Normally cardiac cycle takes...seconds to complete?

Appeared in: DHS 2018 shift 1st

Explanation

The cardiac cycle encompasses all the electrical and mechanical events of one complete heartbeat.
The duration of the cardiac cycle is inversely proportional to the heart rate. It is calculated by dividing 60 seconds by the heart rate in beats per minute (bpm).
For a normal resting heart rate of 75 bpm, the duration is calculated as 60 / 75 = 0.8 seconds.
This 0.8-second cycle is composed of systole (contraction) and diastole (relaxation) phases.

Option A: This duration (0.01 seconds) is physiologically too short to represent a complete cardiac cycle or even one of its major phases.
Option C: This duration (0.08 seconds) is too brief for a full cycle. It is closer to the duration of specific sub-phases like isovolumetric ventricular contraction (approx. 0.05s) but not the entire cycle.
Option D: This value (0.1 seconds) represents the typical duration of atrial systole (the contraction of the atria), which is only the first phase of the cardiac cycle, not the entire duration.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Duration of the cardiac cycle as background academic context rather than a clinical decision trigger.
Understanding the cardiac cycle duration is fundamental for interpreting heart rate changes and their hemodynamic consequences.
In tachycardia (fast heart rate), the cardiac cycle shortens, primarily at the expense of diastole. This reduces ventricular filling time, which can decrease stroke volume and cardiac output, leading to symptoms like dizziness or syncope.
In bradycardia (slow heart rate), the cycle lengthens, which allows for more filling time but may lead to inadequate cardiac output if the rate is excessively slow.

How to Approach the Question

This is a factual recall question testing knowledge of a fundamental concept in cardiovascular physiology.
Step 1: Identify the core concept being asked: the normal duration of a 'cardiac cycle'.
Step 2: Recall that the cardiac cycle's length is dependent on the heart rate.
Step 3: Remember the standard reference heart rate used for this calculation, which is typically 75 beats per minute.
Step 4: Apply the formula: Duration (s) = 60 seconds / Heart Rate (bpm). Calculate 60 / 75, which equals 0.8.
Step 5: Match the calculated value (0.8 seconds) with the provided options to find the correct answer.

Concept Tested & Keywords

Q126q72CURbnrN_-JwL4sE

E6 Physiology Ganong 27e Vol 2 Part 1 pp. 87-89, 88-90

Practise the full DHS 2018 shift 1st

Attempt every question from this paper in a timed mock, then review the full solution for each one.