Vascular age estimation using a consumer wearable sleep tracker

Figures

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  Fig 1. Illustration of devices, protocol and main outcomes. During sleep, participants underwent simultaneous PPG recordings using both a clinical-grade pulse oximeter (Fingertip probe) and a consumer wearable ring (Oura Ring). The data were analysed to assess PPG waveform characteristics and predict vascular age.

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  Fig 2. Pulse waveform similarity between the fingertip sensor and the wearable ring. a. Distribution of cross-correlation coefficients between devices for all participants. b. Average waveforms (derived from all participants) from Fingertip (blue) and Ring (red). Shaded areas show standard deviation at each sample point. c. Average pulse waveforms for three age groups: 20-39, 40-59, and 60 and above. Vertical dashed blue lines indicate systolic and diastolic peak locations on Fingertip pulse; horizontal dashed lines show approximate distance between 2 peaks.

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  Fig 3. Linear relationship between age and PPG features. Scatter plots for Fingertip (left column) and Ring (right column) for CT (Crest time), dT (distance between systolic and diastolic peaks), and RI (Reflection index). Each color (point) is a different participant.

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  Fig 4. Agreement between the chronological age and estimated vascular age. a. Scatter plot of estimated vascular age versus chronological age across cross-validation folds for all subjects for Fingertip (left column) and Ring (right column) (N = 160). Each color represents a fold, with solid lines showing fold-specific regression fits. The dashed gray line marks perfect estimation (identity line). R: Pearson’s correlation coefficient. b. Bland-Altman plot comparing estimated vascular age to chronological age. The solid grey line shows mean difference, with 95% confidence intervals (dashed grey lines) representing the limits of agreement. Fold-specific regression lines and their slope and 95% CI are shown via different colors. c. Age-adjusted ΔAge values across chronological age after proportional bias removal. Fold-specific regression lines and their slope and 95% CI are shown via different colors.

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  Fig 5. Important regions of the PPG waveform for CNN model. Grad-CAM visualizations of PPG waveforms using Fingertip (left) and Ring (right) devices. Results are displayed for different age groups across rows. Top row: all participants included, second row: ages 20–39, third row: ages 40–59, and bottom row: ages 60 and above. The colour intensity reflects the model’s attention, with warmer colours (yellow) indicating areas of higher relevance in age estimation. Across both devices, the focus areas shift with increasing age, highlighting broader regions of intermediate importance in older age groups.

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  Fig 6. Model-adjusted systolic blood pressure (SBP) (a) and diastolic blood pressure (DBP) (b) across ΔAge tertiles derived from Fingertip and Ring. Points represent estimated marginal means from regression models adjusted for age, sex and BMI; error bars indicate 95% confidence intervals. Blue dashed lines show trend. ΔAge values are age-adjusted. Mean ΔAge for T1, T2, and T3 was −5.9, −0.5, and 6.5 years for Fingertip and −6.1, −0.4, and 6.6 years for Ring, respectively.