Because blood flow to the skin can be modulated by multiple other physiological systems, the PPG can also be used to monitor breathing, hypovolemia, and other circulatory conditions.

[6] While pulse oximeters are commonly used medical devices, the PPG signal they record is rarely displayed and is nominally only processed to determine blood oxygenation and heart rate.

However, in cases of shock, hypothermia, etc., blood flow to the periphery can be reduced, resulting in a PPG without a discernible cardiac pulse.

[7] In this case, a PPG can be obtained from a pulse oximeter on the head, with the most common sites being the ear, nasal septum, and forehead.

MPPG also offers significant potential for data mining, e.g. using deep learning, as well as a range of other innovative pulse wave analysis techniques.

This is achieved by using face video to analyze subtle momentary changes in the subject's skin color which are not detectable to the human eye.

For instance, it can be used to monitor the heart rate of newborn babies,[21] or analyzed with deep neural networks to quantify stress levels.

[11] Remote photoplethysmography can also be performed by digital holography, which is sensitive to the phase of light waves, and hence can reveal sub-micron out-of-plane motion.

This method is an efficient way of performing digital holography from on-axis interferograms, which alleviates both the spatial bandwidth reduction of the off-axis configuration and the filtering of physiological signals.

It is however possible to circumvent its influence by subtracting the spatially averaged baseline signal, and achieve high temporal resolution and full-field imaging capability of pulsatile blood flow.