Lecture 37: ventilation perfusion inequality and hypoxemia Flashcards
What is alveolar ventilation VA?
4L/min at rest
what is perfusion? Q
cardiac output 5L/min
what is the ideal VA/Q ( alveolar ventilation to perfusion ratio?
4/5= 0.8
80%
what is a normal alveolar-arterial oxygen A-a O2
5-15 mm Hg
shunts or variations in VA/Q ratio cause this
venous admixtures also cause this variations
what is alveolar to arterial oxygen A-a O2 due to?
venous admixture
What occurs with increased venous admixture?
results in low O2 tension in the blood hypoxemia.
Think: veins take deoxygenated blood to the heart. soooo high venous admixture= low oxygen
What is the definition of Dead Space? VD?
- the volume of inhaled blood that does not participate in gas exchange
- Regions of no gas exchange
what is the name of the dead space at the conducting airways?
anatomic deadspace
what is the name of the dead space at the alveoli with no perfusion?
alveolar dead space
How do you calculate the physiological dead space? VD?
anatomical dead space+ alveolar dead space`
What are the sources of physiological shunts ( total venous admixture)?
50% from anatomic shunt ( right to left shunts); bronchial circulation, thebsian veins
50% from low VA/Q; at the base of the lung/a partially obstructed airway
What is physiological dead space?
basically it means that not all inspired air participates in gas exchange, this results in some wasted air.
what is the definition of a physiological Shunt?
All of the blood entering the lung is not fully oxygenated, leading to some wasted blood.
How do you calculated physiological shunt?
Anatomic+low Va/Q ratio= physiological shunt
aka wasted blood
not all blood is oxygenated
How is the lung like a slinky?
the top part of the lungs have a lot of weight pulling it down so the coils are more spread apart, while the bottom of the lungs has less weight pulling down on it so Its cold are more together.
if you have a peanut lodged into your main bronchi, what is the V/Q ratio like?
it is low
what is pulmonary embolism? why does it cause a high Va?Q ratio?
when you have embolism stuck in pulmonary circulation. this will result in a high V/Q ratio because the ventilation is fine, there is no blockage, but the embolism affects the blood supply to the lung.
Patient with pulmonary embolism has Hypoxemia, in a patient leads to an increase in which of the following? A. anatomical dead space B. Alveolar dead space C. anatomical Shunt D.Physiological shunt
Alveolar dead space increases…
alveoli being ventilated but not perfused
A child has aspiration of peanut fragment they have hypoxemia and airway is affected, her airway mucosa is inflamed no evidence of infection. why does she have hypoxemia? A. anatomical dead space B. Alveolar dead space C. Physiological dead space D. anatomical shunt E.Low V/Q ratio
she has no ventilation, aka low V/Q ratio
How does gravity related to intrapleural pressure ? How does this affect the alveoli of the lungs
when someone is standing, the lung takes up more space at the bottom of the thoracic cavity. Therefore, there is more intrapleural pressure at the top of the lung that is more negative. The alveoli at the top of the lung have a greater transpulmonary pressure which makes them larger.. the ones at the top are larger aka slinky analogy.
slide 25 graph..
how is the alveoli at the top of the lung versus bottom of lung?
the ones at the top are distended at 70% ( apex)
the ones at the bottom are distended at 15% (base)
which part of the alveoli can accommodate more air on distention?
aleveoli at bottom of lung aka Base.
the alveoli at the top of the lung AKA apex less compliant than the alveoli at the bottom. the alveoli at the bottom can expand more because they’re smaller. Top ones cannot expansion much cuz they’re big.
volume during inspiration is significantly less at apex than at the base
At the upper zone of the lung there is _______ ventilation than the bottom.
less
bottom has more ventilation
GRAPH on slide 15
There is ______ blood flow at the bottom of the lung, compared to the top.
more
It is more difficult to pump blood to the _____ of the lung than the bottom of the lung
top
more resistance to flow at the apex of the lung than the base
The bottom of the lung has ____ perfusion and ____ ventilation than the top.
more and more
high alveolar volume in the apex ___ blood flow compared to the base.
decreases
Summary: differences between intrapleural pressure, Transmural pressure, alveoli size compliance and ventilation on top of lung ( apex) versus base:
apex: more negative intrapleural pressure, greater transmural pressure, larger alveoli, less compliant, less ventilation
base: opposite of top.
Summary differences between intravascular pressure, recruitment, distention, resistance, and blood flow of apex versus base
apex: lower intravascular pressure, less recruitment, less recruitment distention, higher resistance, less blood flow…
base= opposite concept
Ventilation and blood flow are both ____ dependent.
gravity
what part of the lung has a higher ventilattion to perfusion ratio?
the apex of the lung has like 3 versus the base has 1.5
Where is gas exchange of the lung more efficient, the base of the lung or the apex?
apex
Increased ventilation means what increased ____ and decreased what_____.
increased PaO2
decreased PaCo2
Compare the ratio of oxygen and carbon dioxide of apex and base of the lung.
PaO2 apex: 130
PaCO2 apex: 28
PaO2 base: 88
PaCO2 base: 42
the ratio of the apex is larger
The upper regions of the lung has less ventilation than the base because of an apical decrease in which of the following factors?
A: airway resistance B: surfectant C: blood flow D: compliance E elastance
upper part of lung has less ventilation because of less compliance
aleveoli is less compliant compared to those at the base.
compare ventilation, perfusion and Va/Q ratio of apex versus base of the lungs
more ventilation at base of lungs,
Va/Q ratio higher at the apex of lungs,
perfusion is higher at the base of lungs
the PH of lung at the apex is ____ than at the base.
higher 7.55 ( higher V/Q ratio)
versus 7.38
what helps normalize the V/Q ratio?
hypoxic vasoconstriction
and
Bronchoconstriction
What is hypoxic vasoconstriction and when is it helpful?
it is for low V/Q ratio ( lots of blood or too little ventilation) causes the blood coming into the area to be directed to other parts of the lung
What is bronchoconstriction and when is it helpful?
it is for high V/Q ratio, the bronchi will constrict slightly to increase the resistance and decrease the amount of ventilation coming into an area that is not well perfused thus limiting the amount of alveolar dead space.
what occurs with a low V/Q ratio?
there is a blockage of the lung.. it is supposed to have like 100mmhg O2 and 40mhg of CO2
when it is blocked it will have like 40 and 45…
ventilation goes down, O2 can’t get in and CO2 increased cus it cant get out
what occurs when you have increased V/Q ratio?
it is supposed to have like 100mmhg O2 and 40mhg of CO2
perfusion is affected (Q). blood supply isn’t getting here CO2 is lower than normal, like 0, no exhancge of CO2 and oxygen goes in and not reaching the blood so high oxygen.
150 mmHg O2 and 0 mmhg of CO2
person has pulmonary embolism what is likely of alveolar air? A.PO2= 30 mmhg B.PO2=100mmhg C. PCO2= 100 mmhg D. PCO2=40 mmhg E. PCO2=25 mmhg
pulmonary embolism causes a high v.q ratio
this means that the alveoli had high ventilation and low CO2
E is the answer…
remember that normal is PO2=100
PCO2=40
what occurs to the A-a gradient with generalized hypoventilation?
the A-a O2 gradient stays the same
what 3 respiratory causes of hypoxemia cause a high A-a O2 gradient?
Regional low VA/Q ratio, Anatomic shunt, Diffusion block
look at slide 29: If patient has hypoxemia, check the A-a gradient. what is it if it is normal?
hypoventilation.
look at slide 29: If patient has hypoxemia, check the A-a gradient. if abnormal what can it be ?
shunt V/q mismatch, diffusion problem…
If it can be corrected with oxygen therapy then it is either a V/Q mismatch or diffusion problem. If DLco is normal then it is a V/Q mismatch if not normal then it is a diffusion problem.
If it cannot be corrected with O2 therapy then it is a shunt.
what occurs if V/q= 0
perfusion of an area with no ventilation this occurs in shunts
what occurs if V/q= infinity?
dead space- ventilation with no perfussion
at high altitude there is hypoxemia because of _____
decreased alveolar pO2
and decreased arterial PO2 ( hypoxemia)
What stimulates ventilation in a hypoxemia state?
carotid and aortic bodies
what occurs to minute alveolar ventilation in an attempt to restore blood oxygen levels?
increases
what occurs to ventilation at altitudes/
hyperventilation cus of low oxygen, decreased PCO2…
what are things that can be seen in the blood of someone living long term at high altitudes?
polycythemia, low PO2 of kidney stimulates erythropoietin- stimulates bone marrow to increase RBC production…
hypoxemia–more RBC to carry more oxygen
increased blood viscosity
2,3BPG increased
hypocapnia from being at high altitudes causes what to the brain?
cerebral vasoconstriction
long term it leads to cerebral vessel vasodilation and hyper perfusion of the vessels. this increases the likelihood of cerebral edema
