One of the most frequently asked questions about lung disease is also one of the most baffling: why do people with COPD experience shortness of breath despite a normalÂ oxygen levelÂ reading? What is normal oxygen saturation? Because COPD seldom exists in a vacuum, we must look beyond the lungs to find the answer.
COPD and Chronic Heart Failure
According to the American College of Cardiology, heart failure and COPD are common long-term health conditions that frequently co-exist. When you have both conditions, itâ€™s often difficult to differentiate which is causing your symptoms.Â Â Because symptoms of both illnesses commonly overlap â€“ and both frequently occur together â€“ itâ€™s important for people with COPD who experience breathlessness with exertion, coughing during the night, or breathlessness and coughing spells during the night, to undergo a thorough physical examination to determine if the symptoms are related to COPD, heart failure, or both.1
What is Heart Failure?
Heart failure occurs when the heart is no longer able to pump a sufficient amount of blood through the body. Similar to COPD, people with heart failure can be somewhat stable, or they can experience exacerbations (periods of time when their symptoms worsen). There are many conditions that can lead to heart failure, the most predominant being coronary artery disease.
When the heart is too weak to pump enough blood to the cells, tissues, and organs, every system in the body is affected: muscles weaken, weight loss occurs, fatigue and breathlessness are common, and physical activity becomes increasingly difficult.1
How Does Heart Failure affect Oxygen Saturation?
Oxygen saturation is a term used to define how much oxygen your blood is carrying. It is commonly measured by a pulse oximetry monitor, a non-invasive device that attaches to the end of your finger. When people with stable COPD (meaning they are not having an exacerbation) also have heart failure, itâ€™s not unusual for them to experience shortness of breath, yet have a normal oxygen levelÂ reading. This is because, as the volume of blood pumped by the heart lessens, the oxygen saturation level isnâ€™t immediately affected. Over time, lack of oxygen affects every organ in the body including the lungs, which may eventually lower oxygen saturation.1
Skeletal Muscle Abnormalities
Rising from bed â€“ getting dressed â€“ taking a shower â€“ going to work â€“ we rely upon our skeletal muscles to perform all our daily activities. Skeletal muscles are found throughout the body. Their primary role is that of supporting the skeleton and voluntarily moving the bones. When our muscles are fit and well-conditioned, daily activities are a breeze; when our muscles fatigue easily from prolonged disuse, daily activities are far more challenging.
Although COPD primarily affects the lungs, skeletal muscle abnormalities are a secondary consequence of the disease. Shortness of breath and fatigue, common symptoms of COPD, often cause patients to limit their physical activity for fear of worsening breathlessness. The vicious cycle of prolonged inactivity, fatigue, and increased breathlessness with exertion leads to decreased muscle fitness and weakness. Remaining immobile for long periods of time causes the skeletal muscles to slowly decrease in size and eventually atrophy, or waste away.2
How Do Skeletal Muscle Abnormalities affect Oxygen Saturation?Â
When your muscles are called upon to perform any type of physical task, they have to work harder, which increases their demand for oxygen; this is why exerting yourself increases your heart rate and breathing. Â In contrast, calling upon weak muscles to perform physical activity requires much more effort, leading to greater fatigue and breathlessness, more so than if your muscles were fit. Take, for example, climbing 3 flights of stairs; even if youâ€™re moderately active, youâ€™re likely to experience some degree of breathlessness by the time you reach the top. Now imagine your muscles are extremely weak from inactivity; simply rising from a chair or walking across a room can lead to breathlessness.
Unlike shortness of breath directly related to lung impairment however, breathlessness caused by skeletal muscle abnormalities may not always correlate with oxygen saturation. This means itâ€™s entirely possible to experience breathlessness, without seeing a drop in your oxygen saturation level.3
Exercise: The Key to Breathlessness
The answer to breathlessness from COPD, heart failure, and/or skeletal muscle dysfunction is exercise. In fact, the American College of Cardiology reports that people who have COPD and heart failure together are prime candidates for exercise training. Whatâ€™s more, skeletal muscle abnormalities can be completely reversed by participating in an exercise training program or a cardiopulmonary rehabilitation program.3
Talk to your health care provider for more information about enrolling in cardiopulmonary rehab. If youâ€™re ready to start an exercise program on your own, donâ€™t miss reading: 11 Tips for Exercising with a Chronic Health Condition.
Author: Deborah Leader RN, BSN, PHN