Exercise and Space Flight

Question 1

What happens to CO during exercise and why?

Answer 1

• HUGE inc in CO (CO = SV x HR)
• Inc HR b/c dec parasympathetic tone and inc symp input –> beta 1 receptors induce conduction velocity
• Inc SV by inc venous return (skeletal muscle pumping, venoconstriction, respiratory muscle contractions) AND inc contractility (also sympathetic)

**Inc HR does NOT compromise SV b/c most filling occurs in passive filling anyway (80%), inc contractility means atrial contraction more powerful into ventricles and Bodwitch effect (less repolarization time - inc force of contraction)

Question 2

What happens to BP during exercise?

Answer 2

• HUGE inc in systolic BP b/c large arteries become less compliant; less blood taken in as potential energy
• Diastolic BP stays the same or may even eventually dec
  
  • Dec TPR –> rapid run-off of blood into capillaries during diastole
• SO HUGE PULSE PRESSURE but MAP only slightly higher

Question 3

How does blood flow distribution change during exercise?

Answer 3

• Inc flow to… heart, skeletal muscles, skin
• Dec flow to… GI, kidney, other
• Same flow to… brain

For skeletal muscle…Alpha vasoconstriction cancels out w/ beta vasodilation SO more dependent on local metabolites so only working muscles get inc flow

Question 4

What happens to O2 delivery to muscle in exercise?

Answer 4

• Dilation of pre-capillary sphincters (due to local paracrine factors)–> more capillaries open –> inc SA for oxygen exchange/delivery
• Inc Ca O2 - Cv O2

Question 5

Central Command

Answer 5

• Just thinking about exercise –> inc HR and contractility which inc BP (but without dec resistance to skeletal musc b/c not actually using muscles)
• Small muscle afferents sense pressure changes and metabolic products in contracting muscle –> trigger inc HR and BP
• Dampen baroreceptor reflex in CNS (inhibit neurons that get baroreceptor signals so less inhibition of RVLM –> more sympathetic outflow)

Question 6

Cardiovascular Drift

Answer 6

• After ~10 min you lose vol by sweat –> dec venous return –> dec CO/SV
• Inc HR to compensate for this dec
• HR also inc b/c heat and baroreceptor reflex

Question 7

2 Major Adaptations of Trained Athletes

Answer 7

1- Hypertrophy (to an extent- not too much b/c must be able to perfuse whole heart) - more actin/myosin –> inc contractility

• When inc contractility then dec HR to maintain CO (AKA can have same SV w/ lower HR)
• Result = lower resting HR; but can still have same level of HR inc in exercise –> HUGE inc in SV in exercise
• “Greater reserve capacity”

2- Also inc vascularity to heart (more O2 delivery)

Question 8

What happens to hemodynamics during space flight?

Answer 8

• Upper and lower body pressures equalize —> no longer pooling in veins (pools in upper body/head instead) and inc venous return to R atrium —> signals inc pressure to baroreceptors and atrial stretch receptors in upper body —> inc firing —> corrections to dec blood volume (inc ANF, dec vasopressin, dec angio II, dec aldosterone)
• Lose about 1 L of fluid in space
• Also atrophy of muscles in space b/c not bearing weight (less skeletal muscle pumping)

Question 9

What happens when astronauts return to earth?

Answer 9

• Orthostatic intolerance (AKA cannot stand w/o syncope) b/c loss of volume —> dec upper body perfusion now that gravity is a factor AND b/c dec skeletal muscle pumping AND down-regulation of baroreceptor reflex

Question 10

Similarities b/n Exercise and Moderate Hemorrhage (7)

Answer 10

1- Inc muscle paracrine factors

2- High epi levels (even higher in hemorrhage - so much that epi binds alpha receptors for vasoconstriction)

3- Vasoconstriction

4- Dec diameter of gut arterioles

5- Maintain diameter of brain arterioles

6- Inc HR

7- Inc in angio-2, aldosterone and vasopressin BUT so much more in hemorrhage; in exercise angio-2 may inc b/c less blood flow to kidney which could then cause small inc in aldosterone then when sweat it inc osmolarity so make vasopressin

Question 11

Differences b/n Exercise and Moderate Hemorrhage (4)

Answer 11

1- baroreceptors fire more in exercise and LESS in hemorrhage

2- BP inc in exercise and BP drastically dec in hemorrhage (then is corrected)

3- CO inc in exercise CO dec in hemorrhage (less venous return)

4- Much greater levels of aldosterone, angio-2 and vasopressin in hemorrhage