The other half of the heart

What’s your circulation? Unless you’re a newspaper editor, I bet you think of it as the heart pumping oxygen-rich blood around your body to the brain, kidneys, muscles, sex organs and other vital destinations.

But the human body has another equally important circulation that is far less well known. The right side of the heart pumps out oxygen-poor blood into the arteries of the lungs at a rate of over five litres per minute. This circulation runs in tandem with the left heart’s output and has a different function. In the lungs, red blood cells are replenished with oxygen so that they can return to the heart to be sent out to the rest of the body.

Although it is the counterpart of the better-known systemic circulation, the pulmonary circulation is mentioned much less. Yet this circulation can develop high blood pressure too — a condition called, logically enough, pulmonary hypertension. The right side of the heart then struggles to cope, and heart failure can result. The consequences include poor exercise capacity, increasing shortness of breath, fluid retention, a swollen liver, cold extremities, and even collapse. It’s a life-threatening condition.

Pulmonary hypertension (PH) is a challenge to treat. Although it was first recognised in 1950s, doctors had no treatment at all for it till the early 1980s. There’s still no permanent cure, but recent years have seen a clutch of promising new treatments.

It’s hard to diagnose PH in the first place. The pulmonary arteries are deep inside the chest, so your GP can’t just sling a blood pressure cuff around them as you perch on the consulting-room chair.

The condition really merits wider recognition. PH is potentially grim and it may not be that uncommon. Overall, 17 people in a million are thought to have it. That’s rare by anyone’s standards, but there’s huge variation from one part of the country to another, which suggests it’s seriously underdiagnosed.

Unfortunately clues are difficult to read. Make an appointment about breathlessness and feeling faint, and chances are PH won’t be at the top of your doctor’s mental list of possibilities, if it’s on the list at all. The symptoms aren’t specific. Breathlessness is often the earliest or even the only sign, but there can also be tiredness, dizziness, feeling faint, and swelling of the ankles. Some people have chest pain, especially on exertion. All of these are common symptoms of many other conditions.

Heart

A complex disorder, PH straddles two specialties: cardiology and respiratory medicine. So the guidelines for its diagnosis and treatment are a joint effort between the European Society of Cardiology and the European Respiratory Society.

There is no single test for PH. Most people have a battery of investigations before they get a full diagnosis of the condition and its cause. These begin with a simple ECG, chest x-ray and blood tests, and usually move on to a lung scan, echocardiogram (ultrasound scan of the heart) and more complicated tests. The bottom line is that it’s impossible to be sure about PH without a right heart catheter. This means a small probe inserted via the neck or groin to measure the pressure in the pulmonary artery and the heart. It confirms the diagnosis of PH and can also shed light on what caused it, so it’s a necessary if somewhat scary procedure.

When it comes to the causes of pulmonary hypertension, these range across the whole encyclopaedia of medicine. Some are easier to understand than others. Many forms of congenital heart disease can lead to PH, such as septal defects (‘hole in the heart’) or transposed great arteries. Adult heart disease is another group. Here PH increases with age, because coronary artery disease and heart failure are more common after mid-life.

Lung diseases too can block off some of the blood vessels in the lungs, leading to a rise in pressure. This group of conditions includes chronic bronchitis and emphysema (together called ‘chronic obstructive pulmonary disease’). Both are common in smokers and some ex-smokers. Around 20 per cent of people with chronic lung disease develop some degree of PH.

Then there are rheumatic diseases like lupus and even rheumatoid arthritis, where blood vessels in the lungs lose their elasticity. Some types of liver disease go hand in hand with PH, though it’s hard to see exactly why. HIV infection is also linked with PH. Again it’s not certain how or why, but, as life expectancy with HIV rises, there are now more long-term problems like PH.

Drugs can trigger PH too. Fenfluramine and other appetite suppressants, popular in the 1960s, were withdrawn for this very reason. It’s also thought that taking cocaine, St John’s wort or amphetamines could lead to PH.

One hugely important category is chronic thrombo-embolic pulmonary hypertension (CTEPH). Here, blood vessels in the lungs are progressively narrowed by blood clots. Think what happens when scale and deposits fur up pipes in a central heating system. The system doesn’t work properly and the pump can fail. That’s pretty much what happens in the human body too, though in CTEPH the clots and debris travel to the pulmonary circulation from veins in the legs or pelvis. Deep vein thrombosis is best known for its link with long-haul flights, but most DVTs occur without going near an airport. Prolonged bed rest, knee replacements and major operations on the pelvis are all linked with DVT and pulmonary embolism, and the risks increase with age and weight.

Symptoms at the time of a pulmonary embolus can sometimes be minor, but there are consequences all the same. Up to 4 per cent of pulmonary embolism survivors develop CTEPH.

When it comes to treatment, there’s a huge amount of international and cross-speciality collaboration which is making all the difference in the outlook for those with PH. New therapies, and new uses for old drugs, are driving down death rates and improving quality of life. Two established drugs, sildenafil and tadalafil, both prescribed for erectile problems, have become accepted treatments because they improve circulation in the lungs.

Surgery is an option too. Unfortunately, with CTEPH you can’t get someone in to power-flush the system to get the poor old boiler to work with a clean circuit. But taking anti-coagulants prevents new clots. And there’s an operation called pulmonary end-arterectomy (PEA) which cores out the debris from the blood vessels in the lungs. PEA is actually major open-chest surgery, done on heart-lung bypass. The surgeon cuts into the pulmonary arteries and then removes the artery lining to clear the blockages. While there are several specialist centres for PH across the UK, this procedure can only be done at Papworth Hospital near Cambridge. When it’s successful, it can give a substantial improvement in life expectancy.

All the advances in treating PH are important, but the most crucial thing is taking the first few steps: paying attention to the symptoms and getting the right tests done.