Lesson 6: Respiratory Compliance and Airways Resistance Flashcards
what is compliance?
the change in lung volume for a given change in transpulmonary pressure
- stiffness of lung
- pressure required to generate lung volume changes
why do we breath where we breathe (in terms of our breath)?
- we don’t breathe at a fully inflated lung with a high recoil pressure and we don’t breathe at a fully deflated lung with very little leak recoil
THEREFORE — there is a specific lung volume (level of inflation) where it is the most efficient and easiest for us to breathe - this is where compliance comes in
- we breath at the steepest portion of a lung volume to pressure ratio. to achieve a change in volume, it is the least amount of pressure because it is steeper
where is the most efficient place to breathe regarding our lung volume?
in the middle part of our breath because we don’t breathe at the ends of our lung volumes (full/empty)
- least amount of pressure required to move air
when is it harder to breath air in?
at the beginning of our breath because …..
why in the middle of our breath is it the easiest?
highly compliant portion of the lung
why is it hard to keep breathing in?
because the transpulmonary pressure is getting too stretched
why do we stay in the steepest point of normal compliance when breathing?
most energy efficient, little effort required
- least amount of pressure change, least amount of recoil pressure, least amount of muscular work
what does a decreased compliance lung have to do in order to get to a given lung volume?
they have to have larger changes in pressure
since the formula for compliance is delta v/ delta p, decreased compliance is due to?
high pressure low volume
if compliance is so bad, what can it constrict?
inflating your lung all the way
what is a disease characterized by a highly compliance lung?
emphysema
- lose elastic recoil of the lung because blood vessels are damaged and it is over stretched
why is having highly compliant lungs a problem?
it would make breathing out harder
why does highly compliant lungs make breathing out harder?
has decreased recoil pressure so you will need to recruit your expiratory muscles each breath
why do we not need muscles to move air out resting?
recoil pressure
increased compliace = __________ stiffness
decreased
decreased compliance = ___________ stiffness
increased
what is the equation for compliance?
= delta V / delta P
what is an example of something characterized by decreased compliance?
lung fibrosis
what is being lost in a highly compliant lung if it is easier to breath in?
the recoil pressure. it will make it harder to breath out
what gets lost when the lungs get stretched out?
all the alveoli capillaries get destroyed and you lose the elastic nature. easy to breath in, but you lose the recoil
what does lungs elastic recoil refer to?
how readily the lungs rebound after having been stretched
what is lungs elastic recoil responsible for?
lungs returning to their preinspiratory volume when inspiratory muscles relax at end of inspiration
what is the importance of recoil pressure on expiration?
allows us to exhale passively
- we would need to recruit expiratory muscles to exhale
lungs elastic recoil depends on what?
- highly elastic connective tissue in the lungs
- alveolar surface tension (the ability to balance out the alveolar pressure from each alveoli throughout the lung) (without this we will have a stiff lung)
What does the lung produce that helps us regulate surface tension?
Surfactant
why does babies have a hard time breathing?
they don’t produce surfactant
- they cannot regulate the tensions and pressures in the alveoli
type ii alveolar epithelial cells reduce?
surface tension in alveoli to make it easier to inflate
what is the equation of Law of Laplace?
P = 2T/R
pressure = 2 surface tension / radius
what are the important benefits of surfactant?
helps us to maintain pressures across alveoli of different sizes. Also maintains surface tension to optimize compliance
- reduces work of the lungs
- reduces recoil pressure of smaller alveoli more than larger alveoli
what does the lung produce that helps us regulate surface tension?
surfactant
what are the two types of alveolar epithelial cells?
type i: flat for gas exchange
type ii: secretes surfactant
what happens if you do not have surfactant within alveolus?
it can cause issues
what is surfactant?
a complex mixture of lipids and proteins secreted by type 2 alveolar cells
where does surfactant disperse?
between the water molecules in the fluid lining the alveoli and lowers alveolar surface tension
what are the two key factors to maintain a healthy compliance?
- the elastic nature of the lung
- the ability to maintain alveolar pressure through the use of surfactant
the use of surfactant helps to maintain _____ across alveoli that may or may not have different volumes.
pressure
- all based on the law of laplace
- surfactant helps regulate surface tension
if there is not surfactant between two alveoli of different radius’, the surface tension will be the same in both but the pressure will be higher in the smaller alveolus. what will happen?
the air goes from high to low pressure. and the smaller alveolus will collapse due to no air being in it
if there is surfactant between two alveoli of different radius’, what happens?
the concentration will be higher in the smaller alveolus, so it is going to uniquely change the surface tension accordingly to allow for the pressure to be maintained in both of them. so now air flow between alveolus
true or false: surfactant helps regulate surface tension to avoid pressure differentials across alveoli (individual alveolus units)
true
this is a key study note
- with surfactant, P(a) = P(b) due to the differential effects of surfactant on surface tension in each alveolus. Therefore air will not flow from a to b and air will be equally distributed throughout the lung
what is Purcells law?
flow = delta pressure / resistance
what generate the velocity or flow of air?
the amount of resistance that it is overcoming
if you have two tubes, one with lower resistance and the other with high resistance, which will have increased flow?
lower resistance
does low or high airway resistance make it easy to breathe?
low airway resistance
is airway resistance normally very high or very low?
very low
what is airway resistance dependent on?
a) tube length (generally fixed)
b) interactions between gas molecules (variable)
c) airway radius (regulated) –> by far most important
decreased radius is often going to need ____ pressure to overcome the increased resistance?
increased
pressure generation in the lung and the airways is highly dependent on the?
resistance
- so if you have high resistance you are going to have to create larger pressures to overcome that
flow = ?
delta pressure / resistance
resistance = ?
delta pressure / flow
same pressure, but resistance is higher in one than the other. which has a higher flow?
the one with the lower resistance
is airway resistance different as we branch out?
yes
- the flows are a little bit slower
- the resistance is different at the terminal bronchioles than it is at the trachea
what are the physical factors that will affect airway resistance?
- transpulmonary pressure (as recoil pressure goes up, the volume in the lung is increasing) (however airway resistance decreases on a breath by breath basis as we inspire)
- mucous accumulation in the lung (decreases diameter so it will increase the resistance)
why is airway resistance decreasing when we breath in?
because there is a very small subtle increase in airway diameter when we breathe in
