2014: Peter Sleight, Oxford, Storbritannien

”Reflex Cardiovascular Control in Man”

Baroreflex control of long term blood pressure It had earlier been proposed (by AC Guyton & others) that arterial baroreflex mechanisms were mainly involved in short term beat to beat blood pressure (BP) control, but not longer-term levels of pressure. At that time it was not known that the arterial baroreflexes had effects on sodium & water elimination via renal nerves, as well as the more easily demonstrated effects on heart rate, cardiac contractility, & peripheral vascular tone. 40 years or so later on a US surgeon, Terry Thrasher, showed that chronic change in pressure in the isolated carotid artery pressure in the dog caused nervously mediated renal sodium retention & thus sustained BP change. Interventions to control blood pressure 60 years ago RH Smithwick published a report on over 1000 patients which showed that it was possible to lower malignant hypertension in man by splanchnic denervation. However this was accompanied by severe postural hypotension, so it had only limited application to very severe hypertension. A later more physiologic surgical approach used chronic stimulation of the carotid sinus nerves (CSN) by an implantable device, & so avoided postural hypotension. Although this was initially successful, longer-term results were marred by damage to the carotid sinus nerve or its blood supply. New methods of CSN stimulation in man are now successful long term, by using stimulation of the receptors by electrodes applied to the adventitia of the sinus. An alternative (or perhaps additional) treatment is the use of renal denervation - effected by electrical denervation of the kidneys, applied by a catheter introduced percutaneously from the groin into each renal artery. Esler & colleagues in Melbourne showed impressive long lasting BP reduction in patients with drug resistant hypertension, & so this technique was rapidly taken up by cardiologists. However in the US the food & drug administration would not approve the method for clinical use without a blinded controlled randomised trial. In January 2014 G. Bakris, the chair of this study, announced to great astonishment that this trial (Symplicity-3) was negative! Preliminary results will be given at the American College of Cardiology meeting at the end of March 2014. So the jury is unexpectedly out, awaiting the full published details. Conclusion Hypertension treatments have multiplied over the last 40-50 years. But many patients fail to continue treatment long-term, due to side effects or cost. There are now potentially very practical physiological alternatives to drug treatment of human hypertension.