Morphometry and Lymph Dynamics of Swine Thoracic Duct.

Background: The goal of this study was to characterize the thoracic duct (TD) both morphologically and hemodynamically. Methods and Results: The lymphatic flow and pressure gradient from the cisterna chyli (CC) to the lymphovenous junction were measured in anesthetized swine (n = 9). After the animals were euthanized, the TD were harvested for histomorphometric analyses in which three samples were perfused with 9% gelatin to obtain the morphometry of the TD valve in both the open and closed configuration. Spectral analyses were performed. An afferent lymphatic vessel of the CC was accessed and cannulated after the animal was euthanized for casting (n = 3) to obtain morphometric data. The in vivo flow rate was 0.7 ± 0.49 mL/minute. Spectral analysis (Fast Fourier Transformation) showed correlation coefficients of 0.858 ± 0.063 and 0.586 ± 0.112 (p < 0.05) for the TD and JVPs, respectively. The average pressure gradient was 8.1 mmHg along the TD. The length of the TD was 35.6 ± 2.2 cm. The maximal width of the CC ranged from 11.4 to 15 mm. The diameter of the TD varied irregularly from 2 to 4.3 mm. The geometry of the TD leaflets was determined to have an area of 1.99 ± 0.53 mm2, a leaflet length of 3.26 ± 0.86 mm, a packet depth of 0.66 ± 0.19 mm, and a wall length of 5.46 ± 2.16 mm. The TD media thickness was ∼7 ± 3 µm. The number of valves ranged from 9 to 13 in the full length of the TD. Conclusions: A relatively constant pressure gradient in the swine TD drives lymph flow from the CC to the jugular vein. The TD is a thin-walled vessel with valves that prevent reflux of lymph flow. This study of morphometric and lymphatic dynamics is important for interventionalists to understand the anatomy and physiology of the TD to design new diagnostic, interventional procedures, and devices.