32. Pathophysiology of Congestion and Oedema Flashcards
What is Darcy’s law?
Blood flow= (difference in pressure)/ resistance
Define congestion.
- Abnormal or excessive accumulation of blood or bodily fluid in vessels of tissue or organ
- Passive process
- acute or chronic
- can be active hyperaemia (excess blood in vessels supplying organs or other parts of the body-too much blood)
- blood (or any fluid) is going in and not going out
Why is congestion NOT like an acute inflammatory process?
- In acute inflammation, vessels deliberately open up and allow more blood into tissues with inflammatory process
- Whereas in congestion, it’s a PASSIVE process and there are no instructions for it since it happens automatically (the body doesn’t mean to do it for any benefit)
What is an example of local acute congestion?
deep vein thrombosis
What is an example of local chronic congestion?
hepatic cirrhosis
What is an example of generalised acute congestion?
congestive cardiac failure
Describe what happens in deep vein thrombosis of the leg in terms of congestion.
- blood backs up in veins, venules and capillaries and gets stuck in vessels
- local acute congestion
- decreased outflow of blood
- decreased pressure gradient
- decreased flow across system (decrease in pressure difference therefore decrease in flow)
- flow is proportional to resistance (if you increase resistance, you decrease flow)
What does acute local congestion in deep vein thrombosis eventually lead to?
- since no O2
- ischaemia and infarction can occur
What happens in hepatic cirrhosis that leads to local chronic congestion?
- regenerative nodules of hepatocytes with intervening fibrosis
- due to liver damage
- loss of normal architecture leading to altered hepatic flow
- liver structure is damaged so therefore so is function
What is the aetiology of hepatic cirrhosis?(6)
- alcohol
- hepatitis B and C
- liver injury
- reaction to prescription medication
- toxic substances
- repeated episodes of heart failure with liver congestion
Which blood flow channel is blocked in hepatic cirrhosis?
Portal blood flow is blocked (congestion in portal vein and branches)
What happens in hepatic cirrhosis to the portal blood flow?
- increased portal venous pressure
- collateral circulation; several sites anastomose with systemic circulation (circulation around a blocked pathway)
- chronic inflammation in hepatocytes also occurs
What is the portal blood flow in the liver?
- carries blood from gastrointestinal tract gallbladder, and spleen to the liver (from gut to liver)
- venous drainage
What is the main risk associated with local chronic congestion like hepatic cirrhosis?
haemorrhage risk
What is the common consequence of cirrhosis? (2)
- Oesophageal varices
- Caput Medusae
What are oesophageal varices?
- very dilated sub-mucosal veins in the lower third of the oesophagus
- if these veins are damaged then blood can spill into oesophagus and blood exits forcefully through the mouth
- mainly as a consequence of hepatic portal system hypertension
- have tendency to start bleeding
What is Caput Medusae?
- anastamosis of veins in the abdominal wall
- engorged superficial epigastric veins which are seen radiating from umbilicus across the abdomen
- caused by dilation of paraumbilical veins which become recanalised (usually close within 1 week after birth) due to portal hypertension
- paraumbilical veins usually carry oxygenated blood from mother to foetus
- anastomosis between the veins of the anterior abdominal wall and the hepatic portal, hypogastric, and iliac veins.
What happens in congestive heart failure?
- heart unable to clear blood from right and left ventricles
- ineffective pump due to ischamia or valve disease for example
- heart works very hard to make up for its loss of function
What is the aetiology of congestive cardiac failure? (9)
- coronary artery disease
- MI
- high BP
- faulty valves (valve disease)
- cardiomyopathy (damage to heart muscle)
- myocarditis
- heart defects( congenital)
- heart arrhythmias
- chronic disease e.g. diabetes, HIV, hyperthyrodism, hypothyrodism, hemochromatosis, amyloidosis (build up of protein)
What is the pathophysiology of congestive cardiac failure in terms of:
- CO
- GFR
- Na and H2O retention
- fluid in the body and veins
- decreased cardiac output
- decreased renal glomerular filtration rate (GFR)
- increase in Na and H2O retention
- increase in amount of fluid in the body
- increase in fluid overload in veins
What is the treatment for fluid overload in the body?
diuretic (so more urine is excreted)
What general and systemic effects does congestive heart failure have on other systems?
- heart can’t clear blood from ventricles
- blood dammed back in veins (back pressure)
- central venous congestion in the liver
- acute and chronic changes in lungs (pulmonary oedema)
Which side of heart is affected for central venous congestion to occur for example in liver?
right heart failure
What does central venous congestion from liver cause which is due to r.heart failure? (3)
- raised JVP
- hepatomegaly (liver swollen)
- peripheral oedema
Which side of the heart is affected for acute and chronic lung changes to occur leading to pulmonary oedema?
left heart failure
What does pulmonary oedema cause in terms of clinical features? (2)
- crepitations in lungs
2. tachycardia
What does a liver look like which has hepatic central venous congestion?
- “nutmeg liver”
- red/brown and pale spotty appearance
What type of hepatocytes are red in colour in hepatic central venous congestion? What is their oxygenation like?
Pericentral hepatocytes:
stasis of poorly oxygenated blood (worse inside) which menas central hepatocytes will not receive as much blood
What type of hepatocytes are pale in colour in hepatic central venous congestion? What is their oxygenation like?
Periportal hepatocytes: relatively better oxygenated due to proximity of hepatic arterioles (better outside)
Describe how normal microcirculation works.
- constant movement of fluid through capillary beds
- process of dynamic equilibrium
- filtration from capillary beds to interstitium