Quantitative Comparison of Photoplethysmographic Waveform Characteristics: Effect of Measurement Site

Abstract

Introduction: Photoplethysmography (PPG) has been widely used to assess cardiovascular function. However, few studies have comprehensively investigated the effect of measurement site on PPG waveform characteristics. This study aimed to provide a quantitative comparison on this.Methods: Thirty six healthy subjects participated in this study. For each subject, PPG signals were sequentially recorded for 1 min from six different body sites (finger, wrist under (anatomically volar), wrist upper (dorsal), arm, earlobe, and forehead) under both normal and deep breathing patterns. For each body site under a certain breathing pattern, the mean amplitude was firstly derived from recorded PPG waveform which was then normalized to derive several waveform characteristics including the pulse peak time (Tp), dicrotic notch time (Tn), and the reflection index (RI). The effects of breathing pattern and measurement site on the waveform characteristics were finally investigated by the analysis of variance (ANOVA) with post hoc multiple comparisons.Results: Under both breathing patterns, the PPG measurements from the finger achieved the highest percentage of analyzable waveforms for extracting waveform characteristics. There were significant effects of breathing pattern on Tn and RI (larger Tn and smaller RI with deep breathing on average, both p < 0.03). The effects of measurement site on mean amplitude, Tp, Tn, and RI were significant (all p < 0.001). The key results were that, under both breathing patterns, the mean amplitude from finger PPG was significantly larger and its Tp and RI were significantly smaller than those from the other five sites (all p < 0.001, except p = 0.04 for the Tp of “wrist under”), and Tn was only significantly larger than that from the earlobe (both p < 0.05).Conclusion: This study has quantitatively confirmed the effect of PPG measurement site on PPG waveform characteristics (including mean amplitude, Tp, Tn, and RI), providing scientific evidence for a better understanding of the PPG waveform variations between different body sites.

Quantitative Comparison of the Performance of Piezoresistive, Piezoelectric, Acceleration, and Optical Pulse Wave Sensors

“…Not surprisingly, we observed that the quality of pulse wave measurement is affected by the measuring site. The finding is consistent with those of Hartmann et al (2019). The stability of the pulse wave obtained from the carotid artery is worse than that of the radial artery (Adji et al, 2006).…”

“…An effective sensor must be robust, stable, and give reproducible signals. Many factors can affect their performance, including the way in which they are applied to the skin, the contact force between the sensor and the skin (Teng and Zhang, 2006), and the measuring site (Lukas et al, 2014;Hartmann et al, 2019). Therefore, we have analyzed the four sensors' susceptibilities to these external factors and compared their stability and reproducibility.…”

Assessing the Quality of Heart Rate Variability Estimated from Wrist and Finger PPG: A Novel Approach Based on Cross-Mapping Method

“…Fingers, earlobes, forehead, and wrist are common PPG recording locations. Finger is the body site most used for clinical applications, being the most practical and the most sensitive to blood volume fluctuations [16][17][18]. From quantitative analysis of waveform characteristics, e.g., mean amplitude and peak point position, the forehead resulted to be related to the least analyzable PPG signal, whereas the finger and the earlobe were reported to be the locations which produce the most reliable PPG signals [17].…”

“…Finger is the body site most used for clinical applications, being the most practical and the most sensitive to blood volume fluctuations [16][17][18]. From quantitative analysis of waveform characteristics, e.g., mean amplitude and peak point position, the forehead resulted to be related to the least analyzable PPG signal, whereas the finger and the earlobe were reported to be the locations which produce the most reliable PPG signals [17]. The same results were found using statistical approaches, e.g., kurtosis and Shannon entropy, to automatically quantify the quality of multi-site PPG signals [17,19,20].…”

“…Moreover, the wrist is a location not affected by the body auto-regulation mechanisms, which can represent a confounding factor when finger location is used to acquire PPG. PPG signal quality was compared computing two well-known statistical indexes: kurtosis and Shannon entropy [17,19,20]. Then, we compare the two PRV signals with the HRV acquired during the experiment by using a wearable ECG acquisition system from Smartex s.r.l.…”