The Topography of Vaping

The idea of a puff topography should not really be news to any of us. After all, it was that young scientist, turn President that said over 25 years ago,

"When I was in England, I experimented with marijuana a time or two, and didn't like it. I didn't inhale and I didn't try it again."

Those three characteristics

• The duration of the inhalation
• The volume inhaled
• The speed at which that volume moves

Together, these reflect the dose of tobacco smoke. Inhalation depth, a mixture of volume and velocity, is known to be greater among cigarette smokers than those who might be smoking a cigar, a hookah, or vaping. So it is not unreasonable to ask if the puff pattern of vapers is, in fact, different and whether that has some unconsidered health consequences.

The current study looked at the puff topography of individuals smoking cigarettes, vaping, or using a hookah. (I am going to ignore the hookah users). Rather than bring subjects into the laboratory for testing, where they might be influenced by the room, white coats, or the environment, the researchers observed these individuals in the wild, on the streets of New York. It is truly an observational study!

An aside

One of the advantages of observing the vapers in the wild is that there is no need to consent. More importantly, there is no need to have the study reviewed in-depth by the medical school or hospital’s Institutional Review Board (IRB). As an avid reader of science articles, I need to point out how many studies no longer need IRB approval since they use surveys and datasets collected by other organizations. It seems a shame that what should be the first and most critical form of peer-review, IRB approval, is increasingly sidestepped by researchers. Perhaps greater IRB oversight would result in fewer papers with glaring and not-so-glaring problems.

But I have digressed. The researchers limited their reporting to confirmed use of a vaping device or cigarette and where the “exhalation pattern could be visually confirmed.” To avoid the appearance of stalking (and perhaps a beatdown, after all, this is New York), the observations lasted no longer than 1 minute or 5 individual puffs. Subjects walking and smoking or vaping were not followed for more than one block.

The exhalation profiles were characterized as exclusively mouth or nose, or “dual exhalations” through both mouth and nose on the same or different puffs. The research on the streets of New York was conducted between March 2018 and February 2019, involving 122 cigarette smokers and 124 vapers. “Subjects that outwardly presented as male accounted for at least two-thirds of all observed individuals, regardless of the product used.”

Some relevant physiology to provide context

I must admit that I am stealing the idea of the Dreaded Chemistry Lesson From Hell^© from Dr. Bloom. We will call this the Dreaded Physiology Lesson From Hell^©.

 Let’s talk for a moment about breathing. Inhalation is primarily an active, muscle-driven process as the diaphragm pulls down, and the muscles of the chest pull the ribs apart. It creates space and a pressure gradient that allows air to enter the lungs. After a pause, we exhale, much more of a passive muscular process as the muscles relax, reducing the space available increasing the pressure as we move air out.

Tidal volume is the amount of air we inhale and exhale. In this diagram, we also see the maximum amount of air we can inhale, the inspiratory reserve volume, and that we can exhale, the expiratory reserve volume. We can inhale a greater volume, at least transiently, than we exhale.

We can assign specific physiology for those previously mentioned parameters of our puff profile or topography. The inhalation depth and its speed are determined by how much those respiratory muscles act and how quickly. The duration of the dwelling period of air in our lungs is, in part, deliberate – we can all “hold our breath” for a few seconds or more. And part is chemical; rising amounts of carbon dioxide are sensed in the carotid body and brainstem and increase our respiratory rate [1]

Our tidal volume is usually pegged at about 500 ml. Not all of that volume enters the lower respiratory tracts, where gas exchange occurs. Some of that tidal volume is found in the nasopharynx, trachea, and bronchi – the tubes directing airflow into the lower parts of the lung. This is considered “dead space volume.” Typically, that is about a third of the tidal volume. Most notably, in understanding this study, the nasopharyngeal component is about 30 ml in the typical adult.

The Study

The taste of tobacco, flavored or not, results from the taste receptors of our tongue and those smell receptors (olfaction sensors) of our nasopharynx. That is why you might see an individual “tasting” wine swish it around their mouth so that the volatiles in the wine are vaporized and reach their olfactory senses. The researchers note that the same can be said for cigar smokers who exhale in a way that allows that smoke to linger in the back of their throat and nose – a process they refer to as “retro haling”—the practice of intentionally exhaling tobacco emissions from the nose to increase flavor intensity.”

Mouth exhalation was the most common route of egress for both groups.

But as the graph demonstrates, vapers exhaled exclusively through their nose almost 4-fold more than cigarette smokers. Vapers were also dual exhalers, almost 3-fold more than cigarette smokers. They also noted that vaping using a modular tank [2] rather than a pod results in more dual exhalations. They ascribed this to the greater volumes generated by modular tanks requiring “both their nose and mouth to facilitate exhalation.” They noted that vapers using the pod system were “twice as likely" to be nasal exhalers compared to their modular vaping colleagues.

The bottom line is that vapers show a significantly different puff pattern than smokers. In addition to vapers inhaling a far different product than cigarette smokers, their exhalation pattern is different. From a health perspective, the nasopharynx has greater exposure to vaping’s vapors. And if Paracelsus is correct, “that the dose makes the poison,” then looking for the same health impacts of cigarettes and vaping is a fool’s errand. 

“Limiting the scope of studies to established cigarette health endpoints may risk missing ATP [alternate tobacco products]-specific behaviors that might foster unique harms.”

Vaping is less harmful than cigarette smoking, but inhaling tobacco smoke or nicotine is not without some risks. The study is easy to make fun of; especially those researchers dressed to be inconspicuous, observing the cigarette smokers and vapers presumably around NYU where the study was written, being careful not to be identified as stalkers. But that said, they raise an interesting point. Should we be searching for health problems where the dose may be more significant, in this case, the nasopharynx?

[1] In a fascinating experiment, individuals were given biologically sufficient levels of oxygen, but their inspired carbon dioxide was increased by only 2-3%. It resulted in everyone removing their masks complaining of severe symptoms of suffocation, a lack of oxygen. That is how powerful the carbon dioxide signaling system can be.

[2] Modular vaping devices generate greater volumes than pod-based models

Source: Exhalation of alternative tobacco product aerosols differs from cigarette smoke—and may lead to alternative health risks Tobacco Use Insights DOI: 10.1177/1179173X221078200