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viperdoc(at)mindspring.co
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 Posted: Mon Jan 22, 2007 6:54 am Post subject: Breathing Clean Air - Masks? |
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Rich was correct. Your were rebreathing your own air. Approximately 19% of the exhaled air is O2. 40% is C02. The rest is nitrogen and inert gases. Without having a fresh air source, you were entraining about 15-20% of your exhaled air. If you had taken your blood gas during this exercise you would have seen a minimal drop in your Pa02 (partial pressure of oxygen) and a increase in your PaC02. Ovetime, you will increase your PaC02 from a normal of 40 to 58 to 60% in an hour of doing this rebreathing. Yes the Air Force and Navy Aviators mask have a flapper valve that pops open when you exhale increasing the ambient pressure in the mask. The problem is some of that exhaled air is vented into the fresh air line. Without a fresh gas source you will rebreath a precentage of your concentrated exhaled air. The fresh air source dilutes that concentration. The problem with accumulation of CO2 is that it eventually acts as a narco tic along with cause some other bad physiological things like dysrythemias, siezures, and generalized system hypoxia at high enough concentration. We actually do closed circuit anesthesia to preserve the loss of body heat, on long cases. We use soda lime (sodium hydroxide, potassium hydroxide, and an indicator, calcium and sodium silica in small amounts) or Baralyme as a scrubber to absorb the C02 from the circuit. We supply fresh 02 to the circuit though so that the O2 concentration does not drop to low. We follow serial blood gases to monitor the Pa02 and PaC02 along with other things during the surgery. While you are sucking on rubber, none of that monitoring is taking place nor is it practical.
But to finish this episle, breathing your own exhaled air for a period of time is not good for you. I personally would not recommend just using the aviators mask and hose without a fresh air source. Particularly if you smoke, have smoked, or have a respiratory disease like asthma or COPD. And yes, the FAA does let people with respiratory diseases fly based on certain tests that I am not going into now. but sucking rubber without a fresh air source is not good for you.
Doc
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pilko2(at)btinternet.com
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| Posted: Mon Jan 22, 2007 7:03 am Post subject: Breathing Clean Air - Masks? |
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So now ya'll know !¬
Phew.....................
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jgriffint28(at)cox.net
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| Posted: Mon Jan 22, 2007 7:36 pm Post subject: Breathing Clean Air - Masks? |
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Hey Roger
Do you think we could use the soda lime in the air desiccators on our planes? It removes water too doesn't it?
Jim Griffin
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viperdoc(at)mindspring.co
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| Posted: Mon Jan 22, 2007 8:24 pm Post subject: Breathing Clean Air - Masks? |
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The formulation we use actually releases some water. It does dry the airway out though particularly the Baralyme. Soda Lime is not as bad. The final answer is yes you could.
Doc
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lrob4783(at)bigpond.net.a
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| Posted: Wed Jan 24, 2007 2:18 pm Post subject: Breathing Clean Air - Masks? |
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Hi Doc,
I have also been thinking of scooping fresh outside air and connecting my mask to the pick up but since reading your post am having doubts.
I was working on my boat yesterday and as I always do got out my 3M filtered mask out and readied it for the job ahead when your post sprang to mind.
When I looked at the mask it looked very similar to my MBU-20/P but obviously without the hose and with the filter elements. But internally they are very similar to each other with inlet and outlet valves etc. If what you’re saying is correct then the very same condition which occurs with the flying mask should indeed happen with the particle mask.
The only exception I can see would be if the inlet valve was to leak back into the inlet pipe then you’d have the same re-breathing situation as if you were using a long swimmers snorkel.
So if your mask and valves were to be in good working order do you still think it unadvisable to use it?
Please excuse my ignorance and Thanks for your input.
Lance Robb
NQ Warbirds
Mareeba
Australia
From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Roger Kemp
Sent: Tuesday, 23 January 2007 12:54 AM
To: yak-list(at)matronics.com
Subject: Re: Breathing Clean Air - Masks?
Rich was correct. Your were rebreathing your own air. Approximately 19% of the exhaled air is O2. 40% is C02. The rest is nitrogen and inert gases. Without having a fresh air source, you were entraining about 15-20% of your exhaled air. If you had taken your blood gas during this exercise you would have seen a minimal drop in your Pa02 (partial pressure of oxygen) and a increase in your PaC02. Ovetime, you will increase your PaC02 from a normal of 40 to 58 to 60% in an hour of doing this rebreathing. Yes the Air Force and Navy Aviators mask have a flapper valve that pops open when you exhale increasing the ambient pressure in the mask. The problem is some of that exhaled air is vented into the fresh air line. Without a fresh gas source you will rebreath a precentage of your concentrated exhaled air. The fresh air source dilutes that concentration. The problem with accumulation of CO2 is that it eventually acts as a narco tic along with cause some other bad physiological things like dysrythemias, siezures, and generalized system hypoxia at high enough concentration. We actually do closed circuit anesthesia to preserve the loss of body heat, on long cases. We use soda lime (sodium hydroxide, potassium hydroxide, and an indicator, calcium and sodium silica in small amounts) or Baralyme as a scrubber to absorb the C02 from the circuit. We supply fresh 02 to the circuit though so that the O2 concentration does not drop to low. We follow serial blood gases to monitor the Pa02 and PaC02 along with other things during the surgery. While you are sucking on rubber, none of that monitoring is taking place nor is it practical.
But to finish this episle, breathing your own exhaled air for a period of time is not good for you. I personally would not recommend just using the aviators mask and hose without a fresh air source. Particularly if you smoke, have smoked, or have a respiratory disease like asthma or COPD. And yes, the FAA does let people with respiratory diseases fly based on certain tests that I am not going into now. but sucking rubber without a fresh air source is not good for you.
Doc
--
21/01/2007 5:12 PM
--
24/01/2007 6:48 PM
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viperdoc(at)mindspring.co
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| Posted: Wed Jan 24, 2007 5:13 pm Post subject: Breathing Clean Air - Masks? |
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Lance,
The issue you face with using the aviator's mask without a fresh air source is related to dead space air. The hose on the aviator's mask is is about 18 to 24 inches long. So each time you exhale you push air high in C02 down that hose. Now when you take a breath, you suck that air back in. Then you repeat the process when you again. This process is known a entrainment. There is a push pull action taking place in the hose. If regular respiration takes place without something diluting it out like sticking it out into the wind stream (pressure breathing per say), the PC02 in the hose will gradually become equal the PC02 of your exhaled air. So over time you would gradually see a rise in your arterial PCO2, With that long hose hanging off the mask that you are breathing through you have increased dead space of your airway. Dead space is defined as that part of the air way that is not involved in gas exchange. So your mouth, nose (n asopharynx), trachea, and the first branch of the Bronchi (primary bronchus) are all what is considered dead space. Now that you have added that extra 2 feet of dead space to your airway, your are increasing your work of breathing and that will result in an increase in your exhaled PC02 also. There some other factors that I could bore you with relating to the pressure differential between alveolar PC02 at inspiration verses exhalation ect. In other words, the blood arriving at the alveolus (the site of gas exchange in the lung) is high in CO2 (the Pulmonary Artery- the only artery in the body that is higher in C02 the a vein, Pulmonary Vein). The freshly inspired air is low in C02 and high in 02. So there is a pressure gradient that exist in the alveolus verses the pulmonary artery. So C02 diffuses easily from an area of higher concentration to lower concentration. Now if you keep sucking fresh air into your alveolus that is high in C02, then you do not get the diffusi on of C02 out of your blood stream. So there is gradual increase in the PAC02 in your blood. Then all the I talked about in the other post starts to take place.
The 3M mask does not present that problem. If it is the version that I am thinking about. It has one or two screw in filters on either side of the rubber mask. Some have a single filter on one side. Even though you will see a slight increase in the PC02, it will be pretty much negligible. The filters on the mask are designed to be very porous so as to facilitate elimination of exhaled gases and decrease work of breathing by not offering alot of resistance to inspiration. Measuring end tidal C02 in the mask does not show a significant increase in C02 in that type of mask in the studies I have seen in the Occupational Medicine texts. That mask can be hot as hell to wear but it is safe to use though. I don't think you have a lot to worry about with the 3 M mask.
Hope this helps alleviate your concern about the 3 M mask,
Doc
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lrob4783(at)bigpond.net.a
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| Posted: Thu Jan 25, 2007 3:38 am Post subject: Breathing Clean Air - Masks? |
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Hi Doc,
That all makes very good sense but do the inlet valves really leak that much exhaled air back into the inlet pipe?
I would have thought that the valve would have closed as soon as there is a positive pressure inside the mask stopping it……..The valve on my mask sure seems to shut tight and quickly.
Is it still not enough and maybe that’s the case as the designers were planning on it being used with a pressurized supply.
Thanks for all your input…….It’s very interesting stuff.
Lance Robb
NQ Warbirds
Mareeba
Australia
From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of Roger Kemp
Sent: Thursday, 25 January 2007 11:12 AM
To: yak-list(at)matronics.com
Subject: RE: Breathing Clean Air - Masks?
Lance,
The issue you face with using the aviator's mask without a fresh air source is related to dead space air. The hose on the aviator's mask is is about 18 to 24 inches long. So each time you exhale you push air high in C02 down that hose. Now when you take a breath, you suck that air back in. Then you repeat the process when you again. This process is known a entrainment. There is a push pull action taking place in the hose. If regular respiration takes place without something diluting it out like sticking it out into the wind stream (pressure breathing per say), the PC02 in the hose will gradually become equal the PC02 of your exhaled air. So over time you would gradually see a rise in your arterial PCO2, With that long hose hanging off the mask that you are breathing through you have increased dead space of your airway. Dead space is defined as that part of the air way that is not involved in gas exchange. So your mouth, nose (n asopharynx), trachea, and the first branch of the Bronchi (primary bronchus) are all what is considered dead space. Now that you have added that extra 2 feet of dead space to your airway, your are increasing your work of breathing and that will result in an increase in your exhaled PC02 also. There some other factors that I could bore you with relating to the pressure differential between alveolar PC02 at inspiration verses exhalation ect. In other words, the blood arriving at the alveolus (the site of gas exchange in the lung) is high in CO2 (the Pulmonary Artery- the only artery in the body that is higher in C02 the a vein, Pulmonary Vein). The freshly inspired air is low in C02 and high in 02. So there is a pressure gradient that exist in the alveolus verses the pulmonary artery. So C02 diffuses easily from an area of higher concentration to lower concentration. Now if you keep sucking fresh air into your alveolus that is high in C02, then you do not get the diffusi on of C02 out of your blood stream. So there is gradual increase in the PAC02 in your blood. Then all the I talked about in the other post starts to take place.
The 3M mask does not present that problem. If it is the version that I am thinking about. It has one or two screw in filters on either side of the rubber mask. Some have a single filter on one side. Even though you will see a slight increase in the PC02, it will be pretty much negligible. The filters on the mask are designed to be very porous so as to facilitate elimination of exhaled gases and decrease work of breathing by not offering alot of resistance to inspiration. Measuring end tidal C02 in the mask does not show a significant increase in C02 in that type of mask in the studies I have seen in the Occupational Medicine texts. That mask can be hot as hell to wear but it is safe to use though. I don't think you have a lot to worry about with the 3 M mask.
Hope this helps alleviate your concern about the 3 M mask,
Doc
--
24/01/2007 6:48 PM
--
24/01/2007 6:48 PM
[quote][b]
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