High blood pressure is almost always present at the time of diagnosing Chronic Kidney Disease. And as time passes during your CKD journey, controlling your blood pressure becomes an essential part of your treatment plan to delay kidney failure.
But why does your blood pressure rise in chronic kidney disease in the first place?!
That, and the basics that you must understand about high blood pressure in CKD is what today’s storytelling is about.
We have taken care to avoid medical jargon but at the same time NOT over-simplifying the concept for you.
Let’s begin then, shall we?
3. HOW DO KIDNEYS HELP WITH REGULATING YOUR BLOOD PRESSURE?
4. WHAT GOES WRONG IN CHRONIC KIDNEY DISEASE THAT RAISES YOUR BLOOD PRESSURE?
NORMAL BLOOD PRESSURE
The pressure exerted by blood on the inner walls of blood vessels, every time your heart pumps out blood to arteries and receives blood from veins with each beat is commonly called Blood Pressure.
In good health, adults should not have a blood pressure (BP) reading higher than 120/80 mmHg at rest. The BP reading maybe higher immediately after a period of intense physical or emotional activity. However, this number should get back to below 120/80 mm Hg after adequate rest (for at least for 15 minutes).
Your blood pressure may be high if you experience the following despite adequate rest after physical or emotional activity:
1. Difficulty breathing
2. Pain in the chest while breathing
3. Headache along your temples (side of the forehead)
4. Pain in the neck or a throbbing sensation in the neck
5. The above, with or without blurred vision
OR
6. Hot flushes
Seek medical help to get your blood pressure checked immediately and receive medication if necessary.
SO, WHAT REALLY QUALIFIES AS HIGH BLOOD PRESSURE?
High blood pressure or Hypertension is a major health problem worldwide. Not just in itself, but because of all the myriad complications that it causes, ranging from Heart attacks, Strokes to Kidney damage & failure, it has dominated research interests and clinical conferences for decades now.
Among such clinical focus groups, two major ones namely the American Heart Association (AHA) and the European Society of Hypertension (ESH) have come up with their definitions for High blood pressure. These definitions and criteria inform day-to-day allopathic clinical practice worldwide.
We are presenting the BP definition basics by AHA and ESH for you below. We recommend you learn about these to be able to monitor your own blood pressure accurately.
As per the ACC-AHA criteria
| CATEGORY OF BLOOD PRESSURE | SYSTOLIC BLOOD PRESSURE (Upper number) | DIASTOLIC BLOOD PRESSURE (Lower number) |
|---|---|---|
| NORMAL BP | Less than 120 | Less than 80 |
| ELEVATED BP | 120-129 | Less than 80 |
| STAGE 1 HYPERTENSION | 130-139 | 80-89 |
| STAGE 2 HYPERTENSION | 140-159 | 90-99 |
| STAGE 3 HYPERTENSION | Greater than 160 | Greater than 100 |
As per the ESH criteria
| CATEGORY OF BLOOD PRESSURE | SYSTOLIC BLOOD PRESSURE (Upper Number) | DIASTOLIC BLOOD PRESSURE (Lower Number) |
|---|---|---|
| OPTIMAL BP | Less than 120 | Less than 80 |
| NORMAL BP | 120-129 | 80-84 |
| HIGH NORMAL BP | 130-139 | 85-89 |
| GRADE 1 HYPERTENSION | 140-159 | 90-99 |
| GRADE 2 HYPERTENSION | 169-179 | 100-109 |
| GRADE 3 HYPERTENSION | Greater than 180 | Greater than 110 |
| ISOLATED SYSTOLIC HYPERTENSION | Greater than 140 | Less than 80 |
HOW DOES YOUR BODY REGULATE YOUR BLOOD PRESSURE?
Amidst all this talk of heart and blood vessels in terms of blood pressure, you must be wondering as to where your kidneys come in all this.
Fact is, as simple as the phrase blood pressure sounds, its effective regulation is equally complex and multi-factorial, if not more.
There are four systems within our body that co-ordinate beautifully with each other to keep our blood pressure in control.
These systems are:
I. HEART & BLOOD VESSELS (CVS)
Your Heart & Blood vessels (fancy term: Cardio-vascular system) regulate blood pressure by:
1. How fast and hard your heart beats and how well your blood vessels widen up in response to this, to handle an increase in blood flow as needed.
&
2. How efficiently your heartbeat slows down upon rest after a period of activity and blood vessels adjust their width to restore only enough blood to other organs. This is to prevent an “angry, shoving and pushing” tsunami of blood flow to organs without need.
II. BRAIN
What is the chief purpose of our heart constantly pumping blood to different organs? It is to ensure regular delivery of nourishment to cells and clear out their metabolic wastes simultaneously so that our body functions efficiently.
An essential part of such nourishment is Oxygen. So, when oxygen levels in the body reduce, for whatever reason, blood pressure MUST rise immediately to maintain adequate oxygen delivery to tissues & prevent them from “feeling suffocated”.
1. In such a scenario, the instant response of the body comes from “oxygen sensing centres” located in the part of our brain at the back of our head.
2. These centers contact a very useful bunch of nerves called the “sympathetic nervous system” for help.
3. These nerves coax the Adrenal gland to release Adrenalin hormone.
4. Adrenaline literally “orders” our heart to beat faster & our blood vessels coming out of our heart to tighten-up so that the heart needs to exert more force to pump blood out.
5. This increases the blood pressure and restores normal oxygen delivery to all tissues of the body in times of need.
Now
Now, our blood pressure simply cannot continue to rise forever, right? There has to be that “Goldilocks point” that’s “just right” to meet fuel demands for our cells in times of intense emotional or physical activity.
To help with this situation, there is a “supervisor section” in the brain that tracks the rise in the blood pressure & keeps the much-needed leash on the activity of the “oxygen sensing area”. This allows for adequate blood pressure regulation as and when needed.
III. KIDNEYS (RAAS)
Among other functions, our Kidneys regulate the balance of “water-attracting” minerals like Sodium in our blood by “suitably adjusting” their levels in our Urine. They do this by either sending Sodium back to bloodstream or removing excess Sodium from the blood via Urine.
Kidneys “direct this Sodium movie” to regulate our blood pressure with the help of a special hormone system comprising of:
Renin from Kidneys
Angiotensin from Liver
Aldosterone from our Adrenal glands Renin from Kidneys
This hormone system is quite naturally called the RAAS i.e. the Renin-Angiotensin-Aldosterone System.
Whenever our blood pressure falls below normal, the pressure at which blood travels to kidneys for filtration & purification also drops down. This is a problem because you need your blood to reach your kidney filters with just enough pressure so that impurities and excessive components are properly filtered-off via urine. Inadequate pressure causes ineffective blood filtration.
To prevent this, a special hormone called Renin secreted from Kidneys themselves, “report” the kidney blood vessels about this fall in pressure.
1. Renin
This hormone co-ordinates with another hormone called Angiotensin from Liver. It acts on Angiotensin to produce a more active version called Angiotensin-II.
2. Angiotensin-II:
Angiotensin refers to “Angion = Blood vessels + Tensin = Protein that “tenses things up” i.e. the hormone that tones up blood vessels
Angiotensin-II tenses-up the tiny blood vessels in kidneys
It “informs” the Adrenal gland located right above each kidney to release one of its hormones called Aldosterone.
3. Aldosterone
Adrenal glands located right above the kidneys secrete Aldosterone. This hormone coaxes kidney filters to send back some of its Sodium in the Urine forming within, back to the bloodstream.
When blood sodium levels increase, it holds onto more water in the blood than necessary. Sometimes it even continues to “attract” more water from urine back into the blood.
This increases the overall blood volume in our body. As a result, the walls of our blood vessels feel stretched. This directly reflects as an increase in our blood pressure.
Once the blood pressure adequately rises & efficient kidney filtration resumes, any more Renin released by kidneys becomes unnecessary. Such “excess” Renin is ultimately “jobless”. So, kidneys reduce & gradually stop releasing any more of Renin hormone.
As a result, the RAAS hormone system increasing your BP comes to a halt. This prevents unchecked rise in BP which could otherwise damage delicate kidney filters beyond repair.
IV. ENDOCRINE (other hormones)
Emotional excitement or prolonged stress literally tires out our cells and makes them demand more Oxygen for survival. This would mean a necessity for increase in blood flow and hence, blood pressure.
Similarly, physical cues such as dehydration imply a decrease in water levels in our blood. This reduces our overall blood volume & the corresponding blood flow to all cells in the body. Ultimately there is a drop in our blood pressure as well, which if not corrected could spell serious health trouble. So, such a situation would again demand a temporary increase in blood pressure to “feed our cells” adequately up until they are “satisfied”.
The heart, blood vessels, kidneys obviously work in tandem to combat such situations. But there are important Hormones that help these organs to initiate BP regulation or prevent potential damage to cells due to an abnormal BP.
These hormones either act on blood vessels directly or on kidney filters in response to emotional & physical cues such as those mentioned above, to suitably alter blood pressure. These hormones include but are not limited to:
Cortisol – “Stress hormone” from Adrenal glands
Vasopressin – “Thirst hormone” from Pituitary gland in the brain
Endothelin-1 & Nitric oxide – “blood vessel relaxing hormones” from cells in blood vessel walls
Dopamine & Natriuretic Peptides
A glitch in any one of the organ systems above clinically presents as a rise in blood pressure. Chronic kidney disease affects all these BP regulation systems over time to varied extent.
On the one hand, this may sound a tad demotivating, while on the other, please understand just how important and complicated your kidney function is, as opposed to the common opinion about them “simply producing urine”.
HIGH BLOOD PRESSURE IN CHRONIC KIDNEY DISEASE
Now that you understand how different organ systems (including kidneys) co-operate & co-ordinate to maintain our blood pressure, let us take you through what goes wrong in Chronic Kidney Disease that your Blood Pressure control goes haywire.
Chronic Kidney Disease is an umbrella term that covers the various medical conditions that can cause your kidney function to progressively decline over time. The way kidney damage begins may differ, but all these conditions have a common end-point. And that is, widespread kidney scarring (fancy term : Renal Fibrosis).
When the scarring sets-in, the following problems accompany it:
1. Permanent damage to tiny blood vessels within kidneys
Scarring permanently damages the tiny blood vessel walls within the kidneys. The specialized “endothelial” cells that line these blood vessels and normally release BP regulating hormones like Endothelin-1 & Nitric Oxide literally buckle under pressure. The technical name for this is “Endothelial Dysfunction”. As a result of all this, the blood vessels lose the ability to relax and widen.
These changes keep the blood flow within these scarred and stiff blood vessels under high pressure. With time, local blood pressure control within kidneys starts to suffer adversely.
2. Increased blood pressure within kidney filters
When tiny blood vessels within kidneys narrow down and turn stiff upon scarring, two things happen:
Local blood pressure starts to rise
However, the quantity of blood flow through those stiff blood vessels fails to increase even in times of need.
Unfortunately, the Kidneys “mistake” this poor blood flow as something that could be corrected with increasing the blood pressure. This triggers the release of Renin from kidneys which go ahead and activate the RAAS on full-steam! Now that’s suicidal, isn’t it?
Such unnecessary RAAS hormone system activation only worsens the blood pressure control scenario within the kidneys.
Before we know it, such unwanted rise in Blood Pressure within kidneys:
Raises the “tension” within delicate kidney filters”
Promotes random protein loss in urine
Adds to further scarring of kidneys
3. High blood sodium levels due to kidney scarring
Kidneys regulate our blood pressure with the help of the Renin-Angiotensin-Aldosterone-System (RAAS). As explained before, this system works by increasing the levels of Sodium in our blood.
When kidneys get scarred over time:
The tiny, delicate kidney filters lose the ability to purge out excess Sodium from blood by themselves.
The cells that produce Renin get less “responsive” over time, so Renin hormone activity falters.
On the other hand, as explained in the above point, the RAAS hormonal system gets erroneously activated at the initial cue of poor blood flow.
But because Renin levels drop, there is nothing to “inform” the “upstream” hormones of the system (Angiotensin-II and Aldosterone) that they need to stop increasing the blood pressure any further.
This whole “communication confusion” leads to constant increase in blood sodium levels beyond normal limits. It manifests as high blood pressure when CKD patients get their vitals examined in the clinic.
4. Effect of vascular resistance on Heart
CKD narrows and stiffens blood vessels. The process first starts with tiny vessels within kidneys and then gradually spreads “outwards” to the rest of the body. This greatly increases the overall effort needed by the blood to flow through these diseased vessels to maintain adequate blood flow to all parts of the body.
Before long, the heart needs to start exerting greater force than necessary to pump out blood.
This shows up as high blood pressure when CKD patients present in the clinic
Over the years this may weaken your heart’s pumping capacity as well.
5. Fluid overload due to poor urination in kidney failure
As kidney failure progresses, the kidney filters get completely scarred. This greatly hampers the urine forming capacity of kidneys. As a result, excess fluids and metabolic wastes collect in the blood.
Among other complications, increase in blood fluid levels due to poor urination or the lack of it increases the overall blood volume. This in turn, increases pressure on already stiff blood vessel walls and adds to the reasons why a patient with kidney failure has high blood pressure.
So, that was a comprehensive insight on why your blood pressure is high when chronic kidney disease (CKD) hits.
Based on all the above mechanisms, pharmaceutical companies come up with different BP lowering medicines for use in CKD patients. These medicines, their types, action, effects, side effects and more form the topic of discussion in our next article here.
Till then, stay vigilant and stay cynical about your health. It’s what matters the most after all!
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REFERENCES
2. Hypertension in Chronic Kidney Disease– Medscape
