A pulse oximetry measurement system uses a pseudo-random noise generator to stimulate one or more light emitting diodes (LEDs). The light amplitudes from these LEDs, after passing through a part of a body, are detected by a phototransistor or photodiode and digitized with an analog-to-digital converter (ADC). The digitized ADC light amplitude values are re-correlated with the outgoing pseudo-random noise stimulus. Spread spectrum techniques are known for their noise mitigation properties, and ability to pass multiple signals through the same medium without interference. Thus, these measurements can be performed substantially simultaneously with minimal interference from each other. The pulse oximetry measurement system correlates the measured light intensities using pseudo-random noise generation and phase division multiplexing, and computes the measured and correlated peak-to-peak detected light amplitudes to obtain a ratio between these light amplitudes for determining oxygen saturation in the blood, and may also be used for heart rate monitoring.