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
More and more people in Hong Kong are living with hypertension. Surveys conducted by the Census and Statistics Department showed that the proportion of people with known hypertension (as told by practitioners of Western medicine) increased from 9.3% in 2008 to 12.6% in 2014.
Of note is that many adults in Hong Kong actually do not realise they have hypertension. A local large-scale cohort study released in 2012 by the School of Public Health of the University of Hong Kong revealed that among those with hypertension documented in the study (about 32% of adults aged 20 and above), only about half of them (46%) were ever diagnosed as hypertensive by a doctor. This territory-wide study also revealed that the management of hypertensive people is suboptimal. Among those ever diagnosed, 70% were prescribed blood pressure lowering medication, but only 42% of this treated group attained good control of blood pressure. The study confirmed the “rule of halves” in hypertension: roughly only half of all hypertensive cases are diagnosed, half of those diagnosed are treated, and half of those treated are well-controlled.
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, the website of our Health Zone and the Hong Kong Reference Framework for Hypertension Care for Adults in Primary Care Settings.