If I’m riding in a car with the window down and we’re moving fast, I can exhale just fine with my head inside the car.
If I lean my head out the window and the wind is blowing directly into my face, when I try to exhale it feels like I’m out of air and I instinctively try not to exhale. What’s up with that?
In: Physics
It’s why you blow air in babies faces before you dunking them under water (when teaching them to swim).
I’ve seen this question multiple times before, and a lot of people answer with the Bernoulli principle (fast travelling air = reduced pressure = mechanical difficulty of lungs to draw any air). Despite the much support from other comments on such posts, as a physiologist I have to say this is incorrect. You can see why if you just put a blow drier with its rear facing an open fridge/freezer and front facing up your nostrils, you’ll notice an immediate reflexive inability to breathe at all, not a difficulty but complete cessation. That is because it is a biological reflex, not a physical phenomenon.
The mammalian diving reflex is a process where as soon as certain parts of your face (trigeminal area, nostrils and eyelids) are suddenly cooled by water, your brainstem sends signals that completely stop breathing and redirect blood towards your heart and brain. It’s a reflex that is supposed to help you survive sudden diving so you don’t breathe water and so your vital organs are protected from low oxygen. Although the mechanism by which this sensation is transmitted to the brain remains poorly understood, it is currently thought that cold and/or fast air gusts onto the nostrils result in the activation of this reflex preventing you from breathing at the level of the brain. Even if the air is not cold, even if at room temperature, being fast means very high rate of heat loss by convection and that’s quite easy to imagine knowing room temp is in the low twenties while your body is around or just below 37 degrees (as nose can be a bit colder).
It’s called the diving reflex, all mammals have it. It’s normally for being under water when you have limited supply of oxygen, so you don’t exhale and waste it, the air blocking the breathing ways make our body think that there is limited oxygen, therefore triggering the reflex 🙂
When air is blowing in your face it is at a higher pressure then when it is still. This results in a lower difference in air pressure between the air that is in front of your face and that which is in your lungs, making you need more effort to increase the pressure in your lungs to exhale
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