# Ventilation Perfusion Relationships Pt. 1 Flashcards Preview

## CPR Exam 2 > Ventilation Perfusion Relationships Pt. 1 > Flashcards

Flashcards in Ventilation Perfusion Relationships Pt. 1 Deck (15)
1
Q

Use the alveolar gas equation to determine alveolar-arterial O2 difference and be able to determine if deficits are present

A

PAO2=PIO2-PaCO2/R

PAO2 is alveolar partial pressure of O2

PIO2 is inspired partial pressure of oxygen accounting for water vapor (47)

PaCO2 is arterial CO2

R=VdotCO2/VdotO2=0.8

2
Q

What is the alveolar gas exchange used for?

A

calculate what inspired O2 needs to be to produce a desired alveolar (and arterial) O2 level

often listed with a small correction factor. This is small and can be ignored

3
Q

PIO2 is calculated as

A

Barometric pressure minus the water vapor P times the FiO2

760-47 x .21

barometric pressure will change with altitude and be given if needed

FiO2 is normally 21% but changes with altitude and will be given if needed

4
Q

What is the Alv-art O2 gradient?

A

useful for determining the health of the alveoli

PalvO2-PartO2=

ex. 121.8-43

=78.8

normal is <20mmHg

5
Q

An increase in the A-A O2 gradient indicates a

A

diffusion impairment (something is wrong at the alveoli)

RtL shunt

COPD/PE

Intstl. lung dz , pulmonary arterial HTN

6
Q

Summary of alveolar gas equation

A

the gas exchange allows us to predict the O2 concentration in the alveoli (non invasive)

once you have the alveolar concentration of oxuygen you can calculate the A-A O2 gradient

If the A-A gradient is freater than normal, you know there is an alveoli problem

if the A-A gradient is normal, but PaO2 and PAO2 are noth low, the problem is elsewhere

7
Q

what is the intrapleural pressure in the apex?

What is the intrapleural pressure at the base?

A

there is less intrapleural fluid, so the intrapleural pressure is more negative (up to -10)

alveoli are large at rest, can only get a little bigger with inspiration

there is more intrapleural fluid, so the intrapleural pressure is less negative (-2 to -3)

alveoli are small at rest, can get much bigger with inspiration

8
Q

the middle apex has normal blood flow and pressure. What is the pressure?

A

-5

9
Q

What is the V/Q ratio?

A

It is the ratio between ventilation and perfusion

over the entire lung it is 4l/min/5l/min=0.8 (avg)

Often spoke of as high or low V/Q

High-high ventilation relative to perfusion

Low: low ventilation compared to perfusion

10
Q

What are the following at high V/Q regions

PaO2

PaCO2

pHa

Volume of blood

A

PaO2: high

PaCO2: low

pHa: high

volume: low

11
Q

What are the following values for the low V/Q regions

PaO2

PaCO2

pHa

Volume of blood

A

PaO2: low

PaCO2: high

pHa: low

Volume of blood: high

12
Q

What is the V/Q ratio of the apex?

What is the V/Q ratio in the mid-lung?

What is the V/Q ratio at the base?

A

At the apex, V/Q is high leading to a higher PaO2 and a lower PaCO2 (PaO2=130, PaCO2=28)

Mid-lung, V/Q is 0.8 and blood gases are as expected (PaO2=90-100, PaCO2=40)

At the base, V/Q is low, blood gases aren’t as good(PaO2=98, PaCO2=42)

13
Q

V/Q parameters at Apex

PaO2

PaCO2

pHa

Volume

A

high

low

high

low

14
Q

V/Q parameters at the base of the lung

PaO2

PaCO2

pHa

Volume of blood

A

Low

high

low

high

15
Q

What can we do to minimize the differences in the V/Q ratios in the different zones of the lung

A

hypoxic vasoconstriction

constriction of pulmonary vessels to redirect blood away from hypoxic regions