I just read the second study on rats 😬
https://www.ahajournals.org/doi/10.1161/ATVBAHA.122.318051
They took 56 rats, anaesthetised them with ketamin and exposed a group of 8 rats to each of the following:
High nicotine, menthol cigarette smoke
Low nicotine, menthol cigarette smoke
High nicotine, non-menthol cigarette smoke
Low nicotine, non-menthol cigarette smoke
acrolein and aldehyde at levels equivalent to second hand smoke
'Inert' ultrafine particles (carbon)
Clean air
Then they took another 56 rats and operated on them to sever their entire vagus nerve at the neck, then divided them into groups of 8 and repeated the above exposures.
Then they took another group of 56 rats and performed sham vagus nerve surgery (same operation except for actually cutting the nerve), and exposed in groups of 8 as above.
Before and after each group's exposure, the rats' endothelial function was tested using 'flow-mediated dilatation' (FMD) which is a test using ultrasound to measure the dilation or constriction of blood vessels.
Then they killed all the rats, wrote up their results and made some really bogus conclusions.
This study has nothing to do with vaping despite attempts to shoehorn it in by the authors (because funding). They claim it's relevant because acrolein, aldehyde and ultrafine particles are found in both cigarette smoke and vapour from ecigs. Technically they are correct, however:
Acrolein and aldehyde
we have known for a long time that products of burning such as acrolein and aldehydes are present in much, much lower levels in vapes than they are in tobacco smoke, to the extent that they are completely undetectable in second hand vape. These chemicals only really show up at all in studies where they have misused a vape by firing it at an unsuitable temperature or puff regime. Burnt vape always tastes nasty and vapers avoid it. Experiments that throw up large quantities of these chemicals invariably fail badly at replicating real world conditions.
PHE have always assessed all studies on these chemicals related to vaping and have included commentary on the least shit ones in their yearly evidence updates. This forms part of their estimated 5% residual risk of vaping compared with smoking.
Ultrafine particles
Not all ultrafine particles are the same. In particular, solid and liquid particles behave very differently. UFPs from vaping are liquids, UFPs from smoking are solids. This study uses 'inert' carbon nanoparticles. They may be chemically inert but they are still physically solids and behave as such in this physical world and in our physical lungs. This study cannot tell us anything about the behaviour of liquid ultrafine particles such as those produced by vaping (or having a shower or boiling a kettle). They have just extrapolated from the ultrafine particles in cigarette smoke, which are solids (soot, basically) and claimed this also applies to vaping. It does not.
But it gets worse.
This is their stated goal:
The goal of this project was to determine why a growing number of inhaled tobacco and marijuana products, including combustible products, dry heat vaporizer and heated tobacco products, and e-cigarettes, all acutely impair endothelial function despite fundamental differences in the products.
Their study provides no insight into any of this. Their only valid conclusion is that severing the entire vagus nerve prevents what they call 'endothelial dysfunction' and what the rest of us call 'the normal thing that happens when you drink a cup of coffee.'
https://pubmed.ncbi.nlm.nih.gov/15799717/
No shit. We know the vagus nerve serves an important function in our brain's communication with our heart and circulatory system, among many other functions. Severing the vagus nerve is not good for you. We evolved it for many good reasons. I am sure that actual clinicians who see patients with vagus nerve damage are already aware of their patients' symptoms, including FMD results, and can advise accordingly.
I count 168 rats' lives in this experiment. I am not averse to animal experimentation when it has the potential to produce important findings that improve human health but this was always only ever a bullshit study. It was never going to tell us anything new.
Frankly, those 168 little guys' lives would have been better sacrificed giving us a new, better mascara.