physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

, intrapleural pressure refers to the pressure within the

pleural cavity The pleural cavity, pleural space, or interpleural space is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication b ...

. Normally, the pressure within the pleural cavity is slightly less than the

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...

, which is known as ''negative pressure''.Khanorkar, p. 205 When the pleural cavity is damaged or ruptured and the intrapleural pressure becomes greater than the atmospheric pressure,

pneumothorax A pneumothorax is an abnormal collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve i ...

may ensue. Intrapleural pressure is different from intrathoracic pressure. The

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

is the space that includes the pleura, lungs, and heart, while the pleural space is only the space between the

parietal pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips be ...

and

visceral pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips b ...

surrounding lungs. Intrapleural pressure depends on the ventilation phase, atmospheric pressure, and the volume of the intrapleural cavity.Blom, p. 7 At rest, there is a negative intrapleural pressure. This provides a

transpulmonary pressure Transpulmonary pressure is the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity. During human ventilation, air flows because of pressure gradients. Ptp = Palv – Pip. Where Ptp is transpulmonary pressu ...

, causing the lungs to expand. If humans didn't maintain a slightly negative pressure even when exhaling, their lungs would collapse on themselves because all the air would rush towards the area of lower pressure. Intra-pleural pressure is sub-atmospheric. This is due to the recoil of the chest and lungs away from each other.

Müller's maneuver Müller's maneuver is a procedure used in medicine to diagnose some types of tinnitus, and other medical problems. Procedure After a forced expiration, an attempt at inspiration is made with closed mouth and nose, whereby the negative pressure i ...

can temporarily but significantly decrease the intrapleural pressure. The relationship between the intra-pulmonary pressure and intra-pleural pressure is that the pressure becomes more negative during inspiration and allows air to get sucked in (

Boyle's law Boyle's law, also referred to as the Boyle–Mariotte law, or Mariotte's law (especially in France), is an experimental gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as: The ...

) vs relationship and during expiration, the pressure becomes less negative (Note: still less than atmospheric pressure, also take note of the partial pressure of carbon dioxide) and the air is given out. The only difference between the pressures is that intra-pleural pressure is more negative than intra-pulmonary pressure. Factors affecting are: Physiological effects: # Müller's maneuver (forced inspiration against a closed glottis results in negative pressure) # # Deep inspiration Pathological effects: # Emphysema # # Pneumothorax Condition
A person breathing at rest inhales and exhales approximately half a liter of air during each respiratory cycle, which is called tidal volume. The respiratory rate is directly affected by the concentration of carbon dioxide in the blood. ''Lungs do not collapse after forceful respiration because of the residual volume.''

References

;Books * * Respiratory physiology Pulmonology {{Lung-stub