Low Tidal Volume reading

[rhwoe]

About a year and a half into my CPAP therapy on my current Resmed Air10, it began making a whistling or whining sound. After checking, it was coming from the blower unit. Suspecting a bad bearing. The machine is still working good except for the annoying noise. However, I noticed a significant drop in my Tidal Volume readings. AHI is still about the same as before. 

So, I ordered a replacement blower and installed it. The Tidal Volume readings remained the same. So nothing has changed with the Tidal Volumes, except for no whining bearing noise. Very quiet. Should I worried about the Tidal Volumes and keep using my machine? 

All other readings seem fairly "normal". My older Resmed Air10 the readings were within my range. Thanks in advance for any and all suggestions or thoughts!

Current Resmed Unit                                       Older Resmed Backup Unit 
Tidal Volume                                                  Tidal Volume
Min:  20.00                                                     Min: 200
Med:  260.00                                                  Med: 540
95%:  500.00                                                  95%: 960
99.5%: 680.00                                                99.5%: 1400
 
Total time in apnea                                          Total time in apnea
00:01:57                                                         00:00:14
Time over leak redline                                      Time over leak redline
0.000%                                                           0.135%

[BoxcarPete]

Are you certain the settings the same? A difference in EPR might account for a change in tidal volume, from my limited experience with that feature my TV increased by like 80% but I never used it sleeping (was just relaxed but awake) so I can't say for sure if the effect still applies.

[rhwoe]

When I compared to my old machine that I used for backup, I adjusted the settings to be the same. Also, the masks the same. This all seemed to happen when blower got noisy. Suspecting a bad bearing I installed a new blower motor. But the TV readings didn't change. The older TV readings seem to be more in my range. Very baffling to me.

[BoxcarPete]

Then the next thing I would look into is the flow sensor. They are very sensitive, and need to contend with constant air passing them, with fluctuations in that air stream being interpreted as either:

1. Mask vent
2. Air into lungs
3. Air out of lungs
4. Unintentional mask leak

It could be your flow sensor was affected by the vibrations, but unfortunately, I don't think there's much that's user-serviceable about that if it is the problem. A simple experiment you could do would be to take as deep a breath as you can several times in a row to get some vital capacity estimates, and compare the two machines to see if they read the same when you are moving as much air as you can while awake.

[rhwoe]

Thanks! I'll give that try. Let know how it turns out.

[enigmatic]

FWIW this exact problem caused me severe issues that took a long time to solve and fix. I suggest getting a new machine and avoiding the headache (they had them brand new for 200 on black friday). I replaced the blower motor and everything seemed fine on the surface, but in reality it was causing severe effects of hypoventilation that took me a long time to get back to normal. After numerous specialists could not figure it out, the one key that helped me figure it out was the very low tidal volume.

Read all about it here https://www.apneaboard.com/forums/Thread...l-fatigued
in particular post #36

[rhwoe]

One thing I've learned after being on CPAP therapy for 15 plus years is that no two nights are ever the same. I've read lately that sleep specialists are saying to also pay attention to the RERA readings and the effect on quality of sleep. My RERA number is higher whenever the tidal volume reading is lower. Is there a link between the two?

[rhwoe]

I did use the CPAP machine as you suggested in the evening while watching tv and I had higher TV readings. I've also had a pulmonary function test done recently at a clinic. Of course this test is done while awake. I'm confident it's not my lungs. I'll keep making minor adjustments and hopefully won't have to buy another machine. I'd have to pay out of pocket for one. Insurance no longer covers CPAP machines.

Thanks for your advice!

[rhwoe]

Then the next thing I would look into is the flow sensor. They are very sensitive, and need to contend with constant air passing them, with fluctuations in that air stream being interpreted as either:

1. Mask vent
2. Air into lungs
3. Air out of lungs
4. Unintentional mask leak

It could be your flow sensor was affected by the vibrations, but unfortunately, I don't think there's much that's user-serviceable about that if it is the problem. A simple experiment you could do would be to take as deep a breath as you can several times in a row to get some vital capacity estimates, and compare the two machines to see if they read the same when you are moving as much air as you can while awake.

So, I swapped blowers between the old and newer machine to see it was the unit itself causing the low TV reading. As it turns out both TV readings are in the normal range for me, based on my height, weight and gender. I was ready to return the new blower/motor back to Amazon. Don't know what had happened but at least things are looking up. Maybe a sensor as you suggested.