Mechanics of Breathing Flashcards
What are the main muscles of inhalation? Two additional accessory muscles for inhalation?
diaphragm and external intercostals
scalenes and sternocleidomastoids
What direction does the diaphragm move if the phrenic nerve is damaged? Why?
The diaphragm is paralyzed and moves up with inspiration because of the negative pressure in the thoracic cavity pulling it upwards
Why is expiration typically a passive function?
the lung has elastic recoil, making it want to shrink
During exercise expiration is an active process with what muscles?
mainly the abdominal muscles (rectus abdominus and obliques) and internal intercostals
The pressure differential required to inflate the lung is _____ than that required to deflate it.
greater - remember that deflation is a passive process for the lung due to the elastic recoil
This means the graphs of negative pressure vs volume is different for exhalation and inhalation. What is this called?
hysteresis
Why does lung volume NEVER go to 0?
Because exhalation makes the pressure in the thoracic cavity increase, which collapses some small airways, leading to a blockage of air movement
What is compliance?
the relationship of volume change per pressure change
Is lung compliance typically high or low?
high - about 200 ml/cm H20
What disease will reduce compliance? What disease will increased compliance?
reduced compliance - fibrosis
increased compliance - COPD
What are two physical characteristics of the lung that cause it’s elastic recoil?
- lots of elastin and collagen
2. surface tension of alveoli
Why do people with COPD need to work hard to expire?
COPD lungs have lost some of the elastin and collagen in the lung, which means they’ve lost some of that elastic recoil and expiration isn’t just a passive process for them
What is surface tension (in general0?
attraction between adjacent molecules - in this case H2O
What does the law of laplace mean for the lung?
T = Pxr/2 for a sphere
means that 2 conected alveoli would have different pressures if one had a smaller radius than the other, which would result in smaller alveoli emptying into larger ones
What alters surface tension to prevent this?
surfactant
surfactant at low volumes or high volumes?
low volumes
WHat is surfactant/
dipalmitoyl phosphatidylcholine
How do they think it works?
detergent that provides a physical barrier preventing the water moleucles from interacting at small volumes = no surface tension
Where is intrapleural pressure more negative - the base or the apex of the lung? Which has a smaller residual volume
apex of the lung is more negative
base has smaller residual volume
Why do people with COPD purse their lips while breathing?
The increased pressure associated with exhalation results in collapse of airways at fucntional residual capacity in people with COPD, so they purse their lips to increase resistance to flow and thus increase the pressure in the airways to work against that compression
What happens to resistance as you branch on down the bronchial tree?
resistance decreases because the cross sectional area (radius) increases
So what is the major site of resistance in the lung?
medium-sized bronchi
Why does airway resistance decline at larger lung volumes?
the negative pressure from inhalation pulls the vessels open
the increased size of the lung (radial traction of tissue) also pulls airways open
Does parasympathetic activity increase or decrease airway resistance?
increases it
How does parasympathetic acitviyt increase airway resistance?
acetylcholine on muscarinic receptors, increases IP3, increases Ca, leading to contraction and airway constriction
(carried by vagus)
How does sympathetic stimulation decrease airway resistance?
Epinephrin on beta 2 receptors increases cAMP, which leads to airway dilation
What happens to the rate of flow during forced expiration?
it is initially rapid and then falls - one cannot overcome this fall in expiratory flow because it’s caused by compression of airways when the thoracic volume is decreased to expel air
What is the FEV1?
it’s the forced expiratory volume that occurs in the first second of expiration after a maximal inhalation - usually about 80% of the forced vital capacity?
What will the FEV1 be in COPD?
they will have a low FEV1 AND a low FEV1/FVC (mostly normal FVC though)
What will the FEV1 be in restrictive diseases?
low FEV1 and FVC, but that means the FEV1/FVC ratio is normal
