5. Respiratory Muscles Flashcards
in terms of control centers, how is respiration unique?
has 2 control centers: voluntary/cortical, and reflex/brainstem. due to cortical, have some voluntary control. due to brainstem, have automaticity.
what is the Central Pattern Generator?
a poorly defined group of neurons in the medulla which generates an automatic resp pattern.
how is the CPG regulated?
modulated by afferent signals, pulm (vagal) receptors, intercostal muscle and tendon proprioceptors
medullary control center is connected to breathing muscles as well as what other cranial nerves?
CN 9,10,11,12 - due to need to control airway and larynx while breathing
Fundamental property of skeletal muscles: a short muscle is a ______ muscle
weak
skeletal muscle energy consumption is det’d by what 2 factors?
- tension produced by the muscle
- velocity of shortening of the muscle
The two functional components of the diaphragm are…?
- vertically-running costal muscles (from the lower ribs and xiphoid)
- horizontally running crural muscles from the lumbar vertebrae
Diaphragm movement: what is the ‘insertional force’?
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.
what happens to the abd pressure when the diaphragm contracts?
increases
what happens to the diaphragm with hyperinflation?
flattens, loses its mechanical advantage. insertional force is lost. instead, the flattened contracting diaphragm pulls IN the lower costal margin.
if the diaphragm is paralyzed, what are the only functioning resp muscles?
intercostals, other accessory muscles.
what happens when the intercostals engage to promote inhalation, with a paralyzed diaphragm?
the thoracic pressure decreases, and the abdominal contents are sucked into the lung area.
what happens to pts with paralyzed diaphragm when supine?
the abdominal contents are further brought into the thorax on inspiration: makes it very hard to lie down and breathe.
what are the accessory muscles for expiration?
rectus, transverse/oblique abdominal muscles. they pull the lower rib cage down and inward.
what is MIP? when is it reduced?
max inspiratory pressure. reduced when insp muscles are weakened (NM disease, CHF), fatigued or shortened
what is MEP? when is it reduced?
max expiratory pressure. reduced with abnormalities of inspiratory muscles function or generalized musc abnormalities.
what is the zone of apposition?
the area where the costal muscles are closely associated with the lower ribs and xiphoid.
what are 4 ways in which the resp muscle function is impaired in COPD?
- shortened/weakened inspiratory muscles
- decr zone of apposition
- incr radius of curvature (ie, flattened diaphragm)
- threshold load. ie, lungs still want to deflate still when pt initiates next breath. have to overcome that elastic recoil.
what are 4 ways in which neuromuscular disease may impact breathing?
- cerebral cortex disease
- brainstorm disorders (stroke, tumor, infection)
- spinal cord trauma
- disorders of motor neuron, peripheral nerve, NM junction, muscle
how might cerebral cortex disease affect breathing?
usually insignificant, prob because resp muscles have bilateral cortical control
how might brainstorm disorders affect breathing?
(tumor, stroke, infection) central alveolar hypoventilation. reflex control of breathing fails. voluntary control is ok. so breathing fails during sleep
how might spinal cord trauma affect breathing?
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.
how might neuromuscular disease affect breathing?
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.
name the main muscles involved in respiration
diaphragm, SCM, scalenes, intercostals, rectus, obliques, upper airway muscles (keep airway patent)
why is a short muscle a weak muscle?
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
skeletal muscle 02 consumption depends on what 2 things?
tension, speed of shortening
resp muscles’ use of 02 becomes significant to the body as a whole when?
when exercising. usually 02 use is insignificant, but when exercising, resp muscles’ use of 02 becomes a much greater % of body 02 usage.
fatigue: gets better with rest or not?
yes. fatigue = loss or decrement in tension development that is reversible with rest.
Occurs when demands outstrip muscle capabilities/supply
is the lower ribcage exposed to abdominal pressure or pleural pressure?
abdominal.
what is the law of laplace?
P = T/r
As r increases, (ie as the diaphragm flattens out) there is less pressure generated for the same Tension.
what is paradoxical motion?
with diaphragm paralysis, the abdominal contents will be sucked into the chest cavity rather than pushed outwards. paradox = abd retracting with inspiration
when are accessory muscles most vital?
during exercise or in disease states. with normal breathing, they are not usually recruited.
how would expiratory muscles be able to assist inspiratory muscles?
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
hyperinflation: worse for inspiration or expiration?
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)
