Natalie - Resistance to Airflow Flashcards
What is the equation for pressure difference?
Pressure difference = flow x resistance
What is the equation for resistance?
Pressure difference/flow (liters)
List three physical factors that affect resistance
Airway collapse as a result of coughing
Pulmonary oedema (fluid in the lung)
Pneumothorax
Why is pressure measured in cmH2O and not mmHg?
This is because pressure differences in the lung are too small to measure with mercury
Write a note on Poiseuille’s Law
- what is it
- why is it used
(3)
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
Define airway resistance
The resistance of the entire system of airways in the respiratory system
How is airway resistance determined?
Determined by Poiseuille’s Law
(8 x n x L)/ Pi x R^4
Poiseuille’s Law:
Resistance = (8 x n x L)/ Pi x R^4
- What is n?
n = viscosity
Poiseuille’s Law:
Resistance = (8 x n x L)/ Pi x R^4
- What is L?
Length of the airways
Poiseuille’s Law:
Resistance = (8 x n x L)/ Pi x R^4
- What is R?
Radius of the airways
Poiseuille’s Law:
Resistance = (8 x n x L)/ Pi x R^4
- What is Pi?
Pi = 3.1415
Poiseuille’s Law:
Resistance = (8 x n x L)/ Pi x R^4
- What is 8?
8 is a constant used in Poiseuille’s Law
Under what conditions might n (viscosity) change?
(3)
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
Why is the resistance the same in the larger bronchi and smaller bronchioles?
(3)
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
Why is low resistance a good thing?
It means that alveolar pressure need not differ much from atmospheric pressure to achieve normal rates of airflow under normal conditions
List the six physical factors affecting resistance
(6)
Disease causing contraction of airways
Secretion of mucous in airways
Oedema in lung
Airway collapse
Coughing
Pneumothorax
Give two diseases that cause the reduction of airways and explain how this occurs
(3)
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
Give two diseases that cause mucous secretion in the lung and explain how this affects resistance
Asthma and bronchitis
Mucous is secreted into the airways
The radii of the airways are reduced
Give a disease that causes oedema in the lung and explain how this affects resistance
Heart failure
Lung becomes stiffer
This affects airways - might cause lung to collapse
Give a disease that causes airways to collapse and explain how this affects resistance
(2)
Emphysema
Loss of alveoli cause airways to collapse due to a loss of radial traction
Explain how coughing affects resistance
Forced expiration aggravates airway collapse
Explain how a pneumothorax affects airflow
(2)
Intra-pleural pressure can be increased to greater than airway pressure
There is no airflow
List the four important parts of a normal bronchiole
Lumen
Short columnar/tall cuboidal epithelium -> ciliated
Band of smooth muscle
Some supporting connective tissue around the edge
Write a note on asthma
(6)
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)
What are the tell tale histological signs of asthma?
(3)
Epithelial hyperplasia (uncontrolled growth and change of type)
Smooth muscle hypertrophy (enlargement due to the increase in size of it’s cells)
Smaller lumen
Write a note on chronic bronchitis
(6)
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
Write a note on Alveolar oedema
(3)
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)
