Pressure Relationships in the Thoracic Cavity – Pulmonary Ventilation (Nursing)

00:01 So now let's move into the physiology of the respiratory system.

00:06 The process of breathing is referred to as pulmonary ventilation.

00:11 Pulmonary ventilation consists of two phases.

00:15 The inspiration or inhaling where gas is going to flow into the lungs and then expiration or exhaling where gases are going to exit the lungs.

00:27 Ventilation is going to depend on a relationship between different types of pressure inside and outside of the thoracic cavity.

00:37 First we have our atmospheric pressure, which is the pressure outside of the thoracic cavity from the atmosphere.

00:46 The next pressure is going to be our intrapulmonary pressure.

00:50 This is the pressure that is inside of the lungs and is sometimes also referred to as the intra alveolar pressure.

00:59 A third pressure is our intrapleural pressure.

01:03 This is the pressure in that pleural cavity.

01:05 Remember that thin space between the parietal and the visceral pleura.

01:12 And finally we have our transpulmonary pressure, which is our intrapulmonary pressure minus our intrapleural pressure. (Ppul - Pip) All of these pressures are going to play an important role in our ability to undergo pulmonary ventilation.

01:31 So recall that the atmospheric pressure is 760 as our diaphragm flattens during inhalation.

01:41 The intrapulmonary pressure is going to drop to about 75.

01:47 This happens when the lung expands and causes air to flow in.

01:53 Another thing that happens is our intrapleural pressure is always negative compared to our atmospheric pressure.

02:01 Because of this it creates a sort of vacuum that suctions the visceral pleura along with the thoracic cavity.

02:10 So as the thoracic cavity expands the visceral pleura, which is attached to the lung, is going to expand with the thoracic cavity.

02:20 The other pressure are transpulmonary pressure is positive and also sometimes referred to as the recoil pressure.

02:29 This is also going to explain why the lungs are able to expand and recoil with the chest cavity.