CVS Labs (tilt tables)

Question 1

Describe what happens, regarding blood flow, when a patient is moved from lying down to standing up.

Answer 1

• Gravity causes blood to flow to lower limbs;
• This can result in venous pooling;
• Less venous return (preload);
• Less blood is pumped from heart to brain;
• This is detected by BR;
• Detected by β1 receptors.

Question 2

How does the body overcome the ‘loss’ of blood flow, to the brain, upon standing up?

Answer 2

• This is detected by BR;
• Detected by β1 receptors;
• Activates bulbar circulatory centres;
• Release of NA;
• Inhibits vagal nerve (ACh);
• Increased HR and force of contraction;
• Increased vasoconstriction (TPR);
• TPR x C.O. = MAP;
• MAP increased.

Question 3

What extra precautions may you need to take with elderly patients?

Answer 3

Less efficient BR so should be given more time to slowly raise up

Question 4

What is hypovolaemia?

Answer 4

The loss of blood resulting in a reduction of circulating blood

Question 5

What happens upon hypovolaemia?

Answer 5

• Venous blood return (preload) is reduced;
• Stroke volume is reduced;
• Arterial BP falls.

Question 6

What is virtual hypovolaemia?

Answer 6

Experience of hypovolaemia, due to a transient fall in BP, upon suddenly standing up after sitting/ lying down (postural hypotension)

Question 7

What is postural hypotension?

Answer 7

A transient fall in BP upon suddenly standing up after sitting/ lying down, this is due to a decreased venous return

Question 8

Why does venous pooling happen upon standing up?

Answer 8

• Walls of veins are more ‘compliant’ than artery walls;

- Distend with extra pressure as a result of gravity.

Question 9

How is venous pooling overcome?

Answer 9

Increased ‘tone’ in the smooth muscles of the leg veins to decrease compliance