16
Tables
Table 1. Functional Classification of Common Impairments
Assessed by Conventional PFTs and Their
Pathophysiological Determinants
Restrictive
ventilatory
impairments
a
Reduction in the size of the lungs. is may reflect lung parenchymal
abnormalities or an inability to fully inhale due to extrapulmonary
factors (e.g., weakness, chest wall abnormalities, obesity). Lung restriction
reduces FEV
1
, FVC, (but not the FEV
1
/FVC ratio) and TLC.
Obstructive
ventilatory
impairments
a
Narrowing of the airways in the lung by physical obstruction or
by dynamic airway collapsing. More proximal airway properties
determine airflow resistance at large lung volumes and drive the FEV
1
/
FVC measurement. More distal airway properties determine airflow
resistance at small lung volumes and drive flow measurements later in a
maximal exhalation. Because airway obstruction impairs lung emptying,
it is oen accompanied by air trapping and hyperinflation that may
reduce the FVC but is more directly assessed by the RV measurement.
Gas transfer
impairments
Reduction in transport of gas (carbon monoxide transfer as a surrogate
for oxygen) between the alveolar spaces and alveolar capillary blood.
is may be due to a reduction in alveolar surface area, abnormal
alveolar-capillary membrane properties, or reduced pulmonary capillary
blood (hemoglobin) volume. Impaired gas transfer is generally assessed
by analysis of carbon monoxide uptake during a breath-hold (D
L
CO).
Some conditions can lead to an increase in gas transfer.
a
Many authorities also use the term "ventilatory impairments" to group obstructive and restrictive
impairments.
