What Does the Liver Do?

The liver is the largest solid organ in the body and plays many essential roles that keep it healthy. These include making a fluid called bile (which helps the body to break down fats in the food we eat), processing digested food from the intestine by breaking down proteins and carbohydrates so that the body can use them, storing vitamins and iron, and fighting infections.

The liver also cleans the blood to remove harmful substances and microbes that can cause infections. As a result, the liver has about 13% of the body’s total volume of blood in it at any one time. It enters the liver via two major blood vessels called the hepatic artery (which supplies oxygen-rich blood to the liver) and the portal vein (which carries blood from the digestive tract and spleen to the liver). This is to ensure that molecules from digestion are taken up into the blood and processed or checked before they start to circulate the body in the bloodstream.

What Is Chronic Liver Disease?

Because the liver filters toxins from the blood, it is vulnerable to becoming damaged and its ability to function reducing if it is exposed to high levels of toxins. Although the liver is able to produce new cells and regenerate itself, its ability to regenerate becomes reduced over time if it keeps having to work too hard. Eventually, chronic liver disease can develop, in which damage to the liver progresses (gets worse) over a long period of time (at least 6 months). This damage cannot be reversed.

Chronic liver disease develops in four stages:

1. The first (called “hepatitis”) means that there is inflammation in the liver tissue. In the short term, this means that the liver can deal with infections and start the healing process. However, if it continues for a long time, hyperactive healing can take place.
2. This eventually causes the second stage, known as “fibrosis” (scarring). During this stage, thin bands of scar tissue build up over time, leading to the liver gradually becoming stiffer and the blood flow through it becoming reduced. Some of this damage can be reversed.
3. If it continues, though, the third stage is eventually reached. This is called “cirrhosis” and is characterized by severe, permanent scarring that is no longer reversible.
4. When the damage becomes so extensive that the fourth stage, “liver failure” (also known as “decompensated cirrhosis”), is reached the liver can no longer function properly.

What Are the Symptoms of Cirrhosis?

Early on in the development of cirrhosis, signs and symptoms may not be noticeable. The first signs can include feeling generally ill, weak or tired; loss of appetite; nausea; pain in the upper abdomen (tummy); and red patches on the palms of the hands or spider-like, visible blood vessels. As cirrhosis progresses, symptoms can include jaundice (yellowing of the whites of the eyes and skin), itchy skin, swollen legs, and bleeding or bruising easily.

Although cirrhosis cannot be reversed, treatment may be able to stop it from getting worse or slow its progression. This is important because cirrhosis is associated with serious complications that can by themselves be life-threatening, including swelling of the abdomen as a result of fluid build-up (called “ascites”) and variceal bleeding (“varices” are veins that have become abnormally widened) in the digestive tract. This results in a person vomiting blood or their poo being black or bloody. Ascites and variceal bleeding are mainly caused by the development of portal hypertension.

What Is Portal Hypertension?

The term “portal hypertension” describes an increase in the blood pressure in the portal vein. It can be caused by resistance in the liver increasing as a result of cirrhosis or because there is a blockage, such as a blood clot. As the drainage of the blood from the abdomen becomes impeded, it starts to try to leave the abdomen via other veins that become more fragile as they are stretched wider.

In addition to ascites and varices, portal hypertension can cause a number of other serious complications. Because prompt treatment of portal hypertension with medication that reduces blood pressure is known to be able to slow the progression of chronic liver disease, it is important that any increases in blood pressure in the portal vein are detected as early as possible. A variety of different techniques are used or are in development to assess whether a patient has pulmonary hypertension.

Detecting Portal Hypertension

Hepatic Vein Catheterization

Hepatic vein catheterization is currently considered to be the most effective way to measure the difference in blood pressure between the portal and hepatic veins.

• First, a flexible tube called a “catheter” with a tiny balloon on the end is inserted into the jugular vein in the neck.
• X-ray imaging is then used to guide the catheter into the hepatic vein so that the blood pressure inside it can be measured.
• The balloon on the end of the catheter is then inflated and a second measurement of blood pressure is taken.
• The two values can then be used to calculate whether portal hypertension is present (classed as a portal venous pressure gradient greater than 5 mm Hg, and regarded as clinically significant if greater than 10 mm Hg).

Although hepatic vein catheterization is effective and it is rare for there to be problems while it is carried out, it is invasive and needs to be done under local or general anesthetic. In addition, it can only be done at highly specialized medical centers and cannot be used to take a series of measurements as the chronic liver disease progresses over time. As a result, researchers are investigating whether non-invasive methods are as effective at assessing pulmonary hypertension.

Serum Biomarkers

These have included serum biomarkers that can be detected by analyzing blood samples that are taken from patients (sometimes called “liquid biopsies”). Serum is the liquid that you have left if all the cells and clotting factors are removed from the blood. The term “biomarker” describes a measurable characteristic, such as a molecule in your blood or a change in your genes, that indicates what is going on in the body.

Endoscopic Ultrasound

Among the other methods available are endoscopic ultrasound, which uses a camera device (endoscope) with a small ultrasound device (which emits high-frequency sound waves) on the end to look at the digestive tract and the surrounding organs. Although this approach is invasive, with the endoscope inserted into the mouth or anus, it can be repeated over time and has been shown to have good accuracy.

Scoring Systems

Scoring systems have also been developed that include measurements of stiffness of the liver and/or spleen being taken using a non-invasive technique called transient elastography. This method works by a vibrating probe and transducer being applied to the skin over the liver or spleen that produces something called a “shear wave”. The speed at which the shear wave travels through the organ is linked to its level of stiffness and indicates how much fibrosis there is.

Conclusion

Although these approaches are not currently as effective as hepatic vein catheterization by themselves, there is some evidence that the combination of different techniques may improve accuracy. Future research in this area aims to improve the non-invasive early detection of pulmonary hypertension.