A pulse oximeter is a common, non-invasive, clip-like device that attaches to a fingertip. It quickly estimates the amount of oxygen carried in the blood (SpO2). While oxygen saturation receives the most attention, the device provides a second measurement: the PR reading. Understanding this second number is essential for a complete picture of cardiovascular function.
Decoding the PR Reading
The abbreviation PR on a pulse oximeter display stands for Pulse Rate. This reading quantifies the number of times the heart beats in one minute (bpm). The pulse oximeter measures this rate by detecting the rhythmic expansion and contraction of arteries in the finger. Although the term “Pulse Rate” is used, the number reflects the Heart Rate (the actual rate of cardiac contractions). In the context of a pulse oximeter, these two terms are functionally interchangeable, providing a peripheral measurement of the heart’s pumping efficiency.
The Technology Behind Pulse Rate Measurement
A pulse oximeter calculates the PR number using photoplethysmography. This method uses light to detect the tiny, rhythmic changes in blood volume that occur with each heartbeat. The device contains a light source, typically red and infrared LEDs, and a light detector.
As arterial blood surges through the capillaries, the amount of light absorbed and transmitted changes predictably. The sensor records these rhythmic fluctuations in light transmission across the tissue. By counting the frequency of these pulsations over a set period, the device’s internal algorithm determines the number of beats per minute.
Interpreting Your Pulse Rate Results
For most healthy adults at rest, the normal range for a pulse rate is between 60 and 100 beats per minute (bpm). A resting rate below 60 bpm is termed bradycardia, which can be normal for highly conditioned athletes but may signal a health issue for others. Conversely, a resting rate consistently above 100 bpm is known as tachycardia. If readings are regularly outside this 60–100 bpm range, especially if accompanied by symptoms like dizziness or shortness of breath, medical consultation is advisable.
Factors Affecting Accuracy
The accuracy of the PR reading can be influenced by several external and physiological factors. To ensure the best measurement, it is recommended to keep the hand warm and remain still.
- Significant movement, such as shivering or shaking, can create “motion artifacts” that disrupt the sensor’s ability to count the pulsations accurately.
- Poor peripheral perfusion, often caused by cold hands or low blood pressure, can yield unreliable results because blood flow to the finger is reduced.
- Wearing nail polish or artificial nails can interfere with the light transmission.