Ventilation:Perfusion

Question 1

Compared with the apex of the lung, the base of the lung exhibits (when the individual is awake and upright) greater or lesser perfusion?

Answer 1

Greater. Perfusion (blood flow) is best in dependent lung. The base of the lung is dependent in the upright (sitting or standing) individual.

Question 2

What is the principle reason blood flow to dependent lung is greater than blood flow to non-dependent lung?

Answer 2

Gravity.

Question 3

Compared with the apex of the lung, the base of the lung exhibits (when the individual is awake and upright) greater or lesser ventilation?

Answer 3

Greater. Total ventilation is best in dependent lung.

Question 4

In the awake spontaneously breathing patient in the lateral decubitus position, where is ventilation best (dependent or nondependent lung), and where is perfusion best (dependent or nondependent lung)?

Answer 4

In the awake spontaneously breathing patient in the lateral decubitus position, ventilation is best in dependent (lower) lung and perfusion is best in dependent (lower) lung.

Question 5

In the anesthetized and paralyzed patient in the lateral decubitus position, where is ventilation best (dependent or nondependent lung), and where is perfusion best (dependent or nondependent lung)?

Answer 5

When the patient in the lateral decubitus position is anesthetized and paralyzed, perfusion is best in the dependent (lower) lung, but ventilation is best in the nondependent upper lung.

Question 6

The healthy adult lung receives each minute an alveolar ventilation of about how many liters and a pulmonary blood flow of how many liters? What is the average resting ventilation:perfusion (V/Q) ratio?

Answer 6

4 l/min is the alveolar ventilation rate (V). 5 l/min is the pulmonary blood flow (Q). Normally, V/Q = 0.8 [(4L/min)/(5 L/min) = V/Q = 0.8].

Question 7

What is the importance of maintaining a normal ventilation-to-perfusion relationship?

Answer 7

A normal ventilation-to-perfusion relationship is required to keep PaCO2 and Pa02 in the normal range.

Question 8

In a lung unit that exhibits absolute shunt, what is the V/Q ratio, the amount of ventilation, and the amount of perfusion?

Answer 8

In a lung unit that exhibits absolute shunt, V/Q = 0 because V = 0; perfusion (Q) may be decreased somewhat because of hypoxic pulmonary vasoconstriction.

Question 9

A V/Q ratio between zero and unity (0 < V/Q < 1) indicates what?

Answer 9

A V/Q ratio between zero and unity (0 < V/Q < 1) indicates a relative shunt.

Question 10

What is indicated by a V/Q ratio that is greater than one (V/Q > 1)?

Answer 10

A V/Q > 1 indicates deadspacing.

Question 11

What is the V/Q ratio in a lung that is ventilated but completely unperfused (eg pulmonary emboli)?

Answer 11

V/Q = infinity if the lung unit is ventilated and completely unperfused, because Q = 0.

Question 12

State the numeric values for absolute deadspace and absolute shunt.

Answer 12

With absolute deadspace, V/Q = infinity (V/0) and with absolute shunt, V/Q = 0 (0/Q).

Question 13

Describe how gravity affects the size of alveoli.

Answer 13

At end-expiration, dependent alveoli are smaller than nondependent alveoli.

Question 14

Compared with the apex of the lung, the base of the lung exhibits (when the individual is awake and upright) higher or lower V/Q ratio?

Answer 14

Lower. The V/Q ratio is high in nondependent lung and low in dependent lung.

Question 15

What are the consequences of clipping a bronchus but

leaving the vasculature intact during left pneumonectomy?

Answer 15

An intrapulmonary shunt develops if a bronchus is clipped and the vasculature is left intact. When a shunt develops, Pa02 decreases.

Question 16

Why does a patient who has two lungs, but only one

functioning properly, present a problem, whereas a patient with one lung lives a fairly normal life?

Answer 16

There is a large shunt when one lung is nonfunctional. Pa02 decreases possibly/probably resulting in arterial hypoxemia. If the lung is removed, there is no shunt and hence there is no arterial hypoxemia.