Review of Pulmonary Physiology Flashcards
Is it inspiration or expiration which is normally completely passive? Which muscles assist if need be?
Expiration -> elastic return
Assistance via abdominal muscles
What is transpulmonary pressure?
Pressure inside alveoli (filling pressure in lungs) - pressure outside in the pleura (negative intrapleural pressure)
What is the slope of the pressure / volume curve and where is it generally measured?
Compliance (change in Volume / change in pressure)
Generally measured at functional residual capacity (FRC)
What is hysteresis? Why does it occur? What redues it?
Tendency of it being more difficult to inflate the lung (Takes more pressure) than to deflate it
Occurs because of surface tension caused by air-water interface tends to pull downward and deflate the alveoli, which are harder to inflate after being deflated.
Reduced by surfactant
What controls the size of the lung at lower than FRC?
The chest wall, which wants to elastically recoil to above FRC
The lung wants to collapse to minimum volume
What controls the size of the lung near TLC?
both the elastic recoil of the chest wall and the lung, as they are both overstretched
What pressures are equal at FRC?
Elastic recoil of the chest wall (intrapleural - atmospheric) = elastic recoil of lungs (alveolar - intrapleural)
What is La Place’s relationship and how is related to surfactant?
P =2T/r
if surface tensions were equal in small vs large alveoli, greater filling pressures would be required to inflate the smaller alveoli.
Surfactant helps reduce T more the small your alveoli, keeping filling pressures equal no matter alveolar size.
What is the resistance formula for the lungs?
R = P/V
Where P = pressure difference and V = airflow
Think of this is a rearrangement of V=IR, where current = airflow, and voltage = pressure difference
Why is it easier to detect diseases of the upper airway faster than lower airway?
Up to the carina (bifurcation cartilage of the trachea), resistances add in series
-> shared airway, blocking one thing will greatly increase resistance
past the carina, resistances add reciprocally (in parallel)
Where is the airways is flow laminar vs turbulent? What is the most important factor in determining this resistance?
Small, peripheral airways -> laminar
Large airways in series -> turbulent, when Reynolds’ number is >2000
Size of the tube’s lumen is most important
What is the Bernoulli effect? Clinical significance?
With flow from a larger to a small cross-sectional area, velocity of flow must increase to maintain the same bulk flow. This results in a pressure drop and major energy expenditure from the small to the large airways.
What type of disease increases airway resistance?
An obstructive process
What is the problem with restrictive processes?
Elastic recoil -> loss of compliance or stretch.
-> by definition reduces total lung capacity
How are lung volume and resistance related?
inversely -> as lung volume decreases, resistance increases
What is meant by effort dependence vs effort independence?
For the first 25% of the expiratory flow curve, increasing the intrapleural pressure more will increase flow more. However, at a certain point, an increase in intrapleural pressure will not generate a greater expiratory flow. This is called “effort independent” expiratory flow.
Will peak flow rate vary with effort?
Yes - peak flow varies with effort, but the latter end of the curve will always follow the same expiratory rate decrease regardless
What is the best explanatory theory as to why expiratory flow limitation occurs?
Wave speed theory -> physical characteristics of the tube and substance flowing create a “speed limit” which is called the choke point
What is frequency dependence of compliance?
A way proposed to detect early COPD which doesn’t work that well.
Breathing faster traps more air in the lungs, so delta V appears to drop despite high inspiratory pressures. This only happens in obstructive conditions. (dynamic compliance is decreased)
What is the rate constant of an alveolus?
The time it takes to empty or fill an alveolus.
RC
R = resistance, C = compliance. Increasing resistance or increasing compliance will increase the filling / emptying time.
Stiffer lungs with lower resistance will empty faster
Which areas of the lungs have the greatest filling and ventilation?
Apex - consistently the most full, due to most negative intrapleural pressures higher in the lungs
Base - greatest change in ventilation over the inspiration / expiration cycle. This is good because they also receive the most blood flow.
What is the nitrogen washout curve / what explains closing volume?
Put a patient on one breath of 100% O2, the slowly exhale while expired volume and nitrogen concentration are measured.
Phase 1 - 100% O2 from dead space
Phase 2 - Rapid increase in nitrogen as lung units start emptying
Phase 3 - plateau
Phase 4 - when near RV, the apex of the lungs which carried high N2 air from the anatomical deadspace begin contributing. From where this nitrogen upslope begins to the end of expiration (RV) is called closing volume.
What is the usefulness of closing volume?
In disease states, the closing volume inflection point is met closer and closer to FRC instead of RV.
What are the two important curves made in spirometry?
Volume vs time
Flow rate vs volume
