Table 6. Selected studies comparing PPG-derived parameters of vascular age to reference indicators.
| Study | PPG Parameter | Subjects (Dataset) | Reference Indicator | Performance |
|---|---|---|---|---|
| Pulse wave velocity (PWV) | ||||
| Tsai et al. (94) | Finger-toe PWV | 100 healthy | carotid-femoral (cf) PWV | Finger-toe PWV correlated with cfPWV (r=0.67, P< 0.01). |
| Millasseau et al.(73) | Stiffness index | 87 healthy | cfPWV | Stiffness index correlated with cfPWV (r=0.65, P< 0.0001). |
| von Wowern et al. (139) | Aging index(AGI) | 112 pregnant and nonpregnant | cfPWV | Heartrate-adjusted AGI correlated with cfPWV (r =0.64, P< 0.0001). |
| Wei (127) | Spring constant | 70 diabetic | cfPWV | Spring constant correlated with cfPWV (r=−0.72, P< 0.001). |
| Jang et al.(140) | Corrected peak-toonsettime (P2Ocd) | 123 healthy | brachial-ankle (ba) PWV | P2Ocd correlated with baPWV (r=−0.77 and r= −0.68 for male and female,P<0.001). Mean absolute percentage error was 7.53 ± 5.37% for average values, and 3.22 ± 1.47% for each cardiac cycle. |
| Pulse transit time (PTT) | ||||
| Obeid et al.(161) | Finger-toe PTT, finger-toe PWV | 101 healthy and hypertensive | cfPTT, cfPWV | Correlation coefficient, root-mean-square error, and mean ± SD error were 0.90 (P<0.001), 5.3 ms, – 10.6 ± 5.5 ms between finger-toe PTT and cfPTT; and 0.87 (P<0.001), 0.7m/s, and 0.3 ± 0.8 m/s between finger-toe PWV and cfPWV. |
| Alivon et al. (86) | Finger-toe PTT, finger-toe PWV | 86 healthy, hypertensive, and cognitively impaired | cfPTT, cfPWV | Correlation coefficient and mean ± SD error were 0.77 (P<0.0001) and – 17.5 ± 19.7ms between finger-toe PTT and cfPTT; and 0.66 (P < 0.0001) and 0.2 ± 2.5 m/s between finger-toe PWV and cfPWV. |
| Systolic (SBP), diastolic (DBP) and mean (MBP) blood pressure (BP) | ||||
| Nitzan et al. (87) | Finger-toe PTT, toe PAT | 44 healthy | Brachial BP | Finger-toe PTT and toe PAT correlated with SBP (r=–0.52, P<0.01, and r=–0.67, P<0.0001), but not with DBP. |
| Xing et al.(35) | 19 pulse wave and 2nd derivative features | 1,249 healthy and hypertensive | Brachial BP | Correlation coefficient and mean ± SD error for subjects ≤ 50 yr were: 0.86 and 0.45 ± 11.3 mmHg for SBP, and 0.83 and 0.31 ± 8.55 mmHg for DBP; and for > 50 yr: 0.79 and −0.68 ± 14.1 mmHg for SBP, and 0.81 and −0.20 ± 9.0 mmHg for DBP using a random forest algorithm. |
| Hasanzadeh etal. (66) | Pulse wave features | 942 critically ill (Cuffless BP Estimation) | Invasive BP | Correlation coefficient, mean ± SD error, and mean absolute error were 0.78, 0.09 ± 10.38 mmHg and 8.22 mmHg for SBP, 0.75, −0.02 ± 5.53 mmHg and 4.58 mmHg for MBP, and 0.72, 0.23 ± 4.22 mmHg and 4.17 mmHg for DBP estimation using an AdaBoost algorithm. |
| Khalid et al. (40) | Pulse area, rise time, width at 25% amplitude | 282 criticallyill (MIMIC) and anesthetized (University of Queensland) | Brachial BP | Mean ± SD error were 0.07 ± 7.1 mmHg for SBP, and -0.08 ± 6.0 mmHg for DBP estimation using BP category-specific regression tree algorithms. |
| BP category | ||||
| Liang et al.(28) | PPG scalogram | 121 criticallyill (MIMIC) | Invasive BP category | F1 scores for classification as normotensive (NT), prehypertensive (PHT), and hypertensive (HT) were 0.81(NTvs.PHT),0.93 (NTvs.HT), and 0.83 [(NT + PHT)vs. HT] using a convolutional neural network. |
| Chronological age | ||||
| Takazawa et al. (88) | AGI | 600 healthyand arteriosclerotic | Chronological age | AGI increased with age (r = 0.80, P < 0.001). |
| Hashimoto et al. (14) | AGI, b/a, d/a | 848 healthy and hypertensive | Chronological age | AGI,b/a and d/a correlated with age (r=0.42, r= −0.35, and r=0.37,respectively, with P< 0.001). |
| Atherosclerosis category | ||||
| Allen et al.(106) | Toe PPG shape index, toe PAT, pulse amplitude | 111 healthy and peripheral artery disease (PAD) | Ankle-brachial index(ABI) | Accuracy (κ) of significant and higher-grade disease detection using: shape index 91% (0.80) and 90% (0.65); bilateral difference in PAT to pulse foot 86% (0.71) and 90% (0.71); bilateral difference in PAT to pulse peak 86% (0.70) and 92% (0.76); pulse amplitude 66% (0.20) and 81% (0.34). |
| Peltokangas et al. (27) | Amplitude ratios, AGI | 82 healthy and atherosclerotic | Abnormal ABI | Area under the ROC curve was 0.70 and 0.79 for finger and toe AGI, respectively, and 0.79 for the best performing toe amplitude ratio. |
| Jönsson et al. (95) | PPG ABI | 43 healthy and PAD | Doppler ABI | PPGABI correlated with Doppler ABI (r = 0.89). Mean ± SD error was 0.05 ± 0.12. |
PPG, photoplethysmogram.