How the heart works
The normal heart consists of two upper chambers and two lower chambers. The upper chambers (i.e., the right and left atria) receive the incoming blood and pump it into the lower chambers (i.e., the right and left ventricles). The lower chambers pump blood out of the heart.
Typically, anaerobic blood from the whole body flows into the right atrium and then into the right ventricle, where it is pumped into the lungs through the great vessels (pulmonary arteries). The blood releases carbon dioxide in the lungs and absorbs oxygen as it flows through the alveoli.
Afterwards, oxygen-rich blood flows back into the left atrium through the pulmonary veins and into the left ventricle via the mitral valve. Finally, the blood leaves the heart via the large arteries (aorta) in the body.
The heart valves keep the blood flowing in the right direction. The aortic valve prevents blood from flowing back into the heart. Blood flows from the aorta to other parts of the body.
Heart-related (cardiogenic) pulmonary edema
Cardiogenic pulmonary edema is pulmonary edema caused by increased pressure in the heart.
This is usually caused by heart failure. When the left lower heart chamber (left ventricle) is unable to adequately pump blood from the lungs due to illness or overexertion, the pressure in the heart increases. The increased pressure will drive blood through the walls of the blood vessels and into the alveoli.
Medical conditions that may cause heart failure and lead to pulmonary edema include
Coronary artery disease. Arteries that supply blood to the heart muscle may narrow over time due to fatty deposits (plaque). Slow narrowing of the coronary arteries can make the left ventricle weaker.
Stenotic arteries sometimes develop blood clots. Blood clots can block blood flow and damage some of the heart muscle, which can cause a heart attack. The damaged heart muscle cannot pump blood properly.
Cardiomyopathy. The term implies damage to the heart muscle. With cardiomyopathy, the heart must pump blood harder, causing the pressure to rise. So that the heart may not be able to pump harder when it needs to, such as during exercise, an infection, or when blood pressure rises. If the left ventricle can't keep up with the body's demands, blood will flow back to the lungs.
Heart valve problems. Narrowing (stenosis) of the aortic or mitral valve or a valve that leaks or does not close properly can affect the flow of blood to the heart. If a valve leaks suddenly, it may lead to sudden, severe pulmonary edema.
Hypertension (high blood pressure disorder). Untreated or uncontrolled high blood pressure may cause the heart to become enlarged.
Other heart problems. Inflammation of the heart muscle (myocarditis), heart disease at birth (congenital heart defects), and arrhythmias (heart rhythm disorders) may also cause pulmonary edema.
Kidney disease. Hypertension due to narrowed renal arteries (renal artery stenosis) or fluid accumulation due to kidney disease may cause pulmonary edema.
Chronic health problems. Thyroid disease and iron deposition (hemochromatosis) or protein deposition (amyloidosis) may also cause heart failure, which can lead to pulmonary edema.
Non-cardiac-related (non-cardiogenic) pulmonary edema
Non-cardiogenic pulmonary edema is defined as pulmonary edema that is not caused by an increase in cardiac pressure.
Possible causes of non-cardiogenic pulmonary edema include
Acute respiratory distress syndrome (ARDS). This serious condition occurs when the lungs suddenly fill with fluid. Many conditions can cause ARDS, including serious injury (trauma), massive infection (sepsis), infectious pneumonia, and severe bleeding.
Drug reactions or drug overdose. Many drugs (from aspirin to illicit drugs such as heroin and cocaine) are known to cause pulmonary edema.
A blood clot in the lungs (pulmonary embolism). If a blood clot moves from a blood vessel in the leg to the lung, it can lead to pulmonary edema.
Exposure to certain toxins. Inhalation of toxins or inhalation of certain stomach contents during vomiting (aspiration by mistake) can cause strong irritation of the small airways and alveoli, leading to fluid accumulation.
High altitude. Mountain climbers, skiers, hikers and others who travel to high altitudes usually develop pulmonary edema above 2400 meters (about 8000 feet). High altitude pulmonary edema (HAPE) usually occurs in people who have not taken days or weeks to gradually acclimate to the high altitude environment. However, people living at high altitude who develop respiratory disease can develop HAPE even if there is no change in altitude.
Near drowning. Inhalation of water can lead to fluid accumulation in the lungs.
Negative pressure pulmonary edema. When an upper airway obstruction occurs, the lungs try to breathe through the obstruction, thus creating negative pressure in the lungs. With treatment, most people with this type of pulmonary edema heal within about 24 hours.
Neurological disease or surgery. A type of pulmonary edema called neurogenic pulmonary edema may occur after a head injury, seizure, or brain surgery.
Smoke inhalation. Smoke from a fire contains chemicals that can damage the membranes between the alveoli and capillaries. The resulting injury can allow fluid to enter the lungs.
Transfusion-associated lung injury. Blood transfusions may lead to excess fluid in the left ventricle, which can lead to pulmonary edema.
Viral diseases. Viruses such as hantavirus and dengue virus can cause pulmonary edema.