Plethysmographic Waveform Devices

Abstract

Plethysmography is a noninvasive technique which measures volume changes. Common instruments include pneumatic or air plethysmographs and photoplethysmographs. These are used in the vascular laboratory to examine both arterial and venous blood flow. The pulse volume recorder (PVR) is a type of pneumatic plethysmograph which provides estimates of arterial blood flow to a limb or digit. The PVR measures pressures changes in a cuff that are the result of volume changes due to arterial blood flow within a segment of a limb or digit enclosed by the cuff. Another type of air plethysmograph is used to measure volume changes within the entire calf after a series of maneuvers. These changes are impacted by status of the venous system and the venous valves. Photoplethysmography measures reflected infrared light in a small sensor applied to a limb or digit. The amount of light reflected is dependent on the volume of blood present. By alternating the display of these changes in the reflected light signals both arterial inflow and venous refilling can be determined. Plethysmography provides qualitative and quantitative data which can be used to estimate global arterial and venous status.