Lecture 12- Control of Cardiac Output Flashcards
cardiac output
volume of blood ejected by each ventricle per minute
heart rate
number of heart beats per minute
stroke volume
volume of blood ejected by each ventricle per beat
formulae for cardiac output
heart rate x stroke volume
how does cardiac output increase when we exercise
both heart rate and stroke volume increases
what is the average cardiac output at rest
5 L/min
what is the average heart rate at rest
70 bpm
what is the average stroke volume at rest
70ml
what is the average cardiac output during exercise
20 L/min
what is the average heart rate during exercise
190bpm
what is the average stroke volume during exercise
105 ml
How would HR and SV in endurance athletes compare to general population at rest?
Lower heart rate and higher stroke volume
Physiological Left Ventricular Hypertrophy
Heart undergoes heart adaptations: increase in heart and chamber size (allows more blood to fill) and muscle mass of left ventricle
which group of people is Physiological Left Ventricular Hypertrophy most common in
athletes
what is the average athletes cardiac output at rest
5.5 L/min
what is the average athletes heart rate at rest
40 bpm
what is the average athletes stroke volume at rest
140 ml
what is the average athletes cardiac output during exercise
40 L/min
what is the average athletes heart rate during exercise
190 bpm
what is the average athletes stroke volume during exercise
210 ml
what is the average weight of a heart in grams
300
what is the average weight of an athletes heart in grams
500 grams
chronotropic effects
factors that affect heart rate
autonomic innervation
modifies intrinsic rate (speeds up or slows down)
cardiac reflex
when the body detects change and impulses are sent along sensory nerves
which region in the medulla oblongata is responsible for increasing heart rate
cardio acceleratory region
which region in the medulla oblongata is responsible for decreasing heart rate
cardioinhibitory
outline process of increasing heart rate
If hr needs to increase, activation of the cardioacceleratory region and inhibition of the cardioinhibitory region leading to increase firing of sym ns, noradrenaline is secreted from the medulla along the sympathetic ganglia (T1-T4) and arrives at the san and tells the pacemaker cells to increase their firing rate
At the same time sym ns stimulates adrenal medulla to secrete catecholamines such as adrenaline and noradrenaline to increase heart rate
outline the process of decreasing heart rate
Activates inhibitory centre to decrease hr and inhibits the cardioaccelaratory centre (increases the amount of nerve impulses sent to the vagus nerve in the parasym ns to decrease heart rate, increases the amount of acetylcholine - this arrives at the san to decrease frequences of excitation)
what neurotransmitter is involved in the parasympathetic nervous system
actetylcholine
what chronotropic effect does the parasympathetic nervous system have
negative
what effect does the parasympathetic nervous system have on heart rate
lowers heart rate
what effect does the parasympathetic ns have on cardiac output
reduces
what hormone is involved in the sympathetic nervous system
noradrenaline and adrenaline
what chronotropic effect does the sympathetic ns have
positive
what effect does the sympathetic heart rate have on heart rate
increases heart rate
what effect does the sympathetic ns have on cardiac output
increases cardiac output
Bradycardia
Pathologically low HR
Tachycardia
Pathologically fast HR
what effect does the sympathetic nervous system have on ionic control at the SA node
increases sodium and calcium entry reducing repolarisation allowing threshold to be reached quicker increasing the firing rate
what effect does the parasympathetic nervous system on ionic control at the SA node
causes the release of acetylcholine
potassium channels are sensitive to acetylcholine therefore more parasym activity and more potassium ions diffusing out of the cell and a more neg resting potential therefore will take longer for depolarisation to reach threshold and decreasing firing activity
vagal tone
parasympathetic activity outweighs the sympathetic
inherent rate of SA node
> 100 bpm
effect of the vagal tone of an average human at rest
reduces HR to 60-100bpm
little/ no sympathetic activity
endurance athlete at rest (vagal tone)
higher vagal tone
heart rate reduces to 30-60bpm
altered ion channel remodelling
venous return
stretching of the SAN
atrial reflex
walls of the right atria get stretched increasing sympathetic activity and noradrenaline release
End Diastolic Volume
volume in left ventricle at the end of diastole
end systolic volume
volume remaining in left ventricle at end of ejection
formula for stroke volume
end diastolic volume - end systolic volume
what effect does increasing end diastolic volume have on stroke volume and cardiac output
increases stroke volume and cardiac output
what effect does decreasing end systolic volume have on stroke volume and cardiac output
increases stroke volume and cardiac output
preload
the degree to which ventricular muscle cells are stretched at the end of diastole
contractility
the force produced by ventricluar muscle cells during systole at a given preload (affects the ESV)
afterload
the force the ventricle needs to overcome to open the semilunar valve and eject blood (affects ESV) (force that’s opposing ejection)
what is preload affected by
the volume of blood which is affected by the rate at which the blood is entering and time
what is preload directly proportional to and what is it dependant on
EDV and dependant on:
-the rate of venous return
-the available ventricular filling time (ventricular diastole)
Frank-Starling Law
The force developed in a muscle fibre is dependent on the extent it is stretched
the longer the diastole (affect on preload)
the greater the preload and the greater the blood volume
factors affecting venous return
posture
skeletal muscle pump
respiratory pump
venous capacitance
how does posture affect venous return
blood pools in leg veins whilst standing due to gravity lowering the venous return
how does skeletal muscle pump affect venous return
movement of skeletal muscle constricts veins aiding venous return, valves prevent backflow increasing venous return
how does the respiratory pump affect venous return
inspiration reduces intrathoracic pressure whilst increasing intraabdominal pressure increasing venous return
how does venous capacitance affect venous return
SNS activity reduces compliance and increases central venous pressure increasing venous return
inotropic effects
factors affecting contractility
how does increased blood ejection affect contractility
greater contractility
what receptors in the heart muscle are involved in contractility of the heart
beta adrenal heart muscle cells which bind to catecholamines e.g adrenaline and noradrenaline are able to bind to the receptors and increase the force of muscle contraction
SNS effects on contractility
increases the force of contraction and velocity of conduction which maximises diastolic time and increased filling
what is the afterload predominantly affected by
the vascular tone (degree of constriction and dilation of mainly smaller arteries)
affect of lumen size of afterload
smaller lumen (vasoconstriction): higher afterload
wider lumen (vasodilation): decreased afterload
affect of stiff valves on afterload
increase afterload
affect of prolonged increases in afterload
damage to the myocardium and lead to heart failure
affect of vasoconstriction on ESV
increases
affect of vasoconstriction on stroke volume
decreases
affect of vasoconstriction on cardiac output
decreases
affect of vasodilation on ESV
decreases
affect of vasodilation on stroke volume
increases
affect of vasodilation on cardiac output
increases
