2.5 cardiac work and coupling of venous return and CO Flashcards
1
Q
define work
A
work = force x height
2
Q
what are the forms of work?
A
External work (physical) - pressure volume and kinetic Internal work (heat) - isovolumetric, sounds/murmurs, electrical activity, base metabolism
3
Q
When is the work done in the heart?
A
during systole (mainly isovolumetric and fast ejection)
4
Q
where is the internal work spent?
A
Isovolumetric work
ionic channels and pumps
sounds/murmurs
base metabolism
5
Q
what is more costly increasing CO by HR or SV?
A
CO increase via HR increase is more costly than increasing SV as this requires increase in internal work
6
Q
what effect does afteroad have on internal work?
A
The greater the afterload, the greater the internal work needed - energetically costly
7
Q
what is the effect of sympathetic stimulation on venous system
A
increases wall tension - decreases venous compliance
8
Q
what are the determinants of venous return?
A
mean systemic filling pressure muscle pump abdominal pressure intrathoracic pressure mechanism of valvular plane
9
Q
what changes mean systemic filling pressure?
A
changing blood volume Decrease = decrease increase = increase peripheral resistance - increase peripheral resistance = decrease MSFP
