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How can I exhale if the pressure in my chest is always lower than the pressure of the atmosphere? I can even blow up balloons.
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[–]ethernaut85 2 points 1 month ago
You have a few different pressures in your chest at any given time. There is a negative intrapleural pressure that keeps your lungs expanded against the interior of your chest wall. This negative pressure exists between the pleura lining the exterior of the lungs and the interior of the rib cage. This negative pressure keeps the lungs in close (but not absolute) contact with the rib cage.
The reason this negative pressure can exist at a lower pressure than the atmosphere is because it is a closed system. (Read: this space is not inside the lungs but between the lungs and rib cage) The ribs are rigid and the lungs have some tension pulling inward, creating a pressure that is negative. This is why large wounds to the chest wall can cause a collapsed lung (aka, pneumothorax). The basis behind this is that when the negative pressure no longer exists due to a hole in the closed system, there is no longer a negative pressure to keep the lung expanded and this allows the intrapleural (between lungs and ribcage) space to equalize with atmospheric pressure. This allows an influx of air into the space, collapsing the lung.
When you inhale, your diaphragm, rib cage and abdominal muscles create a negative pressure gradient between the interior of your lungs and the atmosphere. The pressure equalizes, thus air rushes in.
We passively exhale by the natural recoil of the lungs and rib cage, creating a positive pressure in the lungs, higher than the atmospheric pressure, causing air to flow out.
When you actively exhale you use accessory muscles to force air out. You're essentially creating a greater pressure gradient, which gives you a pressure great enough to inflate a balloon, which is indeed greater than atmospheric pressure. Despite all this, you still have a slightly negative pressure between the pleura, save certain circumstances...
Source: Student Anesthetist... Thanks for making me think this out and review it!

Student Anesthetist Citation

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