Asthma is classified as an Obstructive lung disease and primarily affects the airways. It is characterized by chronic inflammation and constriction of the muscles in the airways. These two processes act to narrow the airways and reduce the speed that air can flow in and out of the lung. Asthma does not tend to affect the alveoli or the structure of the lung.
Asthma status is best monitored by FEV1 and PEF.
A typical PFT pattern for Asthma:
|Spirometry||FVC||Normal or reduced|
|RV||Normal or elevated|
|Diffusing Capacity||DLCO||Normal or elevated|
|Oximetry||SpO2||Normal or reduced|
The severity of obstruction is determined by the reduction in FEV1. When the FEV1 or FEV1/FVC ratio are reduced:
|FEV1 >= 70% of predicted||Mild|
|FEV1 <70% and >=60% of predicted||Moderate|
|FEV1 <60% and >=50% of predicted||Moderately severe|
|FEV1 <50% and >=35% of predicted||Severe|
|FEV1 <35% of predicted||Very severe|
PFT Patient by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.