5. Respiratory Muscles

Question 1

in terms of control centers, how is respiration unique?

Answer 1

has 2 control centers: voluntary/cortical, and reflex/brainstem. due to cortical, have some voluntary control. due to brainstem, have automaticity.

Question 2

what is the Central Pattern Generator?

Answer 2

a poorly defined group of neurons in the medulla which generates an automatic resp pattern.

Question 3

how is the CPG regulated?

Answer 3

modulated by afferent signals, pulm (vagal) receptors, intercostal muscle and tendon proprioceptors

Question 4

medullary control center is connected to breathing muscles as well as what other cranial nerves?

Answer 4

CN 9,10,11,12 - due to need to control airway and larynx while breathing

Question 5

Fundamental property of skeletal muscles: a short muscle is a ______ muscle

Answer 5

weak

Question 6

skeletal muscle energy consumption is det’d by what 2 factors?

Answer 6

• tension produced by the muscle

- velocity of shortening of the muscle

Question 7

The two functional components of the diaphragm are…?

Answer 7

• vertically-running costal muscles (from the lower ribs and xiphoid)
• horizontally running crural muscles from the lumbar vertebrae

Question 8

Diaphragm movement: what is the ‘insertional force’?

Answer 8

where the crural muscles attach to the anterior ribcage, uses the abdominal cavity/contents as a fulcrum to life the anterior ribcage towards the head.

Question 9

what happens to the abd pressure when the diaphragm contracts?

Answer 9

increases

Question 10

what happens to the diaphragm with hyperinflation?

Answer 10

flattens, loses its mechanical advantage. insertional force is lost. instead, the flattened contracting diaphragm pulls IN the lower costal margin.

Question 11

if the diaphragm is paralyzed, what are the only functioning resp muscles?

Answer 11

intercostals, other accessory muscles.

Question 12

what happens when the intercostals engage to promote inhalation, with a paralyzed diaphragm?

Answer 12

the thoracic pressure decreases, and the abdominal contents are sucked into the lung area.

Question 13

what happens to pts with paralyzed diaphragm when supine?

Answer 13

the abdominal contents are further brought into the thorax on inspiration: makes it very hard to lie down and breathe.

Question 14

what are the accessory muscles for expiration?

Answer 14

rectus, transverse/oblique abdominal muscles. they pull the lower rib cage down and inward.

Question 15

what is MIP? when is it reduced?

Answer 15

max inspiratory pressure. reduced when insp muscles are weakened (NM disease, CHF), fatigued or shortened

Question 16

what is MEP? when is it reduced?

Answer 16

max expiratory pressure. reduced with abnormalities of inspiratory muscles function or generalized musc abnormalities.

Question 17

what is the zone of apposition?

Answer 17

the area where the costal muscles are closely associated with the lower ribs and xiphoid.

Question 18

what are 4 ways in which the resp muscle function is impaired in COPD?

Answer 18

1. shortened/weakened inspiratory muscles
2. decr zone of apposition
3. incr radius of curvature (ie, flattened diaphragm)
4. threshold load. ie, lungs still want to deflate still when pt initiates next breath. have to overcome that elastic recoil.

Question 19

what are 4 ways in which neuromuscular disease may impact breathing?

Answer 19

1. cerebral cortex disease
2. brainstorm disorders (stroke, tumor, infection)
3. spinal cord trauma
4. disorders of motor neuron, peripheral nerve, NM junction, muscle

Question 20

how might cerebral cortex disease affect breathing?

Answer 20

usually insignificant, prob because resp muscles have bilateral cortical control

Question 21

how might brainstorm disorders affect breathing?

Answer 21

(tumor, stroke, infection) central alveolar hypoventilation. reflex control of breathing fails. voluntary control is ok. so breathing fails during sleep

Question 22

how might spinal cord trauma affect breathing?

Answer 22

cervical cord trauma above C3 may cause sudden death from apnea. trauma below C5 spares the phrenic n (3, 4, 5) though may lose accessory muscles.

Question 23

how might neuromuscular disease affect breathing?

Answer 23

tend to have reduced MIP and MEP. VC falls with progression of disease. RV tends to increase. TLC tends to decrease. major concerns are hypoventilation and decreased ability to cough/clear mucus.

Question 24

name the main muscles involved in respiration

Answer 24

diaphragm, SCM, scalenes, intercostals, rectus, obliques, upper airway muscles (keep airway patent)

Question 25

why is a short muscle a weak muscle?

Answer 25

think about the overlap between actin and myosin: if very far overlapped, don’t have very far to go. also weak if overstretched and actin/myosin no longer overlap

Question 26

skeletal muscle 02 consumption depends on what 2 things?

Answer 26

tension, speed of shortening

Question 27

resp muscles’ use of 02 becomes significant to the body as a whole when?

Answer 27

when exercising. usually 02 use is insignificant, but when exercising, resp muscles’ use of 02 becomes a much greater % of body 02 usage.

Question 28

fatigue: gets better with rest or not?

Answer 28

yes. fatigue = loss or decrement in tension development that is reversible with rest.
Occurs when demands outstrip muscle capabilities/supply

Question 29

is the lower ribcage exposed to abdominal pressure or pleural pressure?

Answer 29

abdominal.

Question 30

what is the law of laplace?

Answer 30

P = T/r

As r increases, (ie as the diaphragm flattens out) there is less pressure generated for the same Tension.

Question 31

what is paradoxical motion?

Answer 31

with diaphragm paralysis, the abdominal contents will be sucked into the chest cavity rather than pushed outwards. paradox = abd retracting with inspiration

Question 32

when are accessory muscles most vital?

Answer 32

during exercise or in disease states. with normal breathing, they are not usually recruited.

Question 33

how would expiratory muscles be able to assist inspiratory muscles?

Answer 33

if exhale completely (more than usual) give inspiratory muscles a mechanical advantage – the CW will spring out if pulled further in towards midline than it is at FRC

Question 34

hyperinflation: worse for inspiration or expiration?

Answer 34

worse for inspiration. at higher lung volumes, you have

• shortening (shorter muscle = weak muscle)
• decreased zone of apposition
• loss of insertional component
• increased radius of curvature
• presence of “threshold” load (have to inhale against the tendency to exhale due to hyperinflation)