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Intrapulmonary Pressure

The intrapulmonary pressure plays an essential role in respiration. Following the principle stating that the air flows from higher to lower pressure, it allows inspiration and exhalation. In comparison with atmospheric pressure, at the beginning of inspiration, the intrapulmonary pressure is negative, and at the beginning of the expiration, it is positive. At the end of inspiration and expiration, the intrapulmonary pressure equals the atmospheric pressure.

This is an illustration of a human torso where the trachea, the lungs, and the diaphragm are visible. P A is the atmospheric pressure. P I is the intrapulmonary pressure. P I is equal to P A. When P I is equal to minus three millimeters of mercury, it means that the intrapulmonary pressure is 3 millimeters of mercury below P A, which would be 757 millimeters of mercury. When P I is equal to plus three millimeters of mercury, it means that the intrapulmonary pressure is 3 millimeters of mercury above P A, which would be 763 millimeters of mercury.

Figure 1. Overview of the respiratory system and the difference between atmospheric and intrapulmonary pressure when breathing.

Referred from:

Article
Pressure inside the lungs