This is the time between two consecutive R-waves (R-R Interval).
Calculated Heart Rate:0 BPM
Cardiac Frequency:0 Hz
Clinical Classification:Normal
// Sync inputs: when seconds changes, update ms, and vice versa
document.getElementById('cycleDuration').oninput = function() {
var sec = parseFloat(this.value);
if (!isNaN(sec)) {
document.getElementById('cycleDurationMs').value = Math.round(sec * 1000);
} else {
document.getElementById('cycleDurationMs').value = ";
}
};
document.getElementById('cycleDurationMs').oninput = function() {
var ms = parseFloat(this.value);
if (!isNaN(ms)) {
document.getElementById('cycleDuration').value = (ms / 1000).toFixed(3);
} else {
document.getElementById('cycleDuration').value = ";
}
};
function calculateHeartRate() {
var durationSec = parseFloat(document.getElementById('cycleDuration').value);
// Validation
if (isNaN(durationSec) || durationSec <= 0) {
alert("Please enter a valid cardiac cycle duration greater than 0.");
return;
}
// Logic
// HR = 60 / Duration (seconds)
var bpm = 60 / durationSec;
var frequency = 1 / durationSec;
// Display Results
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('resultBPM').innerHTML = Math.round(bpm) + " BPM";
document.getElementById('resultFreq').innerHTML = frequency.toFixed(2) + " Hz";
// Status Determination
var statusSpan = document.getElementById('resultStatus');
var statusText = "";
statusSpan.className = "status-value"; // reset classes
if (bpm = 60 && bpm <= 100) {
statusText = "Normal Resting Rate";
statusSpan.classList.add("status-normal");
} else {
statusText = "Tachycardia (Fast)";
statusSpan.classList.add("status-tachy");
}
statusSpan.innerText = statusText;
}
Understanding Heart Rate and the Cardiac Cycle
The relationship between the cardiac cycle and heart rate is a fundamental concept in cardiovascular physiology. The cardiac cycle represents the complete sequence of events in the heart from the beginning of one beat to the beginning of the next. By measuring the duration of a single cycle, usually derived from an electrocardiogram (ECG), medical professionals can accurately calculate the heart rate in beats per minute (BPM).
The Mathematical Formula
Heart rate is inversely proportional to the duration of the cardiac cycle. Since heart rate is expressed in beats per minute and the cardiac cycle is typically measured in seconds, the formula requires a conversion factor of 60 (the number of seconds in a minute).
In clinical practice, the cardiac cycle duration is most often determined by measuring the R-R interval on an ECG strip. The R-wave is the peak of the QRS complex, representing ventricular depolarization. The time elapsed between two consecutive R-waves is the most reliable measure of one complete cardiac cycle.
Example Calculations
Here are three realistic examples of how cardiac cycle duration translates to heart rate:
Example 1 (Normal): If the time between beats is 0.8 seconds. Calculation: 60 ÷ 0.8 = 75 BPM. This is a standard resting heart rate.
Example 2 (Bradycardia): If the cycle lasts 1.2 seconds. Calculation: 60 ÷ 1.2 = 50 BPM. This indicates a slow heart rate, common in athletes or during sleep.
Example 3 (Tachycardia): If the cycle is short, lasting only 0.4 seconds. Calculation: 60 ÷ 0.4 = 150 BPM. This indicates a very fast heart rate, typical during intense exercise.
Clinical Classifications
Based on the calculated Beats Per Minute (BPM), heart rates are generally classified into three categories for adults:
Condition
Heart Rate Range
Cycle Duration Range
Bradycardia
< 60 BPM
> 1.00 seconds
Normal Sinus Rhythm
60 – 100 BPM
0.60 – 1.00 seconds
Tachycardia
> 100 BPM
< 0.60 seconds
Why This Matters
Calculating heart rate from the cardiac cycle is critical in interpreting ECGs. While digital machines provide automatic readings, manual calculation ensures accuracy, especially when checking for irregular rhythms (arrhythmias). If the cardiac cycle duration varies significantly from beat to beat, it may indicate conditions such as Atrial Fibrillation.