Pulse Assessment With Pulse Oximeter

How to interpret pulse bar or pleth


Many pulse oximeters provide a pulse bar or pleth (plethysmograph); however this information has been largely ignored by most users even when it provides some very important information signals. The pulse bar or pleth is a graphical representation of how your heart beats; although it does not give you a set of numbers, it gives you an indication of your general health and heart conditions. Here we will discuss how and why you should pay attention to this signal.

It is difficult to have one guideline for all people as the pulse is dependent on many variables, such as age, gender, circadian rhythm, body build, stress and emotions, exercise and activities, body temperature... It is important to establish a norm for you at various situations, such as resting after meal or during rigorous exercise. Then pay attention for any deviation from your norm. If you have any questions, ask your doctor.

Pulse assessment has been used in various degrees in medical field. In western medicine, pulse assessment is commonly performed by palpating the pulse at the wrist or listening to the heart beats at the chest with a stethoscope. In oriental medicine, palpation on the wrist is the primary method used. Pulse diagnosis plays an important role in the history of Chinese medicine.

Features of a pulse

When assessing a patient's pulse, there are three important factors; pulse rate, pulse strength and or volume, and pulse rhythm. All three of these factors can be observed through the pulse bar or pleth displayed by an oximeter.

Pulse rate

For a normal adult and under normal conditions, the heart rate ranges from 60 to 100 beats per minute (bpm). For well-trained athletes, the heart rate can go as low as 40bpm.

Tachycardia is a heart condition that causes the heart to beat in excess of 100 bpm. Rapid contraction, if sustained, tends to overwork the heart and reduce blood circulation leading to low blood oxygen saturation level. For this condition medical treatment is required.

Bradycardia is a heart condition with heart beats below 60bpm. Unless you are an athlete, this would merit continued monitoring as bradycardia can be caused by some issues with the heart's electrical system.

Pulse strength (volume)

Pulse strength or volume is related the amount of blood pumped with each heartbeat or the force associated with each contraction. A normal pulse is one that can be felt with mild pressure on the artery. A thready pulse or weak pulse is one that is difficult to feel or obliterated easily with slight pressure. A full or bounding pulse has a pronounced pulsation that does not easily disappear with pressure. A rapid thready pulse is normally a sign of serious concern and must be reported immediately. There are different ways to classify the pulse strength. The following table shows one particular approach.

0NoneNo pulsation is felt with extreme pressure
1ThreadyNot easily felt; disappear under slight pressure
2WeakStronger than thready; disappear under light pressure
3NormalEasily felt; disappear under moderate pressure
4BoundingStrong and does not disappear with moderate pressure

With a pulse oximeter, similar information can be observed from the amplitude of the pleth wave or the fluctuation in the pulse bar. In order to establish a point of reference you can try to get a reading from several people to see what the various patterns look like.

For weak or thready pulses, some oximeters may have trouble getting a reading. It would be a good idea to double check the readings.

Pulse rhythm

The pulse rhythm is the pattern of pulsations, amplitude, and the pauses between each pulse. They should be regular and consistent from beat to beat. An arrhythmia or dysrhythmia (irregular patterns) is cause for serious concern and should be treated by medical professionals as soon as possible. An electrocardiogram should be performed for further clarification.