Ptt equals Palv minus Pbs. This is which pressure?

• A. Transrespiratory Pressure
• B. Pta
• C. Transthoracic Pressure
• D. Ptp

Answer: (C)

The pressure in question is the pressure difference across the chest wall. It is defined as the alveolar pressure (inside the lungs) minus the pressure at the body surface. That gradient—the pressure the chest wall has to work against as the lungs inflate or deflate—is called transthoracic pressure.

So, Palv minus Pbs yields the transthoracic pressure, not the pressure across the airway or the lung wall itself. The other similar terms describe different boundaries (for example, across the lung wall or across the airway), which is why they don’t apply here.