This article was written by Dr Edward Leatham, Consultant Cardiologist
Throughout your life your blood pressure will be largely determined by your genetic makeup, BMI, what you eat and any medications you take. If your parents have or had high blood pressure, the odds are that you will develop it too.
Blood pressure measurements are standardised globally – expressed as two numbers: both are important – when measured in your arm, the top number is the peak pressure, in mmHg, that the heart’s contraction generates during each heartbeat. If you happen to also have a narrowed aortic valve, the pressure seen inside the heart will be even higher.
The bottom number is indicative of the resistance to run off into your vascular beds including muscles, gut and vital organs.
What controls your blood pressure?
Over millions of years, due to enhanced survival benefits in bygone eras when sepsis, childbirth and trauma affected the species ability to multiply, gain of function mutations (GOFM) occurred to protect us from fatally low blood pressure (so called hypotensive or septic shock). Evolution led to multiple different mechanisms that mammals use to maintain their core blood pressure – mostly controlled by subconscious brain activity, for example:
- Adrenaline – which increases force of heart muscle contraction and heart rate.
- Peripheral resistance – smooth muscle bands in small arteries of all muscle beds that contract to constrict (increasing blood pressure) or relax to dilate (lowering blood pressure, also useful to loose body heat).
- Kidney function: salt and water retention controlled by kidney hormones such as renin, aldosterone, and angiotensin (a vasoconstrictor).
Depending on your genetic makeup, diet and lifestyle your body will use the various different systems to maintain what it thinks is a healthy blood pressure. An increase in blood pressure is caused in most cases by the body’s central controls setting the pressure too high – which means powerful physiological systems that have evolved over millions of years to maintain perfusion during crisis, can be activated. This is one of the reasons that in some cases, several different pharmacological inhibitors may be required to get high blood pressure down to normal levels.
Normal values
The body needs a minimum blood pressure to perfuse vital organs, generally the systolic value (the top number) needs to be over 80 mmHg. If it drops below this you may start to feel lightheaded. It is normal for the blood pressure to rise transiently during exercise or stress.
A healthy ‘normal’ blood pressure is therefore anything in the range systolic (top number) 90-130 mmHg and diastolic (bottom number) of 50-75 mmHg.
Possibly due to widespread use of food additives and preservatives such as salt (sodium chloride) beginning in the Middle Ages and high prevalence of gain of function mutations that protected humans from shock in bygone eras, many people’s blood pressure will start to rise above these normal levels in their 30s. Large population studies in the 20th century linked high blood pressure exceeding 140/90 mmHg to adverse outcomes, so once randomised controlled trials proved the benefits of medical interventions, national targets were developed. However it is clear that if humans live for longer, even mild elevation of blood pressure is associated with much higher risk of heart and kidney failure in later life. Large studies have unequivocally demonstrated that lowering blood pressures below national target creates additional health benefits, albeit at the expense of an increase in side effects from low blood pressure.
The optimum blood pressure to have in midlife may therefore be in the region 110-125/70 mmHg or as low as possible without side effects.
What happens with high blood pressure?
High blood pressure, or hypertension, often causes no symptoms for many years, hence it is termed ‘ the silent killer’.
By increasing the wear and tear in the vital organs, high blood pressure is a major risk factor for:
- Kidney and heart failure
- Stroke (‘brain attack’)
- To a lesser extent it can also contribute to coronary artery disease.
Why should everyone know their numbers?
- High blood pressure is very common
- It is often ‘silent’ for many years
- It can be daily treated by lifestyle measures and medication
- Life expectancy is such that untreated mild hypertension in mid life is now the leading cause of of heart failure hospital admissions in the elderly.
Reference
