Variability of partial pressures of CO₂ and O₂ in resting skeletal muscle

We measured tissue P_CO2 and P_O2 in resting skeletal muscles of rats by two gasometric techniques: Gas pockets in contact with the tissue were formed, and small amounts of gas enclosed in 200 μm diam glass capillary tubes were inserted into the tissue. Average P_O2 and variability of P_O2 were essentially the same as usually found with microelectrodes. The P_CO2 varied also, and tended to be reciprocally related to P_O2. Since CO₂ gradients within a single capillary domain are expected to be negligible, these findings are evidence that there is regional variability in the ratio of local perfusion, Q ̇, to local metabolism, q ̇. Variation in the Q ̇ q ̇ ratio is evidence that Q ̇ and q ̇ are not as tightly coupled as would be expected if one were the sole determinant of the other.