Fig. 4: The ocular-cephalic compartment time responses during a head-down tilt maneuver from 80° HUT to 6° HDT.

Panel a: intraocular (IOP), intracranial (ICP), and translaminar (TLP) pressures. Panel b: ocular perfusion pressure (OPP). Panel c: ocular globe (∆Vg), cerebral veins (∆Vcv), and extra-cerebral head veins (∆VH,v) changes in blood volume. In the insets of panels a, b, TLP and OPP mean and pulse (TLPP, OPPP) pressure values before and after the tilt maneuver are also reported. pa,eye indicates eye arterial pressure, t denotes time, and ∆V indicates the absolute volume variation with respect to the initial 80° HUT value.