Vaping has already become one of the big public health stories of 2019. Illegal, unregulated vapes pose serious threats, and even legitimate vaporizer companies like JUUL and have drawn scrutiny from the FDA for marketing their nicotine-heavy products to teenagers. We still know very little about what happens to your body when you inhale a vaporized liquid, but a team of scientists at the University of Pennsylvania now suggest that the results aren’t very positive — even when nicotine isn’t in the picture.
A paper published Tuesday in Radiology showed that even without nicotine, vaping flavored e-liquids caused significant changes in blood flow in the femoral artery, a major artery in the leg. Felix Wehrli, Ph.D., the study’s senior author, tells Inverse that these effects were temporary. But that’s not a reason not to take them seriously, especially for people who vape regularly (and even in 2018, record numbers of teens reported vaping within the last 30 days).
The worry is that with repeated vaping, these reactions wouldn’t return to normal, and over time that might lead to more serious impacts on blood vessels.
“The effects are transient, meaning they go away after some time on the order of tens of minutes or hours, but, obviously, this would not be the case for repeated and regular vaping as the insult would likely occur after each vaping episode,” Wehrli tells Inverse. “We don’t have data but such a projection seems logical.”
How Vaping Affects Blood Flow
Wehrli and Alessandra Caporale, Ph.D., a post-doc in Wehrli’s lab, tested the effects vaping on the femoral arteries of 31 healthy adult participants. These adults underwent only one session with their nicotine-free e-cigarettes, but it was a heavy one: Each person took 16 pulls lasting three seconds each. Doing so had three major effects on the artery and the blood that flowed through it.
That heavy vaping session changed reduced the dilation of femoral artery by 34 percent on average — which means that it didn’t relax in response to an increase in blood flow as much as it did before the vaping session. The team also noted that the acceleration of blood through the femoral artery slowed by 25.8 percent. Finally, they found that vaping decreased hemoglobin saturation by 20 percent. Hemoglobin is the protein in red blood cells that carries oxygen, so this suggests that the blood was less oxygen-rich after a vaping session.
Wehrli adds that these semantics of blood flow make the case that, over time, routine vaping could induce arterial stiffening, which is a marker of heart disease.
“The effects we see are the result of an immune response to the vascular endothelium, collectively called “endothelial dysfunction”, which is the initiating event of atherosclerosis,” he says.
The real metric that bolsters their argument was a change in aortic “pulse wave velocity,” which is essentially a way to measure how stiff an artery is. It’s also used to predict heart disease risk. After a session of vaping, pulse wave velocity increased by three percent, which “suggests acute arterial stiffening.” That’s not a great sign, though Wehrli adds that we still don’t know whether this would translate to prolonged stiffening with repeated use.
“Of course, until these effects would become symptomatic, this might take years, possibly decades, and ultimately, long-term studies will be needed,” he adds.
Where Do These Effects Come From?
Because nicotine wasn’t a factor in this study, this study puts the focus on how traditional e-liquid components interact with the body. Two of these major ingredients in e-liquids are propylene glycol and glycerol. The e-liquid used in this study contained both.
One 2018 study in PLOS Biology showed that these two ingredients, at high doses, were toxic can be human cells. But the authors noted that during a normal vaping session, these chemicals probably wouldn’t reach high enough thresholds to be toxic.
The issue that vapers need to consider, add the team, is what happens to that liquid when it’s heated up, mixed with flavoring agents, and then inhaled. Previous research has suggested that some flavors may be worse than others.
“Another source of toxicity may derive from the reaction between propylene glycol (a common base for the e-juice) and the flavorants, because such mixtures are chemically not stable even at room temperature, [they’re] more so when the liquid gets heated and atomized,” says Caporale.
Of course, this study is hyper-focused on the short-term effects of a single heavy vaping session, but the authors are extrapolating their data to illuminate some very real risks in the long term. If Wehrli’s proposal is correct, we might see the long-term effects of vaping play out in the blood vessels over time, but right now, we’ve only got some early evidence that points us in that direction.
Materials and Methods: In this prospective study (from May to September 2018), nonsmokers underwent 3.0-T MRI before and after inhaling nicotine-free e-cigarette aerosol. Peripheral vascular reactivity to cuff-induced ischemia was quantified by temporally resolving blood flow velocity and oxygenation (SvO2) in superficial femoral artery and vein, respectively, along with artery luminal flow-mediated dilation. Precuff occlusion, resistivity index, baseline blood flow velocity, and SvO2 were evaluated. During reactive hyperemia, blood flow velocity yielded peak velocity, time to peak, and acceleration rate (hyperemic index); SvO2 yielded washout time of oxygen-depleted blood, rate of resaturation, and maximum SvO2 increase (overshoot). Cerebrovascular reactivity was assessed in the superior sagittal sinus, evaluating the breath-hold index. Central arterial stiffness was measured via aortic pulse wave velocity. Differences before versus after e-cigarette vaping were tested with Hotelling T2 test.
Results:Thirty-one healthy never-smokers (mean age, 24.3 years ± 4.3; 14 women) were evaluated. After e-cigarette vaping, resistivity index was higher (0.03 of 1.30 [2.3%]; P < .05), luminal flow-mediated dilation severely blunted (−3.2% of 9.4% [−34%]; P < .001), along with reduced peak velocity (−9.9 of 56.6 cm/sec [−17.5%]; P < .001), hyperemic index (−3.9 of 15.1 cm/sec2 [−25.8%]; P < .001), and delayed time to peak (2.1 of 7.1 sec [29.6%]; P = .005); baseline SvO2 was lower (−13 of 65 %HbO2 [−20%]; P < .001) and overshoot higher (10 of 19 %HbO2 [52.6%]; P < .001); and aortic pulse wave velocity marginally increased (0.19 of 6.05 m/sec [3%]; P = .05). Remaining parameters did not change after aerosol inhalation.
Conclusion:Inhaling nicotine-free electronic cigarette aerosol transiently impacted endothelial function in healthy nonsmokers. Further studies are needed to address the potentially adverse long-term effects on vascular health.