CPAPtalk.com

LoQ wrote:

Hose_Head wrote:Relative humidity is defined as "the ratio of the actual amount of water vapour in the air to the amount it could hold when saturated expressed as a percentage OR the ratio of the actual vapour pressure to the saturation vapour pressure expressed as a percentage." (http://www.bom.gov.au/lam/humiditycalc.shtml) The saturation vapour pressure is directly related to temperature.

According to Charles Law, when you compress a gas (i.e. "air" pressurized by an xpap), the temperature of the gas will rise. As you raise temperature, you increase the saturation pressure for water vapour and you decrease the relative humidity. Thus, when an xpap increases pressure to, say 10 cm h2o above atmospheric pressure, the temperature of that air will increase by some small amount, and the relative humidity of that air will be correspondingly lower. Use of a humidifier can compensate for this reduction in relative humidity. I haven't calculated the effect, but would guess that the actual change due to pressure change is small, perhaps on the order of 5 to 10% relative humidity.

It's way more complicated than your explanation suggests, but I probably am not capable of presenting a thorough case. Here are a few points. You omit that the water vapor capacity is indirectly related to pressure, that is, air at a higher pressure and same temperature can hold less water vapor. When you increase the pressure on air in a closed system, the relative humidity goes up if the temperature stays the same. When you increase the temperature of air in a closed system, the relative humidity goes down if the pressure remains the same.

My point was that the pressure does NOT stay the same. Whether the two effects offset one another is the question. I haven't tried to calcuate it but my guess is that they do not. The residual effect is likely to be small, but perhaps noticeable for some.

LoQ wrote: What we have here is not really a closed system, and I'm not sure how to deal with it. Let me just say that if you push air that is able to remove moisture from skin past someone, the faster you push it, the more dry it will feel to them. Air in people's homes is generally capable of removing moisture from their skin. If it wasn't, it would be downright uncomfortable because sweat would not evaporate. Some people are more tolerant of moisture loss than others, and that is the chief reason why people choose differently with regard to humidifiers. Their choice is obviously affected by their pressure setting and the relative humidity inside their home.

I think the point that's been made by others on this issue is that there really isn't more air pushing past the tissues in your nose and throat. The tidal volume of your breathing with and without cpap should be very similar. Your nasal passages are designed to add moisture to the air when you inhale, offsetting the drying effect of room air. The question we are struggling with is why this doesn't seem to work when people use cpap. This raises the question, do those using full face masks have a greater need for humidification than those using nasal or pillow masks?

Another possible variable:

I've used several masks and it seems that with pillows I need need to turn the humidifier on 1 or 2 to be comfortable. With a nosebag or ffm, I don't seem to need it.

I've speculated--to myself until now-- that the pillows act like a nozzle. Forcing the same volume of air through a smaller opening means the air moves faster; furthermore the nozzle may direct the stream of air onto a smaller area of nasal mucosa.

Just a supposition though.

gvz wrote:

It is our unalienable rights,
from God,
the Declaration of Independence,
the Constitution,
and Slinky,
that we may have humidity.

"Give me humidity, or give me death."

People sometimes use "LOL" but I really did laugh out loud when I read that today. Thank you.

"Give us this day, our daily Humidifier. And forgive us of our apneas. And lead us not into dehydration."

Well, that is not as funny as yours. But thanks again.

"And lead us not into dehydration....forgive us our apneas.....hahahahahaha hope i don't get mixed up in Mass and say the wrong words!"

I have a question, what does "passover mode" mean...and how do I do that on my DeVilbissAuto?

We don't usually use home heating or air conditioning, and our indoor humidity is 50-60%. Normally, I set my S9 humidifier with Climate Control off, at 4.5 humidity level with no heat. It feels comfortable at that level (never "wet") and I don't get rainout. I am sick with a cold right now, so last night I cranked the humidifier up to 5.0 and had the heated hose set at 76 degrees. That allowed me to breathe through my nose with a nasal mask, and I slept pretty well.

It'll be interesting to see what settings work best during the winter. I tried Climate Control set to on when I first got this machine in June, and it was much too dry for me. That feature may work better in the wintertime, though.

Google 'seder' foods for your late-night snack.

Junebug999 wrote:I have a question, what does "passover mode" mean

Passover humidification means that there is water in the humidifier but it is not turned on (there's no heat).

roster wrote:

GumbyCT wrote:

Physician wrote:I have never needed nor used a humidifier with either the RemStar nor the S9 Autoset. It seems some members use the humidifier because it was included with the machine.

May I ask why you would care if others used a humidifier on their machine or not? Isn't that a little out of your span of control?

Gumby, Isn't your wanting to limit Physician's span of control a little out of your span of control?

Am I out of my span of control by commenting on Gumby's span of control over Physician's span of control?

Several people who have acquired the latest Respironics and ResMed machines with advanced humidity control features have reported that the new devices use less water. Assuming that the new algorithms work properly to deliver an appropriate amount of humidity, that means people were using too much humidity when selecting their settings. I do believe that is the case with many CPAPers. cpaptalk members are probably less likely to overuse humidity because of their study, knowledge, and experience.

Please sign me up for a front row seat for the Cage Match between Gumby and Rooster. Rooster should be able to inflict some damage by pecking into Gumby's torso, although I would imagine Gumby could tie up Rooster with his superior flexibility.

I use mine the Old Fashioned Way, without heat, without water, doesn't matter if I'm using a nasal mask or FF. I keep it hooked up to act as a noise muffler for the air flow. I keep the room temp at 65 degrees F, year around. De-humidifier running 24/7 in basement at 50 % HUD. Jim

I realize it's a little early in the season, what with Hanukkah not even begun yet, but how come nobody's come up with a good joke about "passover mode?"

Not to beat the dead horse any further (it's drawing flies), but I think the issue of humidification probably varies depending on the type of mask one wears. Mouth breathers and part-time gapers wear FFMs while nose-breathers who can manage to keep their trap shut all night seem to prefer nasal pillows. I hang with the latter crowd. All of us live in fear of catching a cold or getting the old schnoz congested. Being able to crank up the humidity to just below saturation helps to keep the semisolid mucus, cat hairs, pollen, dander and dust mites that collect there in a semisolid state, allowing the maintenance of a low-restrictive airway. And as has been discussed already, humidification might not be necessary under normal ambient conditions.

I expect some bright individuals have thoroughly investigated the dynamics of airflow through the human sinuses.

I needed a lot of humidification wearing my beloved pillow mask and need little wearing the RespCare Hybrid. I need more in dry winter (indoor heated) air, much less in humid summer (AC) air. I need max when I get a cold. Without the right amt of humidification, my nasal passages dry out and then bleed; with too much, I get rainout in my pillows.

To each his own.

In my unscientific observation, in Houston (humidity average 65-80%) if I did not have the humidifier on my S9 Auto set to 3 (middle setting), I would suffer from nosebleeds and general sinus discomfort during the day. Higher setting had no effect (seems obvious if the humidity is 80%) and lower setting just dried me out badly, causing cracking/nosebleeds.

Now that I'm in Dallas (average humidity 35-55%), I have the humidity setting turned off but still put water in the tank, basically causing a passive increase in humidity. I eventually arrived at this setup after suffering horrible nosebleeds with the humidity set to the same setting as I did in Houston. I stepped it down one notch every few nights and found that I improved each time. A week after setting the active humidifier to off, I was sleeping so well again that I forgot about it...and forgot to fill my tank back up, resulting in two days of very dry sinuses and some moderate nosebleed issues. Refilled the tank and left it set to off and haven't had a single problem in over a month now with no other variations in sinus-related behavior or climate.

I suspect there are two primary factors involved here:

1. The drying effect of higher air turbulence and velocity (identical to blowing on your hands to dry them after washing them) relative to the rate at which your sinus mucous membranes hydrate themselves.
2. The ambient humidity where you live.

With regards to the first point, passive humidification from simply having water in the tank might be enough. Turning on the active humidifier helps when that isn't enough.

As for the second point, when you present a completely different humidity environment at night versus what you experience during the day, you traumatize your sinus mucous membranes. Again, my unscientific observation is that having the higher humidity setting in a dry climate caused me the same issues I dealt with when I originally moved to Dallas from Houston back before I was on CPAP and the same problem I have had for years going to visit my grandmother in a drier part of the south. Adjusting the machine so that I have only a slightly higher than ambient humidity level keeps my sinus and throat from drying out while not going so far overboard that I am having to radically adjust to the dry air while I'm out and about during the day.

These machines can potentially adjust for some environmental variables but they aren't designed to maintain a set humidity level at the mask. Otherwise, they'd have a sensor built into the mask and an actual humidity setting in the user interface.

Just my two (longwinded) cents.

P.S. Physician, I suspect that the reaction you've gotten in this and other threads here may be due to two things:

• Picking a forum name like Physician, regardless of truth, implies authority in this context and seems pretentious and designed to lend weight to your posts which might not otherwise exist purely on the merits.
• Your choice of verbiage, while possibly a result of attempting to avoid implied meanings or leading questions, generally just makes you sound like you're either asking rhetorically to confirm your own opinions or that you're unwilling to just chat openly with us.

Just sayin.

I thought "passover mode" was when it rains during Easter Egg Hunt! jlk

gvz wrote:

It is our unalienable rights,
from God,
the Declaration of Independence,
the Constitution,
and Slinky,
that we may have humidity.

"Give me humidity, or give me death."

People sometimes use "LOL" but I really did laugh out loud when I read that today. Thank you.

"Give us this day, our daily Humidifier. And forgive us of our apneas. And lead us not into dehydration."

Well, that is not as funny as yours. But thanks again.

Yes, it WAS as funny.

Both of you, carbonman and gvz... well, as I've said before (always affectionately!)... "Crazy people. I'm on a message board with crazy people! And I'm lovin' it."

N'Awlins is noted for humidity.

Sometimes I use a humidifier, and some times I don't.

Mid-May, I started waking up with rain-out. So I went with passover humidity. Used quite a bit less water.

Beginning of September, I started waking up with dry nose and throat. So I started heated humidity again.

I use it when I need it and don't use it when I don't.

It all depends on who you are and where you are. Everyone's needs are different.

The original Passover occurred in the desert. Low humidity.