Carbon Dioxide Concentration Alters the Dynamics of Oxygen‐Mediated Capillary Blood Flow Responses in Skeletal Muscle
Alexander Folkins, Gaylene M. Russell McEvoy, Graham M. FraserABSTRACT
Hypothesis
We hypothesize that the dynamics of O 2 ‐mediated blood flow responses in skeletal muscle capillaries are altered under different tissue carbon dioxide concentrations ([CO 2 ]) due to the interaction of overlapping mechanisms.
Methods
Eight male Sprague Dawley rats (164–215 g) were anesthetized and instrumented for systemic monitoring. The extensor digitorum longus muscle was isolated and reflected over a microfluidic gas exchange chamber mounted in an inverted microscope stage. 4‐min intravital video recordings of capillary blood flow during O 2 challenges consisted of a 1‐min baseline at 7% O 2 concentration ([O 2 ]), followed by 3 min at 2% [O 2 ], under constant background [CO 2 ] at 2%, 5%, and 8%. Recordings were analyzed offline using custom MATLAB software. Time transients (τ) of capillary hemodynamic responses were determined using a least squared regression fit to single‐ and double‐exponential models.
Results
Fast component τ of the O 2 ‐mediated capillary red blood cell (RBC) velocity response was 2.1 s for 2% [CO 2 ], 3.8 s for 5% [CO 2 ], and 7.0 s for 8% [CO 2 ]. Third minute low [O 2 ] capillary RBC supply rate increases from baseline were greater for 8% [CO 2 ] (5% [CO 2 ]: 6.4 ± 8.7 cells/s vs. 8% [CO 2 ]: 8.5 ± 10.7 cells/s, p = 0.0007).
Conclusion
The fast component τ of O 2 ‐mediated capillary hemodynamic responses was found to be slower with increasing background tissue [CO 2 ], suggesting that multiple interacting mechanisms are involved to appropriately regulate O 2 delivery under different CO 2 conditions in partial support of the hypothesis.