FlowVolumenDiagramm

FlowVolumenDiagramm, often referred to as a flow-volume diagram, is a graphical representation used in respiratory physiology and clinical spirometry to illustrate the relationship between instantaneous airflow and lung volume during forced breathing maneuvers. It combines the expiratory and inspiratory limbs of a spirometry trace into a single loop, with flow on the vertical axis and volume on the horizontal axis.

The measurement is produced during spirometry, where a person performs a maximal forced expiration from total lung capacity to residual volume, followed by a maximal forced inspiration back to TLC. The resulting loop shows the peak expiratory flow early in expiration and the subsequent decline in flow as lungs empty, followed by the inspiratory limb when the patient inhales rapidly. The diagram visually summarizes dynamic airway function beyond simple volume and rate values.

Interpretation uses several features. A normal loop has a smooth, roughly symmetrical expiratory limb and a corresponding inspiratory limb. Obstructive patterns often produce a scooped or concave expiratory limb, reflecting reduced flow at lower lung volumes and a decreased FEV1 relative to FVC. The inspiratory limb may remain relatively normal unless there is fixed upper airway disease. Conversely, restrictive patterns yield reduced overall loop size due to lower lung volumes, with proportional reductions in flow but a preserved or increased FEV1/FVC ratio. In cases of variable intrathoracic or extrathoracic obstruction, characteristic flattening may appear in the inspiratory or expiratory limb, respectively.

Limitations include reliance on patient effort, technique, and reference values. The diagram complements standard spirometric indices and is used to assess airway obstruction, monitor disease progression, and evaluate response to therapy.