Chapter 3 Disorders of Vascular Flow Yiran Ni M.D

This chapter will describe major disturbances involving hemodynamics and the maintenance of blood flow, including: 1. edema 2. hyperemia and congestion 3. hemorrhage 4. thrombosis 5. embolism 6. infarction 7. shock.

Key points of the last lecture 1. Virchow triad 2. Morphology of thrombus 3. The fate of thrombus

Embolism

Definition Embolism is the occlusion or obstruction of a vessel by an abnormal mass transported from a different site by the circulation An embolus is a detached intravascular solid, liquid, or gaseous mass that is carried by the blood to a site distant from its point of origin. Virtually 99% of all emboli represent some part of a dislodged thrombus, hence the term thromboembolism.

Definition Rare forms of emboli include: fat droplets bubbles of air or nitrogen atherosclerotic debris (cholesterol emboli), tumor fragments bits of bone marrow foreign bodies such as bullets.

Definition However, unless otherwise specified, an embolism should be considered to be thrombotic in origin. Inevitably, emboli lodge in vessels too small to permit further passage, resulting in partial or complete vascular occlusion.

Definition The consequences of thromboembolism include ischemic necrosis (infarction) of downstream tissue. Depending on the site of origin, emboli may lodge anywhere in the vascular tree; the clinical outcomes are best understood from the standpoint of whether emboli lodge in the pulmonary or systemic circulations.

Possible moving pathways of an embolus depends on the sites of its origin Possible moving pathways of an embolus depends on the sites of its origin A. The emboli from systemic vein or right heart B. The emboli from left heart or main artery C. The emboli from mesenteric vein or portal vein D. Crossed embolism E. Retrograde embolism

Crossed embolism

Types of Embolism ThrombembolismThrombembolism FAT EMBOLISM AIR EMBOLISM AMNIOTIC FLUID EMBOLISM

Thrombembolism 1) Pulmonary embolism  The origin of emboli: ＞ 90% from deep leg vein1) Pulmonary embolism  The origin of emboli: ＞ 90% from deep leg vein

 The sequel:  S mall emboli may lodge in the branching arterioles of pulmonary artery,and usually be clinical silent  Large emboli often occlude the main pulmonary artery and cause sudden death

2) Systemic embolism  The origin of emboli: Most arise from intracardiac mural thrombi the remainder may originate from ulcerated atherosclerotic plaques  The sequel: Arteriolar embolization (e.g. the brain, kidneys, spleen and intesrines) 2) Systemic embolism  The origin of emboli: Most arise from intracardiac mural thrombi the remainder may originate from ulcerated atherosclerotic plaques  The sequel: Arteriolar embolization (e.g. the brain, kidneys, spleen and intesrines)

Arteriolar embolization of brain

Arteriolar embolization of kidney

Arteriolar embolization of spleen

Arteriolar embolization of intesrine

（ 2 ） Fat embolism  The origin of emboli: Fat globules in the circulation after fractures of long bone, trauma of sofe tissue and a liver with fatty change

 The sequel: depends on the size and the number of fat globules >20μm in diameter: occlusion of the branching arterioles of pulmonary artery 20μm in diameter: occlusion of the branching arterioles of pulmonary artery < 20μm in diameter: pass through the pulmonary circulation and enter left heart, and consequently cause embolism of cerebral microvasculature

（ 3 ） Air embolism Gas bubbles with the circulation can obsruct cardio-vascular flow. Generally, in excess of 100ml of air is required to produce a clinical effect.

 The origin of gas: Air may enter the circulation during obstetric procedures or as a result of chest wall injury  The sequel: The gas bubbles may form frothy masses with blood in right heart, and then act like physical obstructions to occlude major vessels

Decompression sickness: Occurs when individuals are exposed to sudden change in atmospheric pressure. When air is breathed at high pressure, increase amount of gas (particularly nitrogen) become dissolved in the blood and tissues.If the diver then ascends (depressurized) too rapidly, the nitrogen expands in the tissues and bubbles out of solution in the blood to form gas emboli. Occurs when individuals are exposed to sudden change in atmospheric pressure. When air is breathed at high pressure, increase amount of gas (particularly nitrogen) become dissolved in the blood and tissues.If the diver then ascends (depressurized) too rapidly, the nitrogen expands in the tissues and bubbles out of solution in the blood to form gas emboli.

（ 3 ） Amniotic fluid embolism The amniotic fluid and its component are infused into the maternal circulation via a tear in the placental membranes and rupture of the uterine veins. The onset is characterized by sudden severe dyspnea,cyanosis,DIC and shock, followed by seizures and coma.