Parameters of the cardiac cycle; volume fractions; factors infuencing cardiac output Flashcards
What are the Volume fractions?
- EDV
- ESV
- SV
- CO
What are the parameters describing the heart cycle?
- compliance
- work and performance
What is the EDV?
End Diastolic Volume
- At the end of the diastole (maximal relaxation, right before the next heart contraction), the ventricles are maximally filled.
What is ESV?
End Systolic Volume
- When the ventricles re maximally emptied (end of systole, right before relaxation) there is still some blood remaining in them.
What is SV?
Stroke Volume
- Passes through the aorta at each cycle.
= EDV - ESV
What is CO?
Cardiac output
- The volume of blood pumped into the circulation by the heart in one minute.
CO = (EDV - ESV) x Frequency = SV x Frequency
How can you measure the cardiac output?
- Using Fick´s Principle
2. Using Stewart´s principle.
Why do you measure the Cardiac output?
It is a good measure of cardiac performance
Explain Fick´s principle:
Based on the law of conservation of mass.
- CO is based on the amount of oxygen that is taken up by the lung per unit time hsould equal the amount taken up by the tissues.
CO = total O2 uptake (1/min) / aterio-venous O2 difference (l/l).
Explain the Stewart´s principle:
From volume determination to Volume FLOW determination (V/time instead of V)
- Injecting Evans-blue IV, sample collection and analysis, plot curve, just before recirculation do extrapolation (intercept with X).
- Area under the extrapolated curve = CO.
What is Ventricular Compliance?
Dilating capacity (volume change taking place due to unit-pressure change, delta-V/delta-P
When is Ventricular Compliance important?
Important parameter of the adaptability of the heart. Closely related to the dialting ability of ventricles.
Connection between EDV, EDVP and SV in rest:
the pressure maintained by blood arriving from periphery (EDV ventricular pressure) is 5 Hgmm.
. that creates 60ml EDV.
Increase of EDVP in the connection between EDV, EDVP and SV.
- linearly increases EDV (+SV) until 25 Hgmm (from here Collagen prevents further dilation)
Ventricular compliance in old animals:
Decreased compliance
- The curve shifts to right
- the same EDVP cant dilate the heart to the same EDV
- at least two-fold EDVP is needed to achieve the same EDV.
The Total work of the heart is composed of?
of two parts:
- Outer work (Wo) also called mechanical work.
- Inner work (Wi) also called heat production.
Wt = Wo + Wi
What is the role of the Mechanical work (Wo)?
Mechanical wor serves mostly to maintain average pressure, and only 4% is the kinetic energy, therefore the kinetic energy is neglected.
Wo = SV x deltaP (arterial average pressure)
how can you measure the total work of the heart?
Since the heart gains its energy purely rom oxidative processes, the total work of the heart can be determined by measuring the total oxygen consumption of this tissue.
The performance of the heart can be measured in:
Performance = Work /time W/t = P x V/t
P= cardiac output (CO)
- sine the heart maintaines constant arterial pressure (Pa) therefore the performance (W/t) is mostly determined by Volume Flow of the unit time (V/t) so perfomance is equvalent with cardiac Output!!
How can you measure the Cardiac Work (Wo) during cardiac cycle?
The Rushmer-diagram analyses the cardiac work (Wo) as a function of volume and pressure in the left ventricle during cardiac cycle.
Explain the steps of the Rushmer diagram
A. At the beginning of the systole: mitral valves are closed = isovolumetric contraction.
B. When aortic pressure is reached: semilunar valves open = ejection begins.
C. At end of systole: ventricular P < aortic, so semilunars close, but the P is still a bit > than Artrial pressure, so mitrals are still closed = Isovolumetric relaxation
D. When ventriuclar P < atrial, mitral valves open and filling starts.
What do the Law of Laplace say?
In order to maintain the same pressure (P), the larger ventricle on the right should produce much higher work (oxygen consumption) since it has to produce higher wall tension (T).
What are the factors influencing the Cardiac Output?
CO = (EDV - ESV) + frequency
What are the influencing factors of EDV?
- Diastolic filling time
- Ventricular compliance
- Ventricular filling (preload) maintained by CVP
What are the influencing factors of ESV?
- Aortic pressure (afterload when the semilunar valves are still open)
- Contractility. depends on the isometric max tension and max contraction speed. contractility decreases by Parasymp. and increases by Symp stimulation.
What are the influencing factors of Frequency?
Sympathetic effects and Parasympathetic effects.
Sympathetic effect on the heart can be?
Artificial increase:
- Pacemakers
- Only diastolic duration is decreased
- CO decreased
Natural increase:
- Sympathetic activation
- reduced systolic time
- proportionally reduced diastolic time
- CO increases
