Continuous measurements of renal perfusion in pigs by means of intravascular Doppler

Background. Changes in renal blood flow are considered to play a significan t role in the induction and maintenance of kidney failure, but are difficul t to monitor with currently available techniques. The objective was to vali date renal flow measurements with Doppler guidewires and to apply this tech nique to assess dose and time dependency of the renal vascular effects of n orepinephrine (NE). Methods. In 10 anesthetized pigs, flow velocity in renal arteries (FVart) a nd veins (FVvein) and volumetric renal blood flow (VBF) were measured befor e and after intravenous bolus application of incremental doses of NE (2 to 200 mug). Results. FVart curves exactly reflected the changes in VBF. Beat-to-beat an alysis revealed a strong linear correlation over a mean VBF range of less t han 0.05 to 0.35 L/min (median correlation coefficient with FVart, I = 0.99 8), and significant but less close relationships were also found between VB F and FVvein. Ten seconds after the administration of 200 mug NE, FVart dro pped from 71 to 6 cm/sec and was 90% reversible after 45 seconds. Similarly , the renal vascular resistance temporarily rose from 988 to 13711 mm Hg . min/L. In contrast, NE-induced increases in systemic vascular resistance we re on average a maximum of 1.5-fold but persisted for more than 60 seconds. Conclusions. Doppler flow measurements in the renal artery provide an excel lent surrogate of volumetric blood flow, which may be useful for continuous monitoring of renal hemodynamics. The renal vasculature is more sensitive when compared with the systemic vasculature, but also appears to evoke more efficient counter-regulatory mechanisms in response to NE.