A thin, mercury-(or Indium Gallium)  filled, silicone rubber tube is placed around the limb or digit of interest. As the volume of the limb changes with each heartbeat, the tube is stretched and the electrical resistance increases. This electrical information is processed and conveyed as analog information to a display, recorder or PC software.

The Hokanson strain gauge plethysmograph is easily and accurately calibrated in situ and it can be used in a wide variety of applications. In strain gauge plethysmography there is a direct relationship between the resistance of the gauge and the circumference (and hence the volume) of the 
limb.

Hokanson strain gauges are built so that the length of the gauge is precisely related to the circumference. Although this is not done by all manufacturers, it is a very important requirement. Without it, electrical calibration of the instrument is erroneous.

In addition, all Hokanson gauges use a 4-wire connection which eliminates potential errors that would be caused by lead resistance due to the length of the connecting cable.  Common uses of this instrument are in measuring arterial blood flow into the limbs and digits, venous capacitance, maximum venous outflow to detect deep venous thrombosis in the legs, and blood pressure in the extremities.