Alveolar Ventilation & Perfusion

Question 1

Minute Ventilation = ?

Answer 1

Tidal volume x Resp. Rate

Question 2

All of inspired air in each breath is “fresh air” (True or False)

Answer 2

False: some of it was expired air from the previous breath that occupied the anatomic dead space, and thus never left

Question 3

What equation can we use to tell quantitatively if the lungs are working well to provide oxygen?

Answer 3

The alveolar gas equation

Question 4

Alveolar Gas Equation

Answer 4

[FlO2(Pbarometric-47)] - (PaCO2)/R

Question 5

A-a Difference

Answer 5

Difference in concentration gradients (oxygen) between the Alveoli and arteries

Question 6

Formula for the normal A-a Oxygen difference based on age

Answer 6

(Age/4) + 4

Question 7

Normal/healthy value for A-a oxygen gradient

Answer 7

Less than 8-9 to upper limit using formula

Question 8

What equation can we use to tell quantitatively if the lungs are working well to eliminate carbon dioxide?

Answer 8

Alveolar Ventilation Equation

Question 9

Alveolar Ventilation Equation

Answer 9

0.863*(VC02/PACO2)

Question 10

Doubling alveolar ventilation (halves/doubles) PACO2

Answer 10

Halves

• inverse relationship b/w VA (alveolar ventilation) and PACO2 (alveolar PCO2)

Question 11

normal, physiologic elevation in ventilation caused by a rise in CO2 PRODUCTION (metabolism)

Answer 11

Hyperpnea

Question 12

disproportional increase in ventilation, relative to metabolism, leading to a FALL in ALVEOLAR and ARTERIAL PCO2; can happen due to high anxiety or in patients with various respiratory conditions

Answer 12

Hyperventilation

Question 13

disproportional decrease in ventilation relative to metabolism, leading to a RISE in ALVEOLAR and ARTERIAL PCO2; happens in patients with sedative or alcohol overdose, obstructed airways and in neuro-muscular disorders affecting the muscles of respiration

Answer 13

Hypoventilation

Question 14

Why is ventilation not uniformly distributed in the lung?

Answer 14

More air goes to the base of the upright lung than the apex due to gravity. Gravity creates more negative intrapleural pressure (and therefore higher transpulmonary pressure) at the apex which holds alveoli open during expiration.

Question 15

Why is it beneficial for the pulmonary circulation to be a low pressure, high volume system?

Answer 15

Low pressure helps prevent fluid extravasation (even with the entire cardiac output)

Question 16

Characteristics of pulmonary arterioles

Answer 16

Lack auto-regulation

Highly compliant

Question 17

Class of pulmonary vessels that are not adjacent to alveoli and increase in size and dec. resistance during inflation (Extra-alveolar vs. Alveolar)

Answer 17

Extra-alveolar

Question 18

Class of pulmonary vessels that are surrounded by alveoli and gets stretched/thinner and become smaller with inc. resistance during inflation (Extra-alveolar vs. Alveolar)

Answer 18

Alveolar

Question 19

How is pulmonary vasculature susceptible to increased BOTH pulmonary arterial and venous pressure?

Answer 19

1. Increased arterial pressures distend alveolar capillary diameter (ballooning out). Increased venous pressures also dilate capillaries using back-pressure. Increased pulmonary capillary diameter decreases resistance and increases flow.
2. Increased intravascular pressures in both arterial and venous system recruit previously non-perfused pulmonary capillaries to work to its full potential.

Question 20

Why, like ventilation, does alveolar perfusion exhibit regional differences related to gravity?

Answer 20

In the upper lung, the alveoli are more stretched and open by gravity (more positive transpulmonary pressure). The higher alveolar pressure which is greater than arterial/venous pressure compresses the blood vessels leading to decreased blood flow.

In the lower lung, the alveoli are less stretched. The alveolar pressure is less than arterial/venous pressure and therefore increasing the blood flow.

Question 21

Characteristics of alveoli in the upper lung

Answer 21

Low compliance (but stretched by gravity)
Low ventilation
Lower perfusion
High V/Q ratio
High PAO2

Question 22

Characteristics of alveoli in the lower lung

Answer 22

High compliance (not stretched by gravity)
High ventilation
Higher perfusion
Low V/Q ratio
Low PAO2

Question 23

The homeostatic/reflex mechanism in which Intrapulmonary arteries constrict in response to alveolar hypoxia, diverting blood to better-oxygenated lung segments, thereby optimizing ventilation/perfusion matching and systemic oxygen delivery

Answer 23

Hypoxic Pulmonary Vasoconstriction

Question 24

Long standing pulmonary hypertension due to HPV can lead to

Answer 24

Cor Pulmonale

• Right ventricular hypertrophy that can result in HF

Question 25

Since CO2 is highly soluble/permeable, PACO2 is equal to

Answer 25

PaCO2 = 40

Question 26

Alveolar ventilation in people with normal lung function is

Answer 26

4. 3 L/min

* assuming 200 ml CO2 production per min & 40 mmHg PACO2

Question 27

At a constant level of CO2 production, PACO2 is determined by

Answer 27

alveolar ventilation

• inverse relationship

Question 28

What is the lowest part of the lung in relation to gravity called?

Answer 28

dependent region

Question 29

In the dependent region, smaller alveolar volumes mean

Answer 29

the alveoli are more compliant/distensible and so capable of more gas exchange