cardiac dynamics Flashcards
what is stroke volume
The volume of blood ejected from the left ventricle per beat (ml)
what is heart rate
The number of times the heart beats per minute (bpm)
what is cardiac output
The volume of blood ejected (pumped) from the heart per minute (l/min)
what is bradycardia
hr under 60bpm
what is average resting hr
72bpm
how to calculate maximum HR
220- age
what is the slight increase in HR before exercise called
anticipatory rise
how does HR change during exercise
HR rises proportionately to exercise intensity
At submaximal levels HR will plateau when a steady state is reached and O2 demand is met.
Anticipatory rise before the start
Rapid increase at start of exercise until steady state reached
how is HR post exercise
Initial rapid drop in HR due to less oxygen demand
Then gradual drop to repay oxygen debt
what is the average stroke volume
70 ml
what does stroke volume depend on
Stroke volume depends on venous return - called Starling’s Law
values for SV
Untrained
resting- 60-90 ml per beat
submaxmal exercise- 120-140 ml per beat
maximal exercise Slight Decrease
Trained
resting- 90-110 ml per beat
sub maximal exercise 160-200 ml per beat
maximal exercise- Slight Decrease
why does SV decrease slightly at maximal exercise
due to increased firing rate of SA node.
This is due to reduced time for the heart to fill
what are the to reasons why stroke volume increases
1.Increased venous return
Increased blood back to heart due to venous return mechanism
Leads to greater diastolic filling
2.Starling’s Law
More blood to heart, leads to greater end diastolic volume
Greater stretch of atria walls lead to more forceful contraction
What is Ejection Fraction?
An ejection fraction of 60 % means that 60 % of the total amount of blood in the left ventricle is pushed out with each heartbeat.
what is normal sv
50% and 70%
75% is to high
how to calculate sv
SV = EDV - ESV
what is the equation for cardiac output
HR x SV = Q
e.g average is 5L(72bpmx70ml)
what happens to Q during exercise
Cardiac output increases in line with exercise intensity
Plateaus during maximal exercise, due to inefficient diastolic filling time
what happens to Q in recovery
In recovery there is a rapid decrease followed by a slower decrease to resting levels
what are the values for Q
Untrained
resting 5L/min
sub maximal 10-15L/min
maximal- 20-30L/min
Trained
resting 5L/min
sub maximal 15-20L/min
maximal 30-40L/min
what is starlings law
Increased Venous Return will result in increased SV or Q
More blood returning forces a greater stretch of the ventricle wall, causing a stronger contraction.
Increased stretch = greater SA node firing rate
