Resistance Lecture 10

Question 1

Describe the structure of the airway

Answer 1

Trachea- contains cartilage rings, ligament containing smooth muscle and a ciliated epithelium

Biforcations with alveoli beginning at gen 17

Bronchioles have no cartilage but have smooth muscle and have a less ciliated epithelium- the speed of gas now matches the speed of diffusion- slow

With every generation, we get a bigger and bigger cross sectional area. As cross sectional arrea goes up, speed of gas goes down. At every bification, cross sectional area of 2 new airways is bigger than the parent airway

Question 2

Describe air flow

Answer 2

Flow= pressure/resistance

Air flow in the respiratory system= driving pressure/ airway resistance

V= P(A)-P(B)/R(AW)

V = ventiliation

PA = alveolar pressre

PB = atomospheric pressure

RAW = airway resistance

Resistance is low in normal lungs but higher in diseased lungs

Question 3

Describe airway resistance

Answer 3

Poiseulle’s law would imply that the smaller airways have the most resistance- air flow = dirving pressure / airway resistance

R=kx 1/r^4

Actually it is the larger airways that have the most resistance because of the turbulent flow found there and smaller airways have laminar flow

Airway resistance is dependant on viscosity of gas, length of airway and radius of airway. Change resistance by changing airwy radius. A small change in radius will bring about a big change in resistance

Question 4

Types of air flow

Answer 4

Turbulent = High velocity, large radius (trachea - high resistnace due to small cross sectional area)

Transitional = mix of flow types. At bifications, you get a bit of turbulent flow but it turns back to laminar flow. (Most of bronchial tree - large cross secntional area so resistance is low)

Laminar = low velocity, very small airways, small radius. Highly organised flow, fastest airflow in entre

Type of airflow is dependant on = radius of airway, velocty of gas, density of gas and gas viscocity

Question 5

Describe determinants of airway resistance

Answer 5

Airway smooth muscle tone-

increased sympathetic activity bronchodilation via beta2 receptors- adrenaline>noradrenaline bronchodilators

Bronchoconstriction via M3 receptors- increased parasympathetic activty. ACh Histamine and leukotrines are bronchoconstrictors. INcreased constriction = increased resistance

Mucus build up

Reduces radius of airways

Lung volume

When increasind volume of lungs, airway resistance exponentially decreases. As it increases radius of airways

Increase in airway resistance increase the driving pressure required for a given air flow thus increasinf the work of breathing.