Which pressure is the pressure required to inflate the lungs during positive pressure ventilation?

• A. Transairway
• B. Transpulmonary
• C. Transthoracic
• D. Transrespiratory

Answer: (D)

The key idea is that what actually drives inflation of the lungs when a vent delivers positive pressure is the pressure difference across the whole respiratory system—the transrespiratory pressure. This is the gradient from the airway opening to the body surface (airway pressure minus body surface pressure). When the ventilator raises airway pressure, this creates a driving force that expands both the lungs and the chest wall as a unit, inflating the lungs.

Other gradients describe specific parts of the system but don’t represent the total inflation-driving pressure. Transairway pressure is the drop along the conducting airways. Transpulmonary pressure is Palv minus pleural pressure, the distending pressure on the lung tissue itself. Transthoracic pressure is the gradient across the chest wall. The transrespiratory pressure, by contrast, captures the net pressure applied to the entire respiratory system to produce ventilation.