Ventilation- perfusion Flashcards
what is alveolar gas equation used to determine?
why do we want to know this?
what inspired O2 needs to be have the desired alveolar O2 level
helps determine A-a O2 gradient (PAO2-PaO2)–> tells us about health of alveoli–> should be close to 0 (normal is <20 mmHg)—> helps determine what kind of hypoxia we’re experiencing
what does an increase in A-a indicate?
what does normal level mean?
diffusion impairement!!–> something worng with alveoli
problem is elsewhere (pt may be hypoventilating)
what are the fluid levels and pressure at the apex of the lung?
what does this do to size of alveoli?
less intrapleural fluid (bc of gravity)—> pressure is more negative
large at rest–> can only get a little larger with inspiration (pressure gradiant a lot smaller)
what are the fluid levels and pressure at base of lung?
what does this do to size of alveooli at rest? then during inspiration?
more intrapleural fluid—> pressure is less negative
small at rest (not as expanded by pressure)–> can get much larger with insp (P gradient much larger)
what are normal values in regards blood entering and exiting alveoli?
blood that enters thru pul arteries (looks like venous blood): PaO2= 40 mmHg and PaCO2= 45 mmHg
equilibriates with alveoli (PAO2=100 mmHg and PACO2= 40 mmHg)
blood leaving lung thru pul veins: PaO2= 100 mmHg and PaCo2= 40 mmHg
what is happening when its a low V/Q (in extreme conditions V=0)? what are the values (roughly)?
after this big whole process , what physiological mechanism do we refer this to?
airway is blcocked but blood continues to flow in
PAO2 begins to decrease (to around 80 mmHg) but PACO2 will increase (42 mmHg)–>
alveoli equilibrate with blood leaving lungs and blood starts to represent same screwed up values–>
over time the alveoli will start to equilibrilize with blood entering lungs (venous blood)—>
blood leaving lungs will leave without being oxygenated and will look like venous blood
creates a shunt (as if blood never went to lungs)
what is happening in a high V/Q (extreme case is alveolar dead space (no blood coming to alveoli))? values regarding this?
ventilation continues as normal but blood does not carry O2 away from alveoli (PAO2 increases to 120mmHg) and blood does not bring in CO2 (PACO2 decreases to 20 mmHg)—>
alveoli start to look more like atmoshphere–>
equilibriates with blood leaving lungs (so blood also starts to lok like atmosphere)—>
alveoli and blood leaving lungs eventually will get to PAO2= 150 mmHg and PACO2= 1 mmHg
so whats the problem the problem with a high V/Q?
what does this eventually to do PaO2 and PaCO2?
all would be fine (too much O2 is never a bad thing) however remember that we don’t have any blood to carry it (not getting to THIS alveoli)—>
blood has to go somehere so it will start sending a shit load of blood to the functioning alveoli, overwhelming, and eventually leading to low V/Q anyway
overall PaO2 and PaCO2 decreases (remember that CO2 leaves body WAY quicker than O2, so becuase increase in blood flow to these alveoli, more CO2 is leaving body and we’ll get a decrease in arterial CO2)
in high V/Q, what are the relative values of:
PaO2
PaCO2
PHa
volume of blood
high
low
high
low
in low V/Q, what are relative values of:
PaO2
PaCO2
PHa
volume of blood
low
high
low
high
apex of lung has (high or low) V/Q?
what are its relative values of:
PaO2
PaCO2
PHa
volume of blood
high V/Q
high
low
high
low
base of lung has (high or low) V/Q?
what are its relative values of:
PaO2
PaCO2
PHa
volume of blood
low V/Q
low
high
low
high
what kind of V/Q does middle region of lung have?
normal
what is the alveolar ventilation at apex of lung?
base?
lower at apex
higher at base
** remember that V/Q depends primarily on blood flow… alveoli are small (increasing SA which increases ventilation) its just that blood flow is high so due to gravity that its a low V/Q
what do we do to minimize V/Q differences in zones of lung?
hypoxic vasoconstriciton —> directs blood away from hypoxic regions (base—> apex)
ensures that the large alveoli in apex of lung (which are getting most oxygen) get a fair share of blood
