What is the Difference Between Ventilation and Perfusion

The main difference between ventilation and perfusion is that ventilation is the flow of air in and out of the alveoli, whereas perfusion is the flow of blood into alveolar capillaries. 

Ventilation and perfusion are two processes that occur in the alveoli. They are important for gas exchange in the lungs.  

Key Areas Covered

1. What is Ventilation
– Definition, Features, Importance
2. What is Perfusion
– Definition, Features, Importance
3. Similarities Between Ventilation and Perfusion
– Outline of Common Features
4. Difference Between Ventilation and Perfusion
– Comparison of Key Differences

Key Terms 

Perfusion, Ventilation

What is Ventilation

Ventilation is the exchange of air between the lungs and the atmosphere. Generally, it occurs through inhalation and exhalation of the lungs. Here, inhalation takes air into the lungs, while exhalation liberates air from the lungs. Also, the conducting zones of air in the lungs include the nose, pharynx, larynx, trachea, primary bronchi, bronchial tree, and terminal bronchioles. However, ventilation occurs in the alveoli of the lungs.

Figure 1: Ventilation

The main importance of ventilation is to reduce the partial pressure of carbon dioxide in the blood. It mainly occurs through exhalation. The partial pressure of carbon dioxide is high in the blood in the capillaries, which draw blood into the lungs. However, the partial pressure of carbon dioxide is low in the air. Therefore, carbon dioxide diffuses from the blood to the air. On the other hand, inhalation facilitates oxygenation.

Furthermore, oxygenation is the physiological process that adds oxygen to the body system, occurring in the lungs. A blood capillary network surrounds the alveoli of the lungs. During inhalation, alveoli are filled with fresh air. Therefore, the red blood cells in the blood capillaries take up oxygen from the air. This occurs through simple diffusion. Furthermore, the partial pressure of oxygen is high in the air while the pressure is low in the blood. Therefore, oxygen from the air diffuses into the blood.

What is Perfusion

Perfusion is the process that delivers blood to the pulmonary capillaries. Therefore, the main function of perfusion is to supply blood efficiently as required by the gas exchange. The two factors responsible for the efficient gas exchange are the air volumes inside the alveoli and the volumes of blood inside the pulmonary capillaries. Here, ventilation is the process responsible for air movement into the alveoli space.

Figure 2: Perfusion of Blood into Alveoli

Furthermore, the volume of air that enters the alveolus depends on the diameter of the airways. Here, the increased partial pressure of carbon dioxide inside alveoli causes the dilation of bronchioles. On the other hand, the volume of blood that enters the blood capillaries depends on the diameter of the blood vessels. Also, a higher partial pressure of oxygen inside alveoli causes the dilation of pulmonary arteries, allowing the entrance of relevant amounts of blood volumes required to exchange respiratory gases efficiently.

Similarities Between Ventilation and Perfusion

• Ventilation and perfusion are two processes responsible for gas exchange.
• They occur in the alveoli.
• Both are important for the efficient gas exchange.  

Difference Between Ventilation and Perfusion

Definition

Ventilation refers to the circulation of gases in the lungs or gills that are basic to respiration. In contrast, perfusion refers to the process that forces blood to flow through a network of microscopic vessels within biological tissue, allowing the exchange of oxygen and other molecules across semipermeable microvascular walls.

In Lungs

Ventilation is airflow in and out of the alveoli, while perfusion is blood flow into the alveolar capillaries. 

Importance

Ventilation brings oxygen into the lungs, while perfusion brings carbon dioxide into the lungs.

Conclusion

In brief, ventilation and perfusion are two processes occurring in the lungs. They are important for the gas exchange. Ventilation is the circulation of air in the alveoli. It brings oxygen into the lungs. In comparison, perfusion is the flow of blood into the alveolar capillaries. Therefore, it brings carbon dioxide into the lungs. Hence, the main difference between ventilation and perfusion is their process. 

References:

1. Mechanics of ventilation. Mechanics of Ventilation | SEER Training. (n.d.).
2. Perfusion. Perfusion – an overview | ScienceDirect Topics. (n.d.).

Image Courtesy:

1. “Biology of ventilation” By Eleanor Lutz – Own work (CC0) via Commons Wikimedia
2. “Gas exchange in the aveolus simple (en)” By domdomegg – Own Work (CC-BY 4.0) via Commons Wikimedia