Figure 2

Individual CSF and venous flow. Color-coded flow rates (ml s⁻¹) of all 16 subjects in 16 horizontal lines for each ROI during 90 s breathing protocol (bottom). Vertical lines mark start, middle and end of forced breathing. Note the different scaling for the various ROIs. Normal breathing (0–40 s): low CSF flow (blue = downward; red = upward) is regulated by cardiac pulsation (e.g., in Aqd and L3). Venous blood shows steady downward flow in EV and IJV with cardiac pulsatility. IVC flow is predominantly in upward direction with cardiac and respiratory influences (e.g., #1, #4, #5). Low flow at L3-EV is variable between subjects (e.g., opposite directionality between #10 and #5). Forced breathing (40–80 s): CSF and venous flow synchronized to respiration. During IN CSF moves predominantly upwards (various red shades), downward venous flow in C3-EV and IJV is modulated by IN (darker blue). Upward flow in IVC ceases or reverses (blue). During EX downward CSF movement (blue) prevails at all locations, venous flow decreases (lighter blue) at C3 and resumes upward directionality in IVC at L3 (red). Flow in L3-EV shows greater variability, however, respiratory modulations are observable (e.g. opposite behavior in subject #1 compared to #2). Normal breathing (80–90 s): rapid return of CSF and blood flow to the initial pattern. Aqd = aqueduct, C3 = cervical level 3, L3 = lumbar level 3, EV = epidural veins, IJV = internal jugular vein, IVC = inferior vena cava, IN = inspiration, EX = expiration.