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

1
Q

What are the Volume fractions?

A
  • EDV
  • ESV
  • SV
  • CO
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2
Q

What are the parameters describing the heart cycle?

A
  • compliance

- work and performance

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3
Q

What is the EDV?

A

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

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4
Q

What is ESV?

A

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

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5
Q

What is SV?

A

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

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6
Q

What is CO?

A

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

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7
Q

How can you measure the cardiac output?

A
  1. Using Fick´s Principle

2. Using Stewart´s principle.

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8
Q

Why do you measure the Cardiac output?

A

It is a good measure of cardiac performance

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9
Q

Explain Fick´s principle:

A

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).

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10
Q

Explain the Stewart´s principle:

A

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.
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11
Q

What is Ventricular Compliance?

A

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

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12
Q

When is Ventricular Compliance important?

A

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

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13
Q

Connection between EDV, EDVP and SV in rest:

A

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

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14
Q

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

A
  • linearly increases EDV (+SV) until 25 Hgmm (from here Collagen prevents further dilation)
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15
Q

Ventricular compliance in old animals:

A

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.
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16
Q

The Total work of the heart is composed of?

A

of two parts:

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

Wt = Wo + Wi

17
Q

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

A

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)

18
Q

how can you measure the total work of the heart?

A

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.

19
Q

The performance of the heart can be measured in:

A
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!!

20
Q

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

A

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

21
Q

Explain the steps of the Rushmer diagram

A

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.

22
Q

What do the Law of Laplace say?

A

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).

23
Q

What are the factors influencing the Cardiac Output?

A

CO = (EDV - ESV) + frequency

24
Q

What are the influencing factors of EDV?

A
  • Diastolic filling time
  • Ventricular compliance
  • Ventricular filling (preload) maintained by CVP
25
Q

What are the influencing factors of ESV?

A
  • 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.
26
Q

What are the influencing factors of Frequency?

A

Sympathetic effects and Parasympathetic effects.

27
Q

Sympathetic effect on the heart can be?

A

Artificial increase:

  • Pacemakers
  • Only diastolic duration is decreased
  • CO decreased

Natural increase:

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