Blood flow in exercising muscles by xenon clearance and by micropshere trapping

The accuracy of muscle blood flow measurement by the ¹³³Xe clearance method (Q̇Xe) was assessed against direct venous outflow (Q̇v) and microsphere trapping flow (Q̇μ) determinations in isolated perfused dog gastrocnemius both at rest and during graded stimulation [O₂ consumption (V̇O₂) up to 12 ml.100 g^-1.min^-1] and in the gastrocnemius, vastus lateralis, and triceps of intact dogs at rest and while running on a treadmill at varied speeds up to maximum V̇O₂. In 29 measurements performed in 11 isolated muscles, Q̇μ was in good agreement with Q̇v at rest and at all stimulation levels (Q̇μ/Q̇v = 1.0; r = 0.98). ¹³³Xe clearance yielded musch lower blood flows than the venous outflow and the microsphere trapping methods. In 43 measurements in 11 muscles, the mean Q̇Xe/Q̇v ratio was 0.57 ± 0.03 (SE), independent of blood flow. Similarly, in 65 measurements in 2 intact dogs, the mean Q̇Xe/Q̇μ ratio in all tested muscles was 0.49 ± 0.02 (SE), independent of blood flow. These results show that the ¹³³Xe clearance method considerably underestimates blood flow in dog muscles.