An inflatable "finger-lock" for stabilizing nailfold capillary videos and modulating blood flow velocities

High-resolution video capillaroscopy shows promise as a non-invasive method to directly observe blood cells as they flow through and interact with the microvasculature. When imaging microvasculature in the nailfold, the inherent shaking of the fingers requires physical stabilization to reduce image noise. However, any external force applied to the fingers will affect the blood flow rate. To address this, we designed an inflatable "finger-lock" for nailfold capillaroscopy, stabilizing the finger against a coverslip with constant pressure. Testing 72 participants, we demonstrated that increasing "finger-lock" pressure improves video stability and decreases the velocity of capillary blood cells. Hence, capillary blood cell velocity measurements require monitoring and controlling external pressure. Our work introduces a method to perturb local capillary blood flow and measure the microvascular response, enabling further studies investigating how person-specific factors (e.g., age and disease) impact vascular health.