Photoplethysmography behind the Ear Outperforms Electrocardiogram for Cardiovascular Monitoring in Dynamic Environments

Figures

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  Figure 1. The SPYDR earcup system is a self-contained unit that can act as a functional replacement for earcup in standard flight helmets or headsets. Photograph of SPYDR’s internal processor and circuit board (left) and assembled SPYDR earcup (right) with PPG sensor embedded within the earseal at the red light.

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  Figure 2. Comparison of blood oxygen saturation (SpO2) as measured by SPYDR vs. control finger PPG sensor. Note that SPYDR responds to changing physiological conditions faster than the peripheral finger sensor, especially noticeable during a period of acute hypoxia of Subject #2 in the right panel, supporting findings from a previous study. Correlation by Pearson was 0.92 for test #1 and 0.89 for test #2.

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  Figure 3. Correlation plot of Pulse Rate (PR) as determined by finger PPG sensor control vs. SPYDR for test #1 (Left) and test #2 (Right). Correlation coefficient by Pearson was 0.78 for test #1, 0.93 for test #2.

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  Figure 4. Figure on the left is a Bland-Altman plots of PR measurements comparing the agreement of the systems comparing SPYDR with control finger and forehead PPG sensors for all subjects. The panel on the right is the same data over time, adjusted for the control device’s reduced capture rate.

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  Figure 5. Centrifuge testing of heart rate as determined by electrocardiogram of a test subject in a manned centrifuge simulating high-acceleration flight. ECG was highly unreliable and mostly unusable, especially during periods of motion and acceleration.

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  Figure 6. Manned-centrifuge full data as reported by SPYDR for a test subject simulating high-acceleration flight. Note decreases in blood oxygen saturation (SpO2) and increases in pulse rate commensurate with high-acceleration exposures (red arrows). The presence of a pulsatile waveform suggests that blood is flowing, yet decreased oxygen saturation indicates reduced perfusion which typically pre-empts a G-induced Loss of Consciousness (G-LOC).

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  Figure 7. Acceleration as measured by SPYDR was compared to the acceleration computed by the centrifuge. Interestingly, the centrifuge accelerometers are located at the seat, whereas SPYDR is measuring acceleration at the head. Since the user’s head is 9% closer to the center of rotation of the centrifuge than the seat, acceleration is roughly 9% lower at the head as compared to the acceleration sensed by the centrifuge.