Pressures in Ventilation

What is the pressure of the atmosphere at sea level?

What happens to atmospheric pressure with increasing altitude above sea level?

What is the pressure within the alveoli when equilibrated with atmospheric pressure?

Why does air quickly flow down its pressure gradient in the alveoli?

What is the direction of airflow when intra-alveolar pressure is higher than atmospheric pressure?

What is the value of intra-alveolar pressure during inspiration?

What is the reference point when relating other pressures to atmospheric pressure?

What is the pressure exerted by the weight of the gas in the atmosphere on objects on Earth's surface?

What happens to intra-alveolar pressure at the end of both inspiration and expiration?

What is the pressure within the pleural sac?

What is the normal pressure of the intrapleural space?

What causes the negativity of intrapleural pressure?

What is the function of the diaphragm in relation to intrapleural pressure?

What is the pressure within the alveoli when equilibrated with atmospheric pressure?

What is the term for the space between the lungs and the thoracic cage?

How can intrapleural pressure be measured?

Air flows from an area of high pressure to an area of low pressure due to a pressure gradient
Atmospheric pressure is the pressure of the atmosphere on the earth's surface, with a value of 760 mmHg at sea level
Atmospheric pressure decreases with increasing altitude above sea level and increases below sea level
It is used as a reference point (zero) when relating other pressures to it

Intrapulmonary pressure is the pressure within the alveoli
It changes during inspiration (-1 or 759 mmHg) and expiration (+1 or 761 mmHg)
It is equal to atmospheric pressure (0 or 760 mmHg) at the end of both inspiration and expiration
Because alveoli communicate with the atmosphere through conducting airways, air quickly flows down its pressure gradient until the two pressures equilibrate (become equal)

Intrapleural pressure is the pressure within the pleural sac
It is the pressure exerted outside the lungs within the thoracic cavity
It is not connected to atmospheric or alveolar pressure; thus, it does not equilibrate with them
It is sub-atmospheric at rest, with a value of -4 mmHg (756 mmHg)
It can be measured indirectly by an intra-oesophygeal balloon connected to a manometer
Causes of negativity of intrapleural pressure include:
- Normal lung at rest
- Elastic recoil of the chest wall and lung creates an inward pull
- The chest wall tries to pull outward, while the lung tries to pull inward, resulting in a negative pressure