Publication Date



Physiological Reports


Evidence overwhelmingly suggests that the lymphatics play a critical role in the clearance of cerebrospinal fluid (CSF) from the cranial space. Impairment of CSF outflow into the lymphatics is associated with a number of pathological conditions including spaceflight-associated neuro-ocular syndrome (SANS), a problem that limits long-duration spaceflight. We used near-infrared fluorescence lymphatic imaging (NIRFLI) to dynamically visualize the deep lymphatic drainage pathways shared by CSF outflow and disrupted during head-down tilt (HDT), a method used to mimic the cephalad fluid shift that occurs in microgravity. After validating CSF clearance into the lymph nodes of the neck in swine, a pilot study was conducted in human volunteers to evaluate the effect of gravity on the flow of lymph through these deep cervical lymphatics. Injected into the palatine tonsils, ICG was imaged draining into deep jugular lymphatic vessels and subsequent cervical lymph nodes. NIRFLI was performed under HDT, sitting, and supine positions. NIRFLI shows that lymphatic drainage through pathways shared by CSF outflow are dependent upon gravity and are impaired under short-term HDT. In addition, lymphatic contractile rates were evaluated from NIRFLI following intradermal ICG injections of the lower extremities. Lymphatic contractile activity in the legs was slowed in the gravity neutral, supine position, but increased under the influence of gravity regardless of whether its force direction opposed (sitting) or favored (HDT) lymphatic flow toward the heart. These studies evidence the role of a lymphatic contribution in SANS.


cerebrospinal fluid, CSF outflow, lymphatics, microgravity, near‐infrared fluorescence imaging, neurodegeneration


PMID: 32097544



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.