Microplethysmography: Non-Invasive Measurement of Tissue Volume Changes

Microplethysmography is a non-invasive technique that measures minute volume changes in a tissue bed. These fluctuations correspond to the cyclic blood volume variations that occur with each heartbeat.

Principle of Operation

When tissue expands, the skin surface moves slightly upward, increasing the intensity of light reflected from the measurement spot. Conversely, when tissue contracts, the skin surface moves downward, decreasing light intensity. A photodiode detects these light-intensity changes, and the signal is recorded on a computer for analysis.

Clinical Applications

Microplethysmography is primarily used to assess microcirculation—the flow of blood through the smallest vessels (capillaries, arterioles, venules). Healthy microcirculation is essential for delivering oxygen and nutrients to cells and removing metabolic waste.

The technique helps detect microcirculatory disorders, such as those seen in diabetes, peripheral arterial disease, and connective tissue diseases. It also serves to monitor the effectiveness of treatments aimed at improving microvascular function.