LOW BLOOD PRESSURE - Full extract 

Much has been said about high blood pressure; we know it is a major cause of stroke and coronary heart disease, and that these complications can often be prevented by better blood pressure control. In contrast, low blood pressure rarely gets a mention. However, it can cause a few problems too.

The circulation and the heart is rather like an hydraulic system with a pump. With each pump or pulse the pressure in the system rises. This is called the systolic pressure. The resting pressure between each pulse is the diastolic pressure. Blood pressure readings include both figures, systolic/diastolic, expressed in millimetres of mercury. (see also Heart Foundation) About 140/90 is regarded as the upper limit of normal, although a higher figure may be acceptable in older patients. At the other end of the scale, when the systolic or higher figure drops below 85 or 90 mm.of mercury the blood pressure is getting on the low side. This may be significant and symptoms like dizziness and fainting can occur.

When we stand up from a sitting or lying position, gravity tends to cause a drop in the systolic blood pressure of up to 15-20 mm. However, the diastolic pressure may actually rise 10-15 mm. and the heart rate may increase by 10-20 beats per minute. This reflex mechanism exists to prevent us falling flat on our face every time we stand. It requires the action of a complex set of pressure receptors and nerve pathways. As people get older, the reflex mechanism does not work as well. Similarly, it can be interfered with by medical conditions like diabetes, and by certain medications.

Low blood pressure can happen in an acute situation like a heart attack when the heart may be failing to pump properly. Likewise, acute blood loss can also cause the blood pressure to suddenly fall. In these acute cases urgent resuscitation and medical care is required. A less dramatic, rather chronic tendency to lowish blood pressure is more commonly seen.

An older person might be on blood pressure tablets that are slowing the heart rate too much. Likewise, diuretic tablets might be causing an excessive loss of fluid from the system and dropping the blood pressure too low. Sometimes it is a case of the blood vessels being too dilated and not having enough tone to hold the blood pressure up to a normal level. Alcohol, fever, hot showers, and various medications can all dilate the blood vessels and lower the blood pressure excessively. 

Younger people with lowish blood pressure frequently have no symptoms at all. Because they might be less likely to run into problems with high blood pressure in later years, it could almost be regarded as a bonus. However, low blood pressure can be a major problem with older patients and is a common cause of falls and injuries. 

Tiredness, lack of energy, unsteadiness on the feet, and a tendency to faint are the main symptoms of low blood pressure. It may be very noticeable when rising from a chair or getting out of bed; these changes in posture drop the blood pressure and cause postural hypotension. Frequently a combination of factors is responsible eg. an older person on blood pressure tablets has a flu, gets out of bed to go to the toilet, feels woozy, falls over and breaks a hip. 

If someone does feel faint, the best approach is always to lie down flat so that the blood pressure can correct itself and improve the blood flow to the brain. Naturally, if the person did not come around immediately, prompt medical attention is required in case there is a more serious cause. 

As a general rule, lowish blood pressure is treated only if it is causing symptoms. We warn patients to avoid getting out of bed too quickly, and we adjust any medications that could be contributing to the problem. Occasionally, elasticized stockings can help by assisting the blood flow from the legs back to the heart. In more persistent or troublesome cases there are also specific medications that can be used to elevate the blood pressure.

It should be kept in mind that certain rare heart rhythm abnormalities can cause unsteadiness or collapse episodes, for instance in a younger person playing sport. These symptoms differ from those of low blood pressure and clearly require urgent investigation.

Health Tips:
* If you feel dizzy or unsteady on standing see your doctor for advice; low blood pressure may be the cause.

* If you feel like you might faint, lie down until you recover; it sure beats falling down.

Dr. Andrew Pattison: Common Consultations
North East Valley Division General Practice, Melbourne, Australia.   Disclaimer
  - Last modified: August 18, 2001