Photoplethysmography: Beyond the Calculation of Arterial Oxygen Saturation and Heart Rate

Abstract

In this article, I examine the source of the photoplethysmograph (PPG), as well as methods of investigation, with an emphasize on amplitude, rhythm, and pulse analysis. The PPG waveform was first described in the 1930s. Although considered an interesting ancillary monitor, the "pulse waveform" never underwent intensive investigation. Its importance in clinical medicine was greatly increased with the introduction of the pulse oximeter into routine clinical care in the 1980s. Its waveform is now commonly displayed in the clinical setting. Active research efforts are beginning to demonstrate a utility beyond oxygen saturation and heart rate determination. Future trends are being heavily influenced by modern digital signal processing, which is allowing a re-examination of this ubiquitous waveform. Key to unlocking the potential of this waveform is an unfettered access to the raw signal, combined with standardization of its presentation, and methods of analysis. In the long run, we need to learn how to consistently quantify the characteristics of the PPG in such a way as to allow the results from research efforts be translated into clinically useful devices.

Inter-device differences in monitoring for goal-directed fluid therapy

“…The utility of this information was lost on the developers of pulse oximetry who considered it an ''artifact'' and went so far as to apply a high-pass filter to PPG waveforms in order to remove this unwanted source of ''noise''. 79 Indeed, most commercial pulse oximeters filter out low-frequency oscillations.…”

Impaired endothelium mediated vascular reactivity in endogenous Cushing's syndrome

“…Photoplethysmography (PPG) is an optical measurement technique used to record digital volume pulse by measuring the pulsatile changes in blood volume in the finger microvasculature using light of infrared wavelength [19,20,21]. Photoplethysmographic measurement of peripheral pulse waveform changes is a highly objective and operator independent technique used to assess changes in both the calibre and tone of blood vessels during reactive hyperemia [17,22].…”

Investigation of peripheral photoplethysmographic morphology changes induced during a hand-elevation study

“…Furthermore, despite the similarities between them, the relationship between the recorded pulsatile ac PPG signal and the arterial pressure waveform is complex [18]. As a result, there remains a need for furthering understanding of PPG signals so that new clinical variables can be successfully extracted from this easily acquired but complex waveform [21].…”