Lecture 35: Microgravity and Bed-Rest

Question 1

What were the key findings of the Dallas Bed-Rest study?

Answer 1

Bed-rest decreased VO2 max
Increased HR at every intensity
Decreased SV at every intensity
Decrease in CO (due to SV drop)

Also a shrinking of heart chamber size

Question 2

What are the four different ways in which studies have stimulated microgravity?

Answer 2

Head-down bed-rest
Parabolic flight
Immobilisation
Wheelchair

Question 3

What is orthostatic intolerance?

Answer 3

Inability to stand upright after space flight due to decreased blood pressure

Question 4

What position are people with orthostatic intolerance put in, in order to aid recovery?

Answer 4

Supine

Question 5

How is orthostatic intolerance stimulated?

Answer 5

Microgravity –> Reduced hydrostatic gradient –> Increased GFR, decreased ADH and reabsorption –> Increased diuresis –> Loss of blood volume –> Orthostatic intolerance –> Decreased exercise capacity

Question 6

How do hydrostatic gradient changes causes decreased blood pressure?

Answer 6

Pre-flight:

Head: 70mmHg / Torso: 80mmHg / Legs: 200mmHg

During flight: blood gravitates towards the head, causing reabsorption mechanisms to try and limit this by increasing diuresis and therefore decreasing blood volume

Post-flight: decreased blood pressure
Head: 30mmHg / Torso: 60 mmHg / Legs: 160mmHg

Question 7

Why is there cardiac atrophy after long-term exposure to microgravity?

Answer 7

Decrease in left-ventricle mass
Decrease in stroke volume
Decrease in RBC mass and blood plasma (blood volume decreases)

Question 8

What is the effect of decreased blood volume on heart rate?

Answer 8

The greater the reduction in blood volume, there higher the heart rate