Physiology: Neural Control of Renal Function
An increase in arterial pressure (CO * PR) leads to an increased Una and water excretion via the pressure natriuresis mechanism, with consequent reduction in blood volume until arterial pressure is returned to normal. Factors that decrease renal excretory function and disrupt the above balance by the kidneys lead to an increase in arterial pressure.
Kidney is supplied by T9-T13 nerves leaving the spinal cord and then traversing through sympathetic ganglia to reach the kidney hidden in adventitia of renal vasculature. These nerves are divided into ERSNA (Efferent renal sympathetic Nerve system) to the kidney and afferent nerves from the kidney to the brain (ARSNA). These nerves when fire will cause renal vasoconstriction, increased tubular absorption of sodium, increased Renin Angiotensin System stimulation and reduced GFR (remember these are sympathetic nerves and will do everything they can to maintain/increase blood pressure).
So if you would denervate the kidneys it should result in natriuresis, increased GFR and blood pressure reduction. Cutting the afferent nerve supply to brain would further reduce systemic sympathetic outflow by brain centers.
Trial
Recently, by adrian pharmaceuticals has designed a radiofrequency catheter for ablating nerve supply to renal artery for treatment resistant hypertension.
Multicentre, prospective, randomised trial, patients 18- 85 yrs who had a baseline SBP of 160 mm Hg or more (≥150 mm Hg for patients with type 2 diabetes), despite taking ≥ 3 antihypertensive drugs, were randomly allocated in a one-to-one ratio to undergo renal denervation with previous treatment or to maintain previous treatment alone .
Patients were on average 5.2 medications with e GFR of 77ml/min (many of whom were between 45-60ml/min) were followed for 1 year.
Office based blood pressure measurements in the renal denervation group reduced by 32/12 mm Hg (SD 23/11, baseline of 178/96 mm Hg, p<0.0001), whereas they did not differ from baseline in the control group (change of 1/0 mm Hg [21/10], baseline of 178/97 mm Hg, p=0.77 systolic and p=0.83 diastolic)
Between-group differences in blood pressure at 6 months were 33/11 mm Hg (p<0.0001). At 6 months, 41 (84%) of 49 patients who underwent renal
denervation had a reduction in systolic blood pressure of 10 mm Hg or more, compared with 18 (35%) of 51 controls (p<0.0001).
No serious procedure-related or device-related complications happened.
Occurrence of adverse events did not differ between groups; one patient who had renal denervation had possible progression of an underlying atherosclerotic lesion, but required no treatment.
In Australia and Europe, renal denervation with the Symplicity catheter has received regulator approval and is now entering clinical practice. A US-based trial is planned for the near future, larger than the present one, which will include patients of differing ethnic origin.
Long term follow up at the end of two years should soon be out in press.
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