What is the average cardiac output(CO)? (at rest)
5L/min Cardiac output= heart rate x stroke volume
The average resting heart is 72 bpm
Average stroke volume is 70 ml per beat
Average cardiac output, at rest, is 72 x 70 = 5L/min
CO = ?x?
CO= heart rate x stroke volume
What is preload?
- The ‘filling pressure’ of the heart
- Right atrium (central venous) pressure
What is afterload?
- The pressure against which the heart has to pump
- Aortic pressure
What is venous return ?
Venous return is the rate of blood flow back to the heart. It normally limits cardiac output
Left ventricular end-diastolic pressure
What is a positive inotrope?
something that increases the force of contraction
What is a negative inotrope?
something that decreases the force of contraction
what is the main determinant of the stroke volume?
What can shift the starling curve upwards?
sympathetic stimulation or positive inotropes
positively chronotropic agent function?
increases heart rate
negatively chronotropic agent function
decreases heart rate
what does a positively lusitropic agent do?
increases the rate of relaxation
what does a negatively lusitropic agent do?
decreases the rate of relaxation
What happens to skeletal muscle vessels during dynamic exercise?
They get vasodilated
What is dynamic exercise?
Running, swimming etc.
What is static (isometric) exercise?
weight lifting etc.
What is peripheral resistance(TPR)?
The total resistance to flow of blood in the systemic circuit; the quotient produced by dividing the mean arterial pressure by the cardiac minute-volume.
What happens to peripheral resistance(TPR) during dynamic exercise?
It decreases massively
Why does total peripheral resistance decrease during dynamic exercise?
Metabolic waste products and other signals from exercising muscles causes the arterioles feeding the capillary beds in the working muscles to relax (dilate or open up) in an attempt to increase blood flow to the working muscle. This dilation is generally larger than constriction taking place in capillary beds to other tissues not involved in exercise. The net result is a dilation or opening up of arterioles and reduction in total peripheral resistance.
What happens to peripheral resistance(TPR) during static exercise?
It increases significantly
What is cardiac output?
Cardiac output is the volume of blood pumped by the heart per minute (mL blood/min). Cardiac output is a function of heart rate and stroke volume. The heart rate is simply the number of heart beats per minute. The stroke volume is the volume of blood, in milliliters (mL), pumped out of the heart with each beat.
What is the myocardium?
The myocardium is the muscular wall of the heart, or the heart muscle. It contracts to pump blood out of the heart and then relaxes as the heart refills with returning blood.
The heart is a 'premissive' pump, what does that mean ??
Within physiological limits, it only pumps out what comes back into it!
Cardiac Output = Venous Return
The Frank – Starling Relationship ??
The more blood in the ventricle at the end of diastole the bigger the stroke volume
the first thing to remeber is that the left and right circuits of the heart are in series with each other
So if there is a transient increase in RV output there will flow more blood to the capillaries in the lungs
this means that there will be an increase in the pulmonary veins and thus an increase in the LV
there is an increase in stroke volume and LV output
LV output matches the RV output
What is the explanation of the Frank-Starling mechanism??
(i) The length-tension relationship
(ii) Changes in muscle filament Ca sensitivity
What happens to skeletal ,muscle vessels when you do static exercise?
they get compressed
Examples of sympathetic stimulation??
what does syphatetic stimulation do to the starling curve??
what does it represent??
it makes an upward shift in the curve
The upward shift in the ‘Starling curve’ represents an increase in the intrinsic force of contraction of the heart - this is called ‘contractilty’
This is also called the inotropic state of the heart/muscle
A positive inotrope is something that increases the force of contraction*
A negative inotrope is something that decreases force of contraction*
*at the same preload or fibre length
How strongly the heart contracts at a given fiber length
Afterload has little affect on the Frank - Starling relationship
The SA node (pacemaker) action potential ??
as in the neuronal action potentail voltage gated ion channels play a big role but in the cardiac muscle it is Ca and not Na iosn that
as the voltage gets more and more positive more and more Ca channels open
and they are the ones that give the upstroke in the graph
the If channel is turned on when the voltage gets more negative and since it is an Na channel - Na flows in to the cells
what is the primary cardiac pacemaker ??
the sino-atrial (SA) node
- it drives the heart rate
Why is the pacemaker current also known as the funny current
becuase the If channels open when the area gets more negative, and this is unusual
what does symphatetic stimulation(autonomic agonists) do to the pacemaker action potential??
Increases ‘funny current’
faster rate of diastolic
faster heart rate
what effect does parasympathetic stimulation(autonomic agonists) have on the pacemaker action potential??
decreases ‘funny current’
opens KACh channels
slower rate of diastolic depolarisation
slower heart rate
Rate of relaxation
What happens to TPR during exercise?
Dynamic exercise - it goes down
Static exercise - it goes up
Cardiac output and dynamic exercise ??
Heart rate increases 3-fold
Cardiac output increases 5-6 fold
Stroke volume increases 2 fold
Cardiac output in trained (elite) athletes ??
Heart rate increases 3-fold
Cardiac output increases 6-7 fold
Stroke volume increases 2-3 fold
explain control of cardiac output
When venous return increases End diastolic volume increases. This increases stroke volume which then increases the CO
we can stimulate this with symphetic activity
parasympathetic activity can decrease heart rate and this decreases CO
Exercise can have an affect on this