Pulse ox questions

flyingcheesehead

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How quickly do changes in breathing or oxygen content actually make it to your finger where a pulse oximeter can read them? It almost seems instantaneous (<3 seconds) and I'd have thought that it would take longer for the blood to make it from the lungs to the heart and out to the extremities.

How efficient is a normal adult's breathing? I seem to normally get about 96% on the ground. I was at 10,500 on my last leg to OR and even on oxygen I was in the 80's - I was having some trouble getting enough air breathing through my nose. With oxygen off, breathing through my mouth using slow, deep breaths I got back up to 92%. I guess the second question here is, can anything be done about narrow nostrils? I simply could not get enough air breathing through my nose. :dunno:
 
From what I've read, readings of 90% are common. You can get readings of 85% and be fine which can be from the quality of the pulse oximeter and/or its proper use. Averaging 90% is fine while 95% or greater is ideal. If you're indicating 85% or below, keep the oxygen on continuously. It's not worth the risk otherwise. You can also do mild arm and leg exercises to move around a bit and increase circulation.

As far as how soon indications show up to be seen by the oximeter, that largely depends on your health and environment. Normally, it should be a matter of minutes. If you smoke, obviously your blood won't carry as much oxygen. That's a given to happen if your aircraft develops a CO leak. These are obviously from Hypemic Hypoxia.

Stagnant Hypoxia can affect your reading if you left your arm in such a position for a long period and reduced the blood flow to your finger used for measuring. Hence, the reason for mild exercises while in flight. Reduced blood pressure can also have an effect.

Hypoxic Hypoxia would be a caused by your altitude. Even at FL180, you still have about 20-25 minutes of "time of useful consciousness" at standard conditions. You're flying much lower, presumably around 12,000 so that time would be higher, perhaps 35 minutes.

Your difficulty breathing through narrow nostrils is also Hypoxic Hypoxia. If your breathing tends to be also shallow on the ground, you may have Hypopnea as a result of the narrow nostrils. I'd suggest remaining on oxygen at any point above 10,000 during the day and over 5,000 at night as lower oxygen rates diminish your eye sight at night.

I don't know if it could happen but I have to wonder if attempting to "over breathe" or deep breathing could lead to hyperventilation.

As far as the change to your inner nose, I'd suggest a visit to your favorite ENT. I went through sinus surgery three times in two years back in the early `90s. It ain't fun.
 
Kent, Henning's right.

The only other thing you can do is.......lose weight. I kid you not, the alveoli (air sacs) close prematurely when you are large, and the enrichment from the cannulas then aren't enough.

Short of having your turbinates removed from your nose, there's not much else to do.
 
Hold the cannula between yer teeth and breathe through your mouth! :) Sounds like a joke, but I think it would work, if you find yourself needing more O2 than you're getting and you can't do anything else about it! :)
 
Hold the cannula between yer teeth and breathe through your mouth! :) Sounds like a joke, but I think it would work, if you find yourself needing more O2 than you're getting and you can't do anything else about it! :)

No, you get a mask and avoid requiring O2 until you do.
 
No, I was talking about what to do if you find yourself already up there, but clogging up, nasally... not about faking it from the take-off. :no:
 
No, I was talking about what to do if you find yourself already up there, but clogging up, nasally... not about faking it from the take-off. :no:

Yeah, but now he knows about the situation, and a remedy. He should not again be in that situation.
 
How quickly do changes in breathing or oxygen content actually make it to your finger where a pulse oximeter can read them? It almost seems instantaneous (<3 seconds) and I'd have thought that it would take longer for the blood to make it from the lungs to the heart and out to the extremities.

Not a doc, but I've had a couple CT scans for blood clots in the lungs in the past couple of weeks... You can feel a warming sensation as the radio-opaque dye reaches various parts of the body and it's amazing how fast it gets from the point where it goes in the IV in your arm to being felt in the groin. Your less than 3 seconds number sounds very real to me.
 
Not a doc, but I've had a couple CT scans for blood clots in the lungs in the past couple of weeks... You can feel a warming sensation as the radio-opaque dye reaches various parts of the body and it's amazing how fast it gets from the point where it goes in the IV in your arm to being felt in the groin. Your less than 3 seconds number sounds very real to me.

Yeah, when they put me under for surgeries, I can never recall getting down past 97, and that stuff was cold going through me.
 
We just flew down to Diana's at 12K, and my O2 was showing at 57 when I first measured it. I didn't believe it, so I tried again, and it was 83 or so. Deep breathing brought it up to 98, but it did feel a little like I was starting to hyperventilate. We didn't even pull out the canulas.
 
We just flew down to Diana's at 12K, and my O2 was showing at 57 when I first measured it. I didn't believe it, so I tried again, and it was 83 or so. Deep breathing brought it up to 98, but it did feel a little like I was starting to hyperventilate. We didn't even pull out the canulas.

57??? You been painting or caulking? Finger tip peeling? I'm not sure, but I don't think you'd be conscious at 57, and you'd probably be sustaining brain damage.
 
57??? You been painting or caulking? Finger tip peeling? I'm not sure, but I don't think you'd be conscious at 57, and you'd probably be sustaining brain damage.
As I said, I didn't believe it. I figure a faulty reading. (or is that finger a faulty reading?:goofy:)
 
Normally the delay between lung and finger tip is 5-8 seconds in someone without complicating factors (peripheral vascular disease, COPD, etc). This is not just a function of the blood flow, but also because you have to allow time for the saturation to reach the new level. This is based on the knowledge that results from the part time work I do at a sleep research lab where we focus quite heavily on oxygen levels and the various mechanisms that control work of breathing.

my O2 was showing at 57 when I first measured it. I didn't believe it, so I tried again, and it was 83 or so.
As a general rule, the commonly available pulse oximeters are often unreliable below 70%. Any reading below that should be strongly suspect. However, that being said, I have seen a severe chronic lung patient heavily dependent on oxygen (six liters by nasal cannula while sitting still) who was conscious and talking with a blood gas verified saturation of ~55-60%. One of the few true cases of hypoxic drive I have ever seen first case, this patient would stop breathing if you raised his saturation above ~74%.

Not a doc, but I've had a couple CT scans for blood clots in the lungs in the past couple of weeks... You can feel a warming sensation as the radio-opaque dye reaches various parts of the body and it's amazing how fast it gets from the point where it goes in the IV in your arm to being felt in the groin. Your less than 3 seconds number sounds very real to me.
That is most likely a function of the systemic release of histamine (and/or related chemicals) and not the result of the actual circulation time of the dye. To illustrate this point, there is one drug (adenosine) whose half-life is <10 seconds (it is broken down by an enzyme in red blood cells) and we used it in treating a particular abnormal heart rhythm. We were taught if giving it via a peripheral IV (example: that line in your arm), we should follow it with a push of IV fluid and elevate the extremity to make sure it gets to the heart before it breaks down. Even when this is done, it is often not effective because the circulation time is too long and the drug is already broken down.

From what I've read, readings of 90% are common. You can get readings of 85% and be fine which can be from the quality of the pulse oximeter and/or its proper use. Averaging 90% is fine while 95% or greater is ideal. If you're indicating 85% or below, keep the oxygen on continuously. It's not worth the risk otherwise. You can also do mild arm and leg exercises to move around a bit and increase circulation.
88% is not at all uncommon. According to some texts, it is actually the bottom end of "normal" for an adult.

As far as how soon indications show up to be seen by the oximeter, that largely depends on your health and environment. Normally, it should be a matter of minutes. If you smoke, obviously your blood won't carry as much oxygen. That's a given to happen if your aircraft develops a CO leak. These are obviously from Hypemic Hypoxia.
Just a note, on some oximeters (especially older models) you will actually see a falsly elevated SpO2 reading in the presence of CO poisoning because of a failure of the oximeter to differentiate between oxyhemoglobin and carboxyhemoglobin.

Stagnant Hypoxia can affect your reading if you left your arm in such a position for a long period and reduced the blood flow to your finger used for measuring. Hence, the reason for mild exercises while in flight. Reduced blood pressure can also have an effect
Other examples include ischemic heart disease (angina and heart attacks) and ischemic strokes.

By the way, please be careful in regards to using hyperventilation to raise saturations. I've heard mention of a theory that one could hyperventilate yourself into unconsciousness at altitude in an aviation version of the shallow water blackout that occurs when divers induce hypocapnia by hyperventilating prior to a dive. The safest ways to increase your saturation are:
-Increasing the flow of oxygen
-Descending
-Taking full slow deep breaths....rapid shallow breaths tends to do little in terms of improving saturations since you may not ventilate anything beyond the deadspace of your lungs.

Finger tip peeling?

Since the pulse oximeter measures through the nail and into the nailbed, your fingertip peeling would not affect the reading under any circumstance I can foresee. Things that can commonly affect it are:
-Cold finger
-Poor vascular supply to the finger (Raynaud's phenomenon, peripheral vascular disease)
-Nail polish
-Subungal hematoma (blood "blister" under the fingernail)
-Poor sensor placement (probably the most common problem
-Sensor not plugged into the oximeter (hey, it happens! Even to we professionals! LOL)
 
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Steve, you're missing a little understanding. At what value do the Optical Densities (peak to peak ratios) approximate noise?
 
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Just for the heck of it, I went up to 17,500 yesterday. I came up with a combination breathing technique that seemed to work better: Start inhaling through my nose to pick up the burst of O2 that the OxySaver delivers, keep inhaling through my nose until I think I've pushed it all through my nasal cavity, and finish inhaling through my mouth to push it all to the alveoli faster. I was able to get a reading of 88 at 17,500 that way.
 
I somehow had a sneaking suspicion you might think so. The sense of freedom one gets from being allowed to go down a path of ones own choosing can suddenly change to make one feel so very trapped... LOL
 
Kent, similiarily - I inhale long and slow through the cannula. (Inhaling fast means you will get a lot of ambient air with its low O2 content - as you are exceeding the cannual output when you breathe in too fast.)
Then, a slight abdominal press against a closed glottis (valsalva) for a few seconds will increase the alveolar pressure and aid O2 transfer. Then quick exhale and start over.
I have done this in the Viking with various alterations and the above is what results in the consistently highest O2.
There could well be some scientific reason why this should not work but all I can say is go up to 20K with a p'oximeter and do some experiments, I have and these are my findings.


Just for the heck of it, I went up to 17,500 yesterday. I came up with a combination breathing technique that seemed to work better: Start inhaling through my nose to pick up the burst of O2 that the OxySaver delivers, keep inhaling through my nose until I think I've pushed it all through my nasal cavity, and finish inhaling through my mouth to push it all to the alveoli faster. I was able to get a reading of 88 at 17,500 that way.
 
AXE said:
I somehow had a sneaking suspicion you might think so. The sense of freedom one gets from being allowed to go down a path of ones own choosing can suddenly change to make one feel so very trapped... LOL
Yeah, he's not coming.

You know, I've said a couple of times, "Hmmn. I was wrong." Pilots who cannot do this scare the bejeesus out of me.
 
Yeah, he's not coming.

You know, I've said a couple of times, "Hmmn. I was wrong." Pilots who cannot do this scare the bejeesus out of me.
Not jsut pilots but anyone.

Funny side story. A bunch of us were talking today at work about our weekend. One of my co-workers was telling us about his kid acting up and how he spank him. That led to a discussion on spanking theory and I offered up a story about when I was spanked by my uncle.

I was playing under the sink (it was the 60's and I was playing Apollo moon landing). I accidentally pulled the drain pip apart. I knew I did something and pushed it back together. But later it leaked big time.

A quick investigation was done by my uncle and he knew I did it and I admitted it. He spanked, but not because I broke it. Because I tried to hide it and not own up to what I had done. He said that I would have been punched by having to help him fix it had I told him, but by hiding the damage I had done worse.

I learned to say I was wrong is the better thing to do than to try and hide your mistakes.
 
He said that I would have been punched by having to help him fix it had I told him, but by hiding the damage I had done worse.
Ummmm... Did you actually mean to say "punched", or just "punished"? Maybe we need to go back to that discussion youwere having about corporal punishment, here!
 
Allright, I have let a grossly inaccurate post stand long enough. I bumped your post twice hoping to engage in civil discussion. I will now simply correct the post by SteveR.

As a general rule, the commonly available pulse oximeters are often unreliable below 70%. Any reading below that should be strongly suspect. However, that being said, I have seen a severe chronic lung patient heavily dependent on oxygen (six liters by nasal cannula while sitting still) who was conscious and talking with a blood gas verified saturation of ~55-60%. One of the few true cases of hypoxic drive I have ever seen first case, this patient would stop breathing if you raised his saturation above ~74%.
The point at which a pulse oximeter is most likely to be inaccurate is when it indicates 85%! Why? It because at that saturation, the two optical densities that are measured and sent to the "lookup table" are equal in density. When they are equal peaks, they look more than any other time, like noise, especially when the sample signal is weak or near the bottom end of detection (poor perfusion, fat finger, lots of nail polish, etc).
That is most likely a function of the systemic release of histamine (and/or related chemicals) and not the result of the actual circulation time of the dye. To illustrate this point, there is one drug (adenosine) whose half-life is <10 seconds (it is broken down by an enzyme in red blood cells) and we used it in treating a particular abnormal heart rhythm. We were taught if giving it via a peripheral IV (example: that line in your arm), we should follow it with a push of IV fluid and elevate the extremity to make sure it gets to the heart before it breaks down. Even when this is done, it is often not effective because the circulation time is too long and the drug is already broken down.
The venous to heart circulation time is.....hardly related to the ventricle to periphery time. Lage is more likely related to the avereaging algorithm programmed into the unit in question. In good ones, whe have complete control over this (user select) and in the operating room we turn the averaging off so we get beat-to beat values. The biologic damping is quite enough so we don't need electronic averaging on top of it. The common $100 Pulse oximeter takes a 16 beat average. At a heart rate of 60, that moving average becomes quite slow.
88% is not at all uncommon. According to some texts, it is actually the bottom end of "normal" for an adult.
Maybe joe blow's texts. But below 90% is considered pathologic. See Guyton. There is population data behind this, from the American College of Pathology. You have a copy of course.
Just a note, on some oximeters (especially older models) you will actually see a falsly elevated SpO2 reading in the presence of CO poisoning because of a failure of the oximeter to differentiate between oxyhemoglobin and carboxyhemoglobin.
In all oximeters Arterial SpO2 is near completely unaffected by CO poisoning (until you get to near 80% carboxyhemoglobin, compatible only with death). What is affected is central venous SpO2 as essentially CO poisoned units are unavailable for saturation/desaturation. What remaining blood there is functions normally. It's CARRYING CAPACITY that is reduced, it's as if you had HALF AS MUCH BLOOD available to carry oxygen, it gets totally emptied by the periphery. Back in the lungs, they have to start form 20% saturation rather than 50% to load up the remaining hemoglobin. The two OD's that were selected were selected for RESISTANCE to change by CO-hemoglobin's spectrum as it becomes the dominant species. The Oximeter continues to read just the oxyhemoglobin vs. de-oxyhemoglobin proportion.
Other examples include ischemic heart disease (angina and heart attacks) and ischemic strokes.

By the way, please be careful in regards to using hyperventilation to raise saturations. I've heard mention of a theory that one could hyperventilate yourself into unconsciousness at altitude in an aviation version of the shallow water blackout that occurs when divers induce hypocapnia by hyperventilating prior to a dive. The safest ways to increase your saturation are:
-Increasing the flow of oxygen
-Descending
-Taking full slow deep breaths....rapid shallow breaths tends to do little in terms of improving saturations since you may not ventilate anything beyond the deadspace of your lungs.

Since the pulse oximeter measures through the nail and into the nailbed, your fingertip peeling would not affect the reading under any circumstance I can foresee. Things that can commonly affect it are:
-Cold finger
-Poor vascular supply to the finger (Raynaud's phenomenon, peripheral vascular disease)
-Nail polish
-Subungal hematoma (blood "blister" under the fingernail)
-Poor sensor placement (probably the most common problem
-Sensor not plugged into the oximeter (hey, it happens! Even to we professionals! LOL)
This is the only part of the post that contains any truth.

Professor of Medicine
Univ. of Illinois
and Board Certified Anesthesiologist
 
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What could a guy who puts people to sleep for a living possibly know about breathing and blood circulation?




I jest! :D
 
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