The key difference between intrapleural and intrapulmonary pressure is that intrapleural pressure is the force exerted by gases in the pleural cavity during respiration, while intrapulmonary pressure is the force exerted by gases within the alveoli of the lungs during respiration.
Pulmonary ventilation is the exchange of gases or breathing. Pulmonary ventilation has two main events: inspiration and expiration. During inspiration, air enters the lung, and during expiration, air leaves the lung. It is driven based on pressure differences between the lung and the outer atmosphere. The pressure difference between intrapleural and intrapulmonary pressures is transpulmonary pressure. Two factors determine this pressure: the volume of the space occupied and influence by resistance. Hence, air flows according to a pressure gradient from a space of higher pressure to a space of lower pressure.
CONTENTS
1. Overview and Key Difference
2. What is Intrapleural Pressure
3. What is Intrapulmonary Pressure
4. Similarities – Intrapleural and Intrapulmonary Pressure
5. Intrapleural vs Intrapulmonary Pressure in Tabular Form
6. Summary – Intrapleural vs Intrapulmonary Pressure
What is Intrapleural Pressure?
Intrapleural pressure is the force exerted by gases in the pleural cavity during respiration. Generally, intrapleural pressure is always negative since it acts as a suction to keep lugs inflated. Three factors determine the negative intrapleural pressure: the surface tension of the alveolar fluid, the elasticity of the lungs, and the elasticity of the thoracic wall. The surface tension of the alveolar fluid functions pulls each of the alveoli inward and results in pulling the entire lung inward. The elasticity of the lungs determines negative intrapleural pressure since the elastic tissue in the lung occurs in abundant quantities, and it recoils and pulls the lung inwards, and the lung moves away from the thoracic wall. This increases the area of the thoracic cavity and creates negative pressure. The elasticity of the thoracic wall pulls away from the lung, expanding the pleural cavity further, creating a negative pressure. However, pleural fluids resist the separation of the lung and thoracic wall.
Figure 01: Intrapleural and Intrapulmonary Pressure
Intrapleural pressure changes due to many activities that take place in the respiratory system. When the thoracic wall moves outwards during inspiration, pleural cavity volume increases slightly by decreasing intrapleural pressure. During expiration, the thoracic wall recoils, reducing the volume of the pleural cavity and returns the pressure to a negative value (-4 or 720 mmHg).
What is Intrapulmonary Pressure?
Intrapulmonary pressure is the force exerted by gases within the alveoli of the lungs during respiration. In other words, it is the pressure within the lungs or intra alveolar pressure. In between breathing cycles, the intrapulmonary pressure equalizers to atmospheric pressure of 760 mmHg at sea level. Hence, this generally refers to zero with reference to respiratory pressures. During inspiration, thoracic cavity volume increases and decreases the intrapulmonary pressure below 760 mmHg. This is a negative pressure. Therefore, based on laws of pressure, air moves into the lungs according to the pressure gradient created (high to low pressure).
When the inspiration process stops, intrapulmonary pressure becomes equal to atmospheric pressure (760 mmHg). During expiration, thoracic cavity volume decreases and increases the intrapulmonary pressure above 760mmHg. Hence, air moves out from the lung along the pressure gradient. When the expiration process stops, intrapulmonary pressure becomes equal to atmospheric pressure (760 mmHg). Therefore, intrapulmonary pressure generally becomes zero at the end of each cycle.
What are the Similarities Between Intrapleural and Intrapulmonary Pressure?
- Intrapleural and intrapulmonary pressure take place within the respiratory system.
- Both facilitate inspiration and expiration mechanisms.
- They cause a pressure gradient for the inflow and outflow of air.
- Moreover, they maintain optimum conditions for the gas exchange mechanism.
- Pneumothorax conditions can affect both types of pressures.
What is the Difference Between Intrapleural and Intrapulmonary Pressure?
The key difference between intrapleural and intrapulmonary pressure is that intrapleural pressure is the force exerted by gases in the pleural cavity during respiration, while intrapulmonary pressure is the force exerted by gases within the alveoli of the lungs during respiration. While intrapleural pressure is created in the pleural cavity, intrapulmonary pressure is created at the alveoli of the lungs.
The below infographic presents the differences between intrapleural and intrapulmonary pressure in tabular form for side by side comparison.
Summary – Intrapleural vs Intrapulmonary Pressure
Pulmonary ventilation refers to a breathing process, and it has two main stages: inspiration (air enters the lung) and expiration (air leaves the lung). Intrapleural pressure is the force exerted by gases in the pleural cavity during respiration. Intrapulmonary pressure is the force exerted by gases within the alveoli of the lungs during respiration. Generally, intrapleural pressure is always negative since it acts as a suction to keep lungs inflated. In between breathing cycles, the intrapulmonary pressure equalizes to atmospheric pressure of 760 mmHg at sea level. So, this summarizes the difference between intrapleural and intrapulmonary pressure.
Reference:
1. Biga, Lindsay M., et al. “22.3 The Process of Breathing.” Anatomy Physiology, OpenStax/Oregon State University.
2. Sharpey-Schafer, E., and W. A. Bain. “The Effects of Changes in Intrapulmonary Air‐Pressure on the Pulmonary and Aortic Circulation of the Dog.” The Physiological Society, John Wiley & Sons, Ltd.
Image Courtesy:
1. “2315 Intrapulmonary and Intrapleural Pressure” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia