Employing high-speed camera laser-scanning confocal microscopy with RBC-tracking software,
we previously showed that RBC velocities in intraparenchymal capillaries of rat cerebral
cortex are distributed over a wide range. In the present work, we measured RBC velocities
in mice, whose body weights are less than one-tenth of that of rats. In an isoflurane-anesthetized
mouse, a cranial window was opened in the left temporo-parietal region. Intravenously
administered FITC-labeled RBCs were automatically recognized and tracked frame-by-frame
at 500fps, and the velocities of all RBCs recognized were calculated with our Matlab-domain
software, KEIO-IS2. Among 15241 RBCs detected in the ROI in 21 mice, 1655 were identified
as flowing in capillaries. The velocities of these RBCs ranged from 0.15 to 8.6mm/s,
with a mean of 2.03+/-1.42mm/s. A frequency distribution plot showed that RBC velocities
were clustered at around 1.0mm/s, tailing up to 8.6mm/s, and 59% of the RBCs in capillaries
showed velocities within the range of 0.5 to 2.0mm/s. Unexpectedly, these characteristics
of RBC velocities in mice were very similar to those of rats, despite differences
in RBC diameter (6.0 vs. 6.5microm), body size (25 vs. 327g), heart rate (461 vs.
319bpm) and arterial blood pressure (86 vs. 84mmHg). We speculate that physical factors
relating to oxygen exchange may constrain general RBC velocity in capillaries to a
certain range for optimum oxygen exchange, regardless of species.
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