A simple method to ensure homogeneous drug distribution during intrarenal infusion

In vivo mapping of hemodynamic responses mediated by tubuloglomerular feedback in hypertensive kidneys

The kidney has a sophisticated vascular structure that performs the unique function of filtering blood and managing blood pressure. Tubuloglomerular feedback is an intra-nephron negative feedback mechanism stabilizing single-nephron blood flow, glomerular filtration rate, and tubular flow rate, which is exhibited as self-sustained oscillations in single-nephron blood flow. We report the application of multi-scale laser speckle imaging to monitor global blood flow changes across the kidney surface (low zoom) and local changes in individual microvessels (high zoom) in normotensive and spontaneously hypertensive rats in vivo. We reveal significant differences in the parameters of TGF-mediated hemodynamics and patterns of synchronization. Furthermore, systemic infusion of a glucagon-like-peptide-1 receptor agonist, a potential renoprotective agent, induces vasodilation in both groups but only alters the magnitude of the TGF in Sprague Dawleys, although the underlying mechanisms remain unclear.

Synchronization in renal microcirculation unveiled with high-resolution blood flow imaging

Internephron interaction is fundamental for kidney function. Earlier studies have shown that nephrons signal to each other, synchronise over short distances, and potentially form large synchronised clusters. Such clusters would play an important role in renal autoregulation, but due to the technological limitations, their presence is yet to be confirmed. In the present study, we introduce an approach for high-resolution laser speckle imaging of renal blood flow and apply it to estimate frequency and phase differences in rat kidney microcirculation under different conditions. The analysis unveiled spatial and temporal evolution of synchronised blood flow clusters of various sizes, including the formation of large (>90 vessels) long-lived clusters (>10 periods) locked at the frequency of the tubular glomerular feedback mechanism. Administration of vasoactive agents caused significant changes in the synchronisation patterns and, thus, in nephrons' co-operative dynamics. Specifically, infusion of vasoconstrictor angiotensin II promoted stronger synchronisation, while acetylcholine caused complete desynchronisation. The results confirm the presence of the local synchronisation in the renal microcirculatory blood flow and that it changes depending on the condition of the vascular network and the blood pressure, which will have further implications for the role of such synchronisation in pathologies development.

Real-time visualization of renal microperfusion using laser speckle contrast imaging

SIGNIFICANCE

Intraoperative parameters of renal cortical microperfusion (RCM) have been associated with postoperative ischemia/reperfusion injury. Laser speckle contrast imaging (LSCI) could provide valuable information in this regard with the advantage over the current standard of care of being a non-contact and full-field imaging technique.

AIM

Our study aims to validate the use of LSCI for the visualization of RCM on ex vivo perfused human-sized porcine kidneys in various models of hemodynamic changes.

APPROACH

A comparison was made between three renal perfusion measures: LSCI, the total arterial renal blood flow (RBF), and sidestream dark-field (SDF) imaging in different settings of ischemia/reperfusion.

RESULTS

LSCI showed a good correlation with RBF for the reperfusion experiment (0.94  ±  0.02; p  <  0.0001) and short- and long-lasting local ischemia (0.90  ±  0.03; p  <  0.0001 and 0.81  ±  0.08; p  <  0.0001, respectively). The correlation decreased for low flow situations due to RBF redistribution. The correlation between LSCI and SDF (0.81  ±  0.10; p  <  0.0001) showed superiority over RBF (0.54  ±  0.22; p  <  0.0001).

CONCLUSIONS

LSCI is capable of imaging RCM with high spatial and temporal resolutions. It can instantaneously detect local perfusion deficits, which is not possible with the current standard of care. Further development of LSCI in transplant surgery could help with clinical decision making.

Choroidal Ischemia Sparing the Watershed Zone following Intra-Arterial Chemotherapy for Retinoblastoma

Purpose

Intra-arterial chemotherapy (IAC) has become a mainstay in the management of retinoblastoma, especially in advanced or refractory disease. However, IAC is not without complications, and chemotherapy toxic effects can lead to partial or complete choroidal ischemia, often causing vision loss.

Methods

This is a case report.

Results

A 4-month-old girl with bilateral retinoblastoma was treated with secondary IAC (melphalan 5 mg) for recurrent tumor following intravenous chemotherapy. One month later, complete tumor control was achieved. However, she demonstrated broad choroidal ischemia in the nasal and temporal quadrants but sparing of the watershed zone superior and inferior to the optic disc and in the papillomacular region. Fluorescein angiography revealed poor perfusion of the choriocapillaris with visibility of the large choroidal vessels in the nasal and temporal areas but preserved perfusion of the watershed zone. The watershed zone remained intact on the 10-month follow-up, and the final visual acuity was fix and follow without strabismus.

Conclusion

The pathophysiology of choroidal ischemia is not well understood, but the fortuitous watershed zone preservation in this case could represent uneven distribution of the chemotherapeutic drug, resulting in partial chemo-dilution of the medication in the watershed region, which represents the final downstream overlapping choroidal perfusion from both medial and lateral posterior ciliary arteries.