Lec 4 Mechanics and Pulm Function Testing Flashcards
In a patient with emphysema, lung compliance would be expected to be A) Decreased B) Increased C) Generally unchanged D) Cannot predict
B) increased
Most of the resistance to airflow in the lung comes from
A) Large and medium sized airways
B) Small airways
C) Alveoli
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?
s
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?
increased compliance
What happens to compliance in pulmonary fibrosis?
decreased compliance
What happens to compliance in pulmonary edema?
decreased compliance
What happens to compliance in pneumonia?
decreased compliance
What happens to compliance in normal aging?
increased compliance
What happens to alveolar with inspiration vs expiration?
slightly negative on inspiration
slightly positive on expiration
Is pleural pressure positive or negative?
always 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?
step1
P = 2* surface tension / radius
What does law of laplace tell you about alveoli’s tendency on expiration?
step1
on expiration as radius decreases, alveoli have greater tendency to collapse
What is pressure of airway and alveolar pressures and intrapleural pressure at FRC?
step1
At FRC all is balanced
- airway and alveolar pressures are 0
- intrapleural pressure is always negative
