D11 Plethysmography and Flow Measurement

Topic

Plethysmography and circulatory flow measurement assess blood and lymph volumes in body segments using impedance plethysmography, serial limb circumference measurement, or water-displacement volumetry.

Based on these measurements, the procedure operationalizes normal hemodynamic and lymphatic parameters by quantifying three values: circulatory flow, perfusion pressure, and edema volume.

The first value is circulatory flow: plethysmography records the amount of blood passing through the measured body segment over a specific period; the lower this flow is compared to expected levels, the more compromised the segment's tissue perfusion.

The second value is perfusion pressure: plethysmography estimates the pressure at which blood actually reaches the tissue; the lower this pressure, the less capable the blood is of overcoming the body segment's resistance to complete venous return to the heart.

The third value is edema volume: plethysmography measures the amount of fluid accumulated in the body segment rather than being removed via lymphatic drainage; the greater this volume, the more compromised the segment's lymphatic drainage.

With circulatory flow, perfusion pressure, and edema volume quantified, this method enables the diagnosis and monitoring of circulatory and lymphatic abnormalities: it identifies deviations from normal hemodynamic and lymphatic parameters regarding tissue perfusion, venous return, or lymphatic drainage, and repeats these measurements over time to track whether these three conditions improve or worsen. By repeating these measurements over time, plethysmography and circulatory flow measurement not only diagnose the presence of a circulatory or lymphatic impairment but also monitor whether blood and lymphatic circulation are recovering sufficiently to sustain tissue oxygen availability—and, with it, the functional recovery described by that same model.

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