Limits...
Feasibility of long-distance heart rate monitoring using transmittance photoplethysmographic imaging (PPGI).

Amelard R, Scharfenberger C, Kazemzadeh F, Pfisterer KJ, Lin BS, Clausi DA, Wong A - Sci Rep (2015)

Bottom Line: For this purpose, a novel PPGI system was designed at the hardware and software level.Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction.Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring.

View Article: PubMed Central - PubMed

Affiliation: University of Waterloo, Department of Systems Design Engineering, Waterloo, N2L3G1, Canada.

ABSTRACT
Photoplethysmography (PPG) devices are widely used for monitoring cardiovascular function. However, these devices require skin contact, which restricts their use to at-rest short-term monitoring. Photoplethysmographic imaging (PPGI) has been recently proposed as a non-contact monitoring alternative by measuring blood pulse signals across a spatial region of interest. Existing systems operate in reflectance mode, many of which are limited to short-distance monitoring and are prone to temporal changes in ambient illumination. This paper is the first study to investigate the feasibility of long-distance non-contact cardiovascular monitoring at the supermeter level using transmittance PPGI. For this purpose, a novel PPGI system was designed at the hardware and software level. Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction. Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring. The results support the hypothesis that long-distance heart rate monitoring is feasible using transmittance PPGI, allowing for new possibilities of monitoring cardiovascular function in a non-contact manner.

No MeSH data available.


Summary of the results from Experiment 1 (short-distance measurement) across three participants (P1, P2, P3).The unprocessed acquired signal (row 2) was processed using ambient correction and signal processing, yielding a PPGI signal (row 3), which exhibited a higher correlation to the ground-truth contact PPG signal (row 1). For each participant, the PPGI power spectral density (row 4) closely matched the ground-truth PPG power spectral density, and the heart rate was easily distinguished by the maximum frequency power peak. The windowed correlation (row 5) of the processed PPGI signal with respect to the PPG signal (red) showed unanimous improvement over the unprocessed signal (blue), exemplifying the local temporal similarity across the entire signal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4594125&req=5

f4: Summary of the results from Experiment 1 (short-distance measurement) across three participants (P1, P2, P3).The unprocessed acquired signal (row 2) was processed using ambient correction and signal processing, yielding a PPGI signal (row 3), which exhibited a higher correlation to the ground-truth contact PPG signal (row 1). For each participant, the PPGI power spectral density (row 4) closely matched the ground-truth PPG power spectral density, and the heart rate was easily distinguished by the maximum frequency power peak. The windowed correlation (row 5) of the processed PPGI signal with respect to the PPG signal (red) showed unanimous improvement over the unprocessed signal (blue), exemplifying the local temporal similarity across the entire signal.

Mentions: The goal of Experiment 1 was to validate the base case short-distance setup. Figure 4 shows the effect of processing the PPGI signal for three participants. The processed PPGI signal contained amplified pulsatility over the unprocessed (“raw”) PPGI. Pulsatile signals were extracted for all five participants (“P1” through “P5”), resulting in discernible systolic peaks of each blood pulse. Much of the noise was subdued upon processing. The high-frequency information not expected in the naturally smooth blood pulse waveforms was denoised, yielding smooth blood pulses. Furthermore, non-linear trends were corrected, yielding stable PPGI signals. These non-linear trends resulted in low correlation values between the raw PPGI and the ground-truth PPG (e.g., at 1.5 s for P3). The processed PPGI stabilised the signal, yielding larger correlation values at those time windows. The heart rate was discernible in both raw and processed PPGI as a peak frequency power coincident with the PPG peak. However, although all PPGI signals showed strong spectral similarity to the PPG signal in the PSD, the processed PPGI signal exhibited a stronger peak at the heart rate, thus subduing extraneous frequencies.


Feasibility of long-distance heart rate monitoring using transmittance photoplethysmographic imaging (PPGI).

Amelard R, Scharfenberger C, Kazemzadeh F, Pfisterer KJ, Lin BS, Clausi DA, Wong A - Sci Rep (2015)

Summary of the results from Experiment 1 (short-distance measurement) across three participants (P1, P2, P3).The unprocessed acquired signal (row 2) was processed using ambient correction and signal processing, yielding a PPGI signal (row 3), which exhibited a higher correlation to the ground-truth contact PPG signal (row 1). For each participant, the PPGI power spectral density (row 4) closely matched the ground-truth PPG power spectral density, and the heart rate was easily distinguished by the maximum frequency power peak. The windowed correlation (row 5) of the processed PPGI signal with respect to the PPG signal (red) showed unanimous improvement over the unprocessed signal (blue), exemplifying the local temporal similarity across the entire signal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4594125&req=5

f4: Summary of the results from Experiment 1 (short-distance measurement) across three participants (P1, P2, P3).The unprocessed acquired signal (row 2) was processed using ambient correction and signal processing, yielding a PPGI signal (row 3), which exhibited a higher correlation to the ground-truth contact PPG signal (row 1). For each participant, the PPGI power spectral density (row 4) closely matched the ground-truth PPG power spectral density, and the heart rate was easily distinguished by the maximum frequency power peak. The windowed correlation (row 5) of the processed PPGI signal with respect to the PPG signal (red) showed unanimous improvement over the unprocessed signal (blue), exemplifying the local temporal similarity across the entire signal.
Mentions: The goal of Experiment 1 was to validate the base case short-distance setup. Figure 4 shows the effect of processing the PPGI signal for three participants. The processed PPGI signal contained amplified pulsatility over the unprocessed (“raw”) PPGI. Pulsatile signals were extracted for all five participants (“P1” through “P5”), resulting in discernible systolic peaks of each blood pulse. Much of the noise was subdued upon processing. The high-frequency information not expected in the naturally smooth blood pulse waveforms was denoised, yielding smooth blood pulses. Furthermore, non-linear trends were corrected, yielding stable PPGI signals. These non-linear trends resulted in low correlation values between the raw PPGI and the ground-truth PPG (e.g., at 1.5 s for P3). The processed PPGI stabilised the signal, yielding larger correlation values at those time windows. The heart rate was discernible in both raw and processed PPGI as a peak frequency power coincident with the PPG peak. However, although all PPGI signals showed strong spectral similarity to the PPG signal in the PSD, the processed PPGI signal exhibited a stronger peak at the heart rate, thus subduing extraneous frequencies.

Bottom Line: For this purpose, a novel PPGI system was designed at the hardware and software level.Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction.Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring.

View Article: PubMed Central - PubMed

Affiliation: University of Waterloo, Department of Systems Design Engineering, Waterloo, N2L3G1, Canada.

ABSTRACT
Photoplethysmography (PPG) devices are widely used for monitoring cardiovascular function. However, these devices require skin contact, which restricts their use to at-rest short-term monitoring. Photoplethysmographic imaging (PPGI) has been recently proposed as a non-contact monitoring alternative by measuring blood pulse signals across a spatial region of interest. Existing systems operate in reflectance mode, many of which are limited to short-distance monitoring and are prone to temporal changes in ambient illumination. This paper is the first study to investigate the feasibility of long-distance non-contact cardiovascular monitoring at the supermeter level using transmittance PPGI. For this purpose, a novel PPGI system was designed at the hardware and software level. Temporally coded illumination (TCI) is proposed for ambient correction, and a signal processing pipeline is proposed for PPGI signal extraction. Experimental results show that the processing steps yielded a substantially more pulsatile PPGI signal than the raw acquired signal, resulting in statistically significant increases in correlation to ground-truth PPG in both short- and long-distance monitoring. The results support the hypothesis that long-distance heart rate monitoring is feasible using transmittance PPGI, allowing for new possibilities of monitoring cardiovascular function in a non-contact manner.

No MeSH data available.