What's The Relationship Between Chronic Obstructive Pulmonary Disease (COPD) And Heart Failure?

Heart diseases and chronic lower respiratory diseases are both leading causes of death across the world. While they are both serious diseases on their own, together they make a particularly dangerous liaison. A part of the reason why they often coexist is that they share similar risk factors — cigarette smoking (and other exposure), aging, systemic inflammation, and a sedentary lifestyle.

Moreover, the main symptom of both is shortness of breath, so it’s often hard to differentiate between the two. That can worsen the scenario even further since symptoms of heart failure are often mistaken for COPD and treated with the wrong medications that can affect it negatively. 

What is chronic obstructive pulmonary disease (COPD)?

COPD is a group of inflammatory lung diseases that usually develop as a result of exposure to cigarette smoke or other irritating gases (air pollution, dust, toxic fumes). COPD can also be caused by genetic factors and infectious diseases like tuberculosis and HIV/AIDS and other factors.

They are called obstructive because their main characteristic is the blockage of airflow, which manifests as shortness of breath, first during physical activity and soon at rest as well.

COPD is a progressive disease, which means that it gets worse over time, and while there’s no cure, treatment can help with the quality of life and the severity of symptoms.

The most common conditions from this group are emphysema and chronic bronchitis, and many people with COPD have both simultaneously in varying degrees. Emphysema slowly damages and stretches the air sacks-alveoli in your lungs, which makes it harder to breathe out. Chronic bronchitis makes your airways inflamed and narrows them, making it harder for the air to pass.

The heart and the lungs are an inseparable duo

A molecule of oxygen goes through a wild ride before it reaches even the most distant cells in your body. A muscular movement causes a difference in pressure between the air and our lungs that sucks air molecules into your lungs. They're then sent spinning through a long series of tubes that become narrower and eventually end with an air sack, a thin barrier between lungs and blood vessels.

When it comes through the barrier, it binds to hemoglobin, giving your blood that bright red color. Pulmonary veins carry it to the heart — a muscular pump made up of two upper chambers (called atria) and two lower ones (the ventricles). It first travels to the left upper chamber that slowly collects the blood before it passes it to the left ventricle. With a powerful contraction, the left ventricle pushes the blood with the oxygen to the aorta which then delivers it to every cell through a system of blood vessels.

The oxygen is then used by every cell for its metabolic needs, leaving the blood depleted of oxygen. It then has to go back to the heart, this time to the right side to be pumped by the right ventricle to the lungs and start the cycle all over again. Notice how everything is interconnected and how processes in the lungs inevitably affect the heart and vice versa.

When the heart is not pumping blood well enough to satisfy all your cells' metabolic needs, we say that the person is going through heart failure. Because they function together, the heart also affects the lungs and the pressure inside of them when it’s not as efficient. This results in a fluid build-up that messes with the process of oxygen molecule crossing the barrier, leaving you feeling breathless. The effect is the same as with COPD, but the underlying mechanisms are different.

Partners in crime: COPD and HF

The prevalence of COPD in patients with heart failure in the US is between 11 and 52 percent, depending on different reports using different criteria. On the other side, more than 20 percent of patients with COPD develop heart failure. Data from hospitals also showed that COPD patients with heart failure are three times more likely to be hospitalized than patients with just COPD.

Right-sided heart failure in COPD

The driving force that leads to right-sided heart failure in COPD is hypoxia or the lack of oxygen in the alveoli (air sacks) where oxygen passes to the blood, although there are more contributing factors that still haven’t been elucidated.

Normally, our bodies keep the ratio of oxygen that reaches the surface of alveoli and the oxygen that crosses the barrier and enters the blood tightly regulated, so that the blood can get saturated with oxygen.

Tiny blood vessels that lie on alveoli can sense when there’s not enough oxygen coming in. Our bodies generally don’t like wasting energy on something that’s not efficient, so those tiny blood vessels narrow themselves (contract), so less blood reaches them and more flows to the areas where oxygen flow is good.

In COPD those areas where oxygen flow is good are constantly reduced as the airways are constricted, and not enough oxygen molecules can get through. In addition, emphysema destroys the walls of alveoli, further reducing the available surface for oxygen transport.

The cardiovascular system tries to adapt to these changes, and there are also micro-changes in the area where capillaries and alveoli touch. Low oxygen levels cause the muscle cells of the blood walls to contract, stimulating them to multiply and leading to the formation of fibrosis or scar tissue.

The whole process is called vascular remodeling and it triggers other changes as well. With time, the pressure in the blood vessels in the lungs rises, due to the narrowing of the vessels. Just like you need a bigger force to push water through a narrow pipe, the heart also needs to push harder to get the blood flowing through narrow pulmonary (lung) blood vessels.

Remember that the heart is a muscle, so just like you can pump your biceps by forcing them to work harder, the heart can also experience hypertrophy. Unlike your biceps however, this makes the right ventricle weaker as it dilates and works excessively. Enlarged chambers are not as efficient in pumping blood. This is also called cor pulmonale.

Left-sided heart failure in COPD

The prevalence of left ventricular dysfunction in COPD patients is up to 16 percent. It’s a well-observed phenomenon, but the relationship between COPD and left-side heart failure is less clear and less direct.

Patients with COPD have elevated markers that suggest systemic inflammation. The best hypothesis we have so far is that molecules that mediate inflammation also influence the blood vessels and accelerate the development of atherosclerosis, the build-up of plaque on the wall of arteries.

Again, we have blood vessels that are more narrow, so the pressure is higher and the left ventricle needs to pump harder. After years of doing so, it becomes hypertrophied and thus less efficient in pumping, eventually becoming unable to meet the demands of the body.
Also, right-sided heart failure and left-sided heart failure are connected and one can lead to the other.

COPD and heart failure: How one condition makes the other worse

On the other hand, when the left ventricle doesn’t pump the blood well enough, and can't process all the blood coming from the lungs in the predicted time, fluid builds up in the lungs. This disturbs the exchange of gases, making breathing even harder for someone with COPD.

Changes in the immune system, increased number of inflammatory cytokines (molecules that immune cells used to communicate with each other), increased number of T cells (a type of immune cells) that happen due to inflammation in COPD significantly increase the progression of cardiovascular diseases leading to heart failure.