Flashcards in Lec 4 Mechanics and Pulm Function Testing Deck (52):
In a patient with emphysema, lung compliance would be expected to be
C) Generally unchanged
D) Cannot predict
Most of the resistance to airflow in the lung comes from
A) Large and medium sized airways
B) Small airways
A) large and medium sized airways
Functional Residual Capacity is the volume of the lungs
A) When you take the biggest possible breath
B) When you let all your air out
C) When you are dead
B) when you let all of your air out
What happens to chest wall and lungs if you open the chest?
- chest wall expands
- lungs get smaller
normally intact pleural space with negative pressure keeps this from happening all the time
Are lungs more compliant at smaller or bigger volume?
lungs are more compliant at smaller volume; as you expand more and more you reach a limit and get less compliance
What is the zero point of respiratory system?
zero point is the lung volume where opposing elastic forces are balanced = FRC
- negative pressure of chest wall balances positive pressure of lungs
What is hysteresis?
How does a lung filled with saline compare to a normal lung with and without surfactant?
saline = less pressure to inflate b/c air liquid interface adds to the pressure required to expand lungs
normal lung without surfactant = most pressure/ least compliant
normal lung with surfactant = reduces surface tension = in the middle between saline + no surfactant
What is action of surfactant?
decreases surface tension
= has greater effect when lung is smaller
prevents small airways + alveoli from collapse
What is equation for compliance?
compliance = change in V / change in P
What happens to compliance in emphysema?
What happens to compliance in pulmonary fibrosis?
What happens to compliance in pulmonary edema?
What happens to compliance in pneumonia?
What happens to compliance in normal aging?
What happens to alveolar with inspiration vs expiration?
slightly negative on inspiration
slightly positive on expiration
Is pleural pressure positive or negative?
--> if it becomes atmospheric lung will collapse = pneumothorax
What is reynold's number equation? what does it mean?
density * diameter * velocity / gas viscocity
higher number = more likely to have turbulent flow [rather than laminar]
What is hysteresis?
idea that different pressure-volume curve when you inflate than deflate
- inflate = lower volume for same pressure
- deflate = bigger volume for same pressure
= lung is more compliant on inspiration
What causes hysteresis in lung?
- surface tension of the lung at air-liquid interface and preferential action of surfactant when lung is smallest
What does surface tension and LaPlace's law mean for small alveoli?
small alveoli tend to get smaller and bigger alveoli tend to get bigger
this is fixed by surfactant?
What is equation for collapsing pressure of alveoli?
P = 2* surface tension / radius
What does law of laplace tell you about alveoli's tendency on expiration?
on expiration as radius decreases, alveoli have greater tendency to collapse
What is pressure of airway and alveolar pressures and intrapleural pressure at FRC?
At FRC all is balanced
- airway and alveolar pressures are 0
- intrapleural pressure is always negative
Is lung's tendency to get bigger or smaller?
What are the forces responsible for lung's elastic recoil?
surface forces = air liquid interface surface tension which is slightly reduced by surfactant
tissue forces = beyond certain point of inflation lungs get stiff and below a minimum alveoli stay open b/c of their structure
What is normal lung compliance?
0.2 L/cm H2O
What is order from left to right on a P vs V graph of fibrosis, emphysema, and normal lungs?
shift left = more compliant
emphysema --> normal --> fibrotic
emphysema = most compliant
fibrosis = least compliant
What happens to lung in emphysema?
- decreased elastic recoil = more compliant
- increased airflow resistance
What happens to intrapleural pressure during tidal breath?
most negative just before end of inspiration
What happens to alveolar pressure with tidal breath?
negative pressure with inspiration
positive pressure with expiration
What parts of lung have turbulent vs laminar flow?
turbulent = in large airways
laminar = small airways
What kind of flow in large airways?
- turbulent flow
- resistance increases as flow increases
How can you improve turbulent flow?
- by reducing density --> give heiliox to improve upper airway obstruction
What kind of flow in small airways?
What determines resistance in turbulent flow vs laminar flow?
in turbulent flow = more resistance with more flow
in laminar flow = use poisseuille's law --> bigger radius = less resistance
What is poisseuille's law?
resistance is proportional to
viscosity * length / radius ^ 4
Is overall resistance higher in larger or small airways?
- resistance to flow is much higher in smaller airways
BUT you have lots of small airways in parallel which reduces overall resistance
--> overall resistance is highest in large airways
What are his 3 basic laws for reading PFTs?
1. reduced FEV1/FVC ratio defines obstructive disease
2. restriction is defined by reduced lung volumes [not just spirometry]
3. reduced "diffusion capacity" implies a "gas transport defect" but not much else
What is inspiratory reserve volume?
air that can still be breathed in after normal inspiration
What is tidal volume? normal value?
air taht moves into lung with each normal inspiration
usually 500 mL
What is expiratory reserve volume?
air that can still be breathed out after normal expiration
What is residual volume?
air in lung after maximal expiration
cannot be measured on spirometry
What is inspiratory capacity?
IRV + TV
What is functional residual capacity?
RV + ERV = volume in lungs after normal expiration
Can you measure total lung capacity from spirometry?
NOPE!! because you can't measure residual volume [RV]
What happens to FEV1 in obstructive disease?
How can you measure total lung volumes?
need to measure RV --> do this by using gas dilution technique with helium or a plethysmograph = body box
How do you measure diffusion capacity?
pt inhales small amount of CO and its uptake is measured
What happens in obstructive lung disease?
obstruction of air flow results in air trapping in lungs
airway closes prematurely at high volume
have increased RV and decrease FVC
very decreased FEV1 so
decrease FEV1/FVC ratio = hallmark
Why use CO to measure diffusion capacity
- no consumption
- no back pressure
- similar to O2
--> we don't use CO so everything we inhale goes one way and doesn't really come out.