Reducing systolic blood pressure limit to 120 mm Hg from the currently recommended target SBP level of 140 mm Hg appears beneficial if there is no underlying diabetes, previous stroke or kidney disease.

SHOULD we aim for a lower blood pressure than what is currently recommended? The debate on blood pressure rages on again as the National Heart, Lung, and Blood Institute (NHLBI) announced the initial results of an important trial, the Systolic Blood Pressure Intervention Trial (SPRINT), in September 2015. The study involved the adjustment of blood pressure medication to achieve a systolic blood pressure or SBP (upper blood pressure reading) value of 120 millimetres of mercury (mm Hg) in a group of adults who were 50 years or older.

Compared to the currently recommended target systolic blood pressure level of 140 mm Hg, intensive medication to reduce systolic blood pressure to 120 mm Hg reduced heart complications and stroke by almost one third and reduced the risk of death by almost a quarter.

Objective signs of heart stress

Blood pressure is not a single static reading but rather a continuously fluctuating value that varies with the mental state and the physical activity of the individual and it reflects the pressure generated from the pumping action of the heart. How does one decide on what blood pressure value is considered normal or high? The upper limit of “normal” blood pressure will be defined by blood pressure values which, if exceeded, can damage the organs of the body – primarily the heart, brain and the kidneys. Hence, if blood pressure values exceed the upper limit of “normal” blood pressure over a prolonged period of time, there will be an increased risk of heart disease, stroke and kidney damage.

Among the three organs, the first signs that blood pressure is adversely impacting the body are often seen in the heart. The left upper and lower heart chambers are connected to the aorta which is the main artery providing blood supply to the entire body. Hence, if blood pressure is high enough to adversely affect the organs in the body, it will cause stress to the left heart chambers. The left upper heart chamber is thin-walled and it responds to elevated blood pressure in the heart chamber by enlargement; it is like expanding a balloon as you blow more air into it with higher pressure.

The left lower heart chamber is the main pumping chamber which pumps blood out of the heart to the rest of the body and hence, it has a thicker muscular wall. If blood pressure is elevated, the heart has to work harder to pump blood against a higher resistance in the aorta. This will cause the heart muscle to thicken just as your arm muscles will increase in size if you carry heavier weights.

Hence, two of the earliest objective signs to indicate that the heart is subjected to blood pressure levels is progressive enlargement of the left upper heart chamber and progressive thickening of the muscular wall of the left lower heart chamber. If there is any doubt that a person with persistently high blood pressure in the clinic has “white coat” phenomenon or true high blood pressure, an ultrasound of the heart will provide objective evidence to determine whether the heart has been subjected to the prolonged stress of elevated blood pressure or whether it is just transient elevation due to the “white coat” phenomenon. This will avoid the need for unnecessary medication and overtreatment.

Which BP reading is ‘real’?

While the concept of blood pressure seems simple, its measurement can be quite challenging. It is not uncommon to find that the blood pressure of a person can be different when comparing the reading at home with the reading in a clinic or hospital environment. There are patients whose blood pressure values can be 200/100 mm Hg at the clinic but have home blood pressure recordings of 130/80 mm Hg or less on the same day; this phenomenon is termed “white coat” hypertension.

There are also patients with normal blood pressure values when they are resting in hospital but their blood pressure is elevated when they go back to their busy routines; this phenomenon is termed as “masked” hypertension. Even when in the same environment, the blood pressure reading of the same person can be different when comparing a reading in the morning with a reading at night.

While guidelines state target blood pressure values, the reality is that blood pressure varies in the same person depending on his mental and physical state, the location where blood pressure is being measured, his position when blood pressure is being measured (blood pressure can vary when measured lying down, sitting up or standing up), and the type of equipment being used to measure blood pressure (blood pressure can vary depending on whether it is measured with a wrist cuff digital blood pressure monitor, an arm cuff digital blood pressure monitor or a mercury arm cuff sphygmomanometer). For this reason, it is important to monitor the trend of blood pressure over a period of time and to compare home blood pressure readings with clinic readings which are usually measured with a mercury sphygmomanometer.

Recommendations to follow

How should one reconcile these recommendations from the SPRINT trial with those of the current blood pressure guidelines which advocate blood pressure of less than 140/90 for healthy adults under the age of 60 and blood pressure below 150/90 for healthy adults over the age of 60? What we know from current evidence is that if the person has no underlying heart artery disease or narrowing of brain arteries, lower blood pressure is associated with a lower risk of death, stroke and heart complications. Hence, the SPRINT recommendations do not contradict the findings of current evidence and it is not inappropriate to consider lowering blood pressure to a target of systolic blood pressure of 120 mm Hg in the absence of significant heart, brain or kidney disease.

However, it should be noted that the SPRINT study excluded those with diabetes mellitus, previous stroke or polycystic kidney disease. There is evidence that excessive lowering of systolic blood pressure in those with significant narrowing of the brain arteries can increase the risk of stroke. There is also evidence that excessive lowering of blood pressure may be detrimental in those with significant heart artery disease. Hence, the SPRINT recommendations cannot be routinely applied to those with significant heart artery disease, significant brain artery disease and certain types of kidney disease. Patients with long-standing diabetes often have significant narrowing of the brain, heart and/or leg arteries. Hence, caution should be exercised before attempting to lower blood pressure excessively.

In addition, some patients suffer dizzy spells when blood pressure is lowered to systolic blood pressure of 120 mm Hg. Caution must be exercised in excessive lowering of blood pressure in elderly patients who complain of dizziness as this may predispose the patients to falls and resultant fractures. In addition, lowering blood pressure to systolic blood pressure of 120 mm Hg will often entail more medication and hence expose the patients to more potential side-effects of medication.

Practical tips

• If there is proven high blood pressure, lowering to systolic blood pressure of 120 mm Hg appears beneficial if there is no underlying diabetes, previous stroke or kidney disease.

• If there is a history of significant heart artery disease, stroke, diabetes or kidney disease, seek advice from your physician to determine whether it is beneficial for you to lower systolic blood pressure to 120 mm Hg.

• If there are dizzy spells when taking blood pressure medication, they may be due to insufficient blood flow to the brain or side-effects of medication, and hence, you should inform your physician of these symptoms as it may be necessary to decrease the dose of the medication or change the medication.

• If there is existing significant narrowing of the brain arteries, based on current evidence, it is best to keep the target systolic blood pressure at 140 mm Hg or less.

• If there is pre-existing diabetes mellitus and diabetes-related kidney impairment in the absence of significant brain and heart artery disease, it may not be inappropriate to consider bringing systolic blood pressure to 120 mm Hg.

• As lowering the target systolic blood pressure to 120 mm Hg will usually mean that more drugs and/or higher dosages are necessary, before increasing the medication, it is wise to monitor your home blood pressure readings regularly and present them to your physician to confirm that there is a definite need to do so before medication is increased. This is very important to avoid overtreatment of those with “white coat” phenomenon.

• Finally, “listen” to your body; if your home blood pressure is at the target level and you feel well, you need not worry. If you feel unwell, despite good readings, do consult your doctor as you may be suffering from the side-effects of the medication or your body is unable to tolerate the low blood pressure.