Nasal Nitric Oxide and Regulation of Human Pulmonary Blood Flow in the Upright Position

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Citation

Sánchez Crespo, A., Hallberg, J., Lundberg, J. O., Lindahl, S. G., Jacobsson, H., Weitzberg, E., & Nyrén, S. (2010). Nasal nitric oxide and regulation of human pulmonary blood flow in the upright position. Journal of applied physiology, 108(1), 181-188.

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Note: You can share anything you want from these 411s—the more sharing the better. But this is my attempt to condense the findings into a bite-sized wisdom nugget:

A 2010 study found that nasal breathing redistributes blood flow from the bottom to the top of the lungs and from the back to the front due to nitric oxide. This suggests that nasal nitric oxide may be an evolutionary adaption to counteract gravity and allow us to walk upright.

4 Fundamentals

 

1. Essential Background Material

 

  • Blood flow in the lungs is critical for gas exchange (more blood flow = better gas exchange) and for fighting infections (areas of the lung with less blood flow are more susceptible to infection).

  • In general, gravity makes blood flow greater in the lower portions of the lungs.

  • However, blood flow can also be quite heterogeneous in human lungs, indicating that other factors besides gravity play a role.

  • The authors of this study hypothesized that inhalation of nasally-derived nitric oxide (NO), a potent vasodilator, may be essential to controlling lung blood flow distribution.

  • Moreover, because nasal NO is found mainly in upright primates, they hypothesized that it may have been an evolutionary adaptation to counteract the effects of gravity in the upright position.

 

 

2. What Did this Research Do?

 

This study used two radiotracers to map blood flow in the lungs.

 

The experiment had 14 participants that were broken into three groups:

  • Control Group (N=3): This group was used to ensure the two tracers worked as intended.

  • Nasal Group (N=7): This group sat upright and breathed through their mouths for 20 min.  Then, they were injected with a tracer and switched to nose-in/mouth-out breathing for 10 min.  At the end of the 10 minutes, they were injected with a second tracer.

  • Mouth NO Group (N=4): This group did the same protocol as the Nasal Group.  However, instead of switching to nose breathing, they continued mouth breathing, but with exogenous NO added at levels close to those produced by the paranasal sinuses.  This experiment was performed to see if NO explained blood flow changes between nasal and mouth breathing or if it was some other mechanism associated with the nose.

 

 

3 & 4. What Were the Major Findings and Why Do They Matter?

 

Nasal breathing, and mouth breathing with added NO, both redistributed blood flow throughout the lungs in similar magnitudes.

  •  This is a critical finding because it shows that NO causes blood flow redistribution, not some other factor associated with nasal breathing.

 

Total lung blood flow shifted from the bottom third to the top third of the lung, resulting in a 24% net increase in blood flow in this upper region.  (Blood flow in the middle third of the lung remained basically unchanged.)

  • This indicates that NO specifically redistributes blood flow to counteract gravity, moving more from the bottom to the top of the lung.  This suggests (but doesn’t prove) that it may indeed be an evolutionary adaptation to gravity.

 

 

Blood flow also shifted from the back of the lungs toward to center and front of the lungs, resulting in a 7% net increase in blood flow to each of these regions.

 

  • This is meaningful because it shows that NO doesn’t just redistribute blood flow from bottom-to-top, but also from back-to-front.

 

Altogether, these results help explain how nasal breathing improves oxygenation, protects against infection, and counteracts the effects of gravity.

 

  • Oxygenation: We’ve learned that both nasal breathing and mouth breathing with NO increase oxygenation by 10-18%.  This study’s results provide one reason why: blood flow is redistributed in the lungs, improving gas exchange.

  • Fighting Infection: Lung infections occur more frequently in regions of the lungs that receive less blood flow.  Thus, nasal NO may have been an evolutionary adaptation to redistribute lung blood flow to help protect all areas of the lungs.

  • Counteracting Gravity: In their words: “In this work, we have demonstrated that nasal breathing counteracts the effects of gravity on pulmonary blood flow in the upright position by redistribution of blood to the nondependent lung regions.” 👏

 

 

1 Big Takeaway

 

Due to nitric oxide, nasal breathing redistributes blood flow from the bottom to the top of the lungs and from the back to the front. This suggests that nasal nitric oxide may have been an evolutionary adaption to counteract gravity and allow us to walk upright.

 

 

1 Practical Application

 

This one is straightforward: breathe through your nose as much as possible (and perhaps practice nose-in/mouth-out now and then) to maximize NO delivery, improve blood flow distribution in the lungs, and potentially reduce your risk of lung infections.