Thanks exogenesis. That got me going.
The difference between measured blood levels suggesting low levels of vaping nicotine absorption (often said to be 10%) and the large amount of anecdotal evidence suggesting the number to be more like 40 to 60% is a troublesome discrepancy in our understanding of vaping. (Note: I thought the second number was 40% until recently; the realization that cigarettes are commonly delivering more nicotine than their labels suggest means that the number should be higher than 40%. I'll call it 50% for now.)
I've been reading everything I can find to try to understand this.
I found two reports which substantiate the 10% thinking. (There is a third one but I've left it out because it only did blood nic measurement five minutes after inhalation. I think that measurement by itself tells us very little.)
1) The New Zealand study funded by Ruyan. Data from that study has been presented in various forms but they seem to all derive from one study. I think that this study is useful but has some limitations:
a) It used Ruyan ultrasonic devices. I don't know if these could have substantial differences vs. our current atomizers. Probably not much but we don't know.
b) It has been referenced to support claims that the delivery of nicotine from vaping is very low. But that isn't clear to me. The first link below includes the statement that "Each puff contains one third to one half the nicotine in a tobacco cigarettes puff", which already disagrees with a 10% assumption. And that's before accounting for the study's use of Ruyan 16mg liquid, which it found to actually be 14mg, vs. some vapers' use of 24, 36, or more.
Useful links I found which present the New Zealand study's results:
http://www.healthnz.co.nz/RuyanCartridgeReport30-Oct-08.pdf
http://www.healthnz.co.nz/ecig_effect-2.pdf
http://www.healthnz.co.nz/DublinBenchtopHandout.pdf
2) The blood tests reported by forum user "happily" on this thread:
http://www.e-cigarette-forum.com/forum/nicotine/30623-blood-test-lab-results-nicotine-levels.html. This is one person's measurements and although both the nicotine and cotinine results suggest low absorption, there's an anomaly between those two results which is interesting.
Then there's the other view on how much we're getting. DVap speculated that there's a fixed relationship between the amount of nicotine vapers use in a given time and the established (by amount they previously smoked) amount of nicotine their bodies need. This thinking has appeared less formally many times on the forum in threads like "If I smoked X cigarettes of strength Y, then I must need Z nicotine" or like "Since I smoked X@Y, and vaping delivers 10%, how could I be satisfied with only Z liquid?"
DVap observed that there does seem to be a fixed relationship at around 40% for most people. I now think that number should be higher because DVap's calculations (if I understood correctly) were based on the nicotine level stated on cigarette labels and those numbers turn out to be generally lower than the actual nicotine delivered and absorbed.
exogenesis has rechecked his experiment showing a bit over 90% of e-liquid's nicotine being delivered in the vapor. Although this is higher than DVap's earlier experiments, I think that exogenesis's number is the best available at the moment. It is hard to think that his experiment could falsely find nicotine that wasn't present. It seems more likely that either DVap's experiment missed some nicotine, or that some other difference between the experiments means that there is a wide range of possible nicotine destruction in the atomizer. In does seem that as much as 92% of the nicotine in e-liquid can be presented to our body by vaping.
DVap's work has shown that we can generally believe e-liquids to contain the stated amount of nicotine.
So on the face of it we're left with any absorption number from 0 to 90% of an e-liquid's stated content being possible.
We now know that for some people there's a missing X factor which is not nicotine. And DVap has done excellent work in producing "WTA" which provides that X factor. I don't think this is necessarily related to the nicotine absorption discrepancy because there are also many happy vapers who don't seem to need the X factor.
It has often been suggested that the nicotine discrepancy is due to a placebo effect. I reject this notion. There are very many reports by satisfied vapers which show them to be a group who have failed many other methods of nicotine replacement at reduced levels. Many switched to lower nicotine cigarettes and automatically increased their intake to compensate. On the whole I think this is a group of people who are unlikely to benefit from placebo effects. They need their nicotine and their bodies tell them when they don't get it. There must be a chemical reason for the discrepancy.
I have found some interesting thoughts about the discrepancy which remain unexplored as far as I know. I've included links to them below. I hope that someone may be inspired by these to further our collective understanding.
Atreides Ghola, a biologist who was active on the forum in June 2009, emphasized that it is a misconception that nicotine blood levels reflect the efficacy of nicotine delivery to the brain, and described the chemical processes involved in the following three posts:
http://www.e-cigarette-forum.com/fo...-absorbtion-vaping-research-4.html#post346264
http://www.e-cigarette-forum.com/fo...-absorbtion-vaping-research-4.html#post346460
http://www.e-cigarette-forum.com/fo...-absorbtion-vaping-research-4.html#post346850
Kurt hypothesized variations in people oxidizing nicotine which is delivered orally:
http://www.e-cigarette-forum.com/fo...lab-results-nicotine-levels-2.html#post696047
kinabaloo suggested that nicotine might be persisting in the lungs for a period of time:
http://www.e-cigarette-forum.com/fo...-absorbtion-vaping-research-2.html#post245734
Whatever the reason for it I think that the blood tests we have seen are wrong in some important sense. Atreides Ghola's note about nicotine blood levels rings true to me. Measuring blood nicotine level only determines what "reserve" is available at a given moment. It doesn't necessarily correlate to nicotine absorption and almost certainly doesn't correlate to satisfaction. What we'd ideally like to know is how much nicotine is in use at a given moment and how much remains available in some type of reserve (blood, unabsorbed yet but will be eventually, and perhaps others.) I think that measurements of cotinine and other metabolic products over longer intervals are more likely to give a good indication of how much nicotine was absorbed than snapshots of blood nicotine.
Many vapers seem to move to a practice of vaping continuously, i.e. of vaping at much shorter intervals than they used to have between cigarettes. I think that this practice may result in a more even level of effective (in-use in the brain) nicotine and may offset to some degree the lack of MAOIs in e-liquid. Vapers have this option because the device is capable of one puff at a time with no waste. Due to more frequent doses they may need to absorb less nicotine because they don't need as much reserve circulating in the blood stream. Smokers lose a lot of that reserve (part ends up unused) due to its fairly short half-life. On the other hand, vapers may also need more nicotine at shorter intervals in order to maintain a high level of dopamine because they aren't getting the MAOIs delivered by cigarettes.
In summary, despite the bits of blood evidence which have been interpreted to the contrary, I think that we're absorbing somewhere around 50% of the nicotine in e-liquid. Much remains to be understood in how that nicotine is being delivered and being processed.
. We'll see where this goes. I would like to add, for the benefit of all the mg/ml nic police out there holding danger signs in front of a bottle of 36 or 48, if this is the case we're talking a "sliding" scale of absorption and not one where higher nic consumption puts us any closer to death.
. Now, where's my 250mg bottle, it's here somewhere....oh yeah, next to the bleach.
