Blood Circulation and Venous Pressure
Blood circulation is a dynamic process whereby the heart pumps oxygenated blood to the tissues via the arteries, delivers oxygen and nutrients, after which deoxygenated blood returns to the heart and lungs via the veins.
The heart is a powerful muscular organ that can drive blood to the arteries (whose walls are also surrounded by muscles) producing pulsatile movement of blood towards the organs. However, veins have no muscle cells and rely on surrounding muscles to drive the circulating blood towards the heart, being protected from backflow by venous valves. In order to help propel blood back to the heart, an interplay of the forces of gravity and the contraction of skeletal muscles take place.
Before deoxygenated blood returns to the heart and lungs for oxygenation a large percentage of its volume passes via the portal vein through the liver (the largest internal organ), for detoxification, excretion and other metabolic processes.
Normally, blood pressure in the veins or venous pressure is low. It may be increased a little (still within normal limits) when the patient lies on his back with his feet raised upward, since this position increases the volume of blood returning to the heart (venous return) from the lower extremities.
Causes of Abnormal Increases in Venous Pressure
A. The most common cause of an abnormal increase in venous pressure is heart failure. A defective valve or a hole between the lower chambers (ventricles) of the heart can cause failure of the heart to pump blood effectively into the circulation. Other causes of heart failure are coronary artery disease, irregular heart rates, diseases of the heart muscles and fluids around the heart.
Chronic failure of the heart to pump blood forward into the circulation results in backward dumping of this volume to the veins, leading to venous congestion. This is easily detected physically by observing the neck veins which appear to be engorged, when in normal conditions these should be collapsed or unnoticeable.
Over a period of time, when blood volume is constantly dumped back into the veins, venous pressure increases. Gravitational force causes blood to overcome the venous valves that are supposed to prevent backflow and consequently, fluids leak through the walls of capillaries. This is seen physically as swelling of the feet, or edema.
B. Another cause of increased venous pressure is portal hypertension due to liver disease. Serious liver disease like cirrhosis can lead to increased blood pressure in the portal vein which supplies the liver. Backflow of the blood results in increased venous pressure to the lower parts of the body and is likewise manifested as edema.
When an increase in venous pressure is prolonged, swelling of greater areas of the body proceeds upwards from the ankles to the knees, thighs and the abdomen. Leakage of fluids to the tissues in the abdominal wall (ascites) can lead to difficulty in breathing because of its compression on the chest and lungs.
C. Deep vein thrombosis (DVT) or blood clotting in the vein can cause an increase in venous pressure in one leg. Blood is likewise prevented from moving forward and is dumped back into the vein against the internal valves with the help of gravity. Compared to heart failure and portal hypertension DVT causes local edema in the affected leg only.
Treatment of Increased Venous Pressure
Abnormal increases in venous pressure can only be corrected when the primary cause is treated. The heart must be enabled to pump blood effectively by correcting a valvular defect, a hole between the walls or by treating the primary cause of disease. Likewise, liver disease must be treated to decrease portal hypertension. Deep vein thrombosis must be corrected with anticoagulants.
Another way to decrease venous pressure is to induce diuresis or elimination of fluids by urinary excretion. This is accomplished by taking medications such as diuretics.
Edema can also be relieved by using tight fitting leg or body stockings to enable forward flow and counter gravitational force.
The prognosis for elevated venous pressure depends on the cause and treatment of the underlying condition.
CV Physiology, “Tissue Edema and General Principles of Transcapillary Fluid Exchange” accessed 1/19/11
Gross Physiology of the Cardiovascular System, by Robert M. Anderson, MD accessed 1/19/11