Rat muscle microvascular PO2 kinetics during the exercise off-transient

Dependent upon the relative speed of pulmonary oxygen consumption ((V) over dot o(2)) and blood now ((Q) over dot kinetics, the exercise off-transient may represent a condition of sub- or supra-optimal perfusion. To date, there are no direct measurements of the dynamics of the (V) over dot o(2)/(Q) over dot relationship within the muscle at the onset of the work/recovery transition. To address this issue, microvascular Po-2 < Po-2,m) dynamics were studied in the spinotrapezius muscles of 11 female Sprague-Dawley rats (weight <similar to>220 g) during and following electrical stimulation (1 Hz) to assess the adequacy of (Q) over dot relative to o(2), post exercise. The exercise blood flow response (radioactive microspheres: muscle (Q) over dot increased similar to 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 Po-2,m (i.e. off-transient) rose progressively until baseline values were achieved (Delta end-recovery exercise Po-2,m 14.0 +/- 1.9 Torr) and at no time fell below exercising PO?,m The off-transient Po-2,m was well fitted by a dual exponential model with both fast (tau = 25.4 +/- 5.1 s) and slow (tau = 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 (V) over dot O-2, falls with faster kinetics than muscle (Q) over dot during the off-transient, such that Po-2,m increases systematically, though biphasically, during recovery.