A pulse oximeter does not measure blood pressure. While both pulse oximeters and blood pressure monitors evaluate health, they operate on distinct principles and provide unique information about the body. Understanding what each device measures clarifies their specific roles in health monitoring.
What a Pulse Oximeter Measures
A pulse oximeter primarily measures blood oxygen saturation (SpO2) and pulse rate. Blood oxygen saturation indicates the percentage of hemoglobin carrying oxygen in red blood cells. A healthy oxygen saturation level is typically above 90-92%, a level needed to keep cells healthy. The pulse oximeter also displays the pulse rate, which is the number of times the heart beats per minute.
These measurements offer insights into how efficiently oxygen is delivered to the body’s extremities. Healthcare professionals use pulse oximeters to monitor individuals with conditions affecting blood oxygen levels, such as asthma, pneumonia, or heart failure. Readings can help determine if a person needs supplemental oxygen or if treatments are effective.
How a Pulse Oximeter Works
A pulse oximeter functions by using light to determine oxygen saturation and pulse rate. The device, typically a clip, contains small light-emitting diodes (LEDs) that shine red and infrared light through the tissue. Oxygenated hemoglobin and deoxygenated hemoglobin absorb these two wavelengths of light differently. Oxygen-rich blood absorbs more infrared light, while blood with less oxygen absorbs more red light.
A photodetector measures the light that passes through. By analyzing the ratio of absorbed red and infrared light, the oximeter calculates the percentage of hemoglobin saturated with oxygen. The device also detects changes in light absorption caused by the pulsating flow of arterial blood, which allows it to determine the pulse rate.
Why a Pulse Oximeter Doesn’t Measure Blood Pressure
A pulse oximeter does not measure blood pressure because it relies on light absorption to assess blood oxygen and flow. This is fundamentally different from measuring the physical force exerted by blood. Blood pressure involves the force of blood against arterial walls, requiring a method that applies external pressure. The oximeter’s light-based technology cannot quantify this mechanical force. While a pulse oximeter detects a pulse, indicating blood flow, it does not provide information about the pressure behind that flow.
Inflating a blood pressure cuff can temporarily restrict blood flow, which may affect a pulse oximeter’s ability to get a reading. Some research explores the potential for oximeters to assess blood pressure indirectly with additional algorithms, but currently, they are not designed to directly measure blood pressure.
How Blood Pressure is Measured
Blood pressure is measured using a sphygmomanometer, which is an inflatable cuff that wraps around the upper arm and connects to a measuring unit. The cuff inflates to temporarily stop blood flow in the artery, then slowly deflates.
As the cuff deflates, a healthcare professional listens with a stethoscope or uses an automated sensor to detect specific sounds of blood flow returning. The first sound indicates the systolic pressure, which is the pressure when the heart beats and pushes blood out. The point at which the sounds disappear marks the diastolic pressure, representing the pressure when the heart rests between beats. These two numbers, such as 120/80 mmHg, provide a comprehensive picture of the force exerted by the blood within the arteries.