Alteration in facial skin blood flow during acute exposure to −10° and −30° head‐down tilt in young human volunteers

What is the central question of this study? Facial skin blood flow (SBF) might increase during head‐down tilt (HDT). However, the effect of HDT on facial SBF remains controversial. In addition, the changes in facial SBF in the cheek (cheek SBF) during a steeper angle of HDT (>−12° HDT) have not been investigated. What is the main finding and its importance? This study showed that cheek SBF decreased during −30° HDT, alongside increased vascular resistance. Furthermore, vascular impedance was suggested to be elevated, accompanied by an increased hydrostatic pressure gradient caused by HDT. Constriction of the facial skin vascular bed and congestion of venous return owing to the steep angle of HDT can decrease facial SBF.