Dyspnea (trouble breathing): A symptom with many causes

A baby enters to the world with collapsed, fluid filled lungs.  Within 10 seconds, he gasps, takes a noisy breath and completes his transition to the outer world. From that point, he will inhale and exhale air over 8 million times a year until he takes his last breath at death. Breathing is his link to life, much as his umbilical cord was the link when he was in the womb. As long as his heart and lungs remain healthy and the muscles and bones his chest can move normally, he will maintain a comfortable, laissez-faire relationship with his breathing, seldom paying much attention to the never-ending process of taking in oxygen and getting rid of carbon dioxide. Strenuous physical activity will make him notice his breathing and he will learn the physical limits beyond which breathing harder and faster is ineffective. While he will experience discomfort with breathing at those limits, he will not feel fear or distress because he understands that his gasping for air is a normal response and that he will recover promptly when he rests.

Words used to describe trouble breathing

But when there is trouble somewhere in the respiratory system, the act of breathing becomes distressing in ways that and prompt a variety of different descriptions: “I feel short of breath.” “I can’t catch my breath.”  “My chest is tight.”  “I’m smothering.” “I’m suffocating.” “I can’t take a deep breath.”  “I can’t breathe out all the way.” “Breathing is hard work.”  “I need to more air.”   Doctors use one word to encompass all of these descriptions – dyspnea, defined as abnormally uncomfortable awareness of breathing. Dyspnea is not a diagnosis but a symptom of many different types of respiratory problems. Diagnosis requires discovering where the trouble is in the normal chain of events that make up one breath.

The drive to breathe

The first part of a normal breath is the drive to breathe –  a message from the brain to the muscles that increase the volume of the chest. The ribs move outward and the diaphragm between the chest and the abdomen moves down. The chest cavity expands, much like a fireplace bellows, sucking air down the trachea and the bronchial tubes into the lungs. In the next step, oxygen is absorbed into the blood and carbon dioxide is expelled from it. This gas exchange takes place in the spongy tissue of the lungs, in tiny air sacs called alveoli where red blood cells flow in single file though tiny capillaries. After 3-4 seconds, the muscles relax, the chest cavity diminishes in size and air rushes back out. Normal breathing goes on automatically, beneath conscious awareness unless the body demands more gas exchange because of increased exertion.

The drive to breathe increases when the body’s demand for oxygen goes up.  “Hard breathing” from exertion is not distressing or indicative of illness unless it occurs in someone who has been very fit and previously more capable. Low oxygen pressure at high altitude also stimulates the breathing drive, but true dyspnea is a sign of altitude sickness and need for immediate treatment and evacuation to lower altitude because of fluid in the lungs.  Anxiety and fever increase respiratory drive, as does hyperthyroidism, producing variable awareness of rapid breathing, but little discomfort.

The highway air movement follows

Moving air in and out of the lungs is the next part of normal breathing and a common source of true dyspnea. Infections, chronic inflammation from allergies, cigarette smoke or other environmental toxins can narrow and partially obstruct the trachea and the bronchi. Symptoms include coughing, wheezing and faster breathing to compensate for less air moved with each breath. Breathing “seems like hard work.” Sometimes bronchial spasm from inflammation makes it difficult for people to exhale fully. They have a sense of not being able to empty the air from their lungs and as a result get the feeling that they cannot inhale enough on their next breath. Asthma is the typical illness which causes this type of dyspnea.

Muscle disorders like Lou Gehrig’s disease, overall weakness from chronic illness, or paralysis from spinal cord problems can limit air transport by limiting chest wall movement. Obesity causes breathing problems because even normal muscle may not be strong enough to move the chest wall buried under heavy weight.

The deep reaches of the lungs where the work is done

Farther down into the lungs, dyspnea comes from impaired gas exchange and feels like air hunger – no matter how fast the breathing rate is, there still seems to be insufficient air. Lung infections like viral and bacterial pneumonia, and chronic inflammatory disorders that produce lung scarring are the typical culprits.  Cough, fever and rapid onset of dyspnea are clues to pneumonia.  Gradual onset of dyspnea is more common in the inflammatory scarring and in smoking related lung disease, which causes both obstruction to air flow and loss of the alveoli where gas exchange occurs.

Poor blood flow through the lungs can be the culprit

Normal breathing also depends on the heart, which is the pump that pushes blood through the lungs for gas exchange. A failing heart makes blood flow too sluggish for adequate gas exchange during each breath, causing a sense that air flow is inadequate and making breathing rate go up. People who have cardiac dyspnea also describe feeling suffocated or smothered, especially if fluid begins to leak from the blood into the lung tissue. Gravity influences the symptoms which worsen with lying down and improve with sitting up.

Pulmonary emboli, clots that form in the legs or pelvis and break off and travel upstream, can cause severe and sudden dyspnea by lodging in and blocking major blood vessels in the lungs.  Air reaches the lung segment where the clot is lodged, but gas exchange doesn’t occur because no blood is getting through. Large clots can be fatal immediately.

Should you develop dyspnea, seek help and try to provide a good history of your symptoms.  Symptom history is very important in diagnosis and accurate diagnosis is crucial to proper treatment. The goal of treatment, of course, is a return to the comfortable lack of awareness of breathing that should accompany you from cradle to grave.

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