Fig. 1. Experimental setup. (A) A uniform hydrodynamic flow was generated between the lucite top part and the microscope glass plate on which cells adhere. Cell movements were imaged by an inverted microscope under various illumination types and recorded by a digital camera coupled to a computer. (B) The hydrodynamic shear stress applied to the cells is related to the chamber width l and height e and to flow rate D through Eqn 1 (see Materials and Methods). (C) Representation of cell movements. The cell position is represented as successive points in Cartesian coordinates, where the x axis denotes the direction of the flow. The translational cell velocity during a track <^jv> is defined by Eqn 3 from the cell positions at the initial time (t₀) and the last cell position recorded (t_end). The projections of the translational cell velocity over the directions parallel and perpendicular to the flow are denoted <v_x> and <v_y>. The instant cell velocity ^jv(t_i) is calculated according to Eqn 2 from the cell positions at the previous (t_i–1) and following (t_i+1) instant times and given in orthoradial coordinates, where _i is the angle between the speed and the flow.