Blood pressure refers to the force at which blood flows through the body's blood vessels. Blood supplies necessary nutrients and oxygen to the entire body. Hence, it is important that blood pressure should be within normal limits, to keep the body functioning well.

High blood pressure is harmful and causes many immediate and long-term complications in the body. While people are becoming more aware of this issue, it is important to note that low blood pressure, known as hypotension (below 90/60 mm Hg), is equally harmful.

With a slight decrease in blood pressure, one may experience dizziness and a sensation of falling, accompanied by a darkening of vision. As the blood pressure continues to drop, the individual may find it difficult to maintain an upright position. Severe fall in blood pressure results in shock. If not corrected immediately, this can be fatal due to lack of perfusion to vital parts of the body like the brain and heart.

Low blood pressure can be acute due to loss of fluid and electrolytes from the body as in diarrhoea and or vomiting. Trauma with excess blood loss also leads to low blood pressure. The extent of the fall in blood pressure depends on the quantity of blood or fluid lost. Sepsis due to severe infection is also a cause of low blood pressure. Sometimes, not eating or drinking for many hours can also lower blood pressure.

Chronic hypotension may occur as a result of heart valve damage or the presence of one or more narrow heart valves since birth.

Due to a damaged/narrow heart valve, blood is not pumped out in sufficient quantity to the body parts. Therefore, the blood pressure remains low and one feels giddy. Heart failure also causes low blood pressure. Severe anaemia, where haemoglobin (blood pigment carrying oxygen) is less than normal, impairs perfusion of the heart and results in low blood pressure. Chronic infections like tuberculosis and HIV are also accompanied at times by low blood pressure.

Drugs for hypertension can reduce blood pressure to less than normal. Therefore, it is important to monitor the blood pressure of an individual who is on antihypertensive drugs. Similarly, diuretics (medicines used to mobilise extra salt and water from the body) can also induce low blood pressure.

Varicose veins (dilatation of the veins of the lower limb), is yet another condition which leads to low blood pressure. In this, there is insufficient return of blood to the heart due to the dilated veins. This affects the filling and then pumping of blood by the heart. Some people have a tendency for low blood pressure with a change in position. When they stand up from a lying or sitting position, blood pressure tends to fall. Some individuals develop low blood pressure when they stand in the same position continuously for a long time. This occurs due to the pooling of blood in the lower limbs.

Acute hypotension needs urgent intervention to prevent shock. This includes perfusion with fluids containing saline and electrolytes. Elevation of the legs is very useful as a first aid measure to help improve the return of blood to the heart and its pumping ability. Even those with chronic low blood pressure can benefit by lying down for an hour or so with their legs elevated.

Those having varicose veins should use elastic stockings or a crepe bandage to keep the veins compressed. This augments the amount of blood returning to the heart and thus prevents hypotension.

People with hypotension should avoid sudden changes in position to prevent low blood pressure. Moving the toes while standing upright for an extended period can help prevent hypotension in individuals who are susceptible to it. Additionally, maintaining regular meal times can also be beneficial.

Dr Rachna Pande is a specialist in internal medicine.