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Flashcards in Exercise and Space Flight Deck (11):
1

What happens to CO during exercise and why?

* 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)

2

What happens to BP during exercise?

* 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

3

How does blood flow distribution change during exercise?

* 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

4

What happens to O2 delivery to muscle in exercise?

* Dilation of pre-capillary sphincters (due to local paracrine factors)--> more capillaries open --> inc SA for oxygen exchange/delivery

* Inc Ca O2 - Cv O2

5

Central Command

* 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)

6

Cardiovascular Drift

* 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

7

2 Major Adaptations of Trained Athletes

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)

8

What happens to hemodynamics during space flight?

*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)

9

What happens when astronauts return to earth?

* 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

10

Similarities b/n Exercise and Moderate Hemorrhage (7)

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

11

Differences b/n Exercise and Moderate Hemorrhage (4)

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