At least for the present, face masks are a mandatory part of out lives. Yes, being mandated to wear them is an encroachment on our personal freedoms, but….
There are reasons to swallow our individualism and to take one for the team. There are people who are getting sick and dying from the coronavirus. Businesses and schools will remain closed until we get this virus under control. While most of us will be asymptomatic (if we catch the virus), we can possibly still transmit the virus. I saw a meme1 recently (Isn’t it sad that so much of our information lately is delivered by memes and social media?) that demonstrated the likelihood of the virus being transmitted from an affected to a healthy person depending on who is wearing a mask. When neither individual wears a mask, the risk is high. When the healthy person wears a mask, the risk is moderately high when the COVID-19 carrier doesn’t wear a mask. If the carrier wears a mask, the risk of transmission is low. If both wear masks, the risk is very low. If one has symptoms (of COVID-19, flu, cold, etc.) and doesn’t wear a mask in public, it doesn’t speak well of that person. When we wear a mask in public, it speaks to our respect of others—especially when ones is compromising his/her views on personal freedom. Wearing a mask is also absolutely essential when in the presence of vulnerable friends and family. (Let’s face it. Social distancing is not really practical in all situations.) Masks may be essential if we are going to get back to face-to-face learning and sports in schools.
So, the question comes up: Are masks safe? There are numerous pseudo-scientific demonstrations circulating that are “proving” the safety (or lack thereof) of wearing masks for extended periods. To evaluate these some basic understanding of human physiology is required. We need to understand hemoglobin, Dalton’s Law, and the oxyhemoglobin dissociation curve.
Hemoglobin is a four-subunit protein that is responsible for transporting oxygen in the blood. Each subunit contains an iron atom that can bind an oxygen molecule. Saturation refers to the percentage of these heme groups that are binding oxygen. If every heme group bound an oxygen molecule, the blood would be 100% saturated. Normally, hemoglobin saturation is between 96 and 98%.
Dalton’s Law is the law of partial pressures. It states that the total pressure of a gas mixture is equal to the sum of the partial pressures of the individual gases. The air we breathe is composed primarily of nitrogen (N2, 78.1%), oxygen (O2, 20.9%), and carbon dioxide (CO2, 0.03%). These percentages remain roughly the same no matter the elevation (i.e., the air at 10,000 ft still has 21% O2, but the partial pressure is affected because the total pressure is less). Normal atmospheric pressure at sea level is approximately 760 mmHg. Thus, at sea level the PO2 is 0.21 x 760 mmHg or around 159 mmHg. At 9000 ft, the barometric pressure is about 543 mmHg. So, the PO2 would be around 114 mmHg. Sounds dramatic, but, as we will see it really isn’t because of the functioning of hemoglobin.
The oxyhemoglobin dissociation curve (pictured above) plots the saturation of hemoglobin relative to the partial pressure of oxygen (PO2). My professor in grad school described hemoglobin at the part of the graph where the curve is relatively flat as “greedy”—hemoglobin grabs on to as much oxygen as it can. In the area where the curve is steep (low PO2), hemoglobin is “benevolent”—hemoglobin is more willing to give up oxygen. This dynamic allows hemoglobin to bind oxygen in the lungs where the partial pressure is high and to release it the tissues where the partial pressure of oxygen is lower.
There is some reduction in the percentage of oxygen in the lungs as it mixes with carbon dioxide, but at low intensities of physical activity, this is not as pronounced as it might be during maximal exercise. By the time the air reaches the alveoli in the lungs (where gases are exchanged with the blood), the PO2 in the alveoli is approximately 100 mmHg. Conversely, the PO2 in the pulmonary arteries is approximately 40 mmHg (depending on the amount of oxygen being consumed by the tissues). Gases will move from high pressure to low pressure. So, as long as a pressure difference exists, gases will be exchanges. (The margin of difference for CO2 is quite small—usually somewhere in the neighborhood of 40 mmHg v. 46 mmHg.) The body will get the oxygen it needs.
Let’s look at this relative to the videos that report reduced oxygen with masks. Again, normal atmospheric pressure at sea level is approximately 760mmHg and the PO2 is around 159mmHg. At 9000 ft, the barometric pressure is about 543 mmHg. So, the PO2 would be around 114 mmHg. In one of the videos someone shared on Facebook, the guy recorded the oxygen inside the mask to be around 15%. (The drop was pretty much the same no matter what type of mask you are wearing—neck gaiter, cloth mask, or N95.) As such, the PO2 would be about 114mmHg (760 mm Hg x 0.15)—similar to being at 9000 ft. Obviously this might be a bit uncomfortable, but not necessarily dangerous. Notice (on the oxyhemoglobin dissociation curve) that, even at such a reduced PO2, the hemoglobin saturation is not significantly affected. Now, the “study” in the video where he measured the concentration of O2 inside the mask is flawed for many reasons. Mainly, it is notable that the 15% O2 is because of a degree of CO2 rebreathing—not because the mask is restricting the flow of oxygen. This occurs normally in the lungs, so it is not that significant. (Again, the PO2 is going to drop to about 100 mmHg by the time it reaches the alveoli.) Let’s assume (incorrectly) that drop in PO2 from the atmospheric air to the alveolar air is consistent (i.e., 59 mmHg). As such, the masked air would reach the alveoli with a PO2 of 55 mmHg. Accordingly, the hemoglobin saturation would still be in the “greedy” range and about 90%. The pressure difference between alveolar air and the pulmonary arteries (deoxygenated blood at a PO2 of around 40 mmHg) is still sufficient for gas exchange and the blood remains sufficiently oxygenated. Unless one has a preexisting respiratory disease, wearing a mask should not pose a health risk (though I would encourage workers to take frequent breaks for “fresh” air).
It is more appropriate to look at the oxyhemoglobin (Hb-O2) saturation in response to wearing a mask. Hb-O2 saturation is measured using a device called a pulse oximeter. There are pseudo-science experiments floating about social media that attempt to demonstrate this, but I have not seen a video that appropriately demonstrates the effects of wearing a mask on Hb-O2 saturation, but I don’t need to. We can see the effects of incremental exercise. In most exercisers, the partial pressure of oxygen is maintained within about 10-12 mmHg of resting values. This is shown to be more pronounced in elite endurance athletes with very high oxidative capacities because their maximal exercise is significantly higher, and ventilation just can’t keep up with the high demand for oxygen. Accordingly, it is worth noting that Galen Rupp won the 10,000-meter final in the USA Track & Field Championship in 2011 with a time of 28 minutes and 38.17 seconds wearing a face mask because the pollen count had spiked, and he is allergic. It obviously did not affect his performance. The m2 sports Mask2 is designed to filter pollen, which is larger than the coronavirus, but the effect of PO2 might be expected to be similar to the surgical masks most folks are wearing. It is also notable that work (or grocery shopping) intensity is not as high as running a Championship 10-K. Despite a mask, whatever the type, we can expect the Hb-O2 saturation to remain relatively stable.
There is no evidence that wearing a mask is detrimental—unless you have a respiratory disease. The notion that wearing a mask is going to lead to CO2 poisoning is bullsh**. If you are out for a run or bike ride alone, I personally don’t think a mask is warranted. If required or you expect to come in close proximity of others (which can be quite likely exercising in public) wear a mask that is comfortable for you (any mask will make others feel more comfortable). The neck gaiters are a reasonable choice. Many cyclists and runners already wear these to block dust. They might not guard against transmission as effectively as an N95 masks (masks that should be reserved for health care workers, first responders, and those who are most vulnerable), but they will block large droplets. If your gym ask you to wear one, do so. After all, you are making it possible to the gym to remain open, and exercise is going to do much to boost the health of the herd. If you are concerned about wearing a mask while exercising talk to someone who wears an “altitude” mask during exercise—they will try to convince you of the benefits.
So, yes, wearing a mask is uncomfortable, but it won’t kill you—or anyone. Yes, they look dorky, but, if everyone is wearing then, well, you’ll look like a dork for not wearing one. There are a lot of cool designs available with the pandemic, so find one that suits your personality. (I am waiting for my WVU neck gaiter to arrive. I am also hoping my son’s wrestling team might sell some as a fundraiser.) The sooner we stop complaining about wearing them, the sooner we will be done with them. Given that masks can limit the spread of viruses, I hope it might become the norm for when people have “ordinary” viruses even after COVID-19 is history.
Be your best today; be better tomorrow.
Carpe momento
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