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Why Am I Short of Breath When My Oxygen Saturation Levels Are Normal?

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Updated April 07, 2013

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Question: Why Am I Short of Breath When My Oxygen Saturation Levels Are Normal?
Answer: The percentage of oxygen saturation doesn't always correlate with the sensation of breathlessness. This means that a patient may feel short of breath, despite a normal pulse oximetry reading. In COPD, this phenomena is primarily caused by co-existing heart failure and/or skeletal muscle alterations.

Co-Existing Heart Failure

It is estimated that as many as 20.9% of all patients with COPD also have co-existing heart failure. And patients who have both conditions concurrently have a worse prognosis that those who have COPD or heart failure alone.

Symptoms of heart failure and COPD frequently overlap. Dyspnea with exertion, coughing during the night, or dyspnea accompanied by coughing spells during the night are common to both conditions. Because they share similar characteristics and often co-exist, a thorough assessment should be performed on any patient displaying respiratory symptoms to determine if the symptoms are caused by COPD, heart failure, or both.

What Is the 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. 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 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, predominant 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 the 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 cause the muscles to decrease in size and eventually 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 de-conditioning 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 Can You Do About It?

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 literally 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. Additionally, check out the links below for more information about COPD, heart disease, and exercise:

Sources:

Jelic, Sanja MD, Le Jemtel, Thierry H. MD. Diagnostic Usefulness of B-Type Natriuretic Peptide and Functional Consequences of Muscle Alterations in COPD and Chronic Heart Failure. CHEST 2006; 130;1220-1230. DOI 10.1378/chest.130.4.1220.

Jelic, Sanja MD, Le Jemtel, Thierry H. MD, Padeletti, Margherita MD. Diagnostic and Therapeutic Challenges in Patients With Coexistent Chronic Obstructive Pulmonary Disease and Chronic Heart Failure. American College of Cardiology Foundation. Vol. 49, No. 2, 2007. doi:10.1016/j.jacc.2006.08.046

Kao, Andrew, MD., Loh, Evan, MD. Skeletal muscle dysfunction and exercise intolerance in in congestive heart failure. January 26, 2000.

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