Why it might feel like you can’t breathe while wearing a mask (and how you still can): a simple thread on respiratory physiology from a kid’s lung doctor.

I hear some people say they can’t breathe while wearing a mask and will provide some education and support to those who may be experiencing this. Masks can be uncomfortable due to heat, humidity, and itch, and can affect your breathing, but maybe not in the way you would expect.

While masks do not impair oxygenation or ventilation, they can promote dysfunctional breathing patterns which can promote shortness of breath or difficulty breathing. You can control your breathing to override these patterns, but it may take a bit of mindfulness and practice.

Breathing serves 2 functions: O2 in & CO2 out. Normally breathing occurs at resting lung volume (FRC). Lungs are relaxed, and it takes little effort to breathe. There’s room to take deeper breaths, using IRV (inspiratory reserve volume) such as with talking or physical activity.

CO2 depends on minute ventilation (volume over time). The bigger and more frequent breaths, the lower your CO2. If you feel dizzy and lightheaded, you are probably hyperventilating and dropping your CO2 too low, which your brain doesn’t like. Relax and slow your breathing.

Conversely, you may start to breathe more shallowly or less frequently due to the uncomfortable sensations while wearing a mask (voluntary hypoventilation), which can lead to feeling short of breath. Try to stay calm and maintain a normal breathing depth and rate.

Otherwise, masks do not affect ventilation. CO2 does not get trapped or cause CO2 rebreathing. Even if this was true, normal tidal volume is ~500 mL, so most air actually comes from outside the mask, and your brain would just make you breathe more to get rid of the CO2 anyways.

O2 is more complicated, but still unaffected. Amount of O2 reaching your lungs depends predominantly on the partial pressure of oxygen in the air, which depends on the concentration of O2 (21%), and atmospheric pressure where you live. (Note: CO2 also, but not relevant to this).

Masks don’t filter O2 molecules, unless you forget to take off the plastic. Air on both sides of the mask contains 21% O2. Masks do add a negligible pressure drop (0.00104 cm H2O from https://www.researchgate.net/profile/Gerald_Smaldone/publication/261745047_Respiratory_Source_Control_Using_Surgical_Masks_With_Nanofiber_Media/links/549623a90cf2ec13375b2e98/Respiratory-Source-Control-Using-Surgical-Masks-With-Nanofiber-Media.pdf?origin=publication_detail), but this is only ~0.04% of the pressure drop across the entire airway.

If anything, extra resistance would provide positive end-expiratory pressure (PEEP) which helps prevent airways from collapsing during exhalation in obstructive lung diseases such as asthma and COPD. For reference, minimum CPAP used for OSA is 4 cmH2O and often 10 cmH2O or more.

Normal inspiratory:expiratory breath ratio is 1:2, which means you spend twice as long breathing out as you do in. Exhaling into a mask can be uncomfortable, such as by blowing air and humidity into the eyes, and may make you consciously shorten or stop your exhalation too soon.

However, if you do not completely exhale back to FRC before taking your next breath in, you will be “breath-stacking”. By continually adding more volume in than you let out, you develop hyperinflation. You would be near the top of this volume-time curve http://www.tomhsiung.com/wordpress/2016/09/pressure-volume-relationships-in-the-respiratory-system/

It feels uncomfortable to breathe in at high lung volumes, because the lung is already stiff with air (think of blowing up a balloon when it is already full), and there is no more IRV. It will feel difficult to take each breath in, and you will start to feel short of breath.

To avoid this, focus on exhalation. Breathe all the way out, until your chest & abdomen are completely relaxed. It feels much more comfortable to breathe at FRC. Strategies to help you to breathe out completely can include something called “box breathing”. https://www.maimonidesem.org/blog/box-breathing-technique-nbspnbsp

Another potential dysfunctional breathing pattern is thoracic breathing, by using muscles in the chest, neck, and shoulders to breathe instead of the diaphragm, a domed muscle below your lungs, which is by far the most energy efficient respiratory muscle.
https://fitnessgenes.com/blog/diaphragm/ 

Focus on diaphragmatic, or “belly breathing”, by putting your hand on your belly. You should feel your hand move out when you breathe in, and in when you breathe out. Your shoulders and head shouldn’t bob during relaxed tidal breathing. Your neck muscles should be relaxed.

So while masks can feel uncomfortable, you can definitely still breathe. There is no lung condition aside from the most extreme possible examples that would prevent mask wearing. And we can help protect that person by distancing, hand hygiene, & everyone else wearing a mask!