Table 25-2.

Severity of Pulmonary Impairment²²⁹

Impairment	FEV1*	TLC†	VC†	DlCO
Normal	±95% CI	±95% CI	±95% CI	±95% CI
Mild	<LLN and ≥70	<LLN and ≥70	<LLN and ≥70	<LLN and ≥60
Moderate	60−69	<70 and ≥60	<70 and ≥60	<60 and ≥40
Moderately severe	50–59		<60 and ≥50
Severe	35–49	<60	<50 and ≥35	<40
Very severe	<35		<35

CI, confidence interval; Dl_CO, carbon monoxide diffusion in the lung; FEV₁, forced expiratory volume in 1 second; LLN, lower limit of the 95% confidence interval; TLC, total lung capacity; VC, vital capacity.

^*Airflow obstruction is based on a decreased FEV₁/VC ratio. If the ratio is decreased below the lower 95% confidence interval (CI), the severity of airflow is graded on the percent predicted FEV₁.

^†Pulmonary restriction is based on decreased TLC. If TLC is not available, a reduction in VC without a reduction in the FEV₁/VC ratio is a “restriction of the volume excursion of the lung.”