Ventilation - Perfusion

Question 1

What is perfusion?

Answer 1

blood flow to the lung

Question 2

What is hypoxia?

Answer 2

localized lack of oxygen

Question 3

What is hypoxemia?

Answer 3

a systemic decrease in O2 content

Question 4

What are some causes of hypoxemia?

Answer 4

hypoventilation, diffusion impairment, Low PiO2/F1O2, shunt, ventilation-perfusion mis matches

Question 5

What is the alveolar gas equation?

Answer 5

PaO2 = FiO2 x (Patm - PH2O) - (PaCO2/R)

Question 6

What is FiO2 in the alveolar gas equation?

Answer 6

the fraction of inspired oxygen - 21% in room air

Question 7

What is PH2O at room air?

Answer 7

47 mmHg

Question 8

What is R in the alveolar gas equation?

Answer 8

volume of CO2 produced per unit time/ colume of O2 produced per unit time

Question 9

What is R normally in the aveolar gas equation?

Answer 9

0.8

Question 10

What is PaCO2 in the alveolar gas equation?

Answer 10

arterial CO2 pressure

Question 11

When a patient hypoventilates, what hapens to CO2 in the body?

Answer 11

it builds up (normally 40 mmHg, increases to 80mmHg)

Question 12

Does hypoventilation affect the A-a gradient?

Answer 12

no; PCO2 increases and PAO2 decreases but it does not affect the gradient

Question 13

What type of therapy does hypoventilation respond to?

Answer 13

o2 therapy

Question 14

What is diffusion impairment caused by?

Answer 14

exercise, high altitude, low PiO2, and lung pathologies

Question 15

Why should thickness impact diffusion?

Answer 15

the oxygen has to diffuse out form the alveoli to the RBC, if you increase the thickness, the diffusion will decrease

Question 16

How do you fix an impairment caused by increased thickness?

Answer 16

increase the oxygen

Question 17

What are normal physiologic shunts?

Answer 17

bronchial circulation and thebesian veins

Question 18

What do thebesian veins do?

Answer 18

drain the myocardium of the heart and some of them drain into the left ventricle

Question 19

What are some pathological shunts?

Answer 19

arterial-venous anastomoses, absolute intra-pulmonary shunts/true shunts, patent ductus arteriosus, foramen ovale, intraventricular septal defects

Question 20

Can pathological shunts be fixed by O2 therapy?

Answer 20

no

Question 21

What must be in sync for optimal gas exchange to occur?

Answer 21

the ventilation-perfusion ratio

Question 22

What is the effect of more negative intra-pleural pressure at the apex of the lung cause?

Answer 22

greater transmural pressure gradient, larger alveoli has less compliance and less ventilation, poor perfusion

Question 23

What is the effect of less negative intra-pleural pressure at the base of the lung?

Answer 23

lesser transmural pressure gradient, smaller alveoli, greater compliance, more ventilation, high perfusion

Question 24

How does a blockage at the apex of the lung affect the V/Q ratio?

Answer 24

it causes it to be 0

Question 25

How does an alveolar blockage affect the V/Q ratio?

Answer 25

it causes it to be infinate

Question 26

What level of hemoglobin saturation causes hypoxemia?

Answer 26

60 mmHg or below

Question 27

What is the physiologic response to V-Q mismatches?

Answer 27

 Hypoxic vasoconstriction, brisket disease in cattle, right side heart failure in chicken, COPD, asthma, pulmonary embolism, pneumonia

Question 28

What does hypoventilation do to PaCO2 and the A-a gradient?

Answer 28

increases PaCO2, A-a remains normal

Question 29

What does diffusion impairment do to PaCO2 and the A-a gradient?

Answer 29

PaCO2 remains normal, A-a gradient is increased

Question 30

What does Low PiO2 do to PaCO2 and the A-a gradient?

Answer 30

PaCO2 decreases, A-a remains normal

Question 31

What does a right-left shunt do to PaCO2 and the A-a gradient?

Answer 31

PaCO2 remains normal, A-a is increased

Question 32

What does a V-Q mismatch do to PaCO2 and the A-a gradient?

Answer 32

PaCO2 remains normal, A-a increases