NURS113 Lecture Notes - Lecture 9: Airway Resistance, Pulmonary Artery, Rubber Band
14 Jun 2018
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UNIT 5 - ALTERATIONS IN RESPIRATORY FUNCTION
Physiology respiratory system (so what does the
respiratory system do on a normal basis?)
- The exchange of oxygen and CO2 to support the
metabolic functions of the body’s tissues and cells
- Is dependent on
- Open airways
- You need open airways in order
for the exchange from the tissues
to the alveoli in the lungs of O2
and CO2 to take place
- The O2 needs to enter
through an open airway
from your nose or mouth
and down trachea and into your lungs to your alveoli so it can transfer
the oxygen to the pulmonary veins which come back to the lungs with
oxygenated. The pulmonary arteries at this point switch the CO2 in them
to the alveoli so it exits your body when you breathe out. Pulmonary
veins go to systemic system from heart which then brings to tissues and
the tissues put CO2 into that and go back to the lungs and pulmonary
artery.
- Lung expansion
- Need a lot of volume in order to put a
lot of air inside
- Which is dependent on
pressure; the pressure
differences between the lungs
and the atmosphere
- Pleural space pressure needs
to be negative so that the lung
remains expanded (basically
the pleural space has to be less
than the lung pressure or else
if it’s too high it will collapse
the lung)
- Adequate surface area for ventilation
- Blood flow through the pulmonary capillaries
- Exchange of alveolar air with atmospheric air
- As noted before, alveolar air would be CO2 filled, atmospheric air would be O2
filled so when you exhale you exchange that alveolar air you exhaled with
atmospheric O2 air when you inhale
- Is affected by many temporary and permanent respiratory disorders
- Alveolar ventilation
- Adequate inspiration and expiration
- Perfusion
- Adequate blood flow through the lungs to innervate and to make sure that there is oxygen
for ATP for the lungs to do what they do, as well to change deO2 blood to O2 blood
- Enough blood going by the alveoli (good blood flow thru the pulmonary capillaries)
- Diffusion
- Transfer of gases between the alveoli and blood in the pulmonary capillaries
- Which area of the lung would you get best diffusion? Diffusion is affected by
concentration gradient as well as gravity
- Affected by body position due to gravity
- You get minimal perfusion and diffusion if
- Maximal perfusion and diffusion at the bottom (because of gravity; water and air
does not flow uphill.)
Perfusion
So when you’re sitting right side up (or
standing up), air is in the bottom of
your lungs, which means that perfusion
is 100% (basically gravity causes blood
to flow down and oxygen to flow down
lol)
But when you’re upside down,
perfusion is absent because gravity
doesn’t go up it goes down. This is
why when you are short of breath, you have to be sitting up so that gravity can cause the blood to
flow to the bottom of the lungs, so that there is maximum perfusion and thus maximum diffusion of
O2.
Lung compliance
- The ability of the lungs to stretch and expand
- Low compliance, have stiff lung with high elastic recoil
- The less compliant the lungs are, more work is required to produce a given degree of
inflation
- Because it’s not compliant, then the lungs are more stiff because they have a higher
elastic recoil
-When thinking about elastic recoil, think about a rubber band. If a rubber band
was very stiff and new, it wouldn’t be very compliant to you stretching it, and it
would take more force for you to stretch it. There would be a high elastic recoil
though, because it’s brand new, and if you let go from stretching it snaps very fast
- Hard to get air in bc you can’t stretch the rubber band much in diameter
- High compliance, have floppy lung with low elastic recoil
- So basically if it’s too compliant (can happen if there’s too much pleural fluid as well),
the lung won’t be able to expand well enough because of a low elastic recoil, so it will
end up flopping and not expanding
- Rubber band analogy; high compliance is if you have a very used rubber band. Not
a lot of elastic recoil because it’s used to being stretched, and takes no effort (very
compliant) to stretching it
- So it’s harder to get air out
Air flow
- Volume of air that moves in and out of the lung is
- Related to the pressure difference between the lungs and atmosphere
- Because if a lot of volume is in, pressure is lower. Atmospheric pressure must be
greater than the pressure between the lungs (or else it will cause collapse of the
lungs)
- Inversely related to the resistance that air encounters as it moves through the airways
- The resistance increases when the volume of air that moves in and out is
decreased (because the airways are constricted so resistance then increases)
- Airway resistance
- Ratio of pressure differences to airflow
- R = change in pressure / F
- If airway diameter if reduced, what happens to resistance? To airflow?
- Resistance increases
- Effects of ANS
- Affecting the diameter of
the airways
- Parasympa and sympa;
opposite effects.
Parasympathetic constricts
the bronchial tubes, the
sympathetic bronchodilates.
