Lungs: The hidden biomarker

Chronic obstructive pulmonary disease (COPD), a catch-all term for a spectrum of diseases from chronic bronchitis to emphysema that cause air-flow to be restricted, is the fourth most common cause of death in the United States today. But the process by which COPD becomes debilitating and ultimately even fatal is remarkably long and insidious.

It can be more than15 or 20 years from inception before a person will feel symptoms such as shortness of breath. This means that many people over 40 are in the early stages of lung disease without knowing it.

This is a shame because a simple breathing test, known as spirometry, can be an effective screening tool for COPD—and an indicator of overall health and aging. Despite its technical name (from the Latin word spirare, “to breathe”), spirometry is the least complicated and lowest tech of lab tests. You simply breathe out as much air as you can into a plastic tube.

Pulmonologists use it to monitor patients who have asthma or emphysema. But untold numbers of people might avoid COPD in later life if more primary-care physicians made spirometry part of routine workups of healthy adults over 40.

A lower-than-normal spirometry measurement can identify emphysema and other COPDs early enough for interventions to slow their progression considerably.

Spirometry also turns out to be an informative biomarker of aging. Comparing an individual’s spirometry results to those of a large database of healthy adults, adjusted for height, gender, ethnicity and age, yields a reliable assessment of the physiological age of the lungs of a healthy person.

Spirometry yields two measures of lung capacity, each a biomarker of aging:

Forced vital capacity (FVC): the total amount of air you can force out after a maximum inhalation. This is determined by a combination of factors: the size of your chest, the number and health of your lungs’ air sacs, the elasticity of your large airways and the strength of your breathing muscles.

Forced expiratory volume in the first second (FEV1): The maximum amount of air you can force out in the first second of the FVC manuever. This is largely a function of the elastic recoil of the small airways.

Studies have shown that both measures decline with age—gradually, about 1 percent a year—and made a correlation between these biomarkers and mortality. The Buffalo Health Study, for instance, followed nearly 1,200 men and women between 20 and 89 for nearly three decades and found that lower lung function as measured by spirometry predicted earlier death.

However, there is a nuance: The mortality correlation is not solely between respiratory function and death caused by respiratory disease (as, for instance, the biomarker of arterial stiffness correlates specifically with life-threatening cardiovascular disease). So lower spirometry readings with age—normal lung aging, in other words—do not predict earlier death from lung disease for most people.

The more significant association is one that’s much broader: between lower spirometry readings and increased mortality of all kinds. This indicates that respiratory function over time reflects how the body as a whole is aging, making spirometry one of the most valuable biomarkers of aging. As Dr. Milton Hollenberg of the University of California, San Francisco, Medical Center puts it, FEV1 is less a specific measure of lung function than “a surrogate for a number of unmeasured aging processes.”

Another way in which the pulmonary system differs with the cardiovascular is that it stands up better over time. From a biological engineering and evolutionary standpoint, it has a lot of design overbuild. If you don’t abuse your lungs with cigarette smoke or occupational toxins, they will serve you well, long after one of your other vital organs fails.

That doesn’t mean they don’t age. They do—and it is this aging that is a clue to risk of other diseases. It’s like the body’s canary in a coal mine.