#venous return

[hebasoffar]

The stroke volume (SV) is the amount of blood pumped out from each ventricle per beat. It is about 70-90 ml in a resting man of average size in the supine position. It equals the end-diastolic volume minus the end-systolic volume. End diastolic volume is the volume of blood in each ventricle at the end of the diastole. It equals

[drpaulhaider]

Reversing Low Blood Pressure Without Pills - Case Study 

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[onelittleglobetrotter-blog]

Why your legs get numb while sitting down, are you going to die?

No you are not going to die. But have you ever wondered how in the world does the blood flow back to your heart to pick up more oxygen from the lungs as you’re studying for hours motionless? Surely it has to go to every part of your body, including your legs, so how does it work its way back up against the gravity?

Stroke Volume and Venous Return

Let’s talk about some Frank-Starling law which basically states that as end-diastolic volume increases (diastole – relaxation; when ventricles are fully relaxed they are filled to their max. capacity) the stroke volume increases (the blood volume pumped per contraction). The end-diastolic volume is determined by the venous return (which makes sense because the amount of blood that returns to the heart determines the amount that will FILL your heart). Right so they are factors that affect venous return and they include: contraction or compression of veins returning blood to the heart AKA the skeletal muscle pump, pressure changes in the abdomen and thorax while breathing and the sympathetic innervation of veins. Peachy. So what Ola, why do I care? Well, do you want to know why your legs get numb while you sit for hours and pretend you’re studying? Keep reading then.

Skeletal muscle pump is the pump that functions by skeletal muscles contracting and squeezing veins – particularly in the legs – compressing them and pushing blood towards the heart. But as you know – skeletal muscles are voluntary muscles so when you are standing up or sitting down motionless for a while – the skeletal muscle pump cannot assist the venous return. Now the respiratory pump (pressure changes in the abdomen and thorax cavity) comes into play. As you inhale, your chest expands and moves the diaphragm towards the abdomen, the higher pressure placed on the outside of abdominal veins increases pressure there while decreasing pressure in the thoracic veins which in turn enhances venous return by vena cava. Lastly, when veins constrict (aided by the sympathetic innervation of veins) their diameter decreases which causes more blood to be squeezed out of them. So that is how the blood works its way against gravity. But the skeletal muscle pump works most efficiently. All of these things are taking place as you complain that you have to sit down all day and study – see? Now I have given you a scientific excuse to go outside and have some fun.

[mynotes4usmle]

Cardiac Function Curves

[mynotes4usmle]