Lecture 23 - Ventilation Perfusion Relationships Flashcards
define acinus
single gas exchanging unit (alveolus + pulmonary capillary)
in the ideal lung, what is the relationship between ventilation and perfusion
V / Q = 1
Ventilation (V)
movement of airflow to and from alveoli
Perfusion (Q)
movement of blood to and from alveoli
what is the normal V/Q ratio
0.8
what 2 factors affect the gas concentrations in the blood
- rate of alveolar ventilation
- rate of oxygen and carbon dioxide transfer through the respiratory membrane
T/F: carbon dioxide diffuses much faster than oxygen
TRUE
VT
Tidal volume
describe the relationship of alveolar ventilation to other factors
equal to the product of the frequency of tidal per minute and the difference of tidal volume and physiologic dead space
what is a shunt
good perfusion (blood to alveoli) but no ventilation (oxygen does not reach alveoli)
what is a dead space
good ventilation (oxygen to alveoli) but no perfusion (disrupted blood flow)
in normal anatomy, where does venous blood flow
to alveoli for oxygenation and then to the L-side of the heart
The ____ lung gets more ventilation while the ___ gets less
dorsal; ventral
what could cause a shunt
- airway obstruction
- pneumonia
what could cause a dead space ventilation
- pulmonary embolism
- cardiogenic shock
what is the V:Q in a shunt
<1
What are the 3 types of dead space ventilation
- anatomic dead space
- alveolar dead space
- physiologic dead space
describe an anatomic dead space
conducting airways that do not participate in gas exchange
describe an alveolar dead space
ventilation to alveoli but no perfusion (blockage or low BP)
describe physiologic dead space
anatomic + alveolar dead space
(dead space compared to tidal volume)
air intake that cannot be used
define venous admixture
when less oxygenated blood mixes with oxygenated blood
T/F: the amount of O2 and CO2 in the blood is a summary of diffusion
FALSE - V/Q efficiency
hypoventilation
hyper CO2
hyperventilation
hypo CO2
normal PaCO2
40 mmHg
norm-oxemia
80-100 mmHg
hypoxemia
<60 mmHg
what 3 things could cause an increase in V/Q mismatch
- increase in venous admixture
- decreased arterial oxygen
- increase in carbon dioxide
what does the alveolar gas equation allow
prediction of amount of oxygen in alveoli
what is the alveolar gas equation
PaO2 = PiO2 - (PaCO2/R)
PiO2 = 21% atmosphere
R = 0.8
hypoxic pulmonary vasoconstriction (HPV)
pulmonary vessels constrict in places of low PaO2 and shunt to places with high pressure to decrease mismatching
