Ventilation-Perfusion Relationships

Question 0

What does a pulmonary embolus do to V/Q?

Answer 0

Dead space is created -> “infinite” V/Q

Question 1

How can the body compensate for low V in an area to maintain V/Q balance?

Answer 1

Hypoxic vasoconstriction- lowers Q.

Question 2

Does low V/Q (e.g. from pneumonia, edema) cause predominately hypoxia or hypercarbia?

Answer 2

Hypoxia, predominately.
(Hyperventilation can compensate for the hypercarbia… and CO2 has an easier time diffusing out across fluid in the alveoli?)

Question 3

Does high V/Q cause predominately hypoxia or hypercarbia?

Answer 3

Predominately hypercarbia. (though hypoxia also occurs.)

Question 4

What effect does low V/Q have on neighboring segments?

Answer 4

Hyperventilation -> increased ventilation to neighboring segments.

Question 5

What effect does increased V/Q (dead space) have on neighboring, healthy statements?

Answer 5

Blood flow is increased to healthy segments.

Question 6

In an upright perfusion, where in the lung are ventilation and perfusion the greatest.

Answer 6

Ventilation and perfusion are both greatest in the lower lungs.

Question 7

In an upright person, how does V/Q ratio compare high in the lung vs. low in the lung?

Answer 7

V/Q is high at the top, low at the bottom.

Question 8

If you have an area of high V/Q and an area of low V/Q, why do you still get hypoxemia?

Answer 8

Because of the shape of the hemoglobin O2-binding curve, increased V/Q won’t increase arterial pO2 as much as low V/Q will lower it.

Question 9

What is a typical acid/base status for a person with PE blocking one part of the lung?

Answer 9

Respiratory alkalosis. (dead space -> hypercarbia…)