Fig. A2. Balloon pressure transducer setup. The balloon is stretched to a 2-D disk using a wire and is glued to the end of a tube (grey line), which is connected to a Luer lock adapter (thicker grey line). The adapter is connected to a syringe filled with water and a pressure transducer. The balloon, syringe and pressure transducer were held in the horizontal x–y plane, as shown in the top-view scheme, to minimize variations in pressure (P) with water height.