Respiritory: Restrictive Lung Diseases Flashcards
Extra-pulmonary restriction vs Intra-pulmonary restriction.
Restriction is where the normal expansion of the lungs is impaired.
Extra-pulmonary is where this occurs ouside the lungs in the plaura, chest wall, bones, muscles etc.
Intra-pulmonary is where this occurs within the alveoli and surrounding lung tissue.
Examples of extra-pulmonary restriction
What is lung interstitium?
This is the connective tissue between the aveoli and the small blood vessels. Gas exchange happens over the interstitium.
What happens with the pulmonary interstitium in intra-pulmonary restriction?
The interstitium thickens causeing it to have less elasticity therefore reducing the volume it can expel
Chest wall vs lung, which has tendancies towards inward/outward pressure
Eaxamples of intra-pulmonary restriction
What does compliance mean when refering to tissue?
This is a measure of the distensibility (stretchability) of a tissue.
What is the effect of decreased compliance on inflation? Think lung volume vs pressure graph. How easily does it inflate and deflate?
What is the effect of increased compliance on inflation? Think lung volume vs pressure graph. How easily does it inflate and deflate?
Where is knowing someone’s compliance particularly important clincially?
If putting someone on a ventilator you need to know how much pressure to apply
What is Laplace’s law for a sphere? And what does this mean for alvioli
Because alvioli are moist with alviolar lining fluid this creates an inward surface tension. The smaller the alvioli the more inward constricting force.
How does surfactant reduce surfance tension in alvioli?
It has a gaseous hydrophobic end and a liquid hydrophilic end. Acts like washing up liquid to reduce surface tension.
What is surfactant?
Surface acting agent
This regulates sruface tension in alvioli preventing instability
When does surfactant work best at reducing surface tension?
When they are closer together
How does surfactant reduce alveolar instability?
Without surfactant the smaller alveoli would not inflate properly and would want to empty into larger ones due to increased surface tension.
With surfactant the surfactant is closer together in small alveoli therefore reducing this surface tension more effectively thus evening out alveolar pressure.
When is primary surfactant deficiency clinically relevent?
Respiritory distress syndrome in newborns.
This is in premature births as surfactant is only produced after the 30th week of pregnancy.
The lungs therefore become unstable and collapse
How is surfactant clinically relevent in adults?
Primary surfactant deficiency is extremely rare.
However a surfactant impairment probably contributes to the pathogenesis of common respiritory disorders such as pheumonia and idiopathic pulmonary fibrosis
Why can’t spirometry tell you lung capacity?
Spirometry can tell you vital capacity but it can’t detect the residual capacity which is required in order to know total lung capacity
What are the differences in FEV1, FVC and FEV1/FVC with obstructive and restrictive diseases?
With restrictive diseases where does spirometry fall short?
It can’t tell the difference between extra-pulmonary and intra-pulmonary restrictive diseases
What does TLCO stand for and how can it be thought of?
Transfer factor for carbon monoxide
Can be thought of as the total gas transfer capacity.
What does KCO stand for and how can it thought of?
CO transfer coefficient
This is a direct measurement of the ratio of concentration of CO directly before and after a breath hold therefore is the rate of CO dissapearence from the gas held. Units are min^-1. This isn’t dependent on volume of gas so can thought of as CO exchange per unit of lung.
Describe the test to calculate TCLO?
A patient fully exhales then fully inhales a mixture of CO and He and holds it for 10s.
Both are reletively non-toxic and both are not produced by the body or naturally in the blood to begin with therefore ammounts measured are controlled. The difference is CO is absorbed by the blood where He isn’t.
By measuring the concentration of CO afterwards we get the KCO. By measuring the concentration of He afterwards we get the Va or total lung volume (He will dilute with the reserve volume therefore telling you how much reserve volume there is).
From this we can multiple the KCO by the volume “seen” by the CO aka the Va therefore giving us the total gas transfer potential
What can KCO, TCLO and Va tell you about a restrictive lung condition?
- In an extra-pulmonary restrictive lung condition TCLO will be low as Va is low. However KCO will be normal as the interstitium is undamaged. KCO can even be higher because when not inflated fully the blood vessels in the alvioli are more compact.
- In an intra-pulmonary restrictive lung condition TCLO will be low as Va and KCO are low. Here KCO is also low because the alvioli are abnormal
Useful page on TLCO, KCO and Va
https://rubble.heppell.net/chestnet/t/KCOtransfer.html#:~:text=The%20clinical%20measurement%20of%20TLCO,two%20measurements%20may%20be%20discordant.
