Rat muscle microvascular Po2 kinetics during the exercise off-transient

Abstract

Dependent upon the relative speed of pulmonary oxygen consumption (Vo2) and blood flow (Q) kinetics, the exercise off-transient may represent a condition a condition of sub- or supra-optimal perfusion. To date, there are no direct measurements of the dynamics of the Vo2/Q relationship within the muscle at the onset of the work/recovery transition. To address this issue, microvascular Po2 (Po2,m) dynamics were studied in the spinotrapezius muscles of 11 female Sprague-Dawley rats (weight Ο220 g) during and following electrical stimulation (1 Hz) to assess the adequacy of Q relative to Vo2 post exercise. The exercise blood flow response (radioactive microspheres: muscle Q increased ∼240%), and post-exercise arterial blood pH (7.40 ± 0.02) and blood lactate (1.3 ± 0.4 mM l-1) values were consistent with moderate-intensity exercise. Recovery Po2,m (i.e. off-transient) rose progressively until baseline values were achieved (Δend-recovery exercise PO2,m 14.0 ± 1.9 Torr) and at no time fell below exercising Po2,m. The off-transient Po2,m was well fitted by a dual exponential model with both fast (τ = 25.4 ± 5.1 s) and slow (τ = 71.2 ± 34.2 s) components. Furthermore, there was a pronounced delay (54.9 ± 10.7 s) before the onset of the slow component. These data, obtained at the muscle microvascular level, support the notion that muscle Vo2 falls with faster kinetics than muscle Q during the off-transient, such that Po2,m increases systematically, though biphasically, during recovery.