is the one that is most important in treating apnea, not the IPAP. And with a ResMed APAP the only way you can compensate for EPR use is to allow a higher IPAP therapy pressure. In other words the price you pay for EPR is increased IPAP pressure. In any case here is a link to the article. Warning. It is a bit of a tough read...
Expiratory and Inspiratory Positive Airway Pressures in Obstructive Sleep Apnea: How Much Pressure is Necessary? A Different Point of View
With respect to EPR and pressure causing increased central apnea, I'm having trouble finding a way to justify that this is a significant effect. Why? Well lets take the case of using EPR first. Lets say that by using an EPR of 3 cm you empty the lungs to a level 3 cm lower in pressure, and to compensate for that you pressurize the lungs to a level 3 cm higher. That adds about 6 cm of pressure effect oxygen which is said to be the cause of the centrals. However this needs to be put into context. Atmospheric pressure at sea level in our CPAP units of cm of water is about 1030 cm. 6 cm in comparison is an increase of about 0.1%. Not very much. And as another comparison when we go from a low pressure weather condition to a high pressure condition this is an increase of about 35 cm pressure. If 6 cm is significant, then changes in weather should have an effect that is about 6 times worse. And then there is the issue of traveling from say Denver Colorado to sea level. This is a pressure increase of about 155 cm of water. This should have a huge effect in increasing centrals. I recently traveled to an area about 1300 feet lower than where we live. I had the best AHI's I have ever had. There was a large reduction in centrals, no increase.
The same argument could be made for simply running higher pressure such as 20 cm vs 14 cm. 6 cm is just as insignificant as the 6 cm one could attribute to EPR. Bottom line is that I am having a hard time accepting that in the small pressures involved in CPAP that it really can have that big of an effect on oxygen levels and central apnea. That said, I do know that it is at least claimed that titration tests for treatment pressure frequently report increased centrals with increased pressure. I wonder if it is possible that due to the short duration of a titration test ( an hour or so at each pressure?), what is seen is a transient increase, that is not sustained when the pressure is used for days, months, and years?
So, my answer to the question of whether or not EPR works, my thoughts are: No, it doesn't really help with treatment, and it results in a requirement to increase treatment pressure almost one for one for the amount of EPR that you select. You pay for using EPR with an increased mask pressure and the effects that can have on leaks and comfort. And on the other hand, I find it hard to believe that it has any significant detrimental effects on central apnea frequency.
Comments?
That applies more to me then.
