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Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, which is known as negative pressure. [1] When the pleural cavity is damaged or ruptured and the intrapleural pressure becomes greater than the atmospheric pressure, pneumothorax may ensue. Intrapleural pressure is different from intrathoracic pressure.
The diaphragm is the most important muscle of respiration, [3] and separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs. [4]
If 'transpulmonary pressure' = 0 (alveolar pressure = intrapleural pressure), such as when the lungs are removed from the chest cavity or air enters the intrapleural space (a pneumothorax), the lungs collapse as a result of their inherent elastic recoil. Under physiological conditions the transpulmonary pressure is always positive; intrapleural ...
The pleural cavity transmits movements of the ribs muscles to the lungs, particularly during heavy breathing. During inhalation the external intercostals contract, as does the diaphragm. This causes the expansion of the chest wall, that increases the volume of the lungs. A negative pressure is thus created and inhalation occurs.
Respiratory pump: During inspiration, the intrathoracic pressure is negative (suction of air into the lungs), and abdominal pressure is positive (compression of abdominal organs by diaphragm). This makes a pressure gradient between the infra- and supradiaphragmatic parts of v. cava inferior, "pulling" the blood towards the right atrium and ...
Once air enters the pleural cavity, the intrapleural pressure increases, resulting in the difference between the intrapulmonary pressure and the intrapleural pressure (defined as the transpulmonary pressure) to equal zero, which cause the lungs to deflate in contrast to a normal transpulmonary pressure of ~4 mm Hg. [28]
This negative pressure generates airflow because of the pressure difference between the atmosphere and alveolus. The inflow of air into the lungs occurs via the respiratory airways. In health, these airways begin with the nose. [3] [4] It is possible to begin with the mouth, which is the backup breathing system.
The stroke volume usually rises above normal before returning to a normal level. With the return of blood pressure, the pulse rate returns to normal. In summary, the maneuver increases intrathoracic pressure and, thus, a decrease in preload to the heart.