She reportedly had been living with chronic obstructive pulmonary disease, or COPD, a term used to refer to a group of diseases that damage the lungs and make breathing difficult. COPD includes emphysema, chronic bronchitis, and some cases of asthma. It is considered the third leading cause of death in the U.S., according to the Centers for Disease Control and Prevention (CDC).

About 15.7 million Americans are diagnosed with COPD, and half of people with low lung function are thought to have COPD but not know it, according to the CDC, which means that the true number of Americans living with COPD may be much higher.

While it’s a disease primarily seen in older adults and current or former smokers, here’s what everyone should know about COPD.

COPD is usually caused by smoking, but not always

The National Heart, Lung, and Blood Institute (NHLBI) pinpoints cigarette smoking as the leading cause of COPD but estimates that up to 25% of people with COPD never picked up a cigarette. Bush herself started smoking when she was 18 and quit in 1968, as she detailed in her 2015 memoir.

But other lung irritants, including air pollution and secondhand smoke, can also cause COPD, as can a rare genetic condition called alpha-1 antitrypsin deficiency. Women are also more likely to have COPD than men.

COPD symptoms are common

COPD symptoms include shortness of breath, coughing, wheezing, and a feeling of tightness in the chest—common enough signs that might be chalked up to a cold, a cough, asthma, or simply being out of shape.

But it’s important not to brush these signs under the rug. For the best prognosis, you'll want to get started early with treatment, which usually includes a combination of medications—often known as triple therapy—to relax your airways and bring down swelling in the lungs. COPD treatment can slow down the progression of the disease, which otherwise worsens over time through four stages: mild, moderate, severe, and very severe.

RELATED: 15 COPD Symptoms You Should Know

COPD doesn’t just affect the lungs

Bush was also living with congestive heart failure, which means her heart was struggling to pump enough blood throughout her body. COPD can lead to high blood pressure, which can in turn increase a person’s risk of heart disease. People with COPD are also more likely to have arthritis, depression, and memory loss, according to the CDC.

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It’s never too late to quit smoking

Giving up the habit can help prevent COPD from developing in the first place. But even if you’ve already been diagnosed, it's a smart idea to quit: It can help keep symptoms at bay and slow the progression of the disease. People who stop smoking, exercise, and eat well with COPD will breathe more easily and feel better overall, according to the NHLBI.

A chest x-ray rules out other conditions are causing your symptoms, such as heart failure. An x-ray also can reveal emphysema, one of the causes of COPD.

A CT scan of the lungs will also show signs of COPD, and can also be used to diagnose lung cancer.

Blood tests

An arterial blood gas test measures how well the lungs are bringing oxygen to the blood and removing carbon dioxide. Test results show how severe your COPD is, and whether you may benefit from oxygen therapy.

There are no other lab tests that can diagnose COPD, but your doctor may run them anyway to rule out other conditions that have symptoms similar to COPD.

Smoking is particularly dangerous for those with alpha-1 antitrypsin deficiency; if you smoke and develop COPD at an early age (before age 45), your doctor may test you for the gene. However, because the condition is rare, not everyone is tested for an alpha-1 antitrypsin deficiency.

Being a salesman was stressful, but it also could be boring at times. I had started smoking when I was 17 years old, and when I was working, cigarettes offered a way to deal with stress and pass the time when I was bored. I went through more than two packs a day at one point. Back then, I was like many other young people; I thought I was invincible.

But then things started to change. I picked up a smoker's cough, and by 1994, when I was in my early 50s, I started getting out of breath. I hadn't really noticed it before, but for the first time, I couldn't keep up with people when we were walking in a group.

Now I use oxygen around the clock
I went to the doctor and found out I had COPD. To be honest, I didn't know anything about the condition. I'd heard of bronchitis and emphysema, though, and it turns out that COPD is a combination of both.

When you have COPD, tiny structures within your lungs become irritated and damaged, and breathing becomes more and more difficult. As a result, it becomes harder to do physical activities without getting short of breath. The disease has no cure; the goal is to keep it from getting worse.

The best thing you can do is quit smoking; I finally quit in 2001. I tried everything: the patch, gum, oral medications, and, finally, hypnosis. Hypnosis worked for me; I never had another cigarette. It doesnt even bother me to be in the presence of people smoking.

Shortly after, I had back-to-back surgeries to clean out arteries in my neck—which were clogged due to atherosclerosis—that could have caused a stroke. After that, my breathing became much worse. That's when I started using oxygen.

I use a machine that provides extra oxygen for me to breathe. A tube delivers this oxygen to my nose 24 hours a day, seven days a week. I need 15 liters of oxygen every minute, which is an extremely heavy dose.

At home, a machine called a concentrator provides my oxygen by concentrating the oxygen from the air in the room. When I'm out of the house, I carry a refillable container of liquid oxygen with a strap that goes over my shoulder. I don't even notice the sound anymore, but people have told me it sounds like a garden hose running.

Next Page: Life with COPD is just much slower [ pagebreak ]Life with COPD is just much slower
I was recently talking with someone else who has COPD. We were reminiscing about being in a hurry, how we used to be able to walk fast or even start running when necessary. Today, the pace of my life is much slower.

If I had to pick a word to describe my life these days, it would be changed. When I go up and down stairs, I move slower. When I walk across a parking lot, I walk slower. When you have this disease and it's progressed to the point that it's severe, you notice all kinds of things you can't do anymore. I can't shovel snow or just decide to repaint the woodwork outside my house.

That's not to say I don't get out, though. Twice a week I go to a program at a local hospital where I walk and use exercise machines for an hour. And I go to events hosted by the Respiratory Health Association of Metropolitan Chicago, where I listen to experts speak about the latest research on COPD and other lung diseases.

My one major regret? Smoking. I'd like to tell any readers who are smoking to stop. Someday you're going to want to have the best quality of life you can, and COPD definitely reduces that quality.

When my children were small, I played sports and did other activities with them. Now I have three grandchildren. I thought I would be able to do the same things with them, but I can't.

If you have chronic obstructive pulmonary disease (COPD), you're at an increased risk for developing other health problems, such as osteoporosis, gastroesophageal reflux disease (GERD) , diabetes, and heart disease. But there are certain times when COPD patients are more vulnerable to heart attack or strokes than other people: in the days and weeks after an exacerbation, a serious flare-up in symptoms, which can land you in the hospital.

Exacerbations are often a fact of life if you have severe COPD, according to Byron Thomashow, MD, clinical professor of medicine at Columbia University, medical director of the Jo-Ann F. LeBuhn Center for Chest Disease at NewYork-Presbyterian Hospital, and chairman of the board of the COPD Foundation. Whether it's air pollution, a cold, or another lung infection that sets them off, exacerbations can ramp up your shortness of breath or cough to dangerous levels.

"I think about three-quarters of patients have at least one a year," he says. "Even in those people who successfully get through an exacerbation … it can take months and months to get back to their prior level of quality of life and function even though the symptoms go away quickly."

In general, people with more exacerbations tend to have poor lung function, reduced activity, increased inflammation, and higher mortality rates.

What causes exacerbations
The flare-ups are typically caused by infections from a virus or bacteria (particularly for smokers, who are at an increased risk of getting infected). Medications to treat COPD, including inhaled steroids like Advair, can also increase the risk of pneumonia, which can result in exacerbations. The risks have to be weighed with the potential benefits, and not using medication correctly can itself result in exacerbations.

In about one-third of flare-ups, there is no obvious cause, says William Barkman, MD, MSPH, a pulmonologist and chief of staff at the University of Kansas Hospital, in Kansas City, Kan.

"It could be environmental, or sometimes people stop taking their medications, which can lead to an exacerbation. And occasionally a comorbid disease like heart failure is the cause," Dr. Barkman adds.

Next Page: How does COPD affect heart health?

[ pagebreak ]How does COPD affect heart health?
All COPD patients are at risk for heart problems—about 30% of people with COPD die of cardiovascular disease. And those who have exacerbations are more likely to have heart problems following a flare-up.

Patients who had exacerbations had a 2.27-fold greater risk of a heart attack one to five days after the flare-up, according to a 2009 study in the journal Chest. They had a 1.26-fold greater risk of stroke between one and 49 days after an exacerbation.

A 2006 article in Thorax found that COPD patients with high levels of C-reactive protein (a protein in the blood that rises in response to inflammation) have increased relative risk of mortality, and were 1.85 and 1.51 more likely to die of cancer and cardiovascular events, respectively, than COPD patients with low levels of C-reactive protein.

It is estimated that there's one shared risk factor for both COPD and cardiac events: smoking. Another likely cause is the chronic inflammation that occurs with COPD, which damages blood vessels. This inflammation becomes acute during a flare-up.

Do medications play a role?
Medications given during the events, like inhaled beta agonists (Albuterol, can also negatively affect the heart.

Robert Ostfeld, MD, MSC, a cardiologist and associate professor of clinical medicine at Montefiore Medical Center in Bronx, N.Y., says the beta agonists can increase the heart rate, forcing it to work harder; promote arrhythmia, or irregular heart rate; and increase blood pressure.

There is no guaranteed way to completely avoid exacerbations, but there are many things you can do to help prevent them and thereby reduce the risk of heart attacks triggered by exacerbations, Dr. Thomashow says.

Using long-acting bronchodilators, such as salmeterol, in combination with inhaled corticosteroids, like Flovent and Azmacort, and anticholinergics, which relax and open up airways, such as Spiriva, can reduce exacerbations. Dr. Thomashow says taking the three in combination can also decrease heart attack risk by 60% or more, probably because they reduce exacerbation risk.

In addition, people can also take some very basic actions to help prevent respiratory infections, which can cause exacerbations. Dr. Ostfeld recommends regular hand washing and not touching your face in public places (which can spread germs from hand to mouth before you can wash them). And remember to get your flu shots, to prevent respiratory ailments, too.

And finally, he encourages COPD patients to exercise regularly, eat a largely plant-based diet, and have regular checkups to make sure things like blood pressure and cholesterol are under control.

"Having a healthy lifestyle and keeping underlying medical conditions well treated will go a long way to protecting yourself from any medical problems," Dr. Ostfeld says.

However, even nonsmokers and ex-smokers can get COPD. Exposure to secondhand smoke, air pollution, and chemical fumes can also cause COPD, as can exposure to dust in the workplace or in the environment. Other COPD risk factors include low birth weight and rare genetic factors.

In rare cases, an alpha-1 antitrypsin deficiency can play a role in the development in COPD. Alpha-1 antitrypsin is a naturally occurring enzyme that protects your lungs from damage. Some people are born with a gene variant that results in a deficiency of alpha-1 antitrypsin. There are no symptoms of this deficiency, but if you have the gene, you can develop chronic obstructive pulmonary disease (COPD) more easily and at a younger age than those with adequate amounts of alpha-1 antitrypsin.

Smoking is particularly dangerous for those with alpha-1 antitrypsin deficiency; if you smoke and develop COPD at an early age (before age 45), your doctor may test you for the gene. However, because the condition is rare, not everyone is tested for an alpha-1 antitrypsin deficiency.

I found out I was an alpha-1 (alpha-1 antitrypsin deficiency is a condition that is caused by a gene mutation and that increases COPD risk), and back then, most alpha-1s were given about two to five years of productive life after diagnosis. My doctor told me not to make plans for retirement.

I started on Prolastin therapy and took antibiotics early on when I was sick or had an exacerbation. Eventually I started using albuterol. I also took prednisone when I had an episode and a mucus breaker (like Mucinex) whenever I needed it.

I didn't have any side effects from the Prolastin, but after about a year, the veins that I used to inject the medicine into collapsed. Prolastin is thick and caustic, so it probably caused my veins, which were weak to begin with, to break down. So I had a port implanted in my chest to administer the medication. At the time I was working full-time, going to college at night, and had three teenage children. I didn't have time to go to the doctor's each week to get the treatments, so I started self-infusing, which I still do.

Over the years, I have used Advair and Singulair. After a while, I became immune to them. I have taken Spiriva, too, and went on oxygen in 1993. One of the problems with all the medications is the side effects.

I now have glaucoma and the beginning of cataracts, which can pretty much be caused by any of the medications I take. I have acid reflux, which is probably because of the prednisone, but it could also be the result of Mucinex. And after having low blood pressure my whole life, it's now high probably because of Spiriva. (I don't believe that it is due to prednisone because I took it for years and still had low blood pressure.) My cholesterol is high, which it never was before. I think that is because of the bad diet I followed when I was working. That was the one thing that wasn't a side effect! And because of my stomach problems, I have to take Boniva for osteoporosis through an IV. I also had sudden weight gain from taking prednisone, and sleeplessness, jitters, and shaking from the nebulizers and inhaler.

But those are all things that can be dealt with. I try not to get discouraged if one doesn't work. I just talk to my doctor and we try something else. My doctor and I have always measured the risk versus benefit of any drug, and sometimes it's not worth it.

When I was first diagnosed, it was frightening to have some of these side effects. Still, after this many years, I know my body and what to expect. Right now I'm on four COPD medications, but I take a total of 17 pills a day—most of them for the side effects.

I've come to look for the side effects and be more aware that they are possible. I read all the information that comes with a new drug. I think, to be truthful, the insurance issues cause me more aggravation and sleepless nights than the meds do.

COPD is a serious and potentially life-threatening illness: It is responsible for more than 130,000 deaths in the U.S. each year. There is no cure for COPD, and the lung damage that results in COPD cannot be reversed, so it is very important to identify the symptoms of COPD early on. However, COPD symptoms may be dismissed as "smoker's cough" or as a normal sign of aging. Symptoms may also be confused with asthma, but they are separate conditions (although some people can have both asthma and COPD).

COPD is a serious, long-term illness. It is the fourth leading cause of death in the United States. More than 12 million Americans have COPD and it is thought that at least as many other people have COPD and don't realize it.

Emphysema is often referred to as chronic obstructive pulmonary disease (COPD), a disorder that can include both emphysema and chronic bronchitis. (COPD patients often have both conditions.) COPD is still rare in people in their 20s or 30s, but the disease—which is characterized by lung damage and difficulty breathing—is occurring at earlier ages than in the past.

“We are seeing more and more COPD in younger people,” says Neil Schachter, MD, a professor of pulmonary medicine and the medical director of the respiratory care department at Mount Sinai Medical Center in New York City. COPD used to affect patients who were mostly in their 50s or 60s, but now diagnoses are on the rise in those in their 40s. "Improved awareness of COPD among both physicians and the public and more sensitive methods for diagnosis are the main reasons that we are recognizing the disease in younger individuals," says Dr. Schachter.

In 2000, 3.9% of the U.S. population between the ages of 25–44 were living with COPD; that number was 7.7% for those between ages 55–64, and 9.5% in people over 74 years of age.

“Although we dont see COPD in children, we do realize now that children who have asthma may be at risk of COPD later in life because of the [lung changes] that result from asthma,” explains Dr. Schachter. Whether you think you're at risk or not, people under 40 can reduce their risk of COPD by avoiding cigarette smoke, dust, and pollution.

When it comes to developing COPD at a young age, there is one especially vulnerable group—those with a rare genetic disorder called alpha-1 antitrypsin deficiency. Only about 100,000 people in the United States have it, but it makes the lungs (and liver) incredibly sensitive to damage and can result in an under-30 diagnosis of COPD (even in otherwise healthy nonsmokers.)

The problem is that many people don't know they have the gene until COPD has been diagnosed. However, if you have family members with COPD, you are at greater risk of being a gene carrier.

Bartolome Celli, MD, a professor of medicine in the pulmonary division of the Tufts University School of Medicine, in Boston, recommends that parents with COPD get tested first to check for deficiency; if they have it, their children should get checked. If you have the deficiency, says Dr. Celli, you can help prevent lung problems by avoiding dusty and smoky environments, eating a healthy diet, and getting vaccinations.

Whether you have a genetic predisposition or not, experts agree that the best way to prevent COPD is to avoid smoking, which can set the stage for a COPD diagnosis in your 40s and 50s. Smoking is responsible for about 75% of COPD deaths, according to the Centers for Disease Control and Prevention.