Podcast Summary

Welcome to Dr. Warrick's podcast channel. Warrick is a practicing cardiologist and author with a passion for improving care by helping patients understand their heart health through education. Warrick believes educated patients get the best health care. Discover and understand the latest approaches and technology in heart care and how this might apply to you or someone you love. Hi, my name is Dr. Warrick Bishop and I'd like to welcome you to my podcast and videocast station and of course to the Healthy Heart Network. Today I'd like to talk about a medical condition called renal artery stenosis. Don't expect you to remember that, but it is an interesting one and I'll tell you why. going to a kidney. Narrowing, stenosis, we use those words interchangeably. Renal artery, obviously the artery supplying the kidney. Now remember that about 25% of all the blood pumped from the heart in the resting state goes through the kidneys. So they're an incredibly vascular dependent organ and we need them to be functioning and filtering all the time to maintain all the fluid balance and the iron balance and remove toxins and waste so really important that they're constantly getting good blood flow so that they can constantly filter and look after the needs of our body filtering away the excess fluid and the waste products. If we now think about one artery going to one kidney remember we've got two of course one either side in our loins basically where they're located and the arteries come off the main artery in the body called the aorta. But if we think about one artery going to one kidney and put a narrowing in the middle of that, then we can start to think about what the kidney must be feeling and how it responds to that. Let's think it through. If we narrow that artery to such an extent that it feels like their blood flow is reduced to the kidney then the kidney receptors which assess blood pressure and flow think that the body must be deplete on fluid therefore low blood pressure possibly related to blood loss the sort of thing that we've been evolved to deal with if we were to have a cut or an injury in our evolutionary past we would restore that blood volume lost by retaining fluid and we keep our kidneys working by tightening up blood vessels through the body and making sure that our blood pressure stays up. Well in the setting of renal artery stenosis if our artery is narrowed and reducing flow significantly then the kidney recognizes that and the the receptors within the kidney around where the filtration unit is the juxtaglamegular cells you don't need to remember that it's a mouthful but the cells that regulate and monitor pressure into the filtration unit of the kidney realize that there's a problem and and they respond to try and make sure the body keeps up its filtration rate so that the body doesn't become toxic. Remember the other kidney and the rest of the body are currently working fine. It's just this single kidney with the artery that's narrowed to it is acting, if you like, unilaterally by itself because it doesn't know any different. It's acting on the signals it's being given by the reduced blood flow. So the kidney feeling it's had reduced blood flow releases renin, which is one of the hormones released by the juxtaglomerular cells. Renin is part of a process that starts to convert other hormones in the bloodstream to convert angiotensin 1 to angiotensin 2. And angiotensin 2 is a hormone that leads to constriction. of blood vessels in the body to raise the blood pressure and angiotensin too also constricts the blood vessels on the other side of the filtration unit of the kidney. So the blood rolls into the filtration unit of the kidney well but if you close the exit artery or tighten off that exit artery by doing that you're increasing pressure within the filtration unit. the glomerulus and therefore maintaining filtration. There's also autonomic nerve stimulation from the same process keeping blood pressure up. Well now you've figured it out this renal artery stenosis can be a significant cause of raised blood pressure and often in patients particularly young patients who have significant elevation of blood pressure which is difficult to control. then we will look for renal artery stenosis. We can see it actually in a group of patients where it's called fibromuscular dysplasia. You don't need to remember that, but it's really just a process of fibrosis and narrowing within the muscles, often within middle-aged women. So quite a specific group. We can also see it in the elderly as atherosclerosis or plaque buildup can narrow. the renal arteries so a really interesting condition and the other thing that's really interesting about it is it sort of mimics some of the body's responses that we see if someone's got cardiac failure except when it's cardiac failure both kidneys have a decreased blood flow to them a decreased blood pressure and both kidneys respond but again what they're doing is trying to put in place mechanisms to maintain the filtration rate so that the toxins of the body get filtered away and the waste products taken away in the urine. There is one interesting situation which is probably worth touching on because it really just highlights the point and that is that if we have the unusual situation of bilateral renal artery stenosis meaning that it's occurring in both major arteries on both the left and the right side kidneys if that's occurring and we treat those individuals with agents that block the angiotensin 2 receptor which is the angiotensin converting enzyme inhibitors or ACE inhibitors or angiotensin 2 blockers then these agents work so well that they block the effects of that raised renin and angiotensin system they lead to relaxation of the artery that's downstream of the filtration system so as that artery is opened up the pressures within the filtration unit are diminished and so the filtration rate of the kidneys now drops and if that occurs on both sides the addition of these medications in patients with high difficult to treat blood pressure can lead to a precipitous and significant and concerning drop in their renal function. It is one to keep in mind it's pretty uncommon but certainly as doctors if we're adding in agents and we're adding agents particularly of that type if there's a sudden and precipitous drop in the renal function it may be through renal artery stenosis. Well an interesting little vignette on a particular and specific cause of high blood pressure one that we need to be aware of and certainly one that if it's bilateral gives rise to a significant outcome that we we should pick up if we're checking our blood tests regularly after the addition of these sort of medications. Okay well that's renal artery stenosis it's not that common it is a cause of quite elevated blood pressure it's normally on one side we see it in women with a condition called fibromuscular dysplasia sometimes we see it in older people with atherosclerosis or plaque where the plaque is narrowing the renal artery in the rare situation bilateral renal artery stenosis then the responses by the kidneys the renin angiotensin system and aldosterone system are blocked by the ACE inhibitors and the AT2 blockers with a detrimental effect on the filtration of the kidney. A lot to take on board, but fascinating really. Hope you've enjoyed it. If you have any queries or questions, as always, drop us a note at members at drWarrickbishop.online. If you've got any suggestions for future podcasts, same email address, let us know. I hope you found renal artery stenosis interesting. For now, until next time, I wish you the very best and please don't die from a heart attack. Goodbye. 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