In physiology, intrapleural pressure (also called intrathoracic pressure) refers to the pressure within the pleural cavity. Normally, the pressure within the pleural cavity is slightly less than the atmospheric pressure, in what is known as negative pressure. When the pleural cavity is damaged/ruptured and the intrapleural pressure becomes equal to or exceeds the atmospheric pressure, pneumothorax may ensue.
Intrapleural pressure depends on the ventilation phase, atmospheric pressure, and the volume of the intrapleural cavity.
At rest we have a negative intrapleural pressure. This gives us a transpulmonary pressure expanding the lungs. Intrapleural pressure is sub-atmospheric. This is due to the recoil of the chest and lungs away each other.
Müller's maneuver can temporarily significantly decrease the intrapleural pressure.
The logic in intra-pulmonary pressure and the intra-pleural pressure is that the, pressure becomes more negative during inspiration and allows air to get sucked in (Boyle 's law.) P vs V relationship.....and during expiration the pressure becomes less negative and ( greater than atmospheric pressure, Note :[ the partial pressure of Carbon dioxide.] ) and air is given out ....The only difference in the pressures are intra-pleural pressure is more negative than intra-pulmonary pressure.... Factors affecting are :
Physiological effects - 1.) mullers maneuver -forced inspiration against a closed glottis results in negative pressure.... 2.) Deep inspirationPathological effects : 1.) Emphysema
2.) Pneumothorax Condition.