Venous Return

Did you know: Why prop patient's leg upwards for First Aid (14th May 2009)


After witnessing a trauma with no emergency backup within 15 minutes, all persons are trained to assess the situation firstly and follow the shock treatment protocol.
One of these steps involve placing the patients leg on a pillow 8-10 inches above the level of the head.
Why?
To increase the venous return and thereby increase cardiac output and hence maintain blood flow to the brain and other vital organs.
During hemorrhagic shock, blood volume decreases and so the venous return decreases. After stopping blood leak, the next step is to supply enough blood to the heart to pump.

Did You Know: What happens physiologically when you pick up a large object? (14th May 2009)

What happens physiologically when you are picking up a really large object or are trying to relieve yourself of constipation?
((Warning: if you're not a med student or someone who has studied physiology before, this may sound confusing/weird))

To make it easy I'll take the example of lifting a really large object:

Whilst carrying a really large object and forcing expiration against your glottis you are performing the Valsalva maneuver.

The intrathoracic pressure becomes positive due to compression of the thoracic organs by the contracting rib cage.
This intrathoracic pressure increase compresses the vessels and cardiac chambers.
Veins are compressed and the right atrial pressure increases majorly causing the venous return to decrease.

This reduced venous return, and along with compression of the heart, reduces the cardiac filling.

Reduced filling causes a fall in cardiac output according to the Frank Starling's Law.

And by default a decreased blood pressure.

The compression of the thoracic aorta causes the aortic pressure to increase, initially.
But then the aortic pressure begins to fall after a few seconds because cardiac output is decreasing.

(Heart rate is regulated by the increasing or decreasing blood pressure)

Due to the baroreceptor reflex, the heart rate decreases because aortic pressure is elevated and then the heart rate increases as the aortic pressure falls.

When the person starts to breathe normally again, aortic pressure briefly decreases as the pressure on the aorta is removed, and heart rate briefly increases.

Due to the rapid increase in cardiac filling the cardiac output increases and the aortic pressure increases simultaneously causing the heart rate to decrease again.

Therefore due to the baroreceptors, the Aortic pressure rises above normal {Which was low due to the Valsalva maneuver} and heart rate is brought down low or normal

I know it's confusing... read it only when you have nothing else haunting you.