What is Hypertension?

Before we define hypertension or high blood pressure (BP), we should know what blood pressure is. Blood pressure can be defined as “the lateral pressure that is exerted by the blood on the walls of blood vessels”.

But it is very difficult to define hypertension or blood pressure that should be truly considered as ‘high’ as there is no cut off mark of blood pressure which indicates as high blood pressure. The Multiple Risk Factor Intervention Trial (MRFIT), done on more than 350,000 male participants, demonstrated a continuous and graded influence of both systolic and diastolic blood pressure on CHD (coronary heart disease) mortality, extending down to systolic blood pressures of 120 mmHg. So, systolic blood pressure of more than 120 mmHg can be considered as hypertension. The risk of cardiovascular disease doubles for every 20-mmHg increase in systolic and 10-mmHg increase in diastolic pressure.

Generally the most accepted classification of hypertension is to divide blood pressure based on systolic and diastolic blood pressure as normal blood pressure, pre-hypertension, stage I hypertension, stage II hypertension, and isolated systolic hypertension (where systolic blood pressure is more than 140 mmHg but diastolic blood pressure is normal or below 90 mmHg).

: – Normal blood pressure- systolic BP less than 120 mmHg and diastolic BP less than 90 mmHg.

: – Pre hypertension- Systolic BP 120–139 mmHg and diastolic BP 80–89 mmHg.

: – Stage I hypertension- Systolic BP 140–159 mmHg and diastolic BP 90–99 mmHg.

: – Stage II hypertension- Systolic BP more than 160 mmHg and diastolic BP less than 100 mmHg.

: – Isolated systolic hypertension- Systolic blood pressure is more than 140 mmHg but diastolic blood pressure below 90 mmHg.

Blood pressure varies at different times of the day. Blood pressure is slightly higher in the early morning hours, soon after waking, than at other times of day and due to this higher BP in the morning, myocardial infarction and stroke are more frequent in the early hours of morning. Nighttime blood pressure is generally 10–20% lower than daytime blood pressure. Blood pressure readings taken at home are better (as BP is measured many times over 24 hours) and lower than blood pressure taken at clinics (which may be only few times). Because ambulatory blood pressure recordings yield multiple readings throughout the day and night, they provide a more comprehensive assessment of the vascular burden of hypertension than a limited number of office readings. Increasing evidence suggests that home blood pressures, including 24-h blood pressure recordings, more reliably predict target organ damage than office blood pressures.