Flow is proportional to which of the following factors between the alveoli and atmosphere?

• A. Air resistance
• B. Pressure gradient
• C. Temperature
• D. Compliance of lung tissue

Answer: (B)

Flow between the alveoli and the atmosphere is primarily determined by the pressure gradient. This pressure gradient is the difference in pressure between the alveoli, where gas exchange occurs, and the atmospheric pressure outside the body. The greater this difference, the greater the flow of air into or out of the lungs. During inhalation, the pressure inside the lungs decreases relative to atmospheric pressure, allowing air to flow in; conversely, during exhalation, the pressure inside the lungs increases, driving air out.

While air resistance, temperature, and compliance of lung tissue can influence airflow, they do so in conjunction with the pressure gradient rather than being the primary driver of flow itself. Thus, focusing on the pressure gradient emphasizes its crucial role in the mechanics of ventilation and the gas exchange process.