Parameters of the cardiac cycle; volume fractions; factors infuencing cardiac output

Question 1

What are the Volume fractions?

Answer 1

• EDV
• ESV
• SV
• CO

Question 2

What are the parameters describing the heart cycle?

Answer 2

• compliance

- work and performance

Question 3

What is the EDV?

Answer 3

End Diastolic Volume
- At the end of the diastole (maximal relaxation, right before the next heart contraction), the ventricles are maximally filled.

Question 4

What is ESV?

Answer 4

End Systolic Volume
- When the ventricles re maximally emptied (end of systole, right before relaxation) there is still some blood remaining in them.

Question 5

What is SV?

Answer 5

Stroke Volume
- Passes through the aorta at each cycle.
= EDV - ESV

Question 6

What is CO?

Answer 6

Cardiac output
- The volume of blood pumped into the circulation by the heart in one minute.
CO = (EDV - ESV) x Frequency = SV x Frequency

Question 7

How can you measure the cardiac output?

Answer 7

1. Using Fick´s Principle

2. Using Stewart´s principle.

Question 8

Why do you measure the Cardiac output?

Answer 8

It is a good measure of cardiac performance

Question 9

Explain Fick´s principle:

Answer 9

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).

Question 10

Explain the Stewart´s principle:

Answer 10

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.

Question 11

What is Ventricular Compliance?

Answer 11

Dilating capacity (volume change taking place due to unit-pressure change, delta-V/delta-P

Question 12

When is Ventricular Compliance important?

Answer 12

Important parameter of the adaptability of the heart. Closely related to the dialting ability of ventricles.

Question 13

Connection between EDV, EDVP and SV in rest:

Answer 13

the pressure maintained by blood arriving from periphery (EDV ventricular pressure) is 5 Hgmm.
. that creates 60ml EDV.

Question 14

Increase of EDVP in the connection between EDV, EDVP and SV.

Answer 14

• linearly increases EDV (+SV) until 25 Hgmm (from here Collagen prevents further dilation)

Question 15

Ventricular compliance in old animals:

Answer 15

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.

Question 16

The Total work of the heart is composed of?

Answer 16

of two parts:

• Outer work (Wo) also called mechanical work.
• Inner work (Wi) also called heat production.

Wt = Wo + Wi

Question 17

What is the role of the Mechanical work (Wo)?

Answer 17

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)

Question 18

how can you measure the total work of the heart?

Answer 18

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.

Question 19

The performance of the heart can be measured in:

Answer 19

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!!

Question 20

How can you measure the Cardiac Work (Wo) during cardiac cycle?

Answer 20

The Rushmer-diagram analyses the cardiac work (Wo) as a function of volume and pressure in the left ventricle during cardiac cycle.

Question 21

Explain the steps of the Rushmer diagram

Answer 21

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.

Question 22

What do the Law of Laplace say?

Answer 22

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).

Question 23

What are the factors influencing the Cardiac Output?

Answer 23

CO = (EDV - ESV) + frequency

Question 24

What are the influencing factors of EDV?

Answer 24

• Diastolic filling time
• Ventricular compliance
• Ventricular filling (preload) maintained by CVP

Question 25

What are the influencing factors of ESV?

Answer 25

• 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.

Question 26

What are the influencing factors of Frequency?

Answer 26

Sympathetic effects and Parasympathetic effects.

Question 27

Sympathetic effect on the heart can be?

Answer 27

Artificial increase:

• Pacemakers
• Only diastolic duration is decreased
• CO decreased

Natural increase:

• Sympathetic activation
• reduced systolic time
• proportionally reduced diastolic time
• CO increases