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.
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)