OPO – Optical Pulse Oscillography – Vascular Academy

OPO – Optical Pulse Oscillography

Description

Similar to the pneumatic Pulse Volume Recording (PVR), oscillations of the pulse waves can be recorded using optical photoplethysmography (PPG) sensors. By emitting infrared light, these probes can detect variations in the microcirculatory blood flow of the digits and toes.

PPG probes are applied by attaching them with adhesive rings to the measurement area on fingers or toes. As the application is simpler and quicker, they are often preferred to ultrasonic doppler probes. Additionally, multiple PPG sensors can record pulse oscillations simultaneously (e.g., all ten fingers at the same time).

Measurement Principle

The basic idea of photoplethysmography is based on the fact that the hemoglobin in the blood absorbs light in the near infrared range of the spectrum much more strongly than all other structures of the skin. Light with a wavelength of 940 nm penetrates through the skin into the underlying tissue, is reflected depending on the local level of blood in the transilluminated tissue layers and registered by the measuring probe.

The sensors used in the plethysmograph contain two infrared light-emitting transmitter diodes and a receiver electrode, which are attached to the probe surface at a distance of a few millimeters.

Depending on the planned test or existent indication, the PPG sensors can be arranged in different positions on fingers or toes. While a Thoracic Outlet Syndrome (TOS) measurement requires only two sensors on left and right index fingers, a test for Raynaud’s Syndrome could be conducted by measuring all five digits on both hands sequentially.

Main Parameters

Parameter	Unit	Description
AMPLITUDE	%	The height from the beginning of the steepest rise to the highest point of the pulse curve is the amplitude.
RISE TIME	ms	The rise time marks the time interval of the steepest rise to the highest point of the pulse curve. It should be < 200 milliseconds for normal values.
RISE TO FALL	%	The quotient, stated in percentage, of rise time and fall time. It should be < 33% for normal values.
SKIN TEMPERATURE	°C	Skin temperature on toes recorded by the probes on the optical sensors. Side differences of more the 3 °C should be observed.

Medical Applications

Suspicion of digital arterial occlusions
Suspicion of Raynaud’s Syndrome or TOS (Thoracic Outlet Syndrome)
Suspicion of peripheral circulatory disorders

Test Examples

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Table of Contents

TOS-Test (Thoracic Outlet Syndrome)

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PVR – Pulse Volume Recording

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