Oxygen Saturation and Shortness of Breath in COPD

A man takes a lung function test.
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Ordinarily, shortness of breath reflects a low oxygen saturation, but it is possible to have this symptom with normal oxygen saturation levels. The percent oxygen saturation (O2 sat) is a measure of the degree to which the hemoglobin in your blood is saturated with oxygen. It doesn't always correlate with the sensation of breathlessness (dyspnea). This means you could feel short of breath even though you have a pulse oximetry reading which is completely normal. Your O2 sat may read 95 percent to 100 percent but you may still find it difficult to breathe.

In a patient with chronic obstructive pulmonary disease (COPD) this phenomenon of shortness of breath with normal oxygen saturation is primarily caused by heart failure or by skeletal muscle alterations. Let's take a look at these separately.

Co-Existing Heart Failure

It is estimated that as many as 21 percent of people with COPD also have co-existing heart failure. This is important because people who have both of these conditions have a prognosis that is worse than that for either COPD or heart failure alone.

Symptoms of heart failure and COPD frequently overlap, yet knowing this, it's important to make the distinction. Both conditions may cause shortness of breath with activity (dyspnea with exertion), and night-time coughing spells. Anyone with these symptoms should be evaluated carefully to see if the symptoms are due to COPD, due to heart failure, or related to a combination of both.

Underlying Mechanism of Shortness of Breath in Heart Failure

In heart failure, shortness of breath along with exercise intolerance, muscle wasting, and chronic fatigue result from a reduction in cardiac output—the volume of blood that the heart can pump over a period of time. This occurs because over time, the heart—being a muscle in-and-of itself—becomes weak and is unable to pump sufficient amounts of oxygen-rich blood to the cells, organs, and tissues of the body.

Patients with both stable COPD (meaning they aren't having a COPD exacerbation) and heart failure may display normal oxygen saturation levels, yet still experience the sensation of breathlessness. This is not uncommon because a reduction in cardiac output doesn't always affect oxygen saturation levels—at least not immediately. Over time, however, poor blood flow affects every organ in the body, including the lungs, brain, liver, kidneys, and intestines, leading to a host of other symptoms.

Skeletal Muscle Alterations

Skeletal muscle alterations, with or without existing heart failure, also play a starring role in why COPD patients may experience shortness of breath with normal oxygen saturation levels. In the absence of heart failure, skeletal muscle de-conditioning is the primary reason that people with COPD have shortness of breath that doesn't correlate with their pulse oximetry reading. Additionally, skeletal muscle dysfunction—common in both COPD and heart failure—can lead to muscle wasting, interference with the body's ability to utilize oxygen, and delayed recovery time and a return of normal oxygenation after exercise.

Many people with COPD lead sedentary lifestyles, in part because shortness of breath and fatigue prompt them to avoid all types of physical activity. Persistent inactivity leads to muscle disuse, low-level systemic inflammation, and increased oxidative stress that causes the muscles to decrease in size and eventually waste away (atrophy). When muscles lack conditioning and are too weak to do their job, they fatigue easily. This often leads to shortness of breath, especially when the muscles are called upon to perform any type of physical activity. Shortness of breath due to muscle deconditioning and fatigue may or may not always correlate with oxygen saturation levels, which is why patients can feel short of breath, yet have a normal pulse oximetry reading.

What You Can Do

Patients with COPD and heart failure experience skeletal muscle alterations that affect their ability to function in everyday life. These effects are more pronounced in patients who have both conditions, and contrary to popular belief, people with COPD and heart failure combined are prime candidates for exercise training. In fact, skeletal muscle abnormalities can be reversed by physical exercise and/or cardiopulmonary rehabilitation.

If you are a patient with COPD, heart failure, or both, talk to your doctor today about implementing a  cardio-pulmonary exercise program into your treatment regime. She may begin by talking about some of the strategies for improving exercise in people with COPD such as non-invasive positive pressure ventilation, pulmonary rehabilitation, and medications.

In addition to having a good conversation with your doctor, check out the best exercises for COPD patients and think about which exercises fit your personal preferences. Having someone "guide" you in exercise can help, and exercise DVDs for COPD patients may be just that motivation.

Walking is a great exercise for COPD, but since all muscles develop wasting, flexibility exercises for COPD can do wonders for a complete workout.

The almost universal reason for avoiding exercise is fatigue, so in addition to improving your ability to exercise, improve your life by practicing ways to fight fatigue with COPD.

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