A 38-year-old high school track coach came to see Marvin M. Lipman, Consumer Reports’ chief medical advisor, because of shortness of breath, which had worsened over the past six months. A lifelong nonsmoker, he was a varsity miler in college and had continued running until about two years before, when he began to slow down. Now he noted shortness of breath after walking just a few blocks. Although he had no history of allergies or wheezing, he had once been told that he might have asthma. He was being treated with an inhaler, with no benefit.

As part of his examination, Lipman walked him around the perimeter of the office several times and noticed that, although his pulse rate increased (as it should have), his blood oxygen saturation rate — a measure of how well his blood was carrying oxygen throughout his body — fell from a healthy 98 percent to 90 percent. His blood pressure was normal. The only notable finding on the physical examination was slight swelling of his ankles.

Lipman reviewed the many lab tests the patient had brought with him and could find nothing wrong. He had no family history of heart or lung disease. His chest X-rays, chest CT scan and EKGs were all normal. Breathing tests showed no signs of asthma. At that point, the doctor sent him for a stress echocardiogram (a sonogram of the heart at rest and after exercise), which showed increased pressure in the right side of his heart, with thickening of the right ventricle. Suspecting pulmonary arterial hypertension — increased blood pressure in his lungs — Lipman referred him to an expert at a medical center.

There he underwent right heart catheterization (insertion of a catheter into a groin vein and up into the right ventricle), which showed unequivocal pressure elevations in the right ventricle, a key to elevated pressure in the lungs.

Normally, the blood pressure in our lungs is very low compared with the blood pressure in the rest of our body. But with pulmonary arterial hypertension, the lung’s arteries become narrowed, forcing the right ventricle of the heart, which supplies blood to the lungs, to work harder to force blood through the vessels. As a result, the ventricle’s muscle thickens and then weakens or fails in its pumping ability. That condition then causes a backup of blood in the veins of the abdomen and legs, the first sign of which is swelling of the feet.

The symptoms mimic so many other diseases that it usually takes about two years from the onset of exertional shortness of breath (60 percent of patients) or fatigue (20 percent of patients) for the correct diagnosis to emerge. Without treatment, the condition gets inexorably worse, with death occurring in an average of three years. The mechanism behind the pulmonary hypertension is abnormal though not cancerous growth of cells lining the lungs’ arteries. There is no cure, but treatment can extend and improve the quality of life.

Pulmonary arterial hypertension is a rare, underdiagnosed disorder. About 10 to 15 of every million people develop it each year, women almost twice as often as men. The average age at diagnosis is about 36. It’s often a consequence of diseases that are known to affect the lung’s blood vessels, including some types of heart disease, HIV infection, sickle-cell disease, scleroderma and other collagen-type diseases such as lupus, multiple (often silent) blood clots in the lungs and the use of the now-withdrawn appetite suppressants dexfenfluramine and fenfluramine.

There is also a possible link to antidepressants known as selective serotonin reuptake inhibitors, such as fluoxetine (Prozac and generics) and sertraline (Zoloft and generics), as well as to sleep apnea, chronic obstructive lung disease and interstitial fibrosis of the lungs. When no underlying cause can be found, the disease is called idiopathic pulmonary arterial hypertension, which is what the track coach turned out to have.

Most cases of pulmonary arterial hypertension can be treated with medication, oxygen and exercise. Tests done during the catheterization indicated which of the several available drug treatments might enable the coach to defer the need for a lung transplant, which is the option for advanced disease.

Shortness of breath and undue fatigue in the absence of obvious disease are symptoms that require persistent medical investigation until a cause is found — even if that cause is a long shot.

Copyright 2013. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.