At rest, what is the relationship between alveolar pressure and atmospheric pressure?

At rest, during the respiratory cycle, alveolar pressure is equal to atmospheric pressure. This is an essential aspect of how the respiratory system maintains equilibrium and sets the stage for ventilation.

When a person is at rest and not actively inhaling or exhaling, the pressure inside the alveoli—the tiny air sacs in the lungs where gas exchange occurs—matches the pressure of the atmosphere. This matching pressure is crucial because it prevents the collapse of alveoli and allows for proper lung function.

As a person prepares to inhale, the diaphragm and intercostal muscles contract, leading to a decrease in alveolar pressure. This difference in pressure is what drives air into the lungs. Conversely, during exhalation, the relaxation of these muscles increases the alveolar pressure above that of the atmosphere, forcing air out of the lungs. However, at rest, without any active breathing efforts occurring, the pressures equilibrate, which is why they are equal at that state.