Microvessel hematocrit: measurement and implications for capillary oxygen transport

Area of Science:

• Physiology
• Microcirculation Research
• Hematology

Background:

• Understanding red blood cell distribution in microcirculation is crucial for physiological studies.
• Hematocrit, a measure of red blood cell volume, can be assessed systemically, within microvessels, or upon discharge.

Purpose of the Study:

• To investigate the relationship between systemic, tube, and discharge hematocrit in microvascular networks.
• To determine if red cell distribution is uniform across different microvessel types and sizes.

Main Methods:

• Utilized microvascular preparations from hamster cheek pouch and cremaster muscle.
• Measured systemic hematocrit from toe clip blood samples.
• Quantified tube hematocrit within microvessel segments and discharge hematocrit from micropipette collections.

Main Results:

• Tube hematocrit was found to be low and highly variable, contrasting with a stable systemic hematocrit.
• Discharge hematocrit consistently approximated systemic hematocrit in arterioles and venules (6-98 micron diameter).
• The ratio of discharge to systemic hematocrit did not significantly differ from unity, supporting uniform red cell distribution.

Conclusions:

• Red blood cells are uniformly distributed across capillary networks.
• Variations in tube hematocrit may reflect changes in effective capillary flow cross-section rather than inflow hematocrit.
• Microvessel anatomical volume may differ from the volume available for cell and plasma flow.