Dynamic Renal Blood Flow Autoregulation During Recovery From Acute Kidney Injury (AKI)

Background If efficiency of RBF autoregulation is impaired during recovery from AKI, then the recovering kidney would be susceptible to recurrent injury from fluctuating blood pressure or nerve traffic. Hence, it is worthwhile to know about RBF autoregulation in the injured kidney for someone prescribing treatments to patients with AKI that impinge on systemic hemodynamics, such as hemodialysis. Methods Wistar rats were subjected to 60 minutes of bilateral renal ischemia and studied again after 1, 7, or 28 days (4–7 animals per group). GFR was measured by inulin clearance and while RBF (Transonics flow probe) and BP (arterial catheter) were recorded for 2 hours at 1Hz. Time series were used to calculate admittance gain from short‐term Fourier transforms, and autoregulatory step responses in the time domain by a method of moving averages. Results RBF returned to baseline within 1 day of ischemia‐reperfusion, while GFR normalized some time between the 1 and 4 week time points. Step responses reveal the RBF autoregulation was less efficient at the 1 and 7 day time points when GFR was low but was nearly normal at 4 weeks into renal recovery. Tubuloglomerular feedback (TGF) signatures (resonance in the admittance gain around 0.03 Hz and transient overshoot in the step response at ~ 30 seconds) were missing while the GFR was low, but were restored at 4 weeks when GFR had returned to normal. Admittance gain shown in figure where TGF and myogenic resonance peaks denoted. Step responses shown without error bars for clarity, but the major apparent intergroup differences were significant. Conclusion The findings are consistent with prior prediction that RBF autoregulation should be less efficient in the absence of a varying TGF signal, which is necessarily the case when GFR is low. A caveat is that, while the spontaneous BP power was good enough to yield robust admittance functions and step responses, these studies don't address the response to large BP disturbance, where the deficit in autoregulation could be more profound. Additional experiments with BP forcings would be required for that. Support or Funding Information Department of Veterans Affairs