7 - Respiratory Muscle Dysfunction

Question 1

What is muscle fatigue? What can lead to it?

Answer 1

Fatigue = decreased force generation that improves with rest

Anything that results in an imbalance between load and capacity leads to fatigue

Question 2

What effects does hyperinflation have on the diaphragm? What effect does it have on the overall work of breathing?

Answer 2

• shortens fibers
• decreases force generation
• inability to increase abdominal pressure
• paradoxical movement into chest with inspiration

It changes neuromechanical coupling, resulting in ineffective tension. It requires more work to generate the pressure needed to inspire

Question 3

What are the consequences of respiratory muscle dysfunction?

Answer 3

• hypoventilation
• aspiration
• impaired cough

Question 4

If a patient has respiratory muscle dysfunction, what will their PFTs show?

Answer 4

restriction with a normal DLCO

Question 5

What respiratory impairment is suggested by a large decrease in FEV1 or FVC in supine position?

Answer 5

Respiratory muscle dysfunction

Question 6

In a patient with respiratory muscle dysfunction, they will have a decreased [MIP/MEP] if inspiratory muscles are weak and a decreased [MIP/MEP] if abdominal muscles are weak.

Answer 6

inspiratory muscles = decreased MIP

abdominals = decreased MEP

Question 7

Patients with respiratory muscle dysfunction will have [low/normal/high] PaCO2.

Answer 7

High

Question 8

In an EMG study on a patient with respiratory muscle dysfunction, there will be slowed conduction if the patient has a [neuropathy/myopathy] and normal conduction with decreased amplitude if the patient has a [neuropathy/myopathy]

Answer 8

slowed conduction = neuropathy

normal conduction with decreased amplitude = myopathy

Question 9

What will an ultrasound show if a patient has respiratory muscle dysfunction?

Answer 9

An absence of diaphragm thickening

Question 10

What are the functional differences between respiratory muscles and other skeletal muscles?

Answer 10

Respiratory muscles are much more fatigue resistant, are controlled automatically (instead of voluntarily), and have restrictive and elastic loads (instead of inertial loads)

Question 11

What is Hoover’s sign? What does it indicate?

Answer 11

It is the inward motion of lower rib cage interspaces during inspiration (can see accessory muscles working). It indicates hyperinflation

Question 12

What is the thoracoabdominal paradox? What does it indicate?

Answer 12

Instead of the abdomen and thorax moving outward together during inspiration, the abdomen moves inward as the thorax moves outward. This indicates diaphragm weakness/paralysis or hyperinflation

Question 13

What position (supine or standing upright) is better for someone with diaphragmatic weakness/paralysis? Why?

Answer 13

Standing. It takes advantage of gravity to help pull the diaphragm down

Question 14

What is the function of the scalenes? What happens if they are paralyzed?

Answer 14

Move upper rib cage up and out during inspiration. If paralyzed, upper rib cage paradox is seen (moves opposite what is normal)

Question 15

What is the function of the parasternal muscles? What happens if they are paralyzed?

Answer 15

Move upper rib cage up during inspiration. If paralyzed, upper rib cage paradox is seen (moves opposite what is normal)

Question 16

What are the functions of the intercostal muscles? What happens if they are paralyzed?

Answer 16

External intercostal - lifts ribs up during inspiration; paralysis = upper rib cage paradox (moves opposite what is normal) and increased work of breathing

Internal intercostal - pull ribs down during expiration; paralysis = upper rib cage paradox (moves opposite what is normal) and increased work of breathing

Question 17

What are the functions of the abdominal muscles? What happens if they are paralyzed?

Answer 17

Pull rib cage down and in during expiration, compress abdominal contents upward, displace the diaphragm

Paralysis = trouble breathing out

Question 18

What position (supine or standing upright) is better for someone with abdominal weakness/paralysis? Why?

Answer 18

Supine. It takes advantage of gravity to help push abdominal contents inward, helping expiration

Question 19

Why do people with accessory respiratory muscle use get SOB when they do activities involving their hands?

Answer 19

They can’t use their hands to brace themselves in a tripod position (which is what allows them to activate the accessory muscles)

Question 20

What is the function of the upper airway bulbar muscles?

Answer 20

They keep the airway open and stable (mostly useful during inspiration; sometimes people have an issue with simultaneous breathing and talking if they have bulbar weakness)

Question 21

Inability to ventilate is due to [inspiratory/expiratory/upper airway] muscle weakness.

Answer 21

inspiratory muscle weakness

Question 22

Risk of aspiration is due to [inspiratory/expiratory/upper airway] muscle weakness.

Answer 22

upper airway muscle weakness

Question 23

Inability to cough is due to [inspiratory/expiratory/upper airway] muscle weakness.

Answer 23

inspiratory muscle weakness, expiratory weakness, AND upper airway muscle weakness

Question 24

Someone with respiratory muscle weakness will have a(n) [increase/decrease] in vital capacity going from upright to supine.

Answer 24

decrease (unless they have abdominal weakness, in which they will have an increase)

Question 25

What PFTs (FEV1, FVC, FEV1/FVC, TLC, DLCO, MIP, MEP) will someone with respiratory muscle weakness have?

Answer 25

restrictive (decreased FEV1 and FVC and TLC, but normal FEV1/FVC and DLCO) + decreased MIP and MEP