The answer to the question – what is pulmonary embolism – involves also answering the question – what is deep vein thrombosis. The reason is the correlation between the two. The main effects are clear-cut. The cause is not.
What is pulmonary embolism?
The answer to the question – what is pulmonary embolism – bears acknowledgment of the difference between it and pulmonary embolus. It is important to first distinguish between the terms embolism and embolus.
Embolism is the abrupt blockage of an artery as a result of the lodging of matter in it; the matter having formed in a site proximal to the place of blockade. As such, it is an event. The substance causing the obstruction usually, but not always, forms in the heart, a vein or an artery.
In either case a fragment(s) of the material breaks off from its original site, and then travels downstream with the blood flow current, lodging in a vessel that is too small for it to pass through. Embolization is the process or state of an embolus occurring.
In the case of a pulmonary embolus the matter that breaks off and lodges is clotted blood from a vein or a region of the right side of the heart. Thrombus is the medical term for a blood clot. Thrombosis is the term for the actual formation of a blood clot. A pulmonary embolus is the blood clot lodged in an artery resulting from a pulmonary embolism.
A saddle embolus is a large blood clot or other plug which straddles the bifurcation (branch point) of the main pulmonary artery trunk and extends into the right and left pulmonary arteries. It can cause a marked decrease in flow of blood from the right side of the heart through the lungs. When this results in a significant reduction in blood return to the left side of the heart cardiac output drops. In turn, blood pressure also drops if the body cannot compensate for the decrease in the amount of blood the heart pumps out.
Thus, pulmonary embolism is the breakage of a blood clot from a site in the pulmonary circulation into one or more pieces; the distal travel of it with the blood flow current; and the lodging of it in a pulmonary artery or in one or more of its branches. Laities commonly refer to it as a blood clot to the lungs. It is most commonly a complication of deep vein thrombosis. But it can be the result of a clot in the right side of the heart which breaks.
Interchangeable use of the two terms, which is often the case, is imprecise. Pulmonary embolism is the event itself. Pulmonary embolus is the object and the anatomical aftermath of the event. Its effects are the physiologic consequences of the event.
Deep vein thrombosis is the formation of a blood clot in a deep vein of the body well beneath the skin. It can occur in any large vein, but most commonly involves a vein (s) of the lower limbs or pelvis. The alternate term that doctors and other medical personnel use to refer to the condition is deep venous thrombosis (DVT). Because deep veins are larger than superficial (near the surface) veins, the clots that form in them are larger. Hence, broken fragments from them are more prone to lodge in an artery of the lung.
Pulmonary embolism cause and effects
Causes or risk factors for deep vein thrombosis are well-recognized. They include:
- prolonged inactivity, particularly during bed ridden states
- injury to the area where a clot forms
- certain forms of cancer
- a hereditary tendency
The risk factors for DVT are also risk factors for a pulmonary embolism. But the cause of a pulmonary embolism is not so straightforward. The reason is the triggers that cause a thrombus to break up are not well-understood.
Nevertheless, the clinical manifestations of pulmonary embolism can range from none to death. They depend primarily upon the size and number of emboli. The main factors are the hemodynamic effects and the effect on oxygen transfer from the lungs to the blood. Measureable tangibles include the following:
- hypotension (shock in the worst case scenario)
- dysfunction of the right ventricle
- right sided heart failure
- heart muscle injury evident via EKG or biomarkers
- arrhythmia, particularly tachycardia (or bradycardia when the event is severe)
- hypoxemia and hypoxia
In severe cases, the blood pressure can drop so low as to lead to death. The pumping ability of the left ventricle is one of the main factors to determine cardiac output and the maintenance of adequate systolic blood pressure. But when insufficient amounts of blood return from the right side of the heart to the left side of the heart because of impeded flow through the lungs the left ventricle cannot properly fill during diastole. The result is a drop in cardiac output. When death occurs, it is usually due to this factor and/or inadequate oxygen in the blood. In either case cells cannot sufficiently carry out their functions vital to life.