Equal pressure point

equal pressure point is one of the important phenomenon to must know to study ventilators

1. EQUAL PRESSURE POINT Presented by, : Rekha Marbate

2. Contents Introduction how equal pressure point is generated Changes during obstructive condition

3. Introduction Airway caliber is determined by several factors includes, Anatomical support – cartilaginous tissues, lung parenchyma Pressure differences across their wall larger airways provide support from cartilaginous tissues along with pressure differences along their wall

4. As smaller airways lack cartilaginous support, they depend on support provided by surrounding lung parenchyma and pressure differences along their wall. Transpulmonary pressure gradient [ PL = Pav -pl] helps to stabilize the airways , specially smaller airways Transmural pressure gradient is the pressure difference between pleural pressure and pressure inside airway .

5. During quite breathing , pleural pressure is normally subatmospheric Airway pressure varies minimally and is usually close to 0. Transmural pressure gradient during quite breathing is negative ,even during exhalation[ -5 to-10 cm H2O]. Equal pressure point is found during forced expiration , when airway pressure that is generated in smaller airways has dropped to a level where it equals to pleural pressure

6. HOW EQUAL PRESSURE POINT GENERATED ? During forced exhalation ,contraction of expiratory muscle can increases pleural pressure above atmospheric pressure. This reverse causes transmural pressure gradient to be positive If the positive transmural pressure gradient exceed the supporting force provided by the lung parenchyma . The airway may collapse.

7. In healthy airway, this occurs only with forced expiration at low lung volume but in diseased lung it may occur with normal breathing. Forced contraction of expiratory muscle increase pressure across thorax increase pleural pressure > atmospheric [during exhation ] Alveolar pressure= pleural pressure +elastic recoil pressure of lung itself

8. the pressure along airway drops as gas flow from alveoli to mouth transmural pressure gradient drops continually. At some point along the airway , the pressure inside equals the pressure outside in the pleural space ,, this is reffered to equal pressure point

9. Applied , Downstream from this point , pleural pressure exceed the airway pressure. The resultant positive transmural pressure gradient causes compression of airways & leading to collapse Additional support from elastic tissues and lung parenchyma support the smaller airways to oppose the collapsing force generated by transmural pressure gradient.

10. On emphysema , elastic tissues responsible for supporting smaller airways get destroyed. reduces elastic recoil , also obliterate the anatomical structure responsible for small airway support expiratory flow is limited by airways collapse during exhalation.

11. - Thank you