How many second is the normal duration of a cardiac cycle?

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Physiology

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

The cardiac cycle refers to the complete sequence of events in one heartbeat.
At a standard resting heart rate of 75 beats per minute, the duration of one cycle is calculated as 60 seconds divided by 75 beats, which equals 0.8 seconds.
This 0.8-second duration includes all phases: atrial systole (0.1s), ventricular systole (0.3s), and complete diastole (0.4s).

Option A: A duration of 0.6 seconds corresponds to a heart rate of 100 beats per minute (60/0.6), which is considered tachycardia, a heart rate faster than the normal resting rate.
Option B: This is the typical duration of only the atrial systole (atrial contraction) phase, not the entire cardiac cycle.
Option C: This represents the duration of complete cardiac diastole, the phase when all four chambers of the heart are relaxed. It does not include the systolic phases.

Visual 1: Diagram: A circular or linear diagram illustrating the phases of the cardiac cycle (Atrial Systole, Ventricular Systole, Complete Diastole) with their respective durations (0.1s, 0.3s, 0.4s) and correlation with ECG waves (P wave, QRS complex, T wave) and heart sounds (S1, S2).

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 normal cardiac cycle duration is fundamental for interpreting heart rates. A nurse can quickly identify tachycardia (cycle less than 0.6s) or bradycardia (cycle more than 1.0s) by assessing the pulse.
Knowledge of the cycle's phases and their durations is crucial for understanding ECG readings and identifying abnormalities like arrhythmias or heart blocks.
What if? If a patient's cardiac cycle is 1.2 seconds, their heart rate is 50 beats per minute (60/1.2). This is bradycardia. While this might be a normal finding in a highly trained athlete, in a non-athletic or elderly patient, it could signify a problem like a conduction block, requiring further assessment and possible intervention.

How to Approach the Question

First, identify the core concept being tested, which is the 'normal duration of a cardiac cycle'.
Recall the standard resting heart rate for a healthy adult, which is approximately 72-75 beats per minute.
Use this information to calculate the duration of a single beat (one cycle). The formula is: Duration = 60 seconds / Heart Rate (in beats per minute).
Perform the calculation: 60 seconds / 75 beats = 0.8 seconds per beat.
Compare your calculated result with the given options to find the correct answer.
Alternatively, recall the specific durations of the cardiac cycle phases: Atrial Systole (0.1s) + Ventricular Systole (0.3s) + Complete Diastole (0.4s) = 0.8s.

Concept Tested & Keywords

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