Figure 2

Demonstration of suction (number of experiments (N = 5), results shown for one experiment). (A) Experimental measurement of pressure and diameter traces for p _in = p _out = 3 cmH₂O (red line) during one contractile cycle. As the vessel expands, pressure falls transiently below the upstream reservoir pressure. Suction _amp is the pressure difference between inlet pressure p _in and p _1,min. t _recovery is the time constant of the fitted curve from p _1,min to end-diastolic diameter (EDD). Diameter amplitude, D _amp = D _max−D _min. The external pressure is shown as the dotted line on all pressure traces in this figure. Note that pressure traces for p ₁, p _a and p _b all indicate positive transmural pressure. (B) Pressure (p ₁) vs. diameter (left). Passive pressure-diameter curve (green) obtained in Ca²⁺-free solution. The black loop corresponds to contraction at p _in = p _out = 3 cmH₂O (p ₁ and D traces at right, bottom), grey loops show contractions in response to a ramp increase in p _in = p _out (p ₁ and D traces at right, top). Each loop corresponds to a contractile cycle. For example, there are 14 grey loops (and 14 contractile waves shown in the traces shown at upper right of Fig. 2B) because there were 14 contractile cycles during the pressure ramp. (C) Note that the valve state with both inlet and outlet valve closed occurs only briefly before beginning of suction. Predictions of pressure (p) and diameter (D) in the first lymphangion, and flow rate (Q) through the first valve from mathematical modelling. M _t is the time-dependence of tension activation. Yellow, purple, and black correspond to contraction, relaxation, and diastole, respectively, derived from this curve and superimposed onto other curves. The decay of muscle activation corresponds to the purple (“relaxation”) region of the M _t curve. Background shades correspond to three valve states as indicated at top left (the isovolumetric state, dark grey, is very short). Predicted p ₁ and D closely resemble experimental results. Under these pressure conditions, flow through the first valve only occurred during suction. The timing of flow through downstream valves can be seen in Fig. 4D.