Question

Write a paragraph about the determinants of airway resistance and the relationship between lung volume and airway resistance.

Answer 1

Answer=

determinants of airway resistance = Airway resistance is the resistance to the flow of air through the respiratory tract during inhalation and expiration.The level of resistance depends on many factors,particularly the diameter of the airway and whether flow is laminar or turbulent

These determinants are ;

1.Diameter - Poiseuilles Law,also known as the Hagen-Poiseuille equation,gives us the relationship between airway resistance and the diameter of the airway.The equation is,

R = 8 l /r⁴

It shows that the airway resistance is inversely proportional to the radius to the power of 4.

Hence a small change in diameter has a huge effect on the resistance of the airway

therefore smaller airways such as bronchioles and alveolar ducts all individually have much higher flow resistance than larger airways like the trachea.However the branching of the airways means that there are meny more of the smaller airways in parallel,which reduces the resistance.

2.Nervous system control-diameter od airways is usually determined by the autonomic nervous system.Sympathetic innervation causes relaxation of bronchial smooth muscle,which increases diameter to allow more airflow.This is usefull in exercise for example,to allow more air into the lungs,therefore increasing the rate of gas exchange at alveolar level.Parasympathetic innervation works to increase smooth muscle contraction and reduce diameter,when it is not necessary to have a high airflow into the lungs.

3.Inspiration vs expiration- resistance is also slightly different on inspiration and expiration due to the diameter of the airways.On inspiration,the positive pressure within the alveoli and small airways causes the diameter to increase ,and therefore resistance to decrease.

Relationship between lung volume and airway resistance=

The lung volume is inversely proportional to the airway resistance

The bronchi are supported by radial traction of the surrounding lung tissues,and their calibre is increased as lung expands .

At low lung volumes,compression of the airways and increased airway collapse lead to increased airway resistnace