portal hypertension Flashcards
most complications of cirrhosis result from
portal hypertension
why is there an increased resistance in cirrhosis in the sinusoid space?
stellate cell in the space of disse deposits fibrous tissue that leads to constriction of these spaces
portal hypertension can result from (2)
- increase resistance in the portal flow
2. increase in portal venous inflow
pressure in the venous system is determined by 2 variables
- increased flow and constant resistance
or
- constant flow and increased resistance
in cirrhosis what is the initial mechanism that leads to portal hypertension
an increase in intrahepatic vascular resistance
why is there increase intrahepatic vascular resistance?
distorted sinusoidal architecture leads to increased resistance
small increases in portal flow in a person without cirrhosis is ok because
there is a dilation of the veins and thus there is no increase in portal pressure
in portal hypertension, splanchnic vasodilation results from an increase in
nitric oxide
elevated portal pressure leads to an increase in shear stress in the splanchnic vasculature and thus gives rise to an upregulation of endothelial isoform of NO synthase and increasing its production
in more advanced cirrhosis (when ascites are present) there is a further increase in NO production… why?
increase in translocation of bacteria from the gut
backward theory of portan HTN
intrahepatic vascular tree distorted by fibrosis; portal HTN is solely a consequence of increased vascular resistance
forward theory of portal HTN
portal HTN maintained by increased splanchnic flow despite collaterals
portal hypertension is the result of increases in both ______ to portal flow and in portal venous _____
resistance and inflow
- backward and forward theories apply
with measurement of wedged and free pressures is the simplest, safest, most reproducible and most widely used method to indirectly measure portal pressure.
Hepatic vein catheterization
The FHVP acts as an internal zero to correct for
extravascular, intraabdominal pressure increases
The hepatic venous pressure gradient (HVPG) is obtained by subtracting the
free hepatic venous pressure (FHVP) from the wedged hepatic venous pressure (WHVP):
The normal HVPG ranges from
3 to 5 mmHg
In sinusoidal PHT, intersinusoidal communications are blocked by fibrous tissue. Dissipation of pressure in the wedged vessels is insignificant and the WHVP is then as elevated as the portal pressure. The FHVP is normal and therefore the HVPG is _____
elevated
The normal liver can withstand significant increases in flow, without resulting in increases in portal pressure. The normal portal venous system is a low-pressure system and vessels draining the intraabdominal organs, such as the coronary vein, drain into it.
yep
three major catergories of the causes of portal HTN
- pre-hepatic
- intra-hepatic
- pots-hepatic
prehaptic causes
- thrombosis of the portal or splenic vein
2. fistula of spanchnic arteriovenous