Final answer:
The lowest pressure at rest during respiration is intrapleural pressure, which is lower than atmospheric pressure, resulting in the creation of the transpulmonary pressure that allows air to flow into the lungs.
Step-by-step explanation:
The lowest pressure at rest during respiration is the intrapleural pressure. This pressure is negative relative to atmospheric pressure, meaning it is lower than the atmospheric pressure. Pulmonary ventilation relies on the differences in pressure, essentially following Boyle's Law, which dictates that in a gas, pressure increases as volume decreases. The difference in pressure between the intrapleural and intra-alveolar pressures is what we call the transpulmonary pressure.
Since the intrapleural pressure is typically negative compared to intra-alveolar pressure, this ensures that air flows into the lungs from an area of higher pressure to one of lower pressure during inspiration. Consequently, gases, such as oxygen, will then flow from the lungs (where PO₂ is approximately 150 mm Hg) into the bloodstream (where PO₂ is about 100 mm Hg), facilitating gas exchange vital for respiration.