Pathophysiology of Congestion and Oedema Flashcards
Down what gradient does fluid in the body flow?
Down pressure gradient
What does Darcy’s Law state and what is the equation?
Q = change in pressure / resistance
Velocity of blood flow is in proportion to the pressure gradient in the direction of the flow
What is congestion?
Excess of blood in vessels of tissue or organ
Give an example of local acute congestion
Deep vein thrombosis
Give an example of local chronic congestion
Hepatic cirrhosis
Give an example of generalised acute congestion
Congestive heart failure
Describe the pathophysiology of DVT causing infarction and ischaemia?
Thrombus occludes vessel, causing blood to back up in the veins, venues and capillaries which decreases outflow of blood, pressure gradient and flow.
Decrease in flow leads to less O2 delivery -> ischaemia and infarction
What does hepatic cirrhosis result from?
Serious liver damage i.e. HBV, alcohol
What is the pathophysiology of hepatic cirrhosis?
- Serious liver damage
- Regenerating liver forms nodules of hepatocytes with intervening fibrosis
- This alters hepatic blood flow
- Can block vessels, so causes congestion in portal vein and branches
- Increased portal venous pressure
- Collateral circulation develops
What are some consequences of portal-system hypertension?
Blood is shunted to areas causing features like oesophageal varices and caput medusae
What is dangerous about oesophageal varices?
They only have a thin lining over them so can easily be ruptured, causing haemorrhage
What is congestive cardiac failure?
The heart is unable to clear blood from the right and left ventricles (the heart is an ineffective pump)
What is the pathophysiology of congestive cardiac failure?
- Decrease in cardiac output
- Decrease in renal glomerular filtration rate
- This causes the activation of the renin-angiotensin-aldosterone system
- This causes sodium and water retention
- Therefore increases the fluid in the body
- There is a fluid overload in the veins
What is the pathophysiology of pulmonary oedema caused by left ventricular failure?
- Increase in left atrial pressure
- Back up in pulmonary veins, capillaries and arteries
- Increase in vascular pressure
- Increase in pulmonary blood volume
- Increased hydrostatic pressure leads to increased filtration
What are the signs of central venous congestion?
Increased JVP
Hepatomegaly
Peripheral oedema
What causes central venous congestion?
Right heart failure - blood dams back into systemic circulation
What is the appearance of hepatic central venous congestion?
Liver red brown & pale spotty appearance macroscopically: Pericentral hepatocytes (red) - poor oxygenation Periportal hepatocytes (pale) - better oxygenated due to close BV
Describe the normal microcirculation
Constant movement of fluid through capillary beds; process of dynamic equilibrium
What are the mechanisms involved in microcirculation?
Hydrostatic pressure (filtration to ISF) Osmotic pressure and endothelial permeability Lymphatic system absorbing excess fluid from ISF
What are the 3 components that affect net flux and filtration?
Hydrostatic pressure
Oncotic pressure
Permeability characteristics and area of endothelium
What is the colloid (oncotic) pressure?
Osmotic pressure created by protein in the vessels, drawing fluid from the ISF
Pressure increases from arteries to veins
What is the hydrostatic pressure?
It is the driving force for pushing fluid out of the vessels and into the ISF as the pressure is greater inside the vessel
Decreases from arteries to veins
What can disturbances in the normal starling forces cause?
Oedema
What is oedema?
Accumulation of abnormal amounts of fluid in the extravascular compartment - in ECF or body cavities
Give example of increase fluid in ISF
Peripheral oedema
Give example of increase fluid in body cavities
Effusions - pleural, pericardial, joints or ascites in abdominal cavity
What is a transudate?
Altered haemodynamic forces across vessel wall - increased hydrostatic
What is specific gravity and its relevance in transudates and exudates?
Ratio of the mass of a solution compared to the mass of an equal volume of water
Transudate: low SG as it was high conc. of water which is why fluid is pushed out
Exudate: high SG but increased permeability means fluid and protein lost
What is an exudate?
Part of inflammatory process due to increase vascular permeability
What are the causes of transudate fluid in oedema?
Cardiac failure: fluid back up -> increase hydrostatic pressure -> oedema
Low protein/albumin -> pushes fluid into ISF
Lots of H2O and electrolytes
Low specific gravity
What are the causes of exudate fluid in oedema?
Tumour, inflammation, allergy
High protein/albumin
H2O and electrolytes
High specific gravity
Loss of fluid and protein
What is the pathophysiology of left ventricular failure causing pulmonary oedema?
- Increase in atrial pressure causing back flow to veins
- Increase pulmonary vascular pressure
- Increase pul. blood volume
- Increase in hydrostatic pressure
- Increase filtration and pulmonary oedema
Forms transudate fluid due to increase hydrostatic pressure
What is the effect of pulmonary oedema in the lungs?
Perivascular and interstitial transudate
Oedematous widening of alveolar septa
Fluid in alveolar spaces
What is the pathophysiology of right heart failure causing peripheral oedema?
- Cannot empty RV in systole
- Blood retained in systemic veins
- Increasing pressure and filtration
Also occurs due to portal venous congestion in liver
What happens in the body due to congestive heart failure?
- R and L ventricles fail
2. Pulmonary and peripheral oedema at same time
What happens if the lymphatic vessels are blocked?
Lymphatic obstruction -> lymphoedema
What does abnormal renal function result in?
Salt and H2O retention
What causes abnormal renal function?
Secondary in HF: reduced renal blood flow
Primary: acute tubular damage i.e. hypotension
How does abnormal blood flow result in oedema?
- Increase salt and H2O
- Increase in intravascular fluid volume
- Secondary increase in hydrostatic pressure
- Oedema
How does low protein in vessels cause oedema?
Hypoalbumamia -> decreased oncotic pressure and increases filtration
Transudate
How does hepatic cirrhosis cause oedema?
Diffuse nodules and fibrosis in liver means that the liver is not able to make enough protein -> decrease in oncotic pressure and increase in filtration
How can endothelial permeability cause oedema?
Damage to lining increase number of pores in membrane allows protein and larger molecules to leak out as well as fluid
What are 2 causes of permeability oedema?
Inflammation (pneumonia)
Burns
