Diabetes and Hypertension

In people with Type 1 diabetes, blood pressure usually rises only as a result of kidney damage. Whereas previously mainly normal blood pressure readings were obtained, as soon as microalbuminuria appears, the blood pressure begins to rise, although at first it may stay in the normal range.

For example, if under normal albuminoidal it was 125/80 mmHg, after the onset of microalbuminuria it might rise to 130/85 mmHg, then later to 135/90 mmHg. This is why there is no ‘official’ value for hypertension, but a rise in blood pressure compared with earlier values indicates increased stress for the heart, kidneys and blood vessels.

Should macroalbuminuria then develop, or even renal failure, the blood pressure rises sharply if it is not treated promptly. As well as people with Type 1 diabetes, every second or third person with Type 2 diabetes shows raised blood pressure as soon as metabolic disease begins.

Because there is often no visible cause for the high blood pressure, people talk about ‘essential hypertension’. In those with Type 2 diabetes, the blood pressure also begins to rise as soon as kidney function is impaired. In practice, all patients with renal damage have high blood pressure.

How blood pressure affects the development of kidney damage? - This is most important for people with Type 2 diabetes because, in their case, the blood pressure is often already high when the diabetes is diagnosed.

A large trial has recently shown a significant relationship between the value of the systolic blood pressure and the onset of kidney disease: the lower the systolic pressure, the less frequent is the occurrence of kidney disease. But, as with blood sugar, there is no threshold for blood pressure below which one is definitely protected from kidney failure.

When nephropathy already exists - The more developed the kidney disease is, the more relevant is the degree of high blood pressure for the progression of the disease. If appropriate treatment can keep the blood pressure in the normal range at the stage of micro-or macroalbuminuria, the chances are good that the kidney damage will not proceed or will at least be delayed.

This has been demonstrated in several studies. Figure below shows, as an example, the course of kidney disease in a patient who already had macroalbuminuria as a sign of advanced kidney damage and in whom the blood pressure was at first not well managed. At this time, the kidney function deteriorated fairly rapidly.

However, it was possible, through good management of the blood pressure, to arrest the downwards trend after several months and to stabilize kidney function at a lower level. Why did high blood pressure have such a strong effect in this patient?

At this stage, the corpuscles in the already damaged kidney have often lost their ability to regulate the blood pressure themselves through narrowing of the incoming vessels. Thus, the high circulatory pressure impacts unhindered on the corpuscles and causes further damage.

How low should the blood pressure go? - From what has been said so far, it is clear that the earlier you start treatment and the lower you take the blood pressure, the better it is. Many people with Type 1 diabetes start with a normal blood pressure, which slowly rises over weeks and months with the development of kidney damage.

It helps to treat the rising blood pressure in these patients even while it remains in the normal range, as shown in several trials. In one of these studies, 93 people with Type 2 diabetes and microalbuminuria but no hypertension were treated with a blood pressure-lowering drug from the class of ACE inhibitors. The progress of kidney damage was arrested in nearly all the patients.

During the following five years, only 12% developed macroalbuminuria, compared with 42% in the untreated group. This and other studies have led to the opinion that in every patient with the first signs of kidney failure, be it micro-or macroalbuminuria, the blood pressure should be reduced, even if no actual hypertension is present.

If the blood pressure is already over 140/90 mmHg, treatment must of course be started straight away, even if the kidneys are functioning normally. Obviously, there are lower boundaries for the reduction in blood pressure. If it falls too far, unpleasant side-effects appear, such as fainting, tiredness or other complications.

Care must be taken regarding concurrent illnesses, such as circulatory problems in the legs or brain, since a low blood pressure can aggravate these conditions. The target value for blood pressure management therefore varies from patient to patient and should always be determined individually.

The experts have set a value of 130/80 mmHg as a guideline. Such target values are ideals and will not be achievable by everyone. The aim of blood pressure therapy should be to get as close as possible to the target.

This will not happen overnight – on the contrary, the reduction of high blood pressure should be managed cautiously, since a too-rapid fall in blood pressure can cause problems with balance and often leads to side effects.

There are more than 100 blood pressure-lowering drugs - which are the best? Drugs for lowering blood pressure There are various classes of hypotensive drugs which differ in the first instance in their mechanism of action. Because the cause of the hypertension is not known for most people, it is not so simple to determine the most suitable treatment for each individual.

Often it is simply a case of testing which drugs reduce the blood pressure most effectively and are also well tolerated. There is not such a wide choice of suitable drugs for people with diabetes. For this special group, the so-called ACE inhibitors have established themselves as key players.

This is because they don’t just reduce the pressure in the general circulation, but act particularly in the kidney corpuscles. Thus, they have a special renoprotective effect. ACE inhibitors are therefore usually given to patients with microalbuminuria, even when the blood pressure is still in the normal range.

Their use is also recommended in people with advanced kidney disease (macroalbuminuria), because they reduce protein excretion in the urine more effectively than other hypotensive drugs.

For patients who cannot tolerate ACE inhibitors – for example, a certain percentage of people develop a cough – the alternative is a new class of blood pressure-lowering drugs called the AT1 receptor blockers (also known as angiotensin-II receptor antagonists).

They act in a similar way to the ACE inhibitors to reduce blood pressure and have the same advantage of protecting the kidneys. This has been demonstrated recently in three large trials of people with diabetes with early and advanced nephropathy.

Other drugs that lower blood pressure are the calcium channel antagonists and the beta blockers. The latter are used when there are accompanying circulatory problems with the heart (coronary artery disease) because they also have a protective effect there.

If a hypotensive drug alone is not sufficient, a combination of different drugs is often given. The drugs preferred for use in combination, particularly with the ACE inhibitors, are diuretics. These lower blood pressure by increasing the excretion of sodium (salt) and water from the body.

If there is water retention, as in advanced kidney failure, especially in the legs (oedema), strong-acting diuretics are used to resolve this. In addition to those already mentioned, there are other hypotensive drugs that are not among the first choice of therapies because of their side-effect profiles.

Today, everyone who has high blood pressure should regularly test the effectiveness of their treatment themselves. There are many measuring devices available that can be used at home to determine the blood pressure in the upper arm or wrist without any problem.

An important instrument for assessing blood pressure is the long-term or ambulatory blood pressure meter. This measures and records the blood pressure at certain intervals over 24 hours. These intervals are usually 20 minutes during the day and 30 minutes during the night.

Blood pressure measurement at night can be irritating, but it provides important information concerning the behavior of the circulatory system. In some people, and particularly those with diabetes, the blood pressure does not fall overnight in the normal way, which imposes a much higher burden on the body.

This phenomenon occurs especially often in people with kidney disease. In some, the blood pressure even rises overnight, instead of falling. Detecting this and initiating the right treatment to correct it can be a deciding factor in successfully delaying the progression of nephropathy.

Therefore, the ambulatory blood pressure should be measured repeatedly at regular intervals in patients with renal failure. Measurement is not the only part of blood pressure management: blood tests are also required to monitor for side-effects of the drugs.

The treatment is very complicated, especially when several drugs are given concurrently. It is therefore usually not a good idea for patients to change their medication or even the dose of individual drugs themselves.

Self-responsibility for the patient resides in controlling his or her blood pressure and in knowing about the medicines being taken, both of which can be learned during an appropriate course of education in diabetes and hypertension.