A comparative study: perfusion of the micro- and macrocirculation as a function of the hematocrit value

Area of Science:

• Biophysics
• Physiology
• Microcirculation Research

Background:

• Understanding red blood cell (RBC) suspension fluidity is crucial for comprehending blood flow dynamics in microcirculation.
• In vivo measurements offer a more accurate representation of RBC behavior compared to in vitro methods.

Purpose of the Study:

• To compare in vivo and in vitro measurements of red blood cell (RBC) suspension fluidity.
• To investigate the influence of hematocrit, perfusion pressure, and aggregation on RBC fluidity in the microvasculature.

Main Methods:

• Utilized microcirculatory measurements (RBC velocity, micropressure, vessel geometry) and macrocirculatory data (volume flow, perfusion pressure) in isolated rat mesentery.
• Employed microscopy with a video TV system to record microcirculatory perfusion under varying conditions.
• Compared in vivo data with in vitro viscometry results using human RBCs in Ringer's or Ficoll solutions.

Main Results:

• In vivo microfluidities correlated strongly with macroflow-derived fluidities.
• RBC fluidity decreased with increasing hematocrit but was independent of driving pressure (4-10 kPa).
• In vivo fluidities were higher than in vitro measurements, particularly at higher hematocrit values and specific shear stresses.

Conclusions:

• Microcirculatory and macrocirculatory measurements provide consistent estimates of in vivo RBC fluidity.
• Factors like high hematocrit, low perfusion pressure, and increased RBC aggregability can lead to vessel stagnation.