A Review of Nasal Nitric Oxide's Powerful Effects

Key Points

• Nasal nitric oxide (NO) acts as our first line of defense against airborne pathogens by sterilizing incoming air and enhancing cilia movement

• Nasal NO plays a role in warming the air we breathe as it travels into the lungs

• Humming significantly increases nasal NO and could be used as a test for sinus disorders
  

The Breathing Diabetic Summary

I spend a lot of time reading about nitric oxide (NO).  But, the more I learn, the more interested I become. It seems to pop up everywhere I look. Sometimes I wonder what it can’t do.

Nitric oxide’s physiological relevance was discovered in 1987, the same year I was born. Its effects were known several years prior, but it wasn’t until two separate papers (both in prestigious journals, PNAS and Nature) were published that NO’s benefits became “official.”

In the respiratory system, the primary source of NO is the upper airways. The paranasal sinuses, in particular, produce ~90% of the NO measured in exhaled air.  

Previously, we have learned that NO acts as our first line of defense against airborne pathogens by sterilizing incoming air.  The breathing community often touts aspect of NO.  Here, we learn there is more to it: nitric oxide also increases the cilia motility.  

Cilia are tiny hairs lining the back of your nose and respiratory tract. They oscillate back and forth to move mucus out of the upper and lower airways, bringing pathogens and other potentially harmful agents along for the ride.  Cilia are your lung’s first defense against inhaled particles and nitric oxide enhances their activity.  

Nitric oxide also plays a role in warming incoming air. The precise mechanism is unclear, but increased nasal NO release is associated with increased temperature in the nasal airways.

Here is my speculation: NO increases blood flow in your nose, which warms the nasal passages and airways. As air travels through, it extracts this warmth before entering the lungs. Makes sense, but is just a hypothesis and likely oversimplifies what is going on…

Nasal nitric oxide also redistributes blood flow in the lungs when in the upright position, leading to better oxygen uptake. (Nasal NO might even be an adaptation to gravity, allowing us to walk upright.)  

Finally, humming causes a significant increase in nasal NO. However, some sinus disorders inhibit this enhanced NO release. Therefore, the measurement of nasal NO after humming might be a way to test for sinus disorders.

To summarize, nasal nitric oxide is a powerful gas. It acts as our first line of defense against airborne pathogens by sterilizing incoming air and by improving cilia motility. Additionally, NO helps warm the air we breathe as it travels into our lungs. NO also redistributes blood flow in the lungs, resulting in better oxygen uptake. Lastly, humming increases NO significantly and might provide a way to test for sinus disorders.

Abstract

Exhaled nitric oxide (NO) originates from the upper airways, and takes action, to varying extents, in regulation, protection and defense, as well as in noxious processes. Nitric oxide retains important functions in a wide range of physiological and pathophysiological processes of the human body, including vaso-regulation, antimicrobial activity, neurotransmission and respiration. This review article reports the ongoing investigations regarding the source, biology and relevance of NO within upper respiratory tract. In addition, we discuss the role of NO, originating from nasal and paranasal sinuses, in inflammatory disorders such as allergic rhinitis, sinusitis, primary ciliary dyskinesia, and cystic fibrosis.

Journal Reference:

Maniscalco M, Bianco A, Mazzarella G, Motta A.  Recent Advances on Nitric Oxide in the Upper Airways.  Curr Med Chem. 2016;23(24):2736-2745.

Nitric Oxide Might Outweigh All Other Benefits of Nose Breathing

Key Points

• Nasal nitric oxide (NO) acts as our body’s first line of defense against airborne pathogens

• Nasal NO reduces blood pressure, redistributes blood flow, and increases gas exchange

• The humidifying effects of the nose might not be as important as NO

The Breathing Diabetic Summary

Nitric oxide (NO) has, somewhat quietly, become a staple of breathing science.  NO is produced in the nasal airways and carried into the lungs with each (nasal) breath we take.  This review discussed nasal NO, its origins, and its physiological effects in the body.

The general consensus is that NO is produced in the paranasal sinuses and is continuously released into the nasal airways.  Because of this continuous release, NO’s concentration is dependent on flow rate.  A lower flow rate will allow more NO to build up, thus bringing higher concentrations down into the lungs with each breath.   

This could be yet another benefit of slow breathing: Slower flow rates will increase NO. Each breath then brings in a higher concentration of NO, redistributing blood flow, increasing gas exchange, and potentially increasing infection-fighting capabilities.

Which brings us to the next physiological effect of nasal NO: Host defense.  Some bacteria die when NO concentrations are as low as 100 parts per billion (ppb).  In the paranasal sinuses, the concentration can be as great as 30,000 ppb(!).  Thus, nasal NO might be the first line of defense against airborne bacteria, acting to sterilize the incoming air and reduce infection. 

Nasal NO also increases arterial oxygenation and reduces blood pressure in the lungs.  For example, one study showed that nasal breathing increased tissue oxygenation by 10% when compared to mouth breathing.  That’s pretty remarkable.

For example, one study showed that nasal breathing increased tissue oxygenation by 10% when compared to mouth breathing.

Another study showed that when mouth breathers were given supplemental NO, arterial oxygenation increased and and lung blood pressure decreased similar to nose breathing.  Interestingly, if the mouth breathers were just given moistened air (without NO), these effects did not occur.  Thus, the main benefits of nasal breathing might be due to NO, not the warming and humidifying effects that are typically touted (although they clearly help).

Finally, widening the nostrils via nasal tape also increases arterial oxygenation during breathing at rest.  This could partially be due to an increased delivery of NO to the lungs.  We can naturally unblock our noses using simple breath hold techniques or use something like Intake Breathing for assistance.

Overall, this study highlighted several important aspects of nasal NO.  It acts as our body’s first line of defense against airborne pathogens by sterilizing incoming air.  Then, as NO travels into the lungs, it reduces blood pressure, redistributes blood flow, and increases gas exchange, leading to greater arterial oxygenation.  Finally, we learned that the humidifying effects of the nose might not be as important as NO. 

I am continually amazed by the many roles of nitric oxide in the body.  I believe it might be the most important aspect of nasal breathing. 

Journal Reference:

Lundberg JO, Weitzberg E.  Nasal nitric oxide in man.  Thorax.  1999;54(10):947-52.