Fig. 3: Changes in PTT induced by hydrostatic pressure, as modeled analytically and experimentally validated.
A Relationship between pressure and simulated PTT. A solid black line indicates simulated PTT without Ph effects. Dashed blue and orange lines indicate simulated PTT with Ph minimized and maximized via straight up and down poses, respectively. B Left: heatmap of simulated PTTs for constant BP over all possible arm pose configurations. Positive pitch indicates moving the corresponding limb upward. Right: projection of heatmap simulation with arm pose converted to hand height. A solid line indicates simulated PTT with average Ph effects (i.e., where θu = θf). Dashed blue and orange lines indicate simulated PTT with Ph minimized and maximized, respectively. C Across n = 20 participants, box plots of measured PTT were taken at different hand heights. Each measurement was the participant’s time-averaged PTT for the indicated height (for h = −25, 0, and 25 cm, n = 20, 20, and 19, respectively). Significance determined by mixed-effects model followed by Dunnett post hoc test. For h = −25 vs h = 0 cm, ****P < 0.0001; for h = 0 vs h = 25 cm, ****P < 0.0001. Individual trajectories in Supplementary Fig. 5. D Across n = 20 participants, box plots of h-stratified MAE for best-fit PTT predictions generated using the uncorrected and corrected models, with or without PEP, compared to the measured reference. Each measurement was the participant’s time-averaged MAE for the indicated h. The diagrams above show an illustrative example of the arm pose corresponding to each group (for h = -25, 0, and 25 cm, n = 16, 20, and 15, respectively). Significance determined by mixed-effects model followed by Šídák post hoc test; **P < 0.01; ns, not significant). Individual trajectories in Supplementary Fig. 7. E Repeated measures Bland-Altman plots for the best-fit PTT predictions from the uncorrected (top) and corrected model (bottom) compared to the measured reference across time-averaged participant and height pairs (n = 51; 2 to 3 measurements from each of the 20 participants). The X-axis shows the average of prediction and reference, and the y-axis shows the difference between prediction and reference. The solid line indicates the mean difference, and the dashed line indicates 95% LoA. The enlarged version shows the values of h in Supplementary Fig. 8. F A representative participant’s time series of measured and predicted hand height (top); corresponding time series of PTT predicted using the uncorrected and corrected models compared to the measured reference (bottom). Time series of representative participants PTT prediction error in Supplementary Fig. 10. For (C, D), the box represents the interquartile range, with the horizontal line at the median value. The vertical lines extend to the maximum and minimum data points within 1.5 × IQR.
