Unit 1 Lecture 4: Airways Resistance Flashcards
What is the main factor that influences resistance?
Radius
- Increased radius in airways = decreased resistance
- Decreased radius in airways = increased resistance
What does Poiseuille’s Law state?
Flow = Pressure/Resistance
Flow is inversely proportional to the resistance of the system
What is airway resistance dependant on?
- Tube length (fixed)
- Interactions between gas molecules (variable)
- Airway radius (regulated) = most important!
In this example, pressure is constant. Which one has a higher airway resistance and why?
Using Poiseuille’s Law and accounting for the pressure being the same, we can see that the second tube has a higher airway resistance. The reason for that is the reduced radius which in turn increases pressure. The molecules are interacting more in this small space only because the radius has decreased so there is more resistance than flow
There will be an increase in pressure now because of the decreased radius
Rearranging Poiseuille’s formula we can get Resistance = Pressure/Flow. What relationships do we see here?
It shows that resistance increases or decreases inversely to flow. We know flow is how easily the air moves through that space so increasing resistance for example can lead to decreased flow
Increased resistance = decreased flow
Decreased resistance = increased flow
What is airway resistance influenced by?
- Physical Factors
- Neurological Factors
What physical factor(s) influence airway resistance?
Transpulmonary Pressure
- Transpulmonary pressure increases = Airway Resistance Decreases
- When the lungs inflate, the pleural pressure decreases but expands which causes the bronchioles/airways to slightly open
- Opening of those airways allow for resistance to decrease
Mucus Accumulation
- Inflammed airways with a chronic/excessive buildup of mucus decreases radius of airways which increase resistance
How does forced expiration work with airway resistance?
Forced expiration requires the contraction of expiratory muscles & therefore the increase of pressure in the airways. An excessive increase in pressure leads to compression of the airways which can increase resistance and decrease flow
Forceful expiration that can cause the lung to collapse is called dynamic compression
What neurological factor(s) influence airway resistance?
Parasympathetic (acetylcholine) constricts (↓ radius)
- Bronchioles are surrounded by smooth muscle which can be impacted by neurotransmitters to constrict and reduce radius increasing resistance
Epinephrine = Dilates
Histamine = constricts (allergic reactions)
In this picture, which airway would have an increased flow & which one would have a decreased flow? Explain
- The dilated airway would have an increased flow because the radius is much bigger which allows for less pressure if needed but as well less resistance so it is easier for air to move through
- The constricted airway would have decreased flow because the radius is even smaller than the normal airway which means the flow of air is worse due to resistance being heavily increased
What do Obstructive Diseases mean in terms of flow and resistance?
- Flow is lower as we try to move molecules through a narrow space
- Airflow obstruction caused by airway narrowing which leads to increased resistance
To overcome the resistance, increase pressure so that it is greater than resistance
What is asthma and what triggers it?
- Excess smooth muscle contraction
- Inflammation of the airways is what triggers it
Asthmatic patients are hyperresponsive to things like exercise, pollutants, animals, smoke, etc.
How is Asthma treated?
- Anti-inflammatory drugs leukotriene inhibitors
- Bronchodilators relax the airways
* Mimics epinephrine (beta-2 agonist)
* Inhibit acetylcholine
Epinephrine binds to beta-2 receptors to increase diameters of airways
What is COPD (Chronic Obstructive Pulmonary Disorder) caused by?
Largely caused by exposures/behaviours
How would one be diagnosed with COPD?
If the person has either emphysema or chronic bronchitis or both
