Venous return is the biological process of blood flowing into the heart from other parts of the body. While the heart pumps blood out, a process known as “cardiac output,” it also depends on a steady supply of that same blood actually returning in order to continue. Ideally, output will equal return both in terms of speed and volume of blood. A lot of different processes have to be working together in order to get this result, though. Problems with the return process can lead to stress on the heart and a range of circulatory and blood flow issues.
Basic Anatomy of the Heart
The heart is the core of the circulatory system, and it is responsible for pumping and processing the blood for the entire body. Hearts typically have four chambers: two on the top, and two on the bottom; two on the left, and two on the right. Those on the top are known as atria, while the bottom chambers are ventricles. Blood typically comes in through the right atrium, goes down to the right ventricle, then up to the left atrium and ultimately out through the left ventricle. The chambers contract and expand together to pump and process the blood. The power and strength of the pumps is dictated in part by the volume that comes in through the return process.
How it Works
Blood circulates throughout the entire body, and it’s important that it is constantly moving and circulating in order for it to maintain the right balance of oxygen and nutrients. Although the heart pumps blood through the blood vessels, circulation through the veins is also moved along by other factors. These include skeletal muscle contractions during exercise, falling pressure in the chest when breathing, and the expansion of the upper chambers of the heart, or atria, each time the heart beats.
As a person breathes in, pressure in the chest falls; this negative pressure is transferred to the great veins, causing blood to move along. This is because blood tends to move from high pressure to low pressure areas. At the same time, downward movement of the diaphragm causes pressure in the abdomen to rise, pushing venous blood back to the heart. The blood cannot flow backward because veins contain valves that only allow it to flow in one direction.
When the heart contracts it ejects blood from its ventricles and the closed valves between the ventricles and the atria are pulled downward as a result. This increases the amount of space in the atria. Venous return increases and, if the heart beats faster, the effect becomes greater.
Effects of Exercise and Movement
The heart tends to be at its most efficient during exercise or other strenuous activity. In these situations the veins running through the skeletal muscles become compressed due to muscular contraction. Eventually the contractions become strong enough to stop blood flow completely, but in between each one the flow increases, often dramatically. Pulsating arteries situated nearby can also compress veins to some extent, all of which contribute to more efficient return activity.
Problem Situations
People who are inactive or mostly sedentary sometimes have trouble keeping their circulatory system efficient. A number of problems can result, including plaque and build-up in the coronary arteries, but blood clots are some of the most serious, at least from a return standpoint. Remaining in a sitting position tends to lowers venous return, as blood pools in the veins of the legs. In a person who is at rest, about half of the circulatory blood will be present in the veins, which can cause real problems when that pooled blood tries to return up to the heart.
The condition known as “deep vein thrombosis” happens when blood clots that originate in the veins make their way to the heart through the venous exchange. This condition frequently causes rapid death, since clots that are large enough can get lodged in any of the heart’s chambers, effectively stopping movement and leading to cardiac arrest and, in many cases, death.
Varicose veins can also sometimes lead to circulatory problems with blood return. Veins that are varicosed are weakened and broken, and can often be identified by a spidery, web-like look that appears on the surface of the skin. They can be caused by a number of things, but age and injury are two of the most common.
When this happens, the valves that prevent backflow of blood into the veins stop functioning. This means that venous return is lowered and problems such as swelling of the ankles may result. The veins may be treated in a cardiology clinic using laser technology to effectively remove them, which will normally divert blood flow to healthier veins.