How Respiratory Pump Affects Venous Return, Animation.

How Respiratory Pump Affects Venous Return, Animation.

Venous return is the flow of blood from the
periphery back to the heart’s right atrium. Blood from the upper body returns via the
superior vena cava, blood from the lower body returns via the inferior vena cava. The rate of venous return is determined by
two factors: the pressure gradient between venous pressure and right atrial pressure;
and venous resistance. A decrease in right atrial pressure leads
to an increase in venous return, and vice versa. Breathing is one of the mechanisms that facilitate
venous return. This is known as thoracic pump, or respiratory
pump. During inspiration, the diaphragm moves down,
expanding the thoracic cavity, resulting in a decreased intra-thoracic pressure and a
subsequent expansion of the lungs. Part of this change in pressure is transmitted
across the walls of the heart, lowering right atrial pressure and thus facilitating venous
return. Another aspect of the diaphragmatic descent
is the concomitant increase in abdominal pressure. As the inferior vena cava passes through both
abdominal and thoracic cavities, an increase in abdominal pressure together with a decrease
in thoracic pressure squeeze the blood upward – toward the heart. On the other hand, left ventricular stroke
volume is decreased during inspiration. This is because the expansion of the lungs
causes pulmonary blood volume to increase and the blood flow from the lungs to the left
atrium to decrease. During expiration, the diaphragm moves up,
the pressure in the thoracic cavity reverses. Venous return decreases. Pulmonary blood vessels shrink pumping more
blood through the pulmonary veins into the left atrium. Stroke volume increases as a result.

37 Replies to “How Respiratory Pump Affects Venous Return, Animation.”

  1. Just a note: Looking at the VR ans SV curves, some may wonder why they are changing in reverse directions? Doesn't Frank–Starling law state that increase in VR should increase SV as well? Very good question, and the answer is: there is a small delay for this to happen – the decrease in stroke volume during inspiration rather reflects the decrease in venous return from the previous expiration.

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  3. These videos are absolutely amazing. They have a great way of teaching us physiological effects via dynamic animations. This is so much better than lectures that drone on and on with words salads. Being able to visualize the physiology is so key! Thank you A.M.M.!

  4. Explained it perfectly !! It was difficult to understand how murmurs increased and decreased depending on inhalation or exhale. This background on how breathing effects venous return and stroke volume clarifies everything!

  5. Perfect! This answered my question, and clarified EXACTLY what i was looking for immediately and consisely! amazing work!

  6. Thank you so much for you video. How is the effect in the end diastolic and end systolic related to both respiratory phase. Could you explain about this? if you are possible.

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