Blood vessels, blood pressure and heart disease

1"One forty-five over ninety-five"

At a community health check, a nurse wraps a cuff round a man's upper arm, pumps it up, lets it down slowly and says: "One hundred and forty-five over ninety-five. You should see a doctor." The man feels perfectly well. What do the two numbers measure, and why do they matter when he has no pain at all? The answer lies in the walls of his arteries, and in the small arteries that feed his heart.

2Three kinds of vessel

Blood leaves the heart in arteries, which branch into smaller arteries (arterioles) and then into capillaries; capillaries join into small veins (venules) and then veins, which return the blood to the heart.

Figure 1: Cross-sections of an artery, a vein and a capillary (not to scale).

How each fits its job. An artery's thick, elastic wall withstands the high pressure of each beat; it stretches as the surge arrives and springs back between beats, which keeps the blood moving smoothly. A vein's blood is at low pressure, so it needs a wide lumen, which offers little resistance, and valves to stop blood flowing backwards. Veins in the legs are squeezed by the muscles around them when you walk, and the valves make sure the blood can only go up. A capillary's wall is one cell thick, so oxygen and glucose diffuse out to the cells, and carbon dioxide and wastes diffuse in, over the shortest possible distance. Some plasma is also pushed out through capillary walls, forming the tissue fluid that bathes every cell.

Figure 2: A valve in a vein.

3Blood pressure

A healthy young adult's blood pressure is typically about 120 over 80 mmHg. The World Health Organization defines high blood pressure (hypertension) as a systolic reading of 140 mmHg or more and/or a diastolic reading of 90 mmHg or more, on two different days. Hypertension usually causes no symptoms, which is why it is called a "silent" condition; the WHO estimates that about 1.4 billion adults aged 30 to 79 had it in 2024, and that about 600 million of them did not know. Over years, it damages the arteries and makes the heart work harder, raising the risk of heart attacks, strokes and kidney disease. Too much salt, being overweight, lack of exercise, smoking, alcohol and stress all raise blood pressure.

4Coronary heart disease

The heart muscle never rests, so it needs a constant supply of oxygen and glucose through the coronary arteries. In coronary heart disease, fatty deposits called atheroma build up in the walls of these arteries over many years and narrow them.

Figure 3: How a coronary artery becomes blocked.

• A narrowed artery may still supply enough blood at rest, but not during exercise: the person feels a tight pain in the chest when active, called angina.
• If a plaque breaks, a blood clot forms on it and may block the artery completely. The heart muscle beyond the block is starved of oxygen and starts to die: a heart attack.

Risk factors that a person can change: smoking, a diet high in saturated (animal) fat and salt, lack of exercise, being overweight, high blood pressure, diabetes that is not controlled, and heavy drinking. Factors that cannot be changed: getting older, being male, and a family history of heart disease.

Prevention: don't smoke; be active every day; eat plenty of vegetables, fruit, beans and whole grains, with less fried and fatty meat and less salt; keep a healthy weight; and have your blood pressure checked regularly. Doctors treat the disease with medicines, by widening the artery with a small mesh tube (a stent), or by a bypass operation that carries blood round the block.