DSA Dr. Karius

Question 1

Calculating the Alveolar PO2

Answer 1

PAO2 = Inspired oxygen - oxygen consumed

PAO2 = PIO2 - (PaCO2/RQ)

PIO2 = (Patm - 47mmHg (for water vapor of the body)) x FiO2 (0.21 percentage of oxygen in the atm)

RQ = V(dot)CO2/V(dot)O2
respiratory quotient

PaCO2 = normally 40 mmHg

therefore normal PAO2 = 99.7 mmHg

Question 2

How to determine the RQ

Answer 2

the RQ is given based on the metabolite that is being consumed

normal = RQ is 0.8
IV glucose RQ = 1
Hypoglycemic or Diabetic RQ = 0.7

Question 3

The Alveolar-arterial O2 gradient

Answer 3

the A-a O2 gradient is equal to PAO2 - PaO2

normal should be less than 12 mmHg

Question 4

The Ventilation-Perfusion ratio

Answer 4

ratio between the amount of air getting to the alveoli in ml/min and the amount of blood being sent to the lungs

V/Q = (4l/min)/(5l/min) = 0.8

Question 5

what happens if their is a decrease in the Ventilation perfusion ratio

Answer 5

• Ventilation is not keeping pace with perfusion
• Alveolar oxygen levels will decrease which will lead to a decrease in arterial oxygen levels

-Alveolar CO2 levels will increase and also lead to an increase in arterial CO2

Question 6

what happens if their is an increase in the Ventilation-perfusion ratio

Answer 6

• Increase Ventilation (bring more oxygen to the alveoli, blow off more CO2 from the lungs)
• Decrease the perfusion so the blood takes away less oxygen delivers less CO2
• This will lead to an increase PAO2 and PaO2
• and a decrease in PACO2 and PaCO2

Question 7

how does standing up effect the V/Q ratio

Answer 7

standing up more blood goes to the base of the lung so get a low V/Q low PaO2

at the apex of the lung less blood gets their because of gravity so have a high V/Q, high oxygen PaO2

middle the lungs is average 100 PaO2 and 40 PaCO2

Question 8

how is the V/Q changed pathologically

Answer 8

increase of V/Q: could be caused by a pulmonary embolism and not much oxygen exchange is happening in the blood, creates alot of alveolar dead space

Decrease in the V/Q: maybe something blocking the airway. blood gets to the alveoli but little gas exchange happens, a physiological shunt.

Question 9

how does the body normalize the V/Q ratio

Answer 9

low V/Q: lots of blood or too little ventillation, hypoxic vasoconstriction will occur to move blood to different areas of the lung

high V/Q: Bronchoconstriction to increase resistance and decrease amount of ventilation going to an area in the lung with little blood flow and high alveolar dead space