Lesson 9: Ventilation and Gas Exchange Flashcards
what do we really need to do in order to maintain blood gas homeostasis within the system?
ventilation
what is ventilation?
the amount of air moved into/out of the alveoli
how do we express ventilation?
as a rate
- a volume per minute
how do you have a high ventilation?
if you have a high flow
what is a minute ventilation a product of?
the size of your breath X the frequency of it
what is the size of your breath referred to as?
tidal volume
- about 500 mils per breath
how many L of air do we breath in and out everyday?
8640L/day
what are the two types of ventilation?
- dead space
- alveolar ventilation
what is dead space ventilation?
when we breath in, not all of it goes to the alveoli. some of the air gets trapped in the conducting zone and is then wasted
what is alveolar ventilation?
the amount of air that is ventilated and gets to the alveoli
alveolar and dead space ventilation together makes up?
our total ventilation per ml/minute
about how much of the gas we breathe in does not make it to the gas exchange zones?
roughly 30%
- dead space ventilation
how much air actually reaches the alveolar/capillary gas-exchange interface/zone?
350ml ventilated to and from the alveoli (ie. alveolar ventilation), 150ml wasted ventilation (ie. dead space ventilation)
what happens if you have higher levels of dead space due to clinical diseases?
then you need to breath more to get enough air ventilation
what is Ve?
the total volume of expired ventilation
- the total amount of air that we can measure with a spirometer
why do we look at Ve and not Vi when we are looking at total ventilation?
because we exhale more CO2 so it is going to give us some index of how well we’re ventilation
how do we calculate alveolar ventilation?
(tidal volume - dead space in a single tidal breath) x frequency
what is the amount of air available for gas exchange characterized by?
alveolar ventilation (Va)
what is air moved characterized by?
total ventilation (Ve)
why do we breath?
to bring in oxygen and remove CO2 (biproduct of cellular respiration)
- cellular respiration
how do we know if alveolar ventilation is sufficient?
you can look at your arterial oxygen levels
- oxygen saturation of hemoglobin
MORE IMPORTANTLY
- alveolar/arterial CO2 is within a narrow physiological range (36-40mmHg)
why is alveolar ventilation important?
for the delivery and removal of air at the gas exchange level
what would be the oxygen, hemoglobin saturation levels of someone that has good oxygen levels?
96-100% Hb saturated is the normal physiological range of arterial O2 content
what relationship are we more closely paying attention too when looking at ventilation?
the relationship between the amount of air we are breathing and the actual metabolic CO2 production
- CO2 is actually what drives the breathing
why do we not want a too high or too low CO2 in our alveoli and arteries?
because it means we are either not generating enough ventilation or too much ventilation which could dysregulate acid-base balance and lead to a series of events that disrupt cellular respiration (last part doesn’t really matter)
what is the alveolar ventilation equation / concentration or pressure of expired CO2 in alveoli?
(VCO2/Va) x K
what is “PaCO2”?
the arterial/alveolar concentration/partial pressure of expired CO2
what is VCO2?
the volume of expired CO2
what does expired CO2 represent?
the metabolic CO2 that is produced in all the tissues pushed up through the venous circulation, diffused across the capillary alveolar interface and breathed out
what is the gas exchange zone?
alveoli
alveoli is made up of?
epithelial cells
how many cells thick is alveoli?
1 cell thick (type 1)
what are alveoli surrounded by?
capillaries
how many times does the bronchioles/alveoli branch?
23 times
- millions and millions of them so we have a huge surface area for gas exchange
while gas exchange occurs at the lungs, it also occurs at?
the peripheral tissues
- because we diffuse, we bring O2 into the lungs, goes through the circulation, the cardiovascular system and then also diffuses into the tissue
at both the pulmonary capillary and tissue capillary levels, gas exchange involves the simple _________ of O2 and CO2 _________________________________.
- diffusion
- down partial pressure gradients
the partial pressure exerted by each gas in a mixture equals?
the total pressure multiplied by the fractional composition of this gas in the mixture
what are additional factors that affect the rate of gas transfer?
- as surface area increase, the rate increases
- an increase in the thickness of the barrier separating air and blood decreases the rate of gas transfer
- the rate of gas exchange is directly proportional to the diffusion coefficient for a gas
what is the Law of Partial Pressure (Dalton’s)?
in a mixture of gases the pressure of each gas is independent of the others
- partial pressure = total pressure x gas fraction
