06: Cardiovascular Physiology III

Question 1

Name the phases of the cardiac cycle.

Answer 1

1. Atrial systole
2. Isovolumetric contraction
3. Rapid ventricular ejection
4. Reduced ventricular ejection
5. Isovolumetric relaxation
6. Rapid ventricular filling
7. Reduced ventricular filling (diastasis)

Question 2

What occurs during atrial systole?

Answer 2

• P wave on EKG: atrial contraction
• Increased LAP –> ‘a wave’ on venous pulse
• End of ventricular diastole
• Slight increase in ventricular volume as blood is actively ejected from LA to LV –> S4 if LV stiff

Question 3

What occurs during isovolumetric ventricular contraction?

Answer 3

• Initiated during QRS complex: electrical activation of ventricles
• LV contracts –> LV pressure sharply rises against closed aortic valve
• As soon as LV pressure > LA pressure, MV closes (S1)

Question 4

What occurs during rapid ventricular ejection?

Answer 4

• VP > AP –> aortic valve opens
• Most of SV ejected
• Aortic pressure increases

Question 5

What occurs during reduced ventricular ejection?

Answer 5

• T wave on EKG: ventricles repolarizing
• Ventricular pressure begins falling
• Ejection of blood continues, but at reduced rate
• Last phase of ventricular systole

Question 6

What occurs during isovolumetric relaxation?

Answer 6

• End of T wave: ventricles fully repolarized
• LV pressure falls dramatically
• When LVP < AP, AV closes (S2); PV also closes
• Ventricular volume remains constant

Question 7

What occurs during rapid ventricular filling?

Answer 7

• LVP falls below its lowest level (<lap> MV opens</lap>
• Ventricle begins to rapidly fill with blood from LA –> LV volume increases
• Rapid filling causes S3 (normal in children/athletes; pathologic sign of CHF & anemia

Question 8

What occurs during reduced ventricular filling?

Answer 8

• Also known as diastasis
• Longest phase
• Time to allow filling (EDV); critical for preload
• ↑ HR can shorten phase, compromise filling

Question 9

What limitation does the **Frank-Starling Relationship **demonstrate?

Answer 9

Volume of blood ejected by ventricle depends on volume present in the ventricle at end of diastole.

SV↑ as preload↑, but only to a certain point.

As LVEDV↑, pulmonary venous pressure↑.

As PVP↑, fluid leaks out of capillaries and into insterstitum and alveoli, impairing gas exchange –> pulmonary edema

Question 10

What is preload?

Answer 10

Load on the ventricle at the end of diastole.

Measure of preload: EDV & EDP.

↑preload, ↑CO to a point (pulmonary edema, JVD).

Question 11

What is afterload?

Answer 11

Load on ventricle during ejection; determined by arterial system.

Measure of afterload: AoP, TPR

Question 12

What is compliance?

Answer 12

• Change in volume for a given change in pressure
• C = V/P
• Greatest compliance is at low volumes and is the lowest at high volumes

Question 13

What factors influence myocardial contractility?

Answer 13

1. Alteration of calcium release to myofilaments (↑Ca –> ↑contractility)
2. Alteration in affinity of myofilaments for calcium
3. Alteration in number of myofilaments available for contraction

Slope of ESPVR is an index of contractility (negative inotropic agent –> decreased slope = decreased contractility)

Question 14

What is a normal ejection fraction value?

Answer 14

50-65%

Question 15

What are examples of positive inotropes?