For a normal heart, time taken for atrial systole and diastole are A_S and A_D seconds respectively, while same for ventricular systole and diastole are V_S and V_D. Which one of following equations is correct?

The correct answer is AS + AD = VS + VD

Explanation:

The cardiac cycle consists of a series of events that occur from the beginning of one heartbeat to the beginning of the next. It includes phases of systole (contraction) and diastole (relaxation) of both the atria and ventricles to ensure efficient blood flow through the heart, to the lungs, and to the rest of the body. The duration of these phases needs to be synchronized for the heart to function effectively.

• Atrial Systole and Diastole (A_S + A_D): This period includes the time when the atria contract (atrial systole) to push blood into the ventricles and the time when the atria are relaxed and filling with blood (atrial diastole).
• Ventricular Systole and Diastole (V_S + V_D): This period encompasses the time when the ventricles contract (ventricular systole) to eject blood into the arteries (systemic and pulmonary circulation) and the time when the ventricles are relaxed and filling with blood (ventricular diastole).
• Atrial Systole (A_S): This is the phase where the atria contract to push blood into the ventricles. It's relatively short, lasting about 0.1 seconds. Atrial systole occurs late in the ventricular diastole phase, which assists in topping off the volume of the ventricles before they contract.
• Atrial Diastole (A_D): Following atrial systole, the atria enter a relaxation phase, or diastole, which lasts for the remainder of the cardiac cycle. Given that the average total duration of the cardiac cycle is around 0.8 seconds (at a heart rate of 75 beats per minute), and subtracting the time for atrial systole, atrial diastole approximately accounts for the remaining 0.7 seconds in a broad sense across different phases of the ventricles. However, it's worth noting that the atria are in a state of relaxation even as the ventricles contract and undergo their cycles.
• Ventricular Systole (V_S): This phase follows atrial systole and is divided into two parts: the isovolumetric contraction phase and the ventricular ejection phase. Overall, ventricular systole lasts about 0.3 seconds. During this phase, the ventricles contract, increasing pressure inside them and ejecting blood into the pulmonary artery and aorta.
• Ventricular Diastole (V_D): After ventricular systole, the ventricles relax during ventricular diastole, which is also divided into two phases: isovolumetric relaxation and ventricular filling. This phase lasts approximately 0.5 seconds. It's during this phase that the ventricles fill with blood from the atria, preparing for the next cardiac cycle.

The total time taken for atrial systole and diastole is equal to the total time taken for ventricular systole and diastole.