In situ pressure modulation measurements by video capillaroscopy reveal capillary stiffening and reduced reactivity with age

Understanding tissue degradation with age and disease requires a clear picture of capillary function, but the small size of capillaries makes them difficult to model, perturb, and image. To measure capillary reactivity and stiffness, we recorded videos of nailbed capillaries while applying increasing external pressure to the finger. Combining the velocities at each pressure into participant velocity distributions showed that participants aged fifty and over (n=19) had a significantly higher median velocity than participants under fifty (n=16), whereas the effects of sex and blood pressure were insignificant. Notably, the effects of age were independent of blood pressure, suggesting that this method probes a different aspect of vascular health. Calculating dissimilarity using the earth-mover’s distance between individual and population velocity distributions classified age groups above and below fifty with an AUC of 0.79 ± 0.07. These findings show that pressure-applying video capillaroscopy can measure the effects of capillary stiffening with age and interrogate how individual capillaries respond to the slowing and stopping of blood flow—suggesting that this method could be used to diagnose and evaluate vascular diseases in the future.