Trachte: Mechanics of Breathing Flashcards
How do inspiration and expiration differ?
Inspiration occurs by CONTRACTION of the diaphragm.
Expiration is a PASSIVE PROCESS.
What innervates the diaphragm?
Phrenic nerve
If the phrenic nerve is paralyzed, why does the diaphragm move UP w/ inspiration?
The pressure in the thoracic cavity is lower so it gets sucked in.
Why is the expiration process passive?
Elastic recoil of the lung
Why is expiration active during exercise?
Muscles of the abdominal wall and the internal intercostals pull the ribs downward
When does inflation of the lung occur?
When pressure around the lung becomes SUBATMOSPHERIC
Does it require a greater pressure differential to inflate or deflate a lung?
Inflate
What is hysteresis?
Different shapes of inflation and deflation
Why does the lung volume never go to 0?
Because some air is always trapped in the lung (Residual volume)
What is the airway closure pressure?
The pressure to exhale COLLAPSES some small airways
What is compliance?
The relationship of volume change per pressure change
What is compliance NORMALLY for the lung?
200 ml/cm
What will reduce compliance? How does this affect your breathing?
Fibrotic disease
can’t expand lungs easily–> small breaths
What will increase compliance? How does this affect breathing?
Emphysema
Slower breaths
Why does the lung have elasticity?
Collagen and elastin
Why is it important that the lung collapses after inspiration?
Reduces the work of exhalation
How does surface tension contribute to elastic behavior?
Shrinks the lung
What is surface tension?
Attraction between adjacent molecules
What is the law of LaPlace?
Tension= Pressure x radius/ 2 for a sphere
How can the law of La Place be used to determine pressures in 2 alveoli if one has a smaller radius than the other?
The alveoli with a SMALLER r has to have a GREATER P. This results in the smaller alveoli emptying into the larger one.
What prevents smaller alveoli from emptying into larger ones?
Surfactant
What does surfactant do?
Alters surface tension at small volumes
What is surfactant?
dipalmitoyl phosphatidylcholine (detergent)
How does a detergent reduce surface tension?
Provides a physical BARRIER that prevents WATER MOLECULES from interacting at SMALL volumes
When is surfactant synthesized?
Third trimester
What happens if a baby is born early and it doesn’t have sufficient surfactant?
Respiratory distress (low compliance, atelectasis, and alveoli filled w/ transudate)
Where is intrapleural pressure the lowest? Why?
BASE of the lung
The WEIGHT of the base presses against the chest wall and makes it LESS negative.
The base has a smaller RV
What leads to the collapse of airways one exhalation?
Increased pressure from airways squeezing shut
What do airways collapse on exhalation/to whom?
LOW lung volumes in YOUNG healthy people.
AT FRC in older folks and respiratory disease–> air trapping.
How are the chest wall and lungs normally oriented?
OPPOSE each other keeping the LUNGS somewhat expanded and the the CHEST WALL somewhat compressed.
What causes the chest wall and lung to separate?
Pneumothorax
What causes the lung to collapse?
Elastic recoil
When is the lung at equilibrium?
At LESS THAN residual volume ( minimal capacity)
When is the chest at equilibrium?
At 75% of vital capacity (expanded state)
When is the combined lung-chest curve at equilibrium?
At FRC
What is the airway resistance for laminar flow?
P = flow x Resistance
What happens to the cross sectional area as one progresses down the bronchial tree?
Increases
What is the pressure differential during inspiration?
Atmospheric- alveolar (.1 cm H20)
What are pressures in the breathing cycle in the intrapleural space?
-5 cm water
Decreases to -8 cm water in the intrapleural space
Increases on expiration
What is the major site of resistance in the bronchial tree?
Medium sized bronchi
Why does airway resistance DECLINE at larger volumes?
Negative pressure PULLS airways open
What happens to airway resistance at SMALLER lung volumes during expiration?
INCREASES
How does parasympathetic nervous stimulation affect airway resistance?
Increases it
Describe how parasympathetic stimulation causes airway contraction.
Vagus–> Ach–> muscarinic receptors–> IP3–> Ca–> airway contraction
Describe how sympathetic stimulation DECREASES airway resistance by causing dilation.
EPI> B2 receptors (can't be NE)> Increases cAMP> muscles relax> airway dilation
What happens to the rate of flow during expiration?
RAPID then FALLS
Can one overcome the fall in expiratory flow by increased exertion?
NO
What causes the drop in flow on expiration?
COMPRESSION of airways when the thoracic volume is DECREASED to expel air
What happens to airway pressure as volume decreases?
Airway pressure DECREASES so the increased pressure in the lungs COLLAPSES these airways
What affect does inspiration have on airways?
DILATES and pulls them OPEN
What determines flow in an airway?
Alveolar pressure- pleural pressure
How does emphysema affect airways?
Reduced recoil
Reduced radial traction (easier to compress)
What is the forced expiratory volume (FEV1)?
FIRST second of expiration after maximal inhalation
What is a normal FVC?
80%
How does chronic obstructive lung disease affect FEV1 and FEV1/FVC?
LOWERS FEV1
LOW FEV1/FVC= 50% (hard time getting air out)
How does restrictive lung disease (pulmonary fibrosis) affect FEV1 and FEV1/FVC?
LOW FEV1 and FVC
but NORMAL FEV1/FVC
HOw is work defined?
Force x distance
What is the total work of breathing?
Effort to overcome ELASTIC (collapsing) forces and AIRWAY RESISTANCE
How does a stiff lung affect work?
Stiffer = less compliant>
more work to inflate lungs
Why do pts w/ restrictive lung disease typically take small rapid breaths?
lessen work load
Why do pts w/ chronic obstrutive disease take slow deep breaths?
lessen work load
