Given below are the events of cardiac cycle (column A) associated with marked points (A, B, C, D) in the figure (column B).

Choose the option that matches the events with marked points in the figure.
(1) a- (ii), b – (iii), c- (i), d – (iv)
(2) a- (i), b- (iv), c- (ii), d- (iii)
(3) a – (iv), b- (i), c- (iii), d-(ii)
(4) a- (iii), b- (ii), c- (iv), d- (i)

The cardiac cycle comprises coordinated mechanical events driving blood flow through the heart, reflected by characteristic changes in pressures within the left atrium, left ventricle, and aorta. Accurately matching these pressure changes to the corresponding events in the cardiac cycle is fundamental in physiology.

Key Cardiac Cycle Events and Associated Pressure Changes

• Atrial systole (atrial contraction):
  Left atrial pressure rises as atria contract, pushing blood into the left ventricle. Ventricular pressure remains low but rises slightly as the ventricle fills.

• Isovolumetric ventricular contraction:
  Ventricular pressure rises sharply with all valves closed, causing the mitral valve to close. Atrial pressure decreases as the atrium relaxes.

• Ventricular ejection:
  Ventricular pressure exceeds aortic pressure, opening the aortic valve. Ventricular and aortic pressures both rise; atrial pressure remains low.

• Isovolumetric ventricular relaxation:
  Ventricular pressure rapidly falls after aortic valve closes; aortic pressure shows the dicrotic notch. Ventricles relax before the mitral valve opens.

Matching Events with Points A, B, C, D

From typical pressure waveforms and Wiggers diagrams:

• Point A: Marks the start of isovolumetric ventricular contraction (pressure in ventricle rises, AV valve closes)

• Point B: Indicates the opening of aortic valve and onset of ventricular ejection (ventricular and aortic pressure rise)

• Point C: Corresponds to atrial systole characterized by atrial pressure rise and ventricular filling

• Point D: Represents isovolumetric ventricular relaxation marked by ventricular pressure fall and closure of the aortic valve

Matching the Options

This corresponds exactly to option:

(1) a- (ii), b – (iii), c- (i), d – (iv)

Summary Table

Explanation

• The atrial systole (c) increases left atrial pressure as blood is pushed into the ventricle.

• Isovolumetric ventricular contraction (a) raises ventricular pressure with valves closed.

• Ventricular ejection (b) happens once ventricular pressure exceeds aortic pressure.

• Isovolumetric relaxation (d) follows ventricular ejection, with rapid pressure drop and valve closure.

This detailed correlation between pressure waves and cardiac events is essential for interpreting heart function and diagnosing cardiac disorders.

Conclusion

The correct answer to the cardiac cycle event-to-pressure point matching is:

(1) a- (ii), b – (iii), c- (i), d – (iv)