The intrapleural pressure is negative both during inspiration and expiration because
High-Yield Explanation
Intrapleural pressure is the pressure within the pleural cavity. Intrapleural pressure is always negative, which acts like a suction to keep the lungs inflated. The negative intrapleural pressure is due to three main factors: 1. The surface tension of the alveolar fluid Ref: guyton and hall textbook of medical physiology 12 edition page number:317,318,319