What Impact Would Low Blood Pressure Have On The Kidneys

How Kidneys Influence Blood Pressure

The blood pressure in your body depends upon the following conditions:

• The force of contraction of the heart — related to how much the heart muscle gets stretched by the incoming blood.
• The degree to which the arteries and arterioles constrict — increases the resistance to blood flow, thus requiring a higher blood pressure.
• The circulating blood volume — the higher the circulating blood volume, the more the heart muscle gets stretched by the incoming blood.

The kidney influences blood pressure by:

• Causing the arteries and veins to constrict
• Increasing the circulating blood volume

Specialized cells are located in a portion of the distal tubule located near and in the wall of the afferent arteriole. The distal tubule cells sense the Na in the filtrate, and the arterial cells sense the blood pressure. When the blood pressure drops, the amount of filtered Na also drops. The juxtaglomerular cells sense the drop in blood pressure and the decrease in Na is relayed to them by the macula densa cells. The juxtaglomerular cells then release an enzyme called renin. Renin converts angiotensinogen into angiotensin I. Angiotensin I is then converted to angiotensin II by an angiotensin-converting enzyme , which is found mainly in the lungs. Angiotensin II causes blood vessels to contract — the increased blood vessel constrictions elevate the blood pressure.

As you can see, the kidneys perform many functions that are important to your body:

Effects Of Sbp In Different Strata On Renal Function

The GFR and prevalence of renal insufficiency and proteinuria in different SBP strata are presented in . When SBP decreased from stratum 90-100mmHg to stratum 80-90mmHg, GFR was reduced by 3.6ml/min/1.73m2 while BUN, Scr and UA respectively increased by 0.2mmol/L, 1.93μmol/L and 7.5μmol/L . GFR decreased progressively and continuously with increase in SBP, approximately going down by 1.13ml/min/1.73m2 for every 10mmHg increase in SBP that occurs within the range of 140 to 230mmHg while BUN, Scr and UA increased by 0.08mmol/L, 1.54μmol/L and 1.73μmol/L for every 10mmHg increase in SBP. OR values of renal insufficiency and proteinuria in different SBP strata are shown in .

Effects of different SBP strata on GFR, renal insufficiency prevalence and proteinuria prevalence. GFR was expressed in mean±SE. A, B, C, D, E, F, G, H, I, J, K, L, M and N represents 80-89mmHg, 90-99mmHg, 100-109mmHg, 110-119mmHg, 120-129mmHg, 130-139mmHg, 140-149mmHg, 150-159mmHg, 160-169mmHg, 170-179mmHg, 180-189mmHg, 190-199mmHg, 200-209mmHg and 210-220mmHg stratum, respectively.

What Is Blood Pressure

Blood pressure is one of the vital signs of the body. It refers to the force blood applies on the blood vessel walls during the contraction and relaxation of the heart muscle. Blood pressure measures pressure in the arteries, the vessels that carry blood away from the heart. The responsiveness of the arteries to blood flow helps to determine blood pressure.

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How Is Blood Pressure Determined

Several factors influence blood pressure. Blood volume and blood vessel wall behavior are two important determinants of blood pressure. The more blood pumped with each heartbeat, the higher the blood pressure. The presence of stiff or narrow artery walls that resist blood flow also increases blood pressure. Having lower blood volume and open, flexible arteries decreases blood pressure.

What Are Clinical Trials For High Blood Pressure And Kidney Disease

Clinical trialsand other types of clinical studiesare part of medical research and involve people like you. When you volunteer to take part in a clinical study, you help doctors and researchers learn more about disease and improve health care for people in the future.

Researchers are studying many aspects of high blood pressure and kidney disease, such as

• managing high blood pressure through diet, education, and counseling in patients with kidney disease
• testing new medications to treat high blood pressure and kidney disease

Find out if clinical studies are right for you.

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Summary Of All Study Subjects

Overall, 28,258 subjects with 66% male and at age of 69.4±6.2 years were studied. The prevalence of hypertension, hypotension, obesity, hyperlipidemia and diabetes were 68.2%, 4.4%, 10.4%, 41.2% and 47.6%, respectively. Males were more likely to have hypertension than females but females were more likely to have hypotension than males . SBP was as high in women as in men whereas women had lower DBP and larger PBP than men . Estimated GFR by MDRD formula was higher than that calculated by CKD-EPI equation . There was a mean difference of 3.5ml/min/1.73m2 between MDRD and CKD-EPI eGFR when their average was less than 98ml/min/1.73m2 but the difference became larger and larger when their average value was more than 98ml/min/1.73m2. Many extreme high values of GFR could be easily obtained by MDRD equation .

Comparison between MDRD formula and CKD-EPI equation in the elderly. A: Bland-Altman plot of MDRD and CDK-EPI eGFR B: Boxchart of MDRD and CDK-EPI eGFR. â represents extreme values, â represents outliers.

Treatments For Renal Hypertension

Medications are used first to try to control high blood pressure in renal hypertension. The most important blood pressure medications to treat renal hypertension include:

• ARBs . Examples include candesartan, losartan, olmesartan and valsartan.

For most people with renal hypertension due to renal artery narrowing, medications can effectively control blood pressure. More than one blood pressure drug is often needed, however.

In some people with renal hypertension due to narrowing of the renal artery, even taking three or more medications every day may not adequately control blood pressure. In these situations, a procedure to improve blood flow to the kidneys may help.

Possible procedures include:

Angioplasty. A doctor threads a catheter through a large artery in the groin and advances it into the renal artery. A balloon is then inflated for a few moments. This widens the artery and improves blood flow.

Stenting. During angioplasty, a wire-mesh stent can be expanded inside the renal artery. The stent stays in place. This keeps the artery open after the balloon is removed. Research, however, has not shown that stenting is more effective than medication for renal hypertension.Ã

Surgery. A surgeon can bypass the narrowed renal artery by sewing a healthy blood vessel next to it. Surgery is generally considered only when angioplasty and stenting are not possible.

These procedures are similar to those used to improve blood flow in the heart in people with coronary artery disease.

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How Common Are High Blood Pressure And Kidney Disease

Almost 1 in 2 U.S. adultsor about 108 million peoplehave high blood pressure.1

More than 1 in 7 U.S. adultsor about 37 million peoplemay have chronic kidney disease .2

High blood pressure is the second leading cause of kidney failure in the United States after diabetes, as illustrated in Figure 1.2

Almost 1 in 2 U.S. adultsor about 108 million peoplehave high blood pressure.

Causes Of Renal Hypertension

Renal hypertension is caused by a narrowing in the arteries that deliver blood to the kidney. One or both kidneys‘ arteries may be narrowed. This is a condition called renal artery stenosis.

When the kidneys receive low blood flow, they act as if the low flow is due to dehydration. So they respond by releasing hormones that stimulate the body to retain sodium and water. Blood vessels fill with additional fluid, and blood pressure goes up.

The narrowing in one or both renal arteries is most often caused by atherosclerosis, or hardening of the arteries. This is the same process that leads to many heart attacks and strokes. A less common cause of the narrowing is fibromuscular dysplasia. This is a condition in which the structure of the renal arteries develops abnormally for unclear reasons.

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How Does Blood Pressure Affect The Kidneys

Joe Rutkowski, PhD, an assistant professor in the Texas A& M College of Medicine, explains his research on blood pressure and its effect on the kidneys…and vice versa.

Christina Sumners: Welcome to Science Sound Off, Im Christina Sumners.

Tim Schnettler: And Im Tim Schnettler.

Christina Sumners: Our guest today is Dr. Joe Rutkowski, an assistant professor of medical physiology at Texas A& M College of Medicine. Welcome, Dr. Rutkowski.

Joe Rutkowski: Thank you for having me.

Christina Sumners: So you and some of your fellow researchers have recently received a couple of major grants to study the interaction of renal lymphatics and blood pressure. Could you tell me a little bit about what you guys are up to?

Joe Rutkowski: So the lymphatic system is really underappreciated by most in the medical field. Its part, it closes the circulatory loop, and its responsible for the clearance of fluid, macromolecules, and immune cells from peripheral tissues and bringing them back into central circulation. As such, it plays a critical role in inflammation and immunity. And work over the last decade in many labs has identified that hypertension is in part a disease of chronic inflammation in the kidney. And so we hypothesized that changes in the kidneys lymphatic architecture would play a role in regulating blood pressure.

Christina Sumners: So how can high blood pressure affect your kidneys, or does it affect your kidneys in any way?

Tim Schnettler: The lymphatic. Either one.

What Is High Blood Pressure And How Does It Affect The Kidneys

The National Institute of Diabetes and Digestive and Kidney Diseases defines blood pressure as an increase in the amount of force that blood puts on the vessels as it moves throughout the body.

Over time, blood pressure can damage and weaken blood vessels throughout the body, including those in the kidneys. When the blood vessels in the kidneys become damaged, it can affect how well the kidneys function.

When the kidneys do not function properly, it can lead to excess fluid and waste buildup in the bloodstream. This in turn can cause high blood pressure, resulting in further damage to the kidneys.

Over time, a person can develop kidney failure.

• changes in urine volume
• generalized numbness or itchiness or darkened or dry skin

If a person is taking multiple medications to manage their blood pressure, and these are not having an effect, doctors may suspect that renovascular hypertension could be the cause.

Any condition that affects blood flow to the kidneys can lead to renovascular hypertension.

The most common causes of renovascular hypertension are forms of renal artery stenosis. Atherosclerosis, which is the buildup of plaque in the arteries, is behind 90% of cases. Fibromuscular dysplasia, which is a condition that causes the narrowing of the arteries, is behind 9% of cases.

Other potential causes

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How Does High Blood Pressure Affect The Kidneys

High blood pressure can constrict and narrow the blood vessels, which eventually damages and weakens them throughout the body, including in the kidneys. The narrowing reduces blood flow.

If your kidneys blood vessels are damaged, they may no longer work properly. When this happens, the kidneys are not able to remove all wastes and extra fluid from your body. Extra fluid in the blood vessels can raise your blood pressure even more, creating a dangerous cycle, and cause more damage leading to kidney failure.

Blood Pressure Profile And Targets In Advanced Ckd

Two important patterns characterized the hypertensive phenotype in people with advanced CKD. The first is the high prevalence of nocturnal hypertension17 and uncontrolled masked hypertension due mainly to elevated BP values at night.18,19 The second is the high proportion of patients with apparent or truly resistant hypertension.20 The elevated nighttime BP in patients with advanced CKD can be explained in several ways including an increased prevalence of sleep apnea syndrome due to sodium and water retention,21,22 an increased sympathetic nerve activity and a reduced capacity to excrete sodium during daytime as GFR declines.23 Indeed, a high nocturnal BP enables to maintain the 24 h sodium balance when kidney function is impaired. In this respect, Fukuda et al have nicely shown that as GFR declines sodium excretion, albuminuria and BP increase during the night.24 Regarding resistant hypertension, several studies have demonstrated a high prevalence in patients with advanced CKD. In a recent review written by Georgianos and Agarwal, the prevalence of resistant hypertension in treated hypertensive patients with CKD ranged between 28.1% and 40.4%.20 Both nocturnal and resistant hypertension are associated with an increased risk of cardiovascular events.18,19

Table 1 Target Blood Pressures in the General Population and CKD and Diabetes According to Various Guidelines

Elevated nighttime BP is common and represents an important BP component of the cardiovascular and renal risk.

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Is Low Blood Pressure Bad For Your Health

Lower blood pressure is associated with a lower risk of conditions like heart disease, stroke, and kidney disease. Those who exercise regularly, athletes, non-smokers, and those who maintain an optimal body weight experience lower blood pressures. Lower blood pressure is a good thing as long as it doesn’t cause symptoms that could damage organs and tissues of the body.

What Procedures And Tests Diagnose Low Blood Pressure

In some people, particularly relatively healthy ones, symptoms of weakness, dizziness, and fainting raise the suspicion of low blood pressure. In others, an event often associated with low blood pressure, for example, a heart attack, has occurred to cause the symptoms.

Measuring blood pressure in both the lying and standing positions usually is the first step in diagnosing low blood pressure. In patients with symptomatic low blood pressure, there often is a marked drop in blood pressure upon standing, and patients may even develop orthostatic symptoms. The heart rate often increases. The goal is to identify the cause of the low blood pressure. Sometimes the causes are readily apparent . At other times, the cause may be identified by testing:

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Over Time High Blood Pressure Harms Renal Blood Vessels

The nephrons in the kidneys are supplied with a dense network of blood vessels, and high volumes of blood flow through them. Over time, uncontrolled high blood pressure can cause arteries around the kidneys to narrow, weaken or harden. These damaged arteries are not able to deliver enough blood to the kidney tissue.

• Damaged kidney arteries do not filter blood well. Kidneys have small, finger-like nephrons that filter your blood. Each nephron receives its blood supply through tiny hair-like capillaries, the smallest of all blood vessels. When the arteries become damaged, the nephrons do not receive the essential oxygen and nutrients and the kidneys lose their ability to filter blood and regulate the fluid, hormones, acids and salts in the body.
• Damaged kidneys fail to regulate blood pressure. Healthy kidneys produce a hormone called aldosterone to help the body regulate blood pressure. Kidney damage and uncontrolled high blood pressure each contribute to a negative spiral. As more arteries become blocked and stop functioning, the kidneys eventually fail.

Hypertension Drug Therapy In Severe Ckd

In advanced CKD, recommended BP targets are rarely reached prescribing a single antihypertensive class. This is the reason why European guidelines propose to start immediately with a single pill combination associating a blocker of the renin-angiotensin system and a calcium channel blocker or a diuretic in CKD patients.11 Then, if BP remains uncontrolled, the therapy should be intensified by combining the three drug classes , possibly in a single pill. However, the use of antihypertensive drug classes in patients with a low GFR deserves some comments:

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Does Blood Loss Lower Blood Pressure

Conditions not associated with the neurological system may cause low blood pressure. Anything that causes a loss of fluids, including dehydration from diarrhea, vomiting, or bleeding may cause low blood pressure. Adrenal gland dysfunction, pregnancy, and blood loss may lower blood pressure as well. Medications May Cause Low Blood Pressure.

How Can I Lower My Risk Of Kidney Disease

The changes you can make to your to lower your blood pressure will help to lower your risk of kidney disease, for example, eating healthily, being active, stopping smoking and keeping to a healthy weight. In particular, try to eat less than 6g of a day.

Its also important to make sure any health problems you already have are well controlled, including .

You can get an idea of the health of your kidneys with this online questionnaire. Finding out if you have kidney disease, or are at risk, means you can start taking steps to prevent it or stop it getting worse.

You can also find out if you are at risk of diabetes, use this questionnaire, visit your GP or get an NHS Health Check.

Read moreOur Trustee Dr Rebecca Suckling is a Consultant Nephrologist and looks after people with kidney disease. She explains more about how the kidneys and blood pressure are related, in the .

Information and support for people living with kidney disease, including a counselling service, online community and financial support.

Kidney Care UK. Information and support for people living with kidney disease, including a counselling service, online community and financial support.

Kidney Research UK. Information on kidney diseases.

NKF. Kidney Patients UK, is run by kidney patients for kidney patients, their information includes stories from other patients.

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What Hypertension Does To Your Kidneys

You can see this chicken-or-egg effect with high blood pressure and kidney disease as well. Hypertension puts extra pressure on the kidneys filtering units, which can lead to scarring. This impairs the kidneys ability to regulate fluid, which increases blood pressure.

If this cycle is not stopped, it can lead to kidney disease and kidney failure, says hypertension specialist George Thomas, MD, who is Director of the Center for Blood Pressure Disorders in the Department of Nephrology and Hypertension.

High blood pressure and uncontrolled diabetes are the most common causes of kidney disease.

Unfortunately, the vast majority of people with kidney disease dont realize they have it. The signs and symptoms may be attributed to other conditions and usually appear when the kidneys have already begun to fail. Here are symptoms to watch for:

• Unusual fatigue.
• Blood or foam in the urine.
• Swelling in the ankles, feet or around the eyes.
• Lack of appetite, nausea or vomiting.
• Muscle cramps.
• Confusion.
• Taste abnormality.

If you are experiencing any of these symptoms particularly if you are at risk of kidney disease because youre over age 60, have high blood pressure, have diabetes or have a family history of kidney failure talk to your doctor about your kidney health and salt intake.