L9 - control of cardiac output Flashcards
what is cardiac output
vol of blood ejected by heart per min
what is the equation relating CO , SV and HR
CO = HR x SV
average HR
average SV
average CO
72bpm
70ml per beat
5L/min/side
what is meant by the heart being a permissive pump
it only pumps what comes back to it
CO = venous return
what is the major determinant of CO
venous return
what is preload
‘filling pressure of heart’
pressure into atria from vena cava/pulmonary vein
what is afterload
pressure against which the heart has to pump
eg pressure in aorta/pulmonary artery
what is the frank starling mechanism
more blood in the ventricles at the end if diastole (relaxing, filling) = bigger stroke volume
affects preload
purpose of frank starling mechanism
matches RV and LV output
average preload pressure
3-8 mmhg
what are the two explanations for the starling relationship
- length tension relationship
2. Ca2+ sensitivity
explain the length tension relationship
more stretch of striated muscle = stronger contraction
stretching sarcomere to a point where the most cross bridges can be formed = stronger contraction
explain Ca2+ sensitivity in relation to starling relationship
cardiac muscle filament sensitivity to Ca increases with stretch
what can affect the starling relationship and how
by affecting stroke volume
SNS stimulation (A/NA) inotropic drugs
by increasing contractility (at any sarcomere length)
what is a positive inotrope
something that increases contractility at given fibre length
what is a negative inotrope
something that decreases contractility at a given fibre length
do inotropes affect preload of afterload
preload
effect of afterload on CO
very little effect
what is the main determinant of SV - (CO)
preload
what effect does the SNS have on HR
- A/NA increases funny current
- this increases rate of diastolic depolarisation of SA node
- increases HR
what effect does PSNS have on HR
- ACh decreases funny current
- slower diastolic depolarisation of SA node
- slower HR
what is a positively chronotropic agent
increases HR
what is a negatively chronotropic agent
decreases HR
what is inotropy chronotropy luistropy referring to
contractility
HR
rate of relaxation
what does a
+ve luistropic agent do
-ve luistropic agent do
increases rate of relaxation
decreases rate of reaction
effect of dynamic exercise on :
- skeletal muscle vessels
- TPR
- venous return
- stroke vol
- HR
- CO
- vasodilated
- decreases significantly
- increases moderately
- increases moderately
- increases significantly
- increases significantly
effect of static exercise on
- skeletal muscle vessels
- TPR
- venous return
- stroke vol
- HR
- CO
- compressed
- increases moderately
- decreases significantly
- stays same or decreases slightly
- increases slightly
- stays the same or increases slightly
how is HR increased to 90bpm
entirely by reducing PSNS
how is HR increased above 90bpm
requires SNS input
effect of adrenaline on heart muscle
increases contractility - therefore increases SV-therefore increases CO
