Gravity is pretty awesome. After all, it keeps us here on Earth. And when our bodies are not subject to gravity (say, if you’re an astronaut), some crazy things happen. For example,
Astronauts lose 25% of their aerobic capacity in 7-14 days (it usually takes 10 years to lose 10% here on Earth)
Bone density can decrease as fast as 5% a month (it’s usually about 1% a year on Earth)
Thus, our bodies are clearly meant to be under the influence of gravity. However, as we became upright mammals walking on two feet, gravity could have posed an issue.
Blood flow in our lungs is influenced by several factors, but one of the largest is gravity. Gravity acts to focus blood toward the base of the lungs.
Interestingly, in humans and other primates, the nasal airways produce a considerable amount of nitric oxide (NO). As we’ve learned before, NO is a potent vasodilator that is critical for whole-body oxygenation.
Maybe the NO produced in the nasal airways is an adaptation to walking upright and helps counter gravity’s effects on blood flow? That was the hypothesis of the study I’m sharing this week.
Nasal Nitric Oxide: Nature’s Answer to Gravity?
This research found that when participants breathed through their noses, blood flow in the lungs became more uniform and gas exchange was increased. Breathing through the mouth did not have these effects.
However, if subjects breathed through their mouths but were given supplemental NO, the blood flow in their lungs looked similar to nasal breathing.
This suggests that NO is responsible for making blood flow more uniform in the lungs.
The authors hypothesize that nasal NO might be an evolutionary adaptation to counter the effects of gravity on lung blood flow, allowing greater and more efficient gas exchange to occur.
We often praise nasal breathing for its warming and humidifying effects. But the more I learn, the more convinced I am that nitric oxide is the real hero.
In good breath,
Nick