Feature articles
17 March 2005
Exercise Hypertension
Worryingly, because high blood pressure rarely shows any signs or symptoms until secondary complications in the arteries, heart, kidneys, eyes and other areas occur, and because many people do not have their blood pressure checked regularly, a significant amount of the population are unaware that they have the condition.
In addition, a group of people who have otherwise normal or only slightly raised blood pressure levels during non-strenuous everyday activities may exhibit “exercise hypertension” in which an abnormally high “spike” in blood pressure occurs during physical exertion.
Although doctors are unsure why this exaggerated blood pressure response during exercise occurs in otherwise healthy individuals, some suggest that it may be an early sign of cardiovascular disease and a risk factor for persistent high blood pressure.
What is blood pressure?
The body’s blood circulation system is an enclosed environment in which blood pressure rises and falls constantly in response to the pumping action of the heart and signals from the brain. When the heart contracts, blood is forced through the arteries and blood pressure rises – at it’s height, this is called systolic pressure. When the heart relaxes, chambers in the heart fill with blood and blood pressure falls – this is called diastolic pressure.
Blood pressure is measured in millimetres (mm) of mercury (Hg) and written with the systolic reading foremost, and, although it can vary due to many individual factors, including age, an average reading at rest of 130/85 mmHg or above is considered high.
Blood pressure also rises and falls over the course of each day in response to many factors such as physical exertion, stress, emotional changes and anxiety. Therefore, measurements are usually taken on several occasions under restful conditions to calculate average blood pressure levels – single measurements are often meaningless.
When several measurements have shown that blood pressure has remained abnormally high for a long period of time (around 4 months or longer) a doctor will usually diagnose hypertension and suggest certain lifestyle changes and/or medications to help reduce blood pressure before it leads to serious complications.
Causes
Although the causes of high blood pressure are unknown or non-specific in the vast majority of people diagnosed with the disorder – this is called essential or primary hypertension – a wide range of factors are known to increase the risk of hypertension development. Such factors include a family history of the condition, smoking, excessive alcohol consumption, a poor diet with too much salt intake, obesity, age, artery and heart disease, and stress.
However, in a minority of individuals, high blood pressure has a known underlying cause, such as kidney disease or adrenal gland problems – this is known as secondary hypertension.
Blood pressure during exercise
Blood pressure increases in response to the extra requirement of the muscles and organs for oxygen-rich blood during exercise. However, some otherwise healthy individuals may find that their blood pressure reaches excessively high levels during exercise – for example, instead of reaching a systolic blood pressure of around 200 mmHg at maximal exercise rates, they may spike at around 250mmHg or higher.
Because such people have relatively normal blood pressure levels at rest, some experts believe that this may indicate early signs of artery disease (arteriosclerosis), and therefore they say that measuring blood pressure levels during exercise may be a more accurate test of early artery disease development than one taken at rest.
A research team from Johns Hopkins University in the USA studied 35 adults, aged between 55 and 75 years, who had untreated mild hypertension but were otherwise healthy. The participants’ resting blood pressure was measured on four or five separate occasions and then compared with blood pressure readings recorded during maximal effort on treadmill exercise tests.
Ultrasound scans were also used to measure how well the blood vessels of the participants responded to blood flow during the exercise tests.
They found that abnormally high blood pressures in response to exercise among the participants were associated with a poorer ability of the blood vessels to expand. This, say the researchers, suggests that endothelial cells that line the inside of blood vessel walls fail to dilate enough to handle the extra blood flow in such people, indicating early artery disease.
“Most clinicians focus on the patient’s blood pressure during rest, but our study shows that exaggerated blood pressure during exercise is a more sensitive marker of resistance to blood flow through the arteries, which is a possible sign of atheriosclerosis,” said lead researcher Dr Kerry Stewart, director of clinical exercise physiology at the university. “The higher the blood pressure in response to exercise, the more likely the patient was to have blood vessels that did not expand as expected.”
However, he added that impaired endothelial function is not only related to high blood pressure, but is also associated with aging, menopause, high cholesterol levels, smoking and diabetes, and may be a common process for developing heart disease among all of these risk factors.
"It's too early to recommend that people have exercise tests just to measure their blood pressures," said Dr Stewart.
"However, careful attention should be paid to exercise blood pressure if measured as part of a medical evaluation, or during a workout at a gym, since it may be a warning that your resting blood pressure may also increase."
Hypertension links
Heart and blood circulation interactive tools
Further information:
UK Blood Pressure Association
www.bpassoc.org.uk
British Heart Foundation
www.bhf.org.uk
US National Heart, Lung and Blood Institute
www.nhlbi.nih.gov
American Heart Association
www.americanheart.org
NHS Direct
www.nhsdirect.nhs.uk
