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Flow Volume Loops

The flow-volume loop obtained during the spirometry manoeuvre can have four distinctive shapes that are linked to certain pathologies: obstructive lung disease, restrictive lung disease, mixed lung disease and upper airway obstructions.

The shape of the flow-volume loop can indicate the location of airflow limitation, such as the large upper airways or smaller distal airways. With common obstructive airflow disorders, such as asthma or emphysema, the disease generally affects the expiratory limb and can reduce the effort-dependent peak expiratory flow as well as subsequent airflows that are independent of effort. The descending limb of the expiratory loop is typically concave. In contrast, several unusual anatomic disorders that narrow the large airways can produce a variety of patterns of truncation or flattening of either one limb of the loop (variable upper airway obstruction) or both limbs of the loop (fixed upper airway obstruction).

It is important that the technique is performed correctly on a calibrated spirometer so that the flow-volume loop can be interpreted correctly. Often GPs like to confirm spirometry results in a lung function laboratory with the test being performed by a qualified respiratory scientist.