Is it possible to make a non-invasive ventilator?

[Roger Feeley]

I drove my daughter to work today. We often go on some intellectual exercise and today it was whether it would be possible to make a home brew ventilator. we read about Italy running short of ICU beds and ventilators.

Let’s assume that we have all of Home Depot, Woodcraft and a welding supply at our disposal. Let’s further assume that we have a full wood and machine shop at our disposal. Finally, we can assume that, for a short while, we can have an attendant.

in my case, I also have several Arduino microcontrollers on hand as well as the stuff to drive relays. I also have a Microcenter nearby for electronics. Leveraging Home Depot, that gives me sprinkler valves to turn air on and off.

reading about ventilators, there is a lot of nuance and sophistication there. I’m thinking that if operate on the assumption that we have nothing to lose, we can dispense with the details and make something very basic.

feedback is important. We happen to have an Owlet which is a pulse oximitry device for infants. It would be easy to tape the sensor to a hand or foot.

ideas? How basic could you get to save a life? The assumption is that there is no alternative and that something is better than nothing.

[Jamie Buxton]

I don't know what a ventilator does, and I may not be the only one on this board who doesn't. You might describe what one is.

[Roger Feeley]

Sorry,
in cases of severe pneumonia, patients can’t breath on their own and need mechanical assistance. There are two basic flavors: invasive where they intubate and non-invasive where they use a mask.

it seems that someone out there is working on the idea.

https://panvent.blogspot.com/

loads of good information. In the car, I was going a very different direction. Imagine a rubber dust mask with the two filters. Take one filter off and fit a HVLP pump up. If you turn the air flow on, the idea would be to overcome the leakage through the other filter and inflate the lungs. Turn the flow off and the patient exhales. My idea would require the air source, two sprinkler valves, a microcontroller to run the valves and various stuff to control the pressure.

[Frank Pratt]

Well, as the guys on the old Top Gear used to say "how hard can it be?". Disaster & hilarity followed :D

[mike holden]

I am old enough to remember "iron lungs" and the unfortunates that got trapped in them. They were and are non-invasive ventilators. Not sure they are any quicker to supply than the current invasive types.

[Alan Rutherford]

Anyone who has ever used, or slept next to someone who used, a CPAP will have no trouble thinking of one possible solution.

Then there's SCUBA gear.

[Rod Sheridan]

Anyone who has ever used, or slept next to someone who used, a CPAP will have no trouble thinking of one possible solution.

Then there's SCUBA gear.

A CPAP machine, as the name implies, provides continuous pressure, I wouldn't think that would work as a ventilator as you need to have the ventilator exhale.....Rod.

[Roger Feeley]

I am old enough to remember "iron lungs" and the unfortunates that got trapped in them. They were and are non-invasive ventilators. Not sure they are any quicker to supply than the current invasive types.

MIke, I read a piece about the few iron lungs still in use. They’ve been keeping them running using very old parts, some made of leather. The parts are running out and the people who can work on the machines are getting scarce.

[Alan Rutherford]

A CPAP machine, as the name implies, provides continuous pressure, I wouldn't think that would work as a ventilator as you need to have the ventilator exhale.....Rod.

Given some desperation along with a few Arduinos and someone who knows what to do with them, we could work that out.

Ventilators are not my field, but I believe oxygen is usually continuous flow. With a ventilator which provides positive pressure, I'd think exhaling would take care of itself if you interrupt the pressure.

[Edwin Santos]

I drove my daughter to work today. We often go on some intellectual exercise and today it was whether it would be possible to make a home brew ventilator. we read about Italy running short of ICU beds and ventilators.

Let’s assume that we have all of Home Depot, Woodcraft and a welding supply at our disposal. Let’s further assume that we have a full wood and machine shop at our disposal. Finally, we can assume that, for a short while, we can have an attendant.

in my case, I also have several Arduino microcontrollers on hand as well as the stuff to drive relays. I also have a Microcenter nearby for electronics. Leveraging Home Depot, that gives me sprinkler valves to turn air on and off.

reading about ventilators, there is a lot of nuance and sophistication there. I’m thinking that if operate on the assumption that we have nothing to lose, we can dispense with the details and make something very basic.

feedback is important. We happen to have an Owlet which is a pulse oximitry device for infants. It would be easy to tape the sensor to a hand or foot.

ideas? How basic could you get to save a life? The assumption is that there is no alternative and that something is better than nothing.

Some years ago, the hospital where I worked did a capital overhaul of the respiratory therapy department, and part of it was replacing the legacy fleet of ventilators made by Puritan Bennett with a (then) new technology vent called the Pulmonetics LTV. The PB was the size of a full crash cart, and the LTV was about the size of a laptop computer so the difference was stunning. Also the PB required a compressed air incoming line, and the LTV did not. I was in one of the meetings with the Pulmonetics rep and he said the reason for not needing compressed air was that the LTV was turbine driven. The unit had been developed as a transport vent for use among paramedics in the field but the inpatient hospitals caught on and it became widely adopted.

So as a woodworker, thinking about the turbine driven HVLP spray systems, perhaps your home brew brainstorming could make use of a paint spraying system, even a budget one the likes of which you might find in HD or Harbor Freight. Just an idea, and hat's off for your innovative thinking. That's how many great inventions come to be.

As an aside: the Pulmonetics rep told me the unit had basically been invented by a non-medical engineer whose father became ventilator dependent due to COPD. The LTV was a big breakthrough, but his dream was to develop a ventilator small enough to fit in a pocket, so the patient could come closer to resuming normal life activities. Although I will point out, the LTV was still an invasive ventilator used on intubated patients, at least in standard practice.

[Roger Feeley]

After doing some general noodling on the internet, I find that the one site that already linked is about the only diy effort out there. I found one link on the site that some might overlook called “Design of Vinnie”
https://panvent.blogspot.com/2007/12/progress-report.html
Vinnie is a very nice refinement of his general concept.
1. He got rid of an expensive PLC and went to a microcontroller
2. He replaced micro switches on his bellows with hall effect sensors.
3. The layout is really clean.
the woodworking aspect is pretty trivial and easily reproduced in any good shop.
the electronics are simple to reproduce.
I would replace his valves with sprinkler valves if possible. I don’t know how sprinkler valves would handle very low pressure.

[Stan Calow]

CPAP machines do allow you to exhale. One way valves.

[Roger Feeley]

CPAP machines do allow you to exhale. One way valves.
Stan, I know less than I should about CPAP but I’m pretty sure they wouldn’t function as a respirator. But, your post made me think of a variant of CPAP called BIPAP. That’s a CPAP with two pressure settings for inhale and exhale. BIPAP is supposed to help people who need a bit of breathing help. So for mild cases of pneumonia where full ventilation isn’t required, a BIPAP would suffice.

[Roger Feeley]

I’m in the Dc area inside the beltway and I don’t think I’ve ever heard this much low flying aircraft. We get a lot of choppers out of Quantico and other installations around here. Usually, I hear a half dozen per day. Today it’s been every ten minutes or so.

[roger wiegand]

All ICUs already have non-invasive ventilators. They are insufficient for the kind of respiratory failure that SARS-CoV-2 (the virus causing COVID-19) causes, so the current recommendation for severe cases in the ICU is to intubate as early as possible. What's scary is that people are recovering from the respiratory failure only to die from as-yet-unexplainable heart failure. That report got my attention!

[Bobby Logan]

Cuirass or Curass ventilator.

[Roger Feeley]

All ICUs already have non-invasive ventilators. They are insufficient for the kind of respiratory failure that SARS-CoV-2 (the virus causing COVID-19) causes, so the current recommendation for severe cases in the ICU is to intubate as early as possible. What's scary is that people are recovering from the respiratory failure only to die from as-yet-unexplainable heart failure. That report got my attention!

well nuts!
Amateur Hour ventilator with intubation scares me.
Roger, could you please provide a link for that report?

[roger wiegand]

well nuts!
Amateur Hour ventilator with intubation scares me.
Roger, could you please provide a link for that report?

Haven't seen it in any official way yet, it was taken second hand from a FB post from a doc taking care of Covid 19 patients in the Seattle area, so anecdotal and not verifiable. I should not have posted it, and I apologize. There was a paper (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)30566-3/fulltext) in the Lancet a couple days ago about co-morbidities in Wuhan, underlying heart disease is an indicator of poor prognosis, but that's not the same thing.

The full post is quoted and discussed in the comments on this blog post (https://blogs.sciencemag.org/pipeline/archives/2020/03/10/time-scales-viral-and-human).

[Roger Feeley]

Cuirass or Curass ventilator.
Bobby,
wow, that interesting. It’s sort of a portable iron lung. I’m not a doctor so I’m hoping one will jump in here. It seems to me that there’s a functional difference between inflating the alveoli with positive pressure and manipulating the abdomen to draw in air. As I understand this virus, the reason ventilation is required is pneumonia which is liquid in the lungs. They talk about three different classes of alveoli. There are the ones filled with gunk and can’t be helpful. There are the unaffected ones. The, in the middle, there are ones with some gunk and are kind of collapsed. I read about how they sort of give the lungs an extra hard jolt of air to inflate the iffy ones and get them going.

So they aren’t just using a ventilator to do routine breathing. They are also using it to increase the lungs ability to exchange oxygen.

This is really interesting stuff.

[Myk Rian]

What's scary is that people are recovering from the respiratory failure only to die from as-yet-unexplainable heart failure.!
I've been in heart failure for several years now, so I have to be extra careful. Hand sanitizer in my pocket at all times.

Interesting conversation topic. I was going to suggest an in a pinch possibility using a small squirrel cage fan, but Edwin's HPLV idea is a good one.

[Bobby Logan]

The curass ventilator is non-invasive and is similar in function to an iron lung. Looks like a turtle shell. By "sucking" the abdomen and rib cage out, they allow airflow into the lungs. Negative pressure vs positive pressure (PAP). Don't know enough to even start to find the plumbing you'd need to make 1.

[Eduard Nemirovsky]

Very time sensitive and interesting topic. Right now in the USA only 94,837 ICU beds and not every bed has ventilator. Maybe 74-75 thousand vents for ICU setting. Maybe another 35-45 thousand operating room ventilators. Assuming around 8% from infected would need acute critical care - we are good to cover all ventilators needs.
Ed.

[Roger Feeley]

Very time sensitive and interesting topic. Right now in the USA only 94,837 ICU beds and not every bed has ventilator. Maybe 74-75 thousand vents for ICU setting. Maybe another 35-45 thousand operating room ventilators. Assuming around 8% from infected would need acute critical care - we are good to cover all ventilators needs.
Ed.

Ed,
I would imagine that the number of ICU beds and ventilators you quoted include those that are in use for other illnesses. The question would then be how many spare ICU beds and spare Ventilators are available to serve Covid patients? I think it’s fair to exclude the units in operating rooms because, again, those are there for a purpose.

Right now the name of the game is,”flattening the curve”. Assume some number of infections. If they all happen at once, the medical system is overwhelmed as it is in Italy. If we can stretch the same number of infections over a long period, the medical system can absorb the load.

[Roger Feeley]

This has been fun. My daughter works for the justice department here in DC in the Office of Legal Counsel. I reported to her what I found online and what I learned here. She sent an email to her boss who is deputy attorney general. She also noticed that sen. Marco Rubio had commented on a potential shortage in icu beds and ventilators so she emailed him as well. She knows him from some previous legislation that they worked on. I guess it pays to know people. We’ll see what happens.

[Mike Soaper]

Many moons ago, perhaps in the early 90's, I was working in a research lab that did a one time diy try of making a external/curass type ventilator. It was made of fiberglass and resin, given the shape and the green color of the resin we also called it a turtle.


If I recall correctly one of the bigger issues then was getting a workable vacuum seal between the shell and the skin of the subject because of varying body shapes.

[Tyler Bancroft]

Very time sensitive and interesting topic. Right now in the USA only 94,837 ICU beds and not every bed has ventilator. Maybe 74-75 thousand vents for ICU setting. Maybe another 35-45 thousand operating room ventilators. Assuming around 8% from infected would need acute critical care - we are good to cover all ventilators needs.
Ed.

Estimates are that ~20% of cases will need hospitalization. Most hospitals in the industrialized world run pretty close to (or at) capacity. The world needs more ventilators, right now.

[Wade Lippman]

Anyone who has ever used, or slept next to someone who used, a CPAP will have no trouble thinking of one possible solution.

Then there's SCUBA gear.

Years ago I developed acute pneumonia from a bad reaction to anesthesia. They put me on what I suppose was a ventilator that was very much like scuba gear. Always wondered if you could substitute.

[Larry Edgerton]

Two small Festool sys Hepa vacuums hooked to a two canister spray mask. In between is a rotary valve with adjustable speed switching the mash from pressure to vacuum. Air going in is clean, air coming out is clean> I could build a rotary valve, still thinking about how to rotate it slowly enough? Or a slide valve, could be operated by hand if need be.

[Malcolm McLeod]

I drove my daughter to work today. We often go on some intellectual exercise and today it was whether it would be possible to make a home brew ventilator. we read about Italy running short of ICU beds and ventilators.

Let’s assume that we have all of Home Depot, Woodcraft and a welding supply at our disposal. Let’s further assume that we have a full wood and machine shop at our disposal. Finally, we can assume that, for a short while, we can have an attendant.

in my case, I also have several Arduino microcontrollers on hand as well as the stuff to drive relays. I also have a Microcenter nearby for electronics. Leveraging Home Depot, that gives me sprinkler valves to turn air on and off.

reading about ventilators, there is a lot of nuance and sophistication there. I’m thinking that if operate on the assumption that we have nothing to lose, we can dispense with the details and make something very basic.

feedback is important. We happen to have an Owlet which is a pulse oximitry device for infants. It would be easy to tape the sensor to a hand or foot.

ideas? How basic could you get to save a life? The assumption is that there is no alternative and that something is better than nothing.

The first thing that comes to mind, "How can this go wrong?!" Or maybe that old mantra, "First, do no harm." Often times, nothing IS better than something.

Use a vacuum? Really?!? Who here knows what happens to the human lung when you apply 100"H2O of vacuum to it? How about just 30"H2O? Anybody want to speculate? ...How about volunteers for the beta-test??

I'd recommend y'all leave the practice of medicine to the Docs. Or at least first make sure your shovel is all primed and ready, with a spot for a grave all lined out in your flower garden. Maybe even dig the hole ahead of time? - - YMMV.

[Larry Edgerton]

Lighten up dude, I'm pretty sure no one here was actually planning on building a ventilator. You take yourself way too seriously.

[Frank Pratt]

Lighten up dude, I'm pretty sure no one here was actually planning on building a ventilator. You take yourself way too seriously.

Lighten up dude, he's just expressing a valid thought.

[Roger Feeley]

Lighten up dude, he's just expressing a valid thought.

Malcom makes a very valid point. I freely admit that I have no medical knowledge but I still think this is a reasonable inquiry. Even if I built something, I wouldn’t consider using it without professional help. I also wouldn’t consider it unless it was the only way to save a life. We are talking about a Hail Mary here.

I’ve done some more research and have made initial contact with a member of the White House pandemic team. For myself, it’s an interesting problem. I ordered a couple of parts to see if I can construct a device.

[Frank Pratt]

Malcom makes a very valid point. I freely admit that I have no medical knowledge but I still think this is a reasonable inquiry. Even if I built something, I wouldn’t consider using it without professional help. I also wouldn’t consider it unless it was the only way to save a life. We are talking about a Hail Mary here.

I’ve done some more research and have made initial contact with a member of the White House pandemic team. For myself, it’s an interesting problem. I ordered a couple of parts to see if I can construct a device.

Should you proceed with this, it would make a very interesting build thread.

[Roger Feeley]

Should you proceed with this, it would make a very interesting build thread.

my first step is to see if I can get a cheap Orbit sprinkler valve to operate on about 2lbs of pressure. I know that I can get a some electrically operated ball valves that will work but I’m interested in seeing if can be done using easily sourced parts. If the valve works, I move on to activating it with a microcontroller. Since I’m most familiar with Arduino and I have a few, that’s where I will start. From there, it’s just more valves and a few sensors.

lets see:
three valves
two Hall effect proximity sensors or Reed switches
one pressure sensor

[Mike Soaper]

You might want to take a look at these, hope it helps.



From a semiconductor mfgr
"Ventilator/Respirator Hardware and Software Design Specification"
https://www.nxp.com/docs/en/application-note/DRM127.pdf



"Googler publishes plans for Arduino-based equipment to help hospitals"
https://www.theregister.co.uk/2020/03/18/diy_ventilator_shortage/

[Roger Feeley]

You might want to take a look at these, hope it helps.



From a semiconductor mfgr
"Ventilator/Respirator Hardware and Software Design Specification"
https://www.nxp.com/docs/en/application-note/DRM127.pdf



"Googler publishes plans for Arduino-based equipment to help hospitals"
https://www.theregister.co.uk/2020/03/18/diy_ventilator_shortage/

Mike, if I do a build, it would ba ‘vinnie’. There are other designs out there but this one seems to be the most doable by many people.

https://panvent.blogspot.com/2007/12...ss-report.html (https://panvent.blogspot.com/2007/12/progress-report.html)

In my imagination, I see some central authority putting together kits of parts and distributing them to people willing to build. With the right parts, any cabinet shop, maker space, woodworker club/guild or school shop could retool and start turning the things out.

Heck, I could move furniture aside in my house and go into production. My situation is a bit unusual. I live in in-law quarters on my daughter and SIL’s land. We have a two story house that’s 960 on the 1st floor but 1300 in the basement which is all shop. The bride and I could move back into the main house and give up the first floor and loft to assembly/testing. Parts could be fabricated in the basement.

But only if it would help. That’s the nut im trying to crack right now. In my gut, I doubt that those in power are willing to consider a DIY solution. I suspect they are only looking at approved, expensive devices. The problem there is that it’s hard to radically expand production on devices that specialized and complex. The manufacturers are dependent on any number of specialized parts so all those manufacturers would have to ramp up as well.

As to efficacy, I freely admit that anything I would build in my basement would have the whistles and bells of a commercial unit. But maybe not every patient requires every feature in a commercial device. If I could provide some core functionality, maybe I can free up a fully functional device for a patient that really needs those features.

Years ago, in another life, I wrote software to translate stock exchange ticker feeds. The only device We had to record and play back the data was a $25,000 AR4500 protocol analyzer. I pointed out to my boss that if that thing ever broke, we would be dead in the water. So he gave $25K to get another one. Instead, I bought a pc based product called Serialtest that worked great for 95% of what we needed and only cost $300. True, it didn’t do everything the AR did but it relieved the AR from the routine stuff. We only pulled the AR out when we needed it’s capabilities. We wound up buying a lot more Serialtests and giving one to every programmer. Our lives got infinitely better because we accepted a bare bones solution.

epilog: I Did a lot of business with Frontline Test Equipment that makes Serialtest. When I retired from Thompson Reuters, I wound up working for Frontline for 7 years. When that ended, the former owner of Frontline recruited me for another venture. All from a 1” classified ad in the back of Byte magazine.

[Mark Hennebury]

https://globalnews.ca/video/rd/f33b6924-692f-11ea-97f0-0242ac110005/?jwsource=cl[/video]

https://globalnews.ca/news/6695286/coronavirus-italy-3d-print-valves/


Engineers 3D-print patented valves for free to save coronavirus patients in Italy

[Bruce Wrenn]

As a person who has spent more than one night in a hospital with pneumonia, I can say it's not fun. Last trip was for eleven days, with antibiotic resistant pneumonia. Finally would up having lung sack scraped. As always, my CPAP went with me to hospital. On fourth or fifth day, someone came around to check on my "non hospital medical device."

[Tom Bender]

Bobby,
They talk about three different classes of alveoli. There are the ones filled with gunk and can’t be helpful. There are the unaffected ones. The, in the middle, there are ones with some gunk and are kind of collapsed. I read about how they sort of give the lungs an extra hard jolt of air to inflate the iffy ones and get them going.


A good sneeze should inflate the alveoli. I've always enjoyed a good sneeze.

[Mark Hennebury]

https://coventors.com/?fbclid=IwAR3XUuo0_twrfzOEqUwgd6c4reTuYWjNSHW9nXsH aRerNZDeJ5F0j0jKd6g


https://vimeo.com/399505511

[Kev Williams]

disclaimer: just thinking out loud...

Seems to me that SCUBA gear would actually work great- except for the fact that what SCUBA does isn't to simply supply air to breathe, it's main(?) function is pressurize the lungs to compensate for the water pressure around your body; the deeper you go the more water pressure-obviously. Now if you simply pressurize the lungs, that's likely (I assume) to cause wayyy more problems. Who wants their lungs exploding? ....

So then-- what about putting the patient in a pressurizeable body suit, that would mimic water pressure-
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so not exactly like this, a GOOD one (first thing I thought of ;) )

Keep the suit at XXpsi positive pressure, then cycle air/oxygen flow into the lungs under pressure, when released the pressure suit would take care of exhaling... totally non-invasive-

[Art Mann]

I have sleep apnea and use a bipap machine that has already been mentioned. It provides positive pressure on the lungs during inhale but releases the pressure during exhale. It takes it a few cycles to adjust to your breathing rhythm, but then it is remarkably well synchronized with your natural breathing. When I had bacterial pneumonia several years ago, I used the machine to help me breathe easier during my waking hours and it was pretty effective. I would say it is better than nothing and might actually save someone's life, especially if you adjusted the inhale pressure upward as I did. I am not recommending it could be used as an alternative to hospitalization though.

[Frank Pratt]

AvE discusses making a ventilator here: https://www.youtube.com/watch?v=N1OFMZDNKvU

[Jared Sankovich]

Say this today. Made me think of this thread

https://youtu.be/qqWiykx1dTM

[Kev Williams]

Watching the Nightly News tonight, in one segment a doc explained that- as a last resort- they can tee off a ventilator's tubing allowing them to connect to TWO patients...
https://www.nbcnews.com/nightly-news/video/mass-general-taps-into-emergency-supply-stockpile-as-coronavirus-cases-surge-81210437640
^^^ link to the video, fast forward to 1:10 --

[Bill Dufour]

Now might be. a good time to buy an oxygen concentrator if you ever wanted one. they make 1-5 liters per. minute of 90-95% oxygen out of thin air. Enough to run a SMALL jewellery torch. Probably not too safe around a CPAP machine with greased linkages and sparks in the motors and switches.
It may also be a good time to refill your welding oxygen tanks just in case. Again it may also be a good time to buy a gas welding set or at least the oxygen cylinder if you have been thinking about it. The hoses, torches and acetylene cylinder are optional. At least get one O2 regulator to fit the tank. Some folks run propane with oxygen maybe even natural gas.
Bill D

[Edwin Santos]

A news report says James Dyson, the billionaire inventor and founder of Dyson vacuums came up with a ventilator design in 10 days after being asked to do so by the UK government. He plans to manufacture 15,000 of them. From this image, it looks more sophisticated than a DIY job a woodworker might be able to fashion in his home shop!


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[Mark Hennebury]

https://www.msn.com/en-ca/news/canada/alberta-professors-build-ventilator-prototype-using-shop-vac-home-depot-bucket/ar-BB11KRoJ?ocid=spartandhp

428907

[Stephen Tashiro]

I drove my daughter to work today. We often go on some intellectual exercise and today it was whether it would be possible to make a home brew ventilator. we read about Italy running short of ICU beds and ventilators.

Ventillators used in hospitals are very sophisticated machines. They have several "modes" of operation: https://www.openanesthesia.org/modes_of_mechanical_ventilation/

[Curt Harms]

In a pinch I wonder if you could use an aircraft oxygen mask 'real' oxygen mask, not the 'dixie cup' masks in aircraft cabins. Here's an overview of different types.

Diluter Demand Gets You Higher

Above 25,000 feet, your re-breather mask can't keep the oxygen percentage high enough to keep you safe. Aircraft that operate above 25,000 feet and up to 40,000 feet use a "diluter-demand" oxygen system.

This system uses a face-tight seal to ensure cabin air doesn't unintentionally mix into the mask. The system then automatically mixes cabin air with oxygen to maintain a safe oxygen saturation.

Unlike a continuous-flow system, the diluter-demand mask doesn't constantly pump oxygen. Instead, it only supplies oxygen as you breathe. Since it automatically mixes oxygen and air only as you inhale, a diluter-demand system generally lasts longer than continuous flow.

At 40,000 feet, there isn't enough pressure in the atmosphere to allow your lungs to absorb safe levels of oxygen, even if you're breathing 100% O2. At that point, you'll need some extra pressure.

The Pressure Demand System

A pressure-demand system forces pressurized oxygen into your lungs as you breathe. The high pressure, combined with 100% oxygen, keeps the oxygen's partial pressure high enough for your lungs to absorb a safe level of O2.

Since the system forces air into your lungs under pressure, you'll need to force it back out as you exhale. This is exhausting - it takes a significant amount of force to exhale, you'll be tired after several hours on a pressure-demand system.