Heart Disease: A Major Cause of Trouble Breathing

HOW CAN HEART DISEASE CAUSE TROUBLE BREATHING?

The right side of the heart pumps venous (de­oxygenated) blood to the lungs where it is oxygenated. This oxygenated blood then returns to the left side of the heart and is pumped out to the rest of the body. In heart failure, a very common condition, the left side of the heart is weakened, resulting in a back­up of blood into the lungs. This is called congestive heart failure (CHF). The pumping action of the heart still works but not as efficiently as normal, and the lungs become congested with extra blood. This congestion of the blood capillaries in the lungs causes shortness of breath (dyspnea); it can be relieved by giving heart pills (such as digoxin) and water pills (diuretics).

Since heart disease is more common than lung disease, the most common organic cause of dyspnea is probably heart trouble. It's important to recognize if the dyspnea is due to primary heart or lung disease, since the treatment is different. This distinction requires a thorough medical evaluation. Often breathing tests and chest X­ray will have to be done to determine the cause. In many patients both the lungs and heart are diseased so treatment must be given for both.

WHAT IS THE DIFFERENCE BETWEEN RIGHT AND LEFT HEART FAILURE?

There are two sides of the heart, right and left (see Section A). Each contains two chambers, a right atrium and ventricle and a left atrium and ventricle. Remember that the right side of the heart receives venous blood from the body's tissues and sends it to the lungs to pick up oxygen; the left side of the heart receives oxygenated blood from the lungs and sends it to the body's tissues via the arterial system. Either side of the heart may be stressed to the point of failure. Clinically we speak of patients manifesting either right heart failure, left heart failure, or both. A few generalizations can be made about the two conditions.

Right­sided heart failure is often due to lung disease, most commonly chronic obstructive lung disease (see Section G). The right side of the heart suffers increased stress as it pumps blood into a diseased lung. The end result is a large heart (enlargement of the right atrium and ventricle) and fluid backing up in the systemic venous system. This leads to edema (increased fluid) of the legs, bloating, and occasionally abdominal discomfort and ascites (fluid within the abdomen).

Dyspnea in the presence of right heart failure is due to the underlying lung disease, not the heart failure. Treatment is that of the underlying lung condition, since any improvement in lung function will help relieve stress on the right side of the heart. When hypoxemia is present, oxygen is the best single treatment. Diuretics are also frequently used to help mobilize the excess fluid.

R.H. — A Case of Right­Sided Heart Failure

Mr. R.H., 59, was admitted to the hospital because of shortness of breath and leg swelling. He was a heavy smoker for many years, but had no history of heart disease or high blood pressure. In the hospital a chest X­ray showed an enlarged heart and no fluid in the lungs. His blood oxygen level was low.

Mr. R.H. was treated with bed rest, nasal oxygen, and water pills. Within a week he lost 15 pounds and felt much better. His lung function studies showed severe impairment and a need for continuous oxygen at home.

Diagnosis: right­sided heart failure due to severe chronic bronchitis (see Section G). Treatment: For the lung problem, in this case, mainly oxygen and an occasional water pill.

Left­sided heart failure is often due to primary heart disease, usually of the coronary artery blood vessels or of the left heart valves (aortic or mitral valves). Another common cause of left heart failure is severe high blood pressure. In contrast to right heart failure, which results from lung disease, left heart failure may cause lung disease, or at least lead to back­up fluid within the lungs. When this occurs, dyspnea and abnormal gas exchange result. In severe cases of left heart failure the right side of the heart may also fail. However, before the right heart becomes weakened, patients with left­sided failure may experience profound dyspnea without evidence of bloating or edema elsewhere in their body.

L.H. — A Case of Left­Sided Heart Failure

Mr. L.H., 62, was hospitalized because of shortness of breath and leg swelling. He was a nonsmoker, but did have a history of high blood pressure for many years. His chest X­ray showed a large heart, with fluid in and around both lungs. His blood oxygen tension was low.

Mr. L.H. was treated with bedrest, oxygen, heart and water pills, and antihypertensive medication. Within a week he lost 12 pounds. Lung function studies were near normal and his oxygen level was adequate.

Diagnosis: left­sided heart failure due to high blood pressure. Treatment: for the heart problem, in this case heart pills and blood pressure medication to relieve the strain on the heart.

Both conditions may thus lead to congestive heart failure. Right heart failure leads to congestion of the systemic venous system and back­up of fluid in the visible parts of the body (extremities, abdomen). Left heart failure leads to congestion in the pulmonary vessels; this congestion can be seen on a chest x­ray. When left heart failure is severe, the term "cardiac pulmonary edema" is often used. The differences between right and left heart failure are summarized in Table 1, along with terms common to both.

Figure 1 shows an x­ray picture of normal heart and lungs (la) compared with an x­ray of right heart failure due to chronic obstructive pulmonary disease (lb) and an x­ray of left­sided congestive heart failure (lc). Lines radiating out from the heart represent exaggerated blood vessels in patient with left heart failure. Figure 1d shows x­ray of acute left heart failure: cardiac pulmonary edema. The difference between lc and ld is a matter of degree; in the latter, fluid has leaked out of the capillaries to collect in the alveolar spaces. Such an x­ray appearance, characteristic of pulmonary edema, is often referred to as "batwing ."

Figure 1. Chest X­rays of normal heart (a) and of patients with heart disease (b­d). See above text for discussion.

WHAT IS PULMONARY EDEMA?

Pulmonary edema is water in the lungs. More specifically it is an abnormal accumulation of fluid in the smallest airways and alveoli. This fluid comes from the blood vessels surrounding the millions of alveoli. The most common mechanism for this fluid build­up is increased pressure in the pulmonary blood vessels due to failure of the left side of the heart.

Cardiac pulmonary edema is thus one manifestation of congestive heart failure and the terms are sometimes used interchangeably. As commonly used, cardiac pulmonary edema refers to the acute, severe form of left­sided heart failure, not to chronic, insidious cases. The x-ray shown in Figure 1c could be interpreted as indicating CHF or cardiac pulmonary edema, both meaning the same thing. Figure 1d shows a more classic example of cardiac pulmonary edema.

Pulmonary edema may also occur unrelated to heart disease or CHF, so-called non­cardiac pulmonary edema. Here, the mechanism is not increased pressure from a failing heart, but pulmonary capillary damage and leakage of blood plasma into the alveoli. The heart may function normally in this condition. In contrast to cardiac pulmonary edema, a variety of diseases may lead to non­cardiac pulmonary edema.

HOW IS HEART DISEASE DISTINGUISHED FROM LUNG DISEASE IN A PATIENT WITH DYSPNEA?

There are no reliable physical signs or symptoms that will always distinguish heart from lung causes of dyspnea when either may be present. Difficult diagnostic problems often occur in patients who may have either pulmonary or heart disease as a cause of dyspnea.

Chronic obstructive pulmonary disease (COPD) is a common respiratory cause of dyspnea. Its treatment is different from primary (left­sided) heart failure, yet both can present with nearly identical symptoms and signs.

For example, shortness of breath while lying down, swelling of the legs, and abnormal breathing sounds are all time­honored findings in both left heart failure and COPD.

The most useful test to diagnose left heart failure in such patients is the routine chest x­ray. It shows an enlarged heart and congested pulmonary blood vessels in patients with left­sided CHF. When COPD is accompanied by right heart failure the x­ray will also show a large heart, but not the congested pulmonary blood vessels (unless left heart failure is also present).

Breathing (pulmonary function) tests, along with arterial blood gases, are helpful in diagnosing COPD. These show an obstructive respiratory pattern and (usually) abnormal O₂and/or CO₂ blood tensions.

Pulmonary function tests and chest x­rays can often distinguish between the two common causes of difficult breathing. When these tests fail, more sophisticated methods such as cardiac catheterization may have to be employed.

WHAT IS CARDIAC ASTHMA?

When left heart failure occurs, fluid backs up into the lungs and leads to dyspnea. The patient may also notice wheezing, or wheezes may be heard by the physician. Wheezing due to the left heart failure is "cardiac asthma." It is not the same asthma as described in Section B, and treatment is for the heart problem and not for a primary pulmonary condition. Although some of the same drugs used in treating regular asthma may be used (particularly aminophylline), heart medication and diuretics are also helpful. Normalizing heart function is usually sufficient to correct the wheezing and dyspnea of cardiac asthma; in regular asthma heart function is normal to begin with (unless the patient has two conditions).

As discussed in Section B there are several causes of wheezing, only one of which is "pure" asthma. The distinction between cardiac asthma and the more common variety of asthma described in Section B is best achieved by a chest x-ray and thorough medical evaluation.

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