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
What is a normal FEV1.0?
75% Forced Vital Capacity (seen by first second in volume vs time curve)
What are the spirometry hallmarks of an obstructive process?
FEV1 = reduced FVC = normal or reduced FEV1/FVC = reduced
What are the spirometry hallmarks of a restrictive process?
FEV1 = normal or reduced FVC = greatly reduced FEV1/FVC = normal or increased
What does it mean when both inspiration and expiration curves are equally diminished in peak flow vs volume?
Fixed obstruction of the upper area (in series) i.e. vocal cords or trachea
What does it mean when only inspiration is diminshed and expiration curve is normal in peak flow vs volume?
Vocal cord weakness, expiration not affected
What is the definition of functional residual capacity in terms of lung volumes?
FRC = Residual volume + expiratory reserve volume
FRC is the volume remaining at the end of a normal tidal breath
What is the definition of vital capacity in terms of lung volumes?
VC = TLC - RV
TLC = total lung capacity
What is total lung capacity in terms of lung volumes (do not use capacities)
TLC = RV + ERV + TV + IRV
TV = tidal volume
How does helium dilution measure lung volumes and what is its problem?
Start with known concentration of helium, breath til it comes to equilibrium, and use Boyle’s law (C1V1 = C2V2) to determine the volume change
Problem -> tends to underestimate lung volumes in bad lungs which have a lot of dead space which are not ventilated
What is the most accurate way of measuring all the gas in the thorax?
Body plethysmograph
What is the idea behind diffusing capacity for carbon monoxide?
Normally, a single breath of carbon monoxide should be fully absorbed, and none will be present in exhaled gas, assuming no problems at all with the lungs or cardiovascular system. It is a very sensitive but nonspecific test.
Values lower than 100% absorption indicate a problem
What is the clinical utility of diffusing capacity for carbon monoxide?
If spirometry shows a restrictive process:
- > Low DLCO suggests parenchymal disease
- > normal DLCO suggests chest wall disease
In an obstructive process, will DLCO be lower in emphysema or asthma?
Emphysema -> less ability of gas to mix with lung parenchyma
What does an elevated RV with a low TLC suggest?
Neuromuscular disease
- > cannot fully inspire to TLC
- > Cannot use accessory muscles to fully exhale
What are the causes of increased TLC?
- Obstructive lung diseases
2. Acromegaly - increased size of lung parenchyma
How do emphysema, asthma, and chronic obstruction lead to increased TLC?
Emphysema - decreased lung elastic recoil
Asthma - increased chest wall recoil, increased FRC (only in acute attacks)
Chronic obstruction - air trapping and increased RV
