Pleth or plethysmograph is displayed in many newer pulse oximeters. This information is often ignored by the users dispite the valuable information it provides. We will focus on the interpretation of pleth.
Pleth shows the change in the volume of arterial blood with each pulse beat. Since the blood flow volume is directly affected by how the heart beats, the waveform and its signal strength provide valuable information on the health of the person. The picture below shows examples of various waveforms and their interpretation.
Signal strength, as indicated by the amplitude of the waveform, is directly related to the amount of blood circulating in the area when the oximeter sensor is placed. It can be caused by a weak heart, cold temperature or other circulatory issues. In general, weak signal is a result of low blood perfusion.
Sufficient signal strength is critical to the correct functioning of a pulse oximeter. If the signal problem is caused by cold hands, warm up the hands before taking a reading.
If the oximeter is dirty, the signal may be partially blocked leading to insufficient signal strenth.
The primary function of the heart is to supply blood and nutrients to the body. The regular beating, or contraction, of the heart moves the blood throughout the body. By watching the pleth waveform, the heart beating pattern and its rhythm is clearly displayed in the pleth. Each pleth cycle corresponds to one heart beat. Irregularities, such as missing heartbeats, extra heartbeats, fibrillation, tachycardia, bradycardia, bigeminy, PVC... can be identified easily.
Consult with your doctor if you see anything unusual.