The intrapleural pressure is negative both during inspiration and expiration because
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
Intrapulmonary pressure is always negative
Thoracic cage and lungs are elastic are elastic structure
Transpulmonary pressure determines the negativity
Surfactant prevents the lungs to collapse
Respiratory system