Fig. 4.

Valve closure tests performed on a single-valve vessel in Ca²⁺-free solution. A: confocal reconstruction of a secondary valve in a rat mesenteric lymphatic obtained in Ca²⁺-free solution to prevent contractions. View is taken from downstream, looking back (against normal flow) into the valve. Structures at 1 o'clock and 7 o'clock at the inner edge of the lumen are the valve insertion points, or buttresses. Calibration bar = 40 μm. B: images of a representative vessel with the valve in the open (top) and closed (bottom) positions. Single densitometer window used to detect valve leaflet position is shown in yellow. Calibration bar = 120 μm. C and D: densitometer, pressure, and diameter traces are similar to those described in previous figures (no P_L recordings were necessary under these conditions because all pressures could be controlled). Tests begin with P_in (red trace) and P_out (blue trace) equal in which case the valve is open. A ramp-wise increase in P_out is imposed until the valve closes. P_out and P_in levels at the instant of closure are recorded and the difference (P_out − P_in) is the minimal pressure gradient required for closure. Diameter traces on both sides of the valve are recorded at sites corresponding to the colored windows in B. Test in C starts at the lowest baseline pressure level used (0.2 cmH₂O), whereas the test in D starts at the highest level of baseline pressure used (20 cmH₂O). Both recordings are from the same vessel. Note the difference in the diameter and pressure scales between C and D.