Plethysmography
A plethysmograph is an instrument for determining and registering variations in the size of an organ or limb. The diagnosis of vascular disease is done with several types of plethysmograph, each with advantages. Hokanson manufactures three types:
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Plethysmograph Type |
Transducer Type and Measurement Method |
Standard Applications |
|
Pneumo Plethysmograph |
A blood pressure cuff is placed around the limb to be measured, inflated to a low pressure and sealed off from the inflation device. Changes in limb volume under the cuff are reflected in a pressure change in the cuff, which produces a waveform. |
Pulse volume recording (PVR) in the legs, arms, fingers and toes. |
|
Photo Plethysmograph (PPG) |
An infrared sensor is placed on the skin of the limb, which detects skin color changes that occur with each heartbeat |
Toe and finger blood pressure |
|
Strain Gauge Plethysmograph (SPG) |
A very thin rubber tube, filled with Mercury or Indium-Gallium is placed around the limb or digit of interest. As the volume of the limb changes with each heartbeat, the tube is stretched ectrical resistance increases. This electrical information is processed and displayed as a waveform. |
Arterial inflow, or venous occlusion plethysmography |
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