Respiratory Rally

What happens to TLC (Total Lung Capacity) and VC (Vital Capacity) in patients with fibrosis? Severe emphysema?

from my knowledge, fibrosis scars the lungs, causing the lungs to become stiff and have more recoil. on the contrary, emphysema causes lung tissue to be destroyed, and therefore reducing recoil.

so would fibrosis increase VC but reduce TLC, but emphysema decrease VC and increase TLC?

You’re right as far as fibrosis is scar tissue and causes the lungs to become stiff.. But as they get stiffer, losing compliance, the VC decreases. Fibrosis can occur in the alveoli, connective tissue(which provides structure and support for the various segments and lobes), or in the interstitial spaces. This can be the result of injury, infection or what’s called idiopathic when they don’t know what caused it. Sometimes it’s an immunological disorder. Anyway, It causes the person to have to work harder to expand their lungs and reduces their ability to exhale it thereby reducing VC. TLC is decreased in fibrotic disorders. On a PFT the first sign of a compliance problem is a reduced VC.
Now, that is restrictive disease as opposed to an obstructive disorder such as emphysema. COPD, chronic bronchitis, asthma, bronchiectasis etc. are airway diseases. In other words the flow through the bronchi and bronchioles is limited by inflammation, mucous and/or bronchospasm. At the beginning this can be detected on the PFT by looking at the flowrates, especially on exhalation. The airways normally narrow on exhalation anyway but obstructive disorders exaggerate this narrowing eventually to the point of shutting down completely thereby trapping air in the alveolus. Over time this trapping causes the alveolar septums to stretch and become permanently hyperinflated. This is Emphysema. You can see how chronic bronchitis or chronic untreated asthma can lead to this.
Sorry to be so lengthy in my answer.
So anyway, this hyperinflation leads to a loss of connective tissue, which is what holds bronchioles open(they lack the cartilaginous rings found in bronchi. That’s the anatomical difference between bronchi and bronchioles). This leads to more air trapping and can eventually lead to Bullous Emphysema, which looks very much like blisters on the lungs. But they are whole segments of the once grape-like structure of the alveoli made confluent by the stretching.In emphysema you do see a reduced VC also but it’s from a different mechanism, airway obstruction as opposed to loss of compliance.
In regards to the TLC in emphysema it may remain normal or could decrease slightly. The more important measurement on the PFT is the RV/TLC ratio. When the Residual Volume increases due to the airtrapping This ratio increases. Normal is about 20-25%(don’t quote me on that) and anything >40% is indicative of Emphysema.
Hope this helps clear it up for you.
God bless.