Natalie - Resistance to Airflow

Question 1

What is the equation for pressure difference?

Answer 1

Pressure difference = flow x resistance

Question 2

What is the equation for resistance?

Answer 2

Pressure difference/flow (liters)

Question 3

List three physical factors that affect resistance

Answer 3

Airway collapse as a result of coughing

Pulmonary oedema (fluid in the lung)

Pneumothorax

Question 4

Why is pressure measured in cmH2O and not mmHg?

Answer 4

This is because pressure differences in the lung are too small to measure with mercury

Question 5

Write a note on Poiseuille’s Law
- what is it
- why is it used
(3)

Answer 5

The pressure difference is directly proportional to the flow x resistance

Poiseuille’s Law applies because air in the lung is considered a fluid (because air contains water vapour)

The airways are also tortuous and not parallel therefore Poiseuille’s is applied

Question 6

Define airway resistance

Answer 6

The resistance of the entire system of airways in the respiratory system

Question 7

How is airway resistance determined?

Answer 7

Determined by Poiseuille’s Law

(8 x n x L)/ Pi x R^4

Question 8

Poiseuille’s Law:

Resistance = (8 x n x L)/ Pi x R^4

• What is n?

Answer 8

n = viscosity

Question 9

Poiseuille’s Law:

Resistance = (8 x n x L)/ Pi x R^4

• What is L?

Answer 9

Length of the airways

Question 10

Poiseuille’s Law:

Resistance = (8 x n x L)/ Pi x R^4

• What is R?

Answer 10

Radius of the airways

Question 11

Poiseuille’s Law:

Resistance = (8 x n x L)/ Pi x R^4

• What is Pi?

Answer 11

Pi = 3.1415

Question 12

Poiseuille’s Law:

Resistance = (8 x n x L)/ Pi x R^4

• What is 8?

Answer 12

8 is a constant used in Poiseuille’s Law

Question 13

Under what conditions might n (viscosity) change?
(3)

Answer 13

Change based on environment -> particularly wet environment

In Sauna -> harder to breath (water in air adds to viscosity of water in airways)

In some diseases where the lung becomes very wet -> excess mucous

Question 14

Why is the resistance the same in the larger bronchi and smaller bronchioles?
(3)

Answer 14

The bronchi are large and have a large radius

But there are many small airways with small radii where the resistance is spread across many

Therefore overall resistance to airflow is not affected

Question 15

Why is low resistance a good thing?

Answer 15

It means that alveolar pressure need not differ much from atmospheric pressure to achieve normal rates of airflow under normal conditions

Question 16

List the six physical factors affecting resistance
(6)

Answer 16

Disease causing contraction of airways

Secretion of mucous in airways

Oedema in lung

Airway collapse

Coughing

Pneumothorax

Question 17

Give two diseases that cause the reduction of airways and explain how this occurs
(3)

Answer 17

Asthma and Bronchitis

These diseases increase contractile activity of smooth muscle in the bronchioles

This causes a reduction in the radii of airways and therefore increases resistance

Question 18

Give two diseases that cause mucous secretion in the lung and explain how this affects resistance

Answer 18

Asthma and bronchitis

Mucous is secreted into the airways

The radii of the airways are reduced

Question 19

Give a disease that causes oedema in the lung and explain how this affects resistance

Answer 19

Heart failure

Lung becomes stiffer

This affects airways - might cause lung to collapse

Question 20

Give a disease that causes airways to collapse and explain how this affects resistance
(2)

Answer 20

Emphysema

Loss of alveoli cause airways to collapse due to a loss of radial traction

Question 21

Explain how coughing affects resistance

Answer 21

Forced expiration aggravates airway collapse

Question 22

Explain how a pneumothorax affects airflow
(2)

Answer 22

Intra-pleural pressure can be increased to greater than airway pressure

There is no airflow

Question 23

List the four important parts of a normal bronchiole

Answer 23

Lumen

Short columnar/tall cuboidal epithelium -> ciliated

Band of smooth muscle

Some supporting connective tissue around the edge

Question 24

Write a note on asthma
(6)

Answer 24

Disease of small airways

Inflammation/hypertrophy (pathological change) of the bronchiole wall

Causes reduction in radius of airways which increases resistance to airflow

At the same time increased broncho-constriction also constricts the airways leading to increased resistance (this causes wheezing)

Question 25

What are the tell tale histological signs of asthma?
(3)

Answer 25

Epithelial hyperplasia (uncontrolled growth and change of type)

Smooth muscle hypertrophy (enlargement due to the increase in size of it’s cells)

Smaller lumen

Question 26

Write a note on chronic bronchitis
(6)

Answer 26

Obstructive disorder

Inflammation of the bronchi

Persists for a long period of time

Reduces diameter of airways

A lot of mucous is produced -> airways very blocked -> patients will try to cough mucous up

Coughing can cause damage to airways resulting in a loss of radial traction -> airways close

Question 27

Write a note on Alveolar oedema
(3)

Answer 27

Caused by cor pulmonale (right heart failure)

Fluid builds up in the alveoli

Its serious exudate (cells and fluid that seeps out of blood vessels which also occurs in other places in the body)