Discussion
Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R) :
Assertion (A) : In a cardiac cycle the diastolic phase is larger than the systolic phase.
Reason (R) : An individual with a heart rate of 74 beats per minute would have a diastolic phase of 0.44 sec. and systolic phase of 0.37 seconds.
Which one of the following is correct ?
Answer: D
The key's answer is that (A) is true but (R) is not the correct explanation of (A).
(A) is true: at rest the heart spends longer filling, in diastole, than contracting, in systole. The figures in (R) are consistent with this and with each other, since at 74 beats per minute one cycle lasts 60/74, about 0.81 s, and 0.44 + 0.37 = 0.81 s.
(R) is a numerical example for one heart rate. It shows the diastolic phase being longer, but it does not say why. The textbook split at 75 beats per minute is about 0.3 s of systole and 0.5 s of diastole, so the paper's figures differ a little from it, and I could not confirm them against a published source. The key reads (R) as a true example that does not explain (A), so options A and C do not fit it.
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