Flow Resistance of Vessels with an Enlarged Total Cross-Sectional Area in the Midsection

To understand the hemodynamics of the microcirculation, we compared the resistance of vessels that either had an enlarged cross-sectional area in the midsection (denoted vessel 1) or had a uniform diameter (denoted vessel 2). The length of the two vessels and the pressure difference between the ends were equal. The two vessels were filled with water, and the volume of water flowing through the two vessels per second was measured. The volume of water flowing through vessel 1 was 4.05 ml/sec, and the volume of water flowing through vessel 2 was 4.37 ml/sec. Vessel 1 had a higher resis- tance, and water drained more slowly than from vessel 2. These results demonstrate that vessels with a greater cross- sectional area in the midsection have a lower flow than vessels with a constant cross-section, even though resistance in the midsection is lower when the cross-sectional area is greater.