What factors facilitate venous return?
Venous return is facilitated by a number of factors, including inspiration, increased total blood volume, increased venomotor tone, the cardiac suction effect, the presence of venous valves and the skeletal muscle pump.
What are three factors that are important in promoting venous return?
Factors promoting venous return are:
- Skeletal muscle activity.
- Presence of valves in veins.
- Pressure changes.
What happens to venous return when you stand up?
In this position, venous blood volumes and pressures are distributed evenly throughout the body. When the person suddenly stands upright, gravity acts on the vascular volume causing blood to accumulate in the lower extremities.
What causes venous pooling?
Chronic venous insufficiency occurs when your leg veins don’t allow blood to flow back up to your heart. Normally, the valves in your veins make sure that blood flows toward your heart. But when these valves don’t work well, blood can also flow backwards. This can cause blood to collect (pool) in your legs.
How does breathing affect venous return?
Respiration – During inspiration, venous return increases as the thoracic cavity’s pressure becomes more negative. This reduced intrathoracic pressure draws more blood into the right atrium. This results in greater venous return.
How does venous return work?
A thin layer of smooth muscle in the veins helps squeeze blood back towards the heart. When muscles contract and relax during the inspiration and expiration process, pressure changes occur in the thoracic and abdominal cavities. These pressure changes compress the nearby veins and assist blood return to the heart.
What happens to venous return when you change from lying down to standing up quickly?
The lower venous return reduces the volume of blood that is available to pump out of the heart, which causes a drop in CO and a momentary drop in BP. This drop can be particularly marked when moving from lying down to standing and can increase the risk of falls (see part 1 of this series).