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How hypertension affects kidneys and vice versa

How hypertension affects kidneys and vice versa

The vicious loop of BP leading to renal damage and faulty kidneys triggering hypertension

Unregulated high blood pressure can damage the kidneys

The term hypertension or high blood pressure invokes images of a quick-pounding heart or a throbbing, pulsating brain in most people. They seldom imagine that high blood pressure and kidney disease could have a serious impact on their renal health.

Technically, it is quite simple since kidneys are literally a blood-treatment plant responsible for filtering the blood flowing across our body. However, research has revealed an unhealthy nexus between hypertension and renal conditions that could lead to serious health complications if left unmonitored.

Nephrologists told Happiest Health that unregulated and prolonged high blood pressure could result in serious kidney damage. They said serious renal complications could result in soaring blood pressure, often termed secondary hypertension since it is triggered by separate existing medical conditions (including renal, heart or diabetes-related complications).

High blood pressure and kidney issues

According to Dr Atul Ingale, consultant nephrologist and transplant physician, director, department of nephrology, Fortis Hiranandani Hospital, Vashi, Navi Mumbai, most people have the ingrained belief that heart attacks and brain strokes are the primary blood pressure-related adverse conditions and they tend to ignore how BP (blood pressure) could affect the rest of our organs.

“We should remember that blood travels throughout our vascular system and apart from other organs it also affects our kidneys in a big way,” says Dr Ingale.
Bengaluru-based nephrologist Dr Garima Aggarwal says about 30 to 40 per cent hypertensive people usually have an underlying kidney condition. On the other hand, about 90 per cent of people with kidney disease get secondary hypertension. “That is how closely the two are linked,” says Dr Aggarwal.

She encounters several patients who, due to a lack of awareness (despite having suffered high blood pressure for many years), discover kidney damage only at a late stage. “Unfortunately, when it comes to check-ups, kidneys are the most ignored of the organs even with patients living with high BP,’’ she says. “Most of the time kidney diseases or conditions like renal hypertension are only detected when the kidneys have already been damaged irreversibly.”

The answer, my friend, is flowing in the blood

The vascular dynamics of our body, especially blood flow, is constantly being defined and redefined on the basis of ongoing medical research. The simplest explanation that could be offered for what causes blood pressure would be the force exerted by the blood on the arterial walls as it flows through our body. Existing conditions would also end up playing a major role here – like excess lipid formations which could further hinder the smooth flow of blood. This could eventually lead to arteries becoming stiff and getting scarred, leading to narrowing and obstructing the flow of blood which ends up putting up more pressure on the heart to keep up the blood flow in our body. All these factors further aggravate blood pressure, which is further worsened if the individual has underlying cardiovascular issues, including cholesterol and high blood glucose.

Dr Aggarwal equates arteries with a rubber pipe with a strong flow and pressure of water running in. “After a point the force or rush of water is bound to damage and batter the wall of the pipe,” she says.

Similarly, it is not only the arteries connected to kidneys but also the capillaries (blood vessels) in the kidneys which too come under pressure and get scarred. “Once scarred, the kidney damage is irreversible because that part now is a dead tissue which can’t be revived,” says Dr Aggarwal.

So, while blood pressure can damage kidneys, the damaged kidneys further cause the blood pressure to shoot up because they can no longer keep up with their task of filtering blood or passing fluids. “It is almost like the chicken-and-egg situation,” she says. Both impact each other.

Renal hypertension

So, if left uncontrolled, high BP invariably causes kidney damage. Renal hypertension is one such condition which stems from the kidneys and causes the blood pressure to shoot up.

According to Dr Aggarwal when we talk about renal hypertension it means we are referring to high kidneys and blood pressure that is caused because of the narrowing of arteries (stenosis) carrying blood to the kidneys. Also known as renal artery stenosis, renal hypertension causes the arteries to narrow down, which blocks the blood from flowing into the kidneys. “This, in a way, dehydrates the kidneys and bars their proper functioning,” says Dr Aggarwal.

There are two issues that cause renal artery stenosis: atherosclerosis or fibromuscular dysplasia (FMD).

“While atherosclerosis is caused when plaque builds up, blocks and causes the narrowing and stiffening of the arteries, fibromuscular dysplasia, on the other hand, is a genetic condition which causes the narrowing or enlargement of the arteries in the body,” says Dr Ingale.

According to a research article published in the Journal of Clinical Hypertension, FMD is a vascular disease of unknown cause that can occur in multiple vascular beds. In the kidney, it usually occurs in the mid or distal portion of the renal artery, and it can also be found in smaller accessory renal arteries. FMD is more common in younger patients and in women.



When to worry

According to Dr Aggarwal, anyone with high BP should ideally be screened at the time of diagnosis itself and thereon should go for annual screening. “However, often early onset of kidney disease will not have any major external symptoms,” says Aggarwal. “So, it is very important to go for regular checks for blood pressure and screening for kidney function at least on an annual basis.”

So, if your previously controlled blood pressure is again beginning to rise or is very high despite medications, you should be alarmed and consult a doctor.

Prevention is better than cure

According to Dr Aggarwal, although renal hypertension cases are not very common or are less than 2 per cent, the bigger issue is the blood pressure causing kidney damage. “Unfortunately, there is little awareness about the issue,” says Aggarwal. “Usually, there are no exclusive symptoms that indicate that the kidneys are affected, which is why people with high blood pressure should routinely go for the kidney and urine test, which are quiet, simple and inexpensive.” She feels especially youngsters in their 30s and less, and older people in their 50s who have hypertension should get the kidney function tests done on priority.

Dr Ingale says, “Most of the time renal hypertension is an accidental discovery when people go for a full-body check-up or an executive health check-up.”

The Journal of Clinical Hypertension says FMD tends to be present in younger women (although many cases are not diagnosed until after age 40), while atherosclerotic disease is usually seen in older patients with traditional risk factors for atherosclerosis. 
All it takes is a simple blood test to test the creatinine and protein built-up in the urine.

Dr Ingale says changing blood pressure medication isn’t always the answer if your BP is constantly shooting up. “You should question it and get the kidneys checked first,” he says. He suggests first and foremost the blood pressure must be brought down through medication and lifestyle modification. “Minimising salt intake is another key point to keep BP under check in a big way,” he says.

Dr Aggarwal says early kidney disease can be managed with medications and lifestyle changes, but in advanced stages – known as end-stage kidney disease – patients require dialysis or kidney transplantation.

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