Optical tracer size differences allow quantitation of active pumping rate versus Stokes-Einstein diffusion in...

Area of Science:

• Biomedical Engineering
• Physiology
• Medical Imaging

Background:

• Lymphatic transport involves passive uptake driven by interstitial gradients and active propulsion via vessel contractions.
• Understanding these processes is crucial for diagnosing and treating lymphatic disorders.

Purpose of the Study:

• To quantitatively measure passive and active lymphatic transport components using novel imaging techniques.
• To differentiate the size-dependent nature of passive uptake versus the size-independent nature of active propulsion.

Main Methods:

• Utilized near-infrared fluorescence imaging in mice to track two differently sized molecules: methylene blue (MB) and immunoglobulin G (IgG).
• Analyzed temporal imaging data to estimate parameters like time-to-peak signal, signal intensity, and lymphatic vessel contraction rates (peristaltic pulses).

Main Results:

• Passive uptake, indicated by time-to-peak signal, was size-dependent (0.6 min for MB vs. 8 min for IgG).
• Active lymphatic propulsion rates were similar for both molecules (approx. 3.4 pulses/min) and decreased with distance from the injection site.
• Propulsion rates showed size independence, suggesting intrinsic smooth muscle control influenced by interstitial pressure.

Conclusions:

• Developed a method to separate and quantify passive and active lymphatic transport mechanisms.
• Demonstrated that lymphatic uptake is influenced by molecular size, while propulsion is not.
• This imaging approach can aid in noninvasively characterizing lymphatic diseases affecting uptake and flow.