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