Intrapleural pressure is most negative at the completion of inspiration.
Because the negative pressure is the major factor preventing the lungs from collapsing. If the intrapleural pressure became equal to atmospheric pressure the lungs would recoil and collapse.
Intrapleural pressure is maintained by the opposing forces of the elastic recoil of the lung and chest wall. During inspiration, the diaphragm contracts and the intercostal muscles expand the thoracic cage, causing a decrease in intrapleural pressure. This negative pressure helps keep the lungs inflated.
The lung will collapse (atelectasis) because the negative intrapleural pressure gradient that keeps the lung inflated has is now at equilibrium with atmospheric pressure.
Intrathoracic pressure
The intraplural pressure becomes more negative simply because as the inspriatory muscles (diaphragm, external intercostals) act to increase thoracic volume, the intrapleural space increases in volume somewhat, thereby decreasing the pressure (Boyle's Law). Its explained well in most Physiological texts if that doesn't help
Intrathoracic pressure is the pressure inside of the pleural cavity. It is also called intrapleural pressure and the normal pressure is called negative pressure.
intrapleural pressure
Intrapulmonary pressure is the pressure inside the lung alveoli, while intrapleural pressure is the pressure in the pleural cavity. During normal breathing, intrapleural pressure is lower than intrapulmonary pressure, creating a pressure gradient that helps keep the lungs inflated.
The intrapleual pressure is always below atmospheric pressure. Because of the connection between the two plurae which is similar to two wet pieces of paper adhered to each other, the negative intrapleural pressure helps to expand the lungs during ventilation. If intrapleural pressure was equal to atmospheric pressure, the lungs would collapse. Such a case is seen in a penetration of the thoracic cavity (pneumothorax), where a puncture in the thoracic cavity, and subsequently the plurae, will result in a collapsed lung.
Intrapleural pressure becomes positive during forced expiration or coughing when the muscles contract forcefully to increase the pressure within the thoracic cavity. This positive intrapleural pressure helps to push air out of the lungs.
surfactant- the substance that your lungs produces. Also continuous pressure from the air in there.
During quiet breathing, the intrapleural pressure decreases during inspiration as the diaphragm contracts and the thoracic cavity expands, leading to a decrease in pressure inside the lungs. During expiration, intrapleural pressure increases as the diaphragm relaxes and the thoracic cavity decreases in volume, causing an increase in pressure inside the lungs.