One cardiac cycle completes in \ \ \ \ \ \ \ \ \ \ \ ? - ESIC Nursing Officer - 2019 (Shift-2)

ESIC Nursing Officer - 2019 (Shift-2)

Applied Physiology

Easy

Appeared in: ESIC Nursing Officer - 2019 (Shift-2)

Explanation

A normal cardiac cycle lasts for approximately 0.8 seconds.
This value is based on a standard resting heart rate of 75 beats per minute (60 seconds / 75 bpm = 0.8 seconds).
The cycle consists of two main phases: systole (contraction) and diastole (relaxation).
The total duration is a sum of its phases: Atrial Systole (0.1s), Ventricular Systole (0.3s), and Complete Cardiac Diastole (0.4s).

Option A: A duration of 0.12 seconds is too brief for a complete cardiac cycle. It is closer to the duration of atrial systole (0.1s) or the normal PR interval on an ECG (0.12-0.20s).
Option B: A cycle duration of 0.57 seconds corresponds to a heart rate of approximately 105 beats per minute (60 / 0.57 ≈ 105). This represents tachycardia (a heart rate over 100 bpm), not a normal resting state.
Option C: A duration of 0.9 seconds corresponds to a heart rate of about 67 beats per minute (60 / 0.9 ≈ 67). While this is within the normal range, 0.8 seconds (based on 75 bpm) is the standard value used in medical and nursing education for a typical cardiac cycle.

Visual 1: Diagram: The Wiggers diagram, which synchronizes the ECG, heart sounds, and pressure/volume changes in the left ventricle and aorta over the 0.8-second cardiac cycle.
Visual 2: Flowchart: A visual sequence of the cardiac cycle events, starting with atrial systole and ending with ventricular filling, with timings for each phase.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of the Cardiac Cycle as background academic context rather than a clinical decision trigger.
Understanding the 0.8-second cycle and its phases is fundamental for interpreting electrocardiograms (ECGs). Deviations in the timing of the P wave, QRS complex, and T wave can indicate specific cardiac pathologies.
In tachycardia, the diastolic period shortens disproportionately. This is clinically significant as it can compromise coronary artery perfusion (which occurs during diastole) and reduce ventricular filling time, potentially lowering cardiac output.
What if? If a patient has sinus bradycardia with a heart rate of 50 bpm, the cardiac cycle duration would lengthen to 1.2 seconds (60/50). This increase is primarily due to a longer diastolic (filling) phase.

How to Approach the Question

Recognize that this is a factual recall question asking for a standard physiological value.
Identify the core concept: the duration of one complete cardiac cycle (one heartbeat).
Recall the standard resting heart rate used for textbook calculations, which is typically 75 beats per minute (bpm).
Apply the formula to find the duration of one beat: Cycle Duration (seconds) = 60 seconds / Heart Rate (bpm).
Calculate the value: 60 / 75 = 0.8 seconds.
Match this calculated value to the provided options to select the correct answer.

Concept Tested & Keywords

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