Table 2. Overview of the characteristics of studies assessing (ultra)-short-term pulse rate variability from video recordings.
BVP, blood volume pulse; CFL, compact fluorescent light; CMOS, complementary metal-oxidesemiconductor; d, distance between camera and measuring site; DC, direct current; DLSR, digital single-lens reflex camera; ECG, electrocardiography; F, female; HF, high-frequency band; IR, infrared; LED, light-emitting diode; LF, low-frequency band; M, male; Ns, number of subjects; pNN50, percentage of normal-to-normal (NN) intervals that differ by more than 50 ms; PRV, pulse rate variability; RGB, red, green, and blue; RGBCO, red, green, blue, cyan, and orange; RMSSD, root mean square of successive NN interval differences; SD1, Poincaré plot standard deviation perpendicular to the line of identity; SD2, Poincaré plot standard deviation along the line of identity; SDNN, standard deviation of the NN intervals; t, duration of the recordings; TP, total power; VLF, very-low-frequency band.
| Study characteristics | |
|---|---|
| Poh, McDuff & Picard (2011) | |
| PRV metrics: LF, HF, LF/HF | Camera: RGB (15 fps) |
| Ns: 12 (4F + 8M) | Lighting: daylight only |
| t (s): 60 | Recording setup: sitting still |
| Measuring site: face | Skin color: different |
| d (m): 0.5 | Reference measurement: BVP sensor (256 Hz) |
| Sun et al. (2012) | |
| PRV metrics: SDNN, LF, HF, LF/HF | Camera: monochrome CMOS (200 fps) |
| Ns: 10 (3F + 7M) | Lighting: 2× IR light only |
| t (s): 240 | Recording setup: rest, cushion placed under the left palm |
| Measuring site: left palm | Skin color: not given |
| d (m): 0.4 | Reference measurement: pulse oximeter |
| McDuff, Gontarek & Picard (2014) | |
| PRV metrics: LF, HF, LF/HF | Camera: RGBCO DLSR (30 fps) |
| Ns: 10 (7F + 3M) | Lighting: daylight and indoor illumination |
| t (s): 120 | Recording setup: (1) sitting still, (2) sitting, performing mental arithmetic test |
| Measuring site: face | Skin color: Asian, Caucasian, Hispanic |
| d (m): 3 | Reference measurement: BVP sensor |
| Moreno et al. (2015) | |
| PRV metrics: SDNN, RMSSD, pNN50, VLF, LF, HF, LF/HF | Camera: RGB (30 fps) |
| Ns: 20 (5F + 15M) | Lighting: dedicated light illuminating the face |
| t (s): 300 | Recording setup: (1) sitting, (2) lying (supine) still with eyes closed |
| Measuring site: face | Skin color: Caucasian |
| d (m): 0.8 | Reference measurement: chest strap (1 kHz) |
| Blackford, Piasecki & Estepp (2016) | |
| PRV metrics: SDNN, LF, HF | Camera: RGB (29.97 fps) |
| Ns: 19 | Lighting: daylight and fluorescent indoor illumination |
| t (s): 300 | Recording setup: sitting still |
| Measuring site: face | Skin color: not given |
| d (m): 25 | Reference measurement: ECG (16 kHz downsampled to 1,200 Hz) |
| Huang & Dung (2016) | |
| PRV metrics: SDNN, RMSSD, SDSD, SD1, SD2 | Camera: RGB frontal smartphone camera (30 fps) |
| Ns: 6 (2F + 4M) | Lighting: not given |
| t (s): 60 | Recording setup: (1) static, (2) occasional motion, (3) frequent motion |
| Measuring site: face | Skin color: not given |
| d (m): not given | Reference measurement: chest strap (unclear sampling rate) |
| Iozzia, Cerina & Mainardi (2016) | |
| PRV metrics: SDNN, RMSSD, pNN50, VLF, LF, HF, LF/HF | Camera: RGB camera (60 fps) |
| Ns: 58 | Lighting: daylight and artificial light |
| t (s): 300 | Recording setup: rest-to-stand maneuver (i.e. from lying on bed to standing still) |
| Measuring site: face | Skin color: Fitzpatrick scale II-IV |
| d (m): not given | Reference measurement: ECG (256 Hz) |
| Purtov et al. (2016) | |
| PRV metrics: HF, LF, VLF, TP | Camera: RGB camera (30 fps) |
| Ns: 20 | Lighting: 2× fluorescent lights only |
| t (s): 1,200 | Recording setup: sitting still |
| Measuring site: face | Skin color: not given |
| d (m): 3 | Reference measurement: ECG (250 Hz) |
| Cerina, Iozzia & Mainardi (2017) | |
| PRV metrics: RMSSD, pNN50, HF | Camera: RGB (60 fps) |
| Ns: 57 | Lighting: daylight and artificial light (CFL bars) |
| t (s): 300 | Recording setup: supine position |
| Measuring site: face | Skin color: Fitzpatrick scale II-IV |
| d (m): 1 | Reference measurement: ECG (256 Hz) |
| Melchor Rodriguez & Ramos-Castro (2018) | |
| PRV metrics: SDNN, RMSSD, pNN50, LF, HF, LF/HF | Camera: RGB (15 fps) |
| Ns: 15 (3F + 12M) | Lighting: daylight only |
| t (s): 50 | Recording setup: (1) sitting still, (2) sitting, performing lateral and forward/backward movements |
| Measuring site: face | Skin color: fair skin |
| d (m): 0.3 | Reference measurement: finger pulse sensor (1 kHz) |
| Yu et al. (2018) | |
| PRV metrics: SDNN, LF, HF | Camera: 2× monochrome camera, 1× RGB camera (R channel only) (50 fps) |
| Ns: 4 | Lighting: (1) white ambient light, (2) white ambient light + 1× red (625 nm) light, (3) white ambient light + 1× IR (850 nm) LED brick light |
| t (s): 300 | Recording setup: lying still in supine position |
| Measuring site: face | Skin color: not given |
| d (m): 1.8 | Reference measurement: ECG (500 Hz), PPG (125 Hz) |
| Benezeth et al. (2018) | |
| PRV metrics: VLF, LF, HF, (VLF+LF)/HF | Camera: RGB camera (50 fps) |
| Ns: 16 | Lighting: 2× direct DC lights |
| t (s): 120 | Recording setup: sitting still, watching videos with (1) neutral, (2) emotional content |
| Measuring site: face | Skin color: not given |
| d (m): 1 | Reference measurement: pulse oximeter |