Background
Disturbances in renal microcirculation play an important role in the pathophysiology of chronic kidney disease (CKD), but the lack of easy accessible techniques hampers our understanding of the regulation of the renal microcirculation in humans. We assessed whether contrast-enhanced ultrasonography (CEUS) can identify differences in cortical perfusion and alterations induced by different dietary salt intakes in CKD patients and controls.
Methods
Participants underwent CEUS twice: once after 5 days of high salt intake (HS), and again after 5 days of low salt diet (LS). Sonovue® (0.015 ml/kg/min) was perfused as contrast agent and four consecutive destruction-reperfusion sequences were analyzed per visit. Primary outcome measure was the (change in) mean perfusion index (PI) of the renal cortex.
Results
Forty healthy volunteers (mean age±SD 50±8 years) and 18 CKD stage 2-4 patients (aged 55±11 years, eGFR 54±28 ml/min/1.73m²) were included and underwent CEUS without side effects. Under HS conditions, cortical PI was significantly lower in CKD patients (1618±1352 vs 3176 ±2278 arbitrary units in controls, p = 0.034). Under LS, renal PI increased in CKD patients (with +1098 to 2716 ±1540 a.u., p = 0.048), whereas PI remained stable in controls. In continuous analysis, PI correlated with eGFR (spearman's r = 0.54, p = 0.005) but not with age, sex, blood pressure or aldosterone levels.
Conclusion
CEUS identified important reductions in cortical micro-perfusion in patients with moderate CKD. Lowering salt intake increased perfusion in CKD patients, but not in controls, underlining the benefits of a low salt diet in CKD patients. Whether a low perfusion index is an early sign of kidney damage and predicts renal function decline needs further study.
BackgroundRenal microcirculation is essential for regulation of the glomerular filtration rate, the reabsorption of salt and water from the interstitium, and hence the blood pressure. Renal ultrasonography coupled to Doppler analysis and contrast-enhanced ultrasound enables the study of renal perfusion. So far, physiologic interventions have rarely been performed to assess the renal perfusion. The objective of our study was to measure the renal perfusion in response to a cold pressor test (CPT).MethodsHealthy adult participants were exposed to a 2 min CPT or a sham exposure (body temperature). Systemic hemodynamics, renal resistive index (RRI) and renal perfusion index (PI) were measured before and during the CPT or the sham exposure. Renal responses were compared using a paired Student's t-test or Wilcoxon signed rank test. Pearson correlation test was used to test association of variables of interest.ResultsForty-one normotensive participants (21 women) were included in the study. Mean blood pressure and heart rate both increased with the CPT. The RRI decreased from 0.60 ± 0.05 arbitrary units (AU) to 0.58 ± 0.05 AU (p < 0.05) and the PI increased from 2,074 AU (1,358–3,346) to 3,800 AU (2,118–6,399) (p < 0.05) (+66% (24–106%)). Compared to the sham exposure, the increase in PI with the CPT was more marked. There was a negative association between the increase in heart rate and mean blood pressure with the RRI (r: −0.550, p = 0.002 and r: −0.395, P = 0.016), respectively.ConclusionDoppler Ultrasound and CEUS enable the detection of physiological changes within the macro- and microvascular renal circulation. The CPT decreases the RRI and increases the PI. Whether these changes are present in pathological states such as diabetes or hypertension will need additional studies.
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