Transpulmonary pressure is the difference between:

Transpulmonary pressure is the pressure difference between alveolar pressure and intrapleural pressure. Before the sta of inspiration or at the end of expiration it is about +5cm H2O. Positive transpulmonary pressure keeps the alveoli open. Intrapleural pressure is the pressure between two layers of pleura. It is about -5cm H2O before the sta of inspiration or at the end of expiration. Alveolar pressure is the pressure within the terminal air spaces. It is the sum of pleural pressure and elastic recoil pressure of the lung. It is atmospheric before the sta of inspiration or at the end of expiration. Transthoracic pressure is the pressure difference between alveolar pressure and pressure at the body surface. Ref: Guyton 12th Ed.