A pulse oximeter does not measure blood pressure. While both are used for monitoring health, these distinct medical devices operate on different principles and provide unique information. This article clarifies how each device works and why they measure separate health indicators.
How a Pulse Oximeter Works
A pulse oximeter is a non-invasive device that measures the oxygen saturation level in the blood, often referred to as SpO2, and simultaneously detects heart rate. It typically clips onto a translucent part of the body, such as a fingertip or earlobe. The device works by emitting two wavelengths of light: red light at 660 nm and infrared light at 940 nm.
Oxygenated hemoglobin and deoxygenated hemoglobin absorb these light wavelengths differently. Oxygenated blood absorbs more infrared light, allowing more red light to pass through, while deoxygenated blood absorbs more red light and allows more infrared light to pass. The pulse oximeter detects the amount of light transmitted through the tissue. It then calculates the percentage of hemoglobin saturated with oxygen using the Beer-Lambert law, which relates light absorption to the concentration of the absorbing substance. This provides a quick and painless way to assess how efficiently blood is carrying oxygen to the body’s extremities.
How Blood Pressure is Measured
A blood pressure monitor, also known as a sphygmomanometer, measures the force of blood pushing against the walls of your arteries. Blood pressure readings consist of two numbers: systolic pressure and diastolic pressure. Systolic pressure is the higher number, indicating the pressure in your arteries when your heart beats and pumps blood.
Diastolic pressure is the lower number, representing the pressure in your arteries when your heart rests between beats. To measure blood pressure, a cuff is typically placed around the upper arm and inflated to temporarily stop blood flow in the brachial artery. As the air is slowly released from the cuff, a healthcare professional listens for specific sounds, called Korotkoff sounds, with a stethoscope, or an automated device detects oscillations in blood flow. The pressure at which the first sound is heard corresponds to the systolic pressure, and the pressure at which the sounds disappear marks the diastolic pressure.
Distinct Physiological Information
Pulse oximeters and blood pressure monitors provide distinct physiological information because they measure fundamentally different parameters of cardiovascular health. A pulse oximeter focuses on the oxygen content of the blood and the heart’s pumping rhythm, assessing peripheral oxygen saturation (SpO2). Conversely, a blood pressure monitor quantifies the mechanical force exerted by blood against artery walls, reflecting the heart’s pumping strength and blood vessel resistance. One device cannot perform the function of the other. While a pulse oximeter provides heart rate, it does not measure systolic and diastolic blood pressure. Both measurements are independently valuable for a comprehensive health assessment.