In vivo manipulation and continuous measurement of muscle blood flow with venous effluent sampling

1. An acute in vivo hindlimb skeletal muscle preparation was developed in a naesthetized sheep in order to facilitate studies of the effects of altered blood flow states on drug kinetics in skeletal muscle. 2. A continuous index of blood flow was recorded via ultrasonic Doppler pro bes on the femoral artery and vein. Skeletal muscle effluent blood was samp led via a catheter in the femoral vein proximal to the probe. Low- and high -blood flow states were achieved by direct femoral artery infusion of adren aline (0.002-0.006 mg/min) or magnesium (0.4-1 mmol/min), which produced me an (+/- SD) stable flow states of 25 +/- 12 and 185 +/- 56% (both n = 5) of baseline, respectively. The correlation coefficients between arterial and venous Doppler frequency shifts in five sheep during and after adrenaline i nfusion were 0.96 (indicating these vessels probably supplied and drained c ommon tissue). 3. The venous Doppler frequency shifts were calibrated against timed collec tions of the femoral vein outflow to provide estimates of the low and norma l blood flow states (mean flows of 2.8 +/- 1.7 and 9.3 +/- 5.7 mL/100 g per min; both n = 3) and against an indirect Kety-Schmidt method during low- a nd high-blood flow states (mean flows of 2.2 +/- 1.3 and 18.2 +/- 7.0 mL/10 0 g per min; both n = 5). There was a generally good agreement between the two methods. 4. The tissue was neither hypoxic nor acidotic in the low- or high-flow sta tes and altering the flow produced no change in muscle oxygen consumption, suggesting the flow changes were largely due to changes in resistance vesse l tone. 5. Postmortem femoral artery dye injection and dissection of stained tissue s showed the artery supplied 657 +/- 96 g (n = 5) of skeletal muscle and 42 +/- 20 g (n = 5) of other tissues. 6. It is concluded that the method is suitable for sampling predominantly m uscle effluent blood at low- or high-blood flow states according to experim ental requirements.