Hypertension, or high blood pressure, is a chronic disease in which the blood pressure in the arteries is persistently elevated. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. A normal blood pressure is required to push the blood through the body and supply oxygen and nutrients to the tissues. But if blood pressure rises and stays elevated over time, a number of serious health problems may ensue, including stroke, coronary heart disease and heart failure, chronic kidney disease, and even early death.
Blood pressure is written as two numbers. The first number (systolic pressure) represents the pressure in the blood vessels when the heart contracts to pump blood, whereas the second or bottom number (diastolic pressure) represents the pressure when the heart relaxes between beats.
Blood pressure changes from minute to minute throughout the day with posture, physical activities, emotions, and sleep, etc. But for an adult, if systolic blood pressure (SBP) is persistently ≥ 140 millimetres of mercury (mmHg) or diastolic blood pressure (DBP) is persistently ≥ 90 mmHg, the person is said to have hypertension. SBP between 120 mmHg and 139 mmHg or DBP between 80 mmHg and 89 mmHg is considered pre-hypertension and should also be of concern. A child or adolescent is said to have hypertension if he or she has a SBP or DBP ≥ 95th percentile for age, height and gender on repeated measurements.
Situation in Hong Kong
According to the Population Health Survey (PHS) 2014/15 conducted by the Department of Health, the total prevalence of hypertension combining cases that were self-reported or detected by measurement during health examination was 27.7% (25.5% for females and 30.1% for males) among persons aged 15-84, with 47.5% of them being undiagnosed before the PHS. The total prevalence of hypertension increased steadily with age from 4.5% among those aged 15-24 to 64.8% among those aged 65-84.
Hypertension seldom causes symptoms until complications develop. That is why it is considered a "silent killer". Extremely high blood pressure may cause symptoms like dizziness, visual disturbance, headache, fatigue and facial flushing.
In over 90% of cases, no specific cause can be identified. These cases are called primary hypertension. A number of risk factors predispose a person to develop hypertension. These factors include: high salt intake, obesity, having a sedentary lifestyle, smoking, heavy drinking, inadequate sleep, stress, family history of hypertension and increasing age. In a small minority of patients, specific causes may be identified. These include renal diseases, endocrine diseases and some drugs.
Having a balanced diet that is low in salt, keeping physically active, avoiding obesity, quitting smoking, refraining from alcohol consumption and managing stress are useful in preventing hypertension. Periodic checks for blood pressure can detect hypertension early. Proper management of hypertension can prevent its complications.
For more information on hypertension, please visit our World Health Day 2013 (Hypertension) Page and the Hong Kong Reference Framework for Hypertension Care for Adults in Primary Care Settings.