<unk>  is the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity. During human ventilation, air flows because of pressure gradients.<unk>  = Palv – Pip. Where<unk>  is<unk> , Palv is alveolar pressure, and Pip is intrapleural pressure. Physiology== Since atmospheric pressure is relatively constant, pressure in the lungs must be higher or lower than atmospheric pressure for air to flow between the atmosphere and the alveoli. If<unk> ' = 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<unk>  is always positive; intrapleural pressure is always negative and relatively large, while alveolar pressure moves from slightly negative to slightly positive as a person breathes. For a given lung volume, the<unk>  is equal and opposite to the elastic recoil pressure of the lung. The<unk>  vs volume curve of inhalation (usually plotted as volume as a function of pressure) is different from that of exhalation, the difference being described as hysteresis. Lung volume at any given pressure during inhalation is more than the lung volume at any given pressure during exhalation.
Transpulmonary pressure
Right atrial pressure
Pulmonary wedge pressure
Alveolar pressure
Intrapleural pressure
Left atrial volume
Arteriovenous oxygen difference
Coronary perfusion pressure