Flashcards in Pathophysiology of Congestion and Oedema Deck (24)
What does Darcy's Law state?
Q = (change in) P/R, where Q = blood flow, P = pressure and R = resistance
What is congestion?
A relative excess of blood in the vessels of a tissue or organ
What is the pathophysiology of a deep vein thrombosis of the leg?
Vein blocked causing localised acute congestion
Blood backs up in veins, venules and capillaries
Decreased outflow of blood
Local acute congestion
Decreased pressure gradient
Decreased flow across system
No oxygen, ischaemia and infarction
What is the pathophysiology of hepatic cirrhosis?
Regenerative nodules of hepatocytes with intervening fibrosis which results from liver damage e.g. due to alcohol
Loss of normal architecture leading to altered hepatic blood flow
Portal blood flow blocked, congestion in portal vein and branches, increased portal venous pressure
Local chronic congestion
What is the pathophysiology of congestive cardiac failure?
Heart unable to clear blood from left and right ventricles e.g. valve disease
Decreased cardiac output
Decreased renal glomerular filtration rate, activation of renin-angiotensin-aldosterone system increased Na and water retention
Increased amount of fluid in the body
Fluid overload in veins and back pressure
Central venous congestion in liver
Acute and chronic changes in the lungs
What does central venous congestion in the liver lead to?
Right heart failure
What do acute and chronic changes in the lungs result in?
Left heart failure
Crepitations in the lungs
What is the pathophysiology of hepatic central venous congestion?
Stasis of poorly oxygenated blood in the hepatocytes
What is an exudate?
A fluid with a high content of protein and cellular debris that has escaped from blood vessels and been deposited in tissues or on tissue surfaces
What is a transudate?
An extravascular fluid with a low protein content and a low specific gravity (<1.012). It has low nucleated cell counts and the primary cell types are mononuclear cells e.g. macrophages, lymphocytes and mesothelial cells
What are the features of the normal microcirculation?
Constant movement of fluid through the capillary beds
Driven by hydrostatic pressure from the heart
Balanced by osmotic pressures and endothelial permeability
Filtration from capillary beds to the interstitium
What components of the circulation affect net flux and filtration?
Permeability characteristics and area of endothelium
What does disturbance of the normal components of the microcirculation lead to?
What is oedema?
An accumulation of abnormal amounts of fluid in the extravascular space i.e. in inter-cellular tissue spaces and body cavities
What are effusions?
Fluid collections in body cavities e.g. pleural, pericardial, joint effusions, ascites
What are the features of transudate oedema?
Alterations in the haemodynamic forces which act across the capillary wall
Cardiac failure, fluid overload
High water and electrolytes
Low specific gravity
What are the features of exudate oedema?
Part of the inflammatory process due to increased vascular permeability
Tumour, inflammation or allergy
High protein/albumin content
Water and electrolytes
High specific gravity
How does left ventricular failure lead to pulmonary oedema?
Increased left atrial pressure, passive retrograde flow to the pulmonary veins, capillaries and arteries
Increased pulmonary vascular pressure
Increased pulmonary blood volume
Increased Pc leading to increased filtration and pulmonary oedema
What happens in the lungs in pulmonary oedema?
Perivascular and interstitial transudate
Progressive oedematous widening of the alveolar septa
Accumulation of oedema fluid in the alveolar spaces
What is the pathophysiology of peripheral oedema?
Right heart failure, cannot empty the right ventricle in systole
Blood retained in the systemic veins leading to increased pressure in the capillaries, increased filtration and peripheral oedema
Also causes secondary portal venous congestion via the liver
In congestive cardiac failure, pulmonary oedema and peripheral oedema occur at the same time
What is the pathophysiology of lymphatic blockage?
Lymphatic obstruction due to hydrostatic pressure upset
Lymphatic drainage is required for normal flow
If lymphatic system is blocked, lymphoedema occurs
What is the pathophysiology of oedema in abnormal renal function?
Abnormal renal function results in salt and water retention
Secondary in heart failure due to reduced renal blood flow
Primary in acute tubular damage e.g. hypotension
Decreased renal function
Increased salt and water, increased intravascular fluid volume, secondary increase in Pc - all result in oedema
What is the pathophysiology of low protein oedema?
In order to maintain endothelial permeability to water, normal protein levels are required
Hypoalbuminaemia results in decreased ability to maintain endothelial permeability and increased filtration