Busting The CO2 Myths of Face Masks

This is a follow up to "Unmasking The Mask Debate In The Social Media"

Myth: Facial masks increase carbon dioxide (CO2) in our body due to re-breathing effect. Fact: Facial masks do not increase CO2 in our body due to re-breathing effect

Myth: Do not use masks if you do not want to breathe in CO2. Fact: Do not use fossil fuels if you do not want to breathe in CO2.

Myths are being circulated on social media by even educated professionals and practicing physicians that face masks can make us re-breathe our own expired CO2 and somehow harmful. As a pediatric pulmonologist where I breathe pulmonary physiology for a living, let me bust this myth using pulmonary physiology.

In plain language, I am going to walk you through the common terms we use in pulmonary physiology such as, 1) Respiratory Cycle 2) Respiratory Rate 3) Inspiratory Time Fraction 4) Tidal Volume and 5) Inspiratory Flow Rate. I will then show you how to bust the myth.

We suck the outside air at a rate of 15L/min through the face mask. Any residual carbon dioxide hanging between the nose and the mask gets entrained or diluted by the outside air that gushes through the pores in the mask at a rate of 15L/min.

Respiratory Cycle: A cycle of start of inspiration (breathing in) until the end of expiration (breathing out). A normal respiratory cycle often has pauses between inspiration & expiration or sometimes during inspiratory and expiratory phases.

There is more than enough time for the expired air which has little more carbon dioxide than the inspired air to escape into the environment.

Each respiratory cycle has inspiratory phase & expiratory phase with or without pauses.

Respiratory Rate: Number of respiratory cycles per minute.

Fact: Normal respiratory rate in adults at rest is about 12-15

Let us imagine that a 75-year-old male is breathing at 12 breaths per minute or in other words, has a respiratory rate (RR) of 12.

Each respiratory cycle would last for 5 seconds during which, he breathes in (inspiration), takes a short pause, breathes out (expiration) and may take another short pause before beginning to take the next breath.

Inspiratory Time Fraction: The fraction of each respiratory cycle, during which inspiration occurs is called Inspiratory Time fraction or (Ti)

Fact: We normally take 2x or more time to breathe out than breathe in.

Let’s imagine that in the example of our 75-year-old male with a respiratory cycle of 5 seconds, breathing in (inspiratory phase) occurs for 2 seconds and breathing out (expiratory phase) occurs for 4 seconds with a pause of 1 second in between.

In this case, the Ti would be 2/5 or 0.4

It means, there is more time (2.5x more time to be precise) for expired air to diffuse during each respiratory cycle. In other words, there is more than enough time for the expired air which has little more carbon dioxide than the inspired air to escape into the environment.

Tidal Volume: The volume of gas that we breathe in or breathe out during each respiratory cycle at restful breathing is called Tidal Volume (Vt). Although there might be some breath to breath variations, when averaged out, the volume we breathe out is always equal to the volume we breathe in.

Fact: The normal Tidal Volume or Vt is about 500 mL or 0.5L.

Inspiratory Flow Rate: The rate of flow of gas through our nose or mouth during inspiration is called inspiratory flow rate V̇i

In the above example of 72-year-old adult male, his V̇i is 0.5L/2s = 0.25L/sec or 15L/min.

In other words, when we have a face mask which to some extent acts as a filter, we suck the outside air at a rate of 15L/min through the face mask. If there is any residual carbon dioxide hanging between the nose and the mask, it gets entrained or diluted by the outside air that gushes through the pores in the mask at a rate of 15L/min. At the end of the day, we inhale the tiny fraction of CO2 that is already in the environment.

The best way to avoid re-breathing CO2 is not going after the masks but the CO2 producing fossil fuels.