[#7] MECÂNICA RESPIRATÓRIA: RESISTÊNCIA DAS VIAS AÉREAS (VIAS RESPIRATÓRIAS) | MK Fisiologia

Summary

In this video, Miriam explains the resistive properties of the lungs and chest wall, focusing on airway resistance during pulmonary ventilation. She breaks down how factors like airway radius, fluid viscosity, and tube length affect airflow, using Poiseuille's law. The video emphasizes that small airways, despite having smaller diameters, actually offer less resistance due to a larger total cross-sectional area and laminar flow. Larger airways, on the other hand, have higher resistance due to turbulent flow. Miriam also discusses how lung volume impacts airway resistance, and the role of the autonomic nervous system in regulating this resistance.

Takeaways

• 😀 Understanding pulmonary ventilation requires overcoming the elastic recoil of the lungs and the thoracic wall.
• 😀 The resistance of the airways is a significant factor in pulmonary ventilation, contributing to 80% of the total resistance.
• 😀 The flow of air is determined by the pressure gradient and the resistance within the airways.
• 😀 The resistance of the airways is primarily influenced by their radius, with smaller airways having higher resistance.
• 😀 According to Poiseuille's Law, the resistance of a tube is determined by the viscosity of the fluid, the tube's length, and its radius.
• 😀 The total cross-sectional area of the airways increases as they branch out, which lowers the overall resistance despite the smaller diameter of individual bronchioles.
• 😀 Laminar airflow occurs in smaller airways, where it flows in layers, whereas turbulent airflow occurs in larger airways like the trachea, increasing resistance.
• 😀 The majority of the airways experience transitional airflow, switching between laminar and turbulent flows.
• 😀 During inspiration, as the lungs expand, the interdependence of alveoli and small airways can reduce resistance by pulling open the airways.
• 😀 Conditions like chronic obstructive pulmonary disease (COPD) can shift the resistance curve to the right, increasing the resistance even at normal lung volumes.

Q & A

What is the main topic of the video?

The main topic of the video is the resistance in the airways and how it affects pulmonary ventilation, with a focus on understanding the factors that influence airway resistance.

What is the key difference between elastic properties and resistive properties of the lungs?

Elastic properties refer to the ability of the lungs and chest wall to return to their resting state after being stretched, whereas resistive properties are related to the opposition to airflow in the airways, which is influenced by factors like the diameter of the airways and the viscosity of the air.

How much does airway resistance contribute to the total resistance in the lungs?

Airway resistance contributes approximately 80% to the total resistance in the lungs, while the resistance from lung tissue and the chest wall contributes about 20%.

How is airflow influenced by pressure gradient and resistance?

Airflow is primarily determined by the pressure gradient between the atmosphere and the interior of the airways. The greater the pressure gradient, the greater the airflow. However, resistance also plays a role, as higher resistance requires a larger pressure gradient to maintain the same flow.

What factors influence the resistance in the airways?

The resistance in the airways is influenced by the viscosity of the air, the length of the airways, and, most importantly, the radius of the airways. The smaller the radius, the greater the resistance.

How does the structure of the airways affect their resistance?

The structure of the airways, specifically their branching pattern, significantly affects resistance. As the airways branch and the diameter decreases, the total cross-sectional area increases, reducing overall resistance. Smaller airways, despite their smaller diameter, have a lower total resistance due to this increased area.

Why does the airway resistance in small airways differ from that in larger airways?

In smaller airways, resistance is lower because the total cross-sectional area increases as the airways branch. Additionally, the airflow tends to be laminar, which also contributes to lower resistance. In contrast, in larger airways like the trachea, airflow can become turbulent, increasing resistance.

What is the difference between laminar and turbulent airflow?

Laminar airflow occurs in layers, with the air near the wall flowing slower than air in the center of the tube. This type of flow is common in small airways. Turbulent airflow, on the other hand, is chaotic and occurs in larger airways like the trachea, causing greater resistance due to eddies and vortices in the flow.

How does the volume of air in the lungs influence airway resistance?

As the lungs fill with air during inspiration, the resistance in the airways decreases. This is due to the mechanical interdependence of the alveoli and airways, where the expansion of the alveoli during inspiration pulls open the small airways, reducing resistance.

What happens in conditions like chronic obstructive pulmonary disease (COPD) with regard to airway resistance?

In conditions like COPD, airway resistance increases significantly. This results in higher effort required for breathing, as the resistance to airflow is greater, especially at higher lung volumes.