What is low pressure?

What is low pressure?

There are several persons who say that they have “low pressure”, meaning that they have low blood pressure. But most of them have low normal blood pressure rather than a truly low blood pressure. Very few of them do have blood pressure just below the lower limit of normal. Low normal blood pressures can occur without any symptom or significant heart disease. Some of them have dizziness on getting up, due further fall in blood pressure on assuming the standing posture. Blurring of vision or even fainting can occur due to low blood pressure.

Fall in blood pressure on standing is called postural hypotension while low blood pressure is called hypotension. Postural hypotension is common in the elderly and in those on certain medications for high blood pressure. Postural hypotension is also known as orthostatic hypotension. When the body fluid content is low due to poor intake or excessive sweating in a warm climate, blood pressure can fall in the standing position.

Fall in blood pressure is more common in the elderly because the normal reflexes in the body which bring up the falling blood pressure on standing get weakened. This can also occur after prolonged bed rest due to some illness. When you are bedridden for a long time, these reflexes get weakened as they are no longer needed when you are in the horizontal position. Doing regular leg exercises while bed ridden can help in preventing this from occurring.

Similarly, while getting up to go to toilet at night, especially in the elderly, it will be useful to sit up in bed and do a few warm up exercises with the legs to prevent fall in blood pressure. Many of the falls in toilet at night in elderly are due to fall in blood pressure making them dizzy. This is more likely in those taking medications for high blood pressure like those which increase the urine flow. These falls and consequent injuries which range from fractures to head injury, can be prevented to some extent by taking some precautions.

Dose of medications may be adjusted by your doctor or the type of medications changed if there is significant fall in blood pressure while standing up. Increase in intake of fluids in a warm climate is also useful to counteract loss of fluids by excessive sweating. Some may benefit by using compression stockings for the legs to prevent the rapid fall in blood pressure on standing.

So the commoner variety of “low pressure” is fall in blood pressure while standing. But there are some individuals who have low blood pressure in the lying down posture as well. Though these could be just a normal variant, it is important to rule out significant heart disease in such persons. Reduced pumping function of the left ventricle, the lower left chamber of the heart can cause a low blood pressure. Left ventricle pumps oxygenated blood to the whole body. If left ventricular output is low, blood pressure can fall.

The output of the left ventricle can also fall if the aortic valve is obstructed. Aortic valve is the valve between the left ventricle and aorta. Aorta is the largest blood vessel, taking oxygenated blood to the whole body. Left ventricular output can also fall when it is not able to fill well when it relaxes. Poor filling can occur due to stiffness of left ventricular muscle. Another reason is obstruction to the blood flow into the left ventricle.

Obstruction to flow of blood into the left ventricle can be at various levels. The mitral valve between the left atrium, the upper chamber and left ventricle can be narrowed. Flow of oxygenated from the lungs to the left atrium may be reduced due to disease of the blood vessels of the lungs. By all these mechanisms, filling of the left ventricle may be low and cause a low blood pressure.

Some persons, especially the elderly, can have low blood pressure after a meal. This is because the digestive system needs more blood flow during the process of digestion. Normally this is met with by increasing the output from the heart. If that mechanism does not work well, blood pressure may fall. It is more likely in those with some diseases of the nervous system (brain).

Some diseases of the hormone producing organs like the adrenals can also cause low blood pressure. The hormones are required for maintaining normal blood volume and blood pressure. This occurs in a condition called Addison’s disease, in which the production of the hormone cortisone from the adrenal gland in the tummy is reduced.

Other important causes of low blood pressure are major illnesses like infections in the blood, major heart attack, major blood loss, an allergic reaction, and loss of a lot of fluids from the body due to vomiting or diarrhea. But these are not the conditions which people usually mean when they say that they have ‘low pressure’. In these conditions, other important symptoms due to the basic illness will be more prominent.