Intrapulmonary pressure becomes more positive during which phase of breathing?

During exhalation, intrapulmonary pressure increases and becomes more positive relative to atmospheric pressure. This occurs because the diaphragm and intercostal muscles relax, reducing the volume of the thoracic cavity. As the volume decreases, the pressure within the lungs rises above atmospheric pressure, leading to air being expelled from the lungs.

In contrast, during inhalation, intrapulmonary pressure becomes negative as the lungs expand and the volume increases. This allows air to flow into the lungs. Resting breathing involves a balance of these pressure changes but does not distinctly highlight the positive shift in pressure typical of exhalation. Forced inhalation would further decrease intrapulmonary pressure as additional muscles are engaged to increase lung volume even more. Thus, the correct understanding of intrapulmonary pressure dynamics during breathing phases highlights that it is during exhalation that this pressure rises and becomes more positive.