What is a typical characteristic of a flow-volume loop in restrictive lung disease?

In restrictive lung disease, the primary characteristic observed in a flow-volume loop is the flattening of the loop. This is indicative of reduced lung volumes due to impaired expansion of the lungs, which is characteristic of restrictive conditions. Unlike obstructive lung diseases, where the loop shows a scooped appearance due to difficulty in expiration, the flow-volume loop in a restrictive disease will demonstrate a more diminished overall volume, resulting in a loop that appears flattened or reduced in height.

This flattening occurs because patients with restrictive lung disease, such as pulmonary fibrosis or sarcoidosis, are unable to fully inflate their lungs, leading to a reduction in forced vital capacity (FVC). As a result, both inspiratory and expiratory efforts are affected, altering the shape of the flow-volume loop.

Peak expiratory flow rate is generally not increased in restrictive lung disease; rather, it may be normal or decreased depending on the severity of restriction. Greater expiratory effort is often a characteristic seen in obstructive diseases rather than restrictive ones. Exaggerated inspiratory capacity is also not a feature of restrictive lung disease, as the capacity to inspire is usually compromised due to reduced lung volumes.