Classes of Respiratory Impairment

 

Parameters studied:

(1) FVC

(2) FEV1

(3) FEV1/FVC

(4) diffusing capacity of carbon monoxide

(5) exercise capacity in mL of oxygen per kg per min, or as METs

 

NOTE: The division based on measured oxygen capacity is similar to that used for impairment in ischemic heart disease (above).

 

AMA Rating Scheme

 

Class 1: No impairment of the whole person (0%)

(1) FVC: >= 80% of predicted, AND

(2) FEV1: >= 80%of predicted, AND

(3) FEV1/FVC: >= 0.70, AND

(4) diffusing capacity D(CO): >= 70% of predicted

OR

(5) VO2 max (measured exercise capacity): > 25 (mL O2)/kg/min; > 7.1 METs

 

Class 2: Mild impairment of the whole person (10-25%)

(1) FVC: 60-79% of predicted, OR

(2) FEV1: 60-79% of predicted, OR

(3) diffusing capacity D(CO): 60-69% of predicted

OR

(4) VO2 max (measured exercise capacity): 20 - 25 (mL O2)/kg/min; 5.7 - 7.1 METs

 

Class 3: Moderate impairment of the whole person (26-50%)

(1) FVC: 51-59% of predicted, OR

(2) FEV1: 41-59% of predicted, OR

(3) diffusing capacity D(CO): 41-59% of predicted

OR

(4) VO2 max (measured exercise capacity): 15 - 20 (mL O2)/kg/min; 4.3 - 5.69 METs

 

Class 4: Severe impairment of the whole person (51-100%)

(1) FVC: <= 50% of predicted, OR

(2) FEV1: <= 40% of predicted, OR

(3) diffusing capacity D(CO): <= 40% of predicted

OR

(4) VO2 max (measured exercise capacity): < 15 (mL O2)/kg/min; < 4.3 METs

 

where:

• The FEV1/FVC is expressed as an absolute number and not as a percentage of the predicted value.

• Equations to predict expected values: These are described in Crapo. A more complete overview is available in the chapter on Respiratory and Acid-Base Disorders.

• The resting maximum oxygen consumption in mL per minute per kilogram is defined as 1 MET = 3.5 (mL O2)/kg/min.

 

ATS Rating Scheme

 

This is similar to the AMA rating scheme.

 

Additions

(1) Class 2 FEV1/FVC: 0.60 to 0.74

(2) Class 3 FEV1/FVC: 0.41 to 0.59

(3) Class 4 FEV1/FVC: <= 0.40

 

Differences

(1) Class 1 FEV1/FVC: >= 0.75

(2) Class 1 diffusing capacity D(CO): >= 80% of predicted

(3) Class 2 diffusing capacity D(CO): 60-79% of predicted

(4) measured exercise capacity not utilized