FEASIBILITY OF DETERMINING DYNAMIC RENAL AUTOREGULATION IN HUMANS USING COMBINED INTRARENAL PRESSURE AND FLOW MEASUREMENTS

Abstract

Objective: Renal autoregulation is important for maintenance of renal perfusion, glomerular filtration and may be of prognostic value in hypertensive-induced kidney damage. In animal models, transfer function analysis of spontaneous blood pressure fluctuations has been used to assess the (patho)physiology of renal autoregulation. Our aim was to determine the feasibility of measuring renal autoregulation in humans using combined intrarenal pressure and flow measurements. Design and method: We performed intrarenal pressure and flow velocity measurements in clinically stable patients with an indication for renal or coronary angiography, aged 18–75 and with eGFR > 45 ml/min/1.73m2. Measurements were conducted at baseline and under hyperaemia following intrarenal injection of dopamine 30 μgram/kg. Transfer function analysis was performed on the beat-to-beat pressure and flow data. Autoregulation was assessed by the time difference between the peaks in the pressure and flow signal, and was quantified as the average phase difference over the manually selected coherent peak around the sympathetic frequency (period 6 to 14 seconds).Results: We included 21 patients, of which assessment of autoregulation was successful in 11 patients. In the remaining group it was not possible to find a coherent signal, mostly due to lack of blood pressure variations in the sympathetic frequency domain. During baseline, the mean phase difference was 32 degrees (range 11 to 45 degrees), where flow leads pressure. Under hyperaemia, in 7 patients the phase difference could be determined, which showed a reduction to a phase difference of 10 degrees (range −12 to19 degrees, p = 0.003 compared to baseline). An example of the spectrum before and after infusion of dopamine is shown in Figure A. The individual phase differences at baseline and under hyperaemia are shown in Figure B. Conclusions: Measurement of renal autoregulation in humans is feasible provided that patients have sufficient spontaneous blood pressure variations. The disappearance of renal autoregulatory responses during dopamine infusion may provide useful information regarding the degree of induced hyperaemia.