function updateRRInputLabels() {
var mode = document.getElementById('rrCalcMode').value;
var label = document.getElementById('rrInputLabel');
var input = document.getElementById('rrInputValue');
if (mode === 'rr_to_hr') {
label.innerText = 'Enter R-R Interval (milliseconds):';
input.placeholder = 'e.g., 800';
} else {
label.innerText = 'Enter Heart Rate (BPM):';
input.placeholder = 'e.g., 75';
}
// Hide previous results and errors when switching modes
document.getElementById('rrResult').style.display = 'none';
document.getElementById('rrErrorMsg').style.display = 'none';
input.value = ";
}
function calculateHeartMetrics() {
var mode = document.getElementById('rrCalcMode').value;
var inputVal = parseFloat(document.getElementById('rrInputValue').value);
var errorMsg = document.getElementById('rrErrorMsg');
var resultBox = document.getElementById('rrResult');
// Validation
if (isNaN(inputVal) || inputVal <= 0) {
errorMsg.style.display = 'block';
resultBox.style.display = 'none';
return;
} else {
errorMsg.style.display = 'none';
}
var hr, rrMs, rrSec;
if (mode === 'rr_to_hr') {
// Input is R-R in ms
rrMs = inputVal;
rrSec = rrMs / 1000;
// HR = 60 / RR(s) or 60000 / RR(ms)
hr = 60000 / rrMs;
} else {
// Input is HR in BPM
hr = inputVal;
// RR(ms) = 60000 / HR
rrMs = 60000 / hr;
rrSec = rrMs / 1000;
}
// Calculations complete, update DOM
// Rounding for display
document.getElementById('resHR').innerText = hr.toFixed(2) + ' BPM';
document.getElementById('resRRms').innerText = rrMs.toFixed(1) + ' ms';
document.getElementById('resRRs').innerText = rrSec.toFixed(3) + ' s';
// Frequency (Hz) is 1 / Period(s)
var freq = 1 / rrSec;
document.getElementById('resFreq').innerText = freq.toFixed(3) + ' Hz';
resultBox.style.display = 'block';
}
Understanding the Heart Rate and R-R Interval Relationship
The relationship between heart rate (HR) and the R-R interval is fundamental to cardiology, electrophysiology, and the analysis of Electrocardiograms (ECG/EKG). The R-R interval represents the time elapsed between two successive R-waves of the QRS complex, which corresponds to the electrical depolarization of the ventricles.
Accurately converting between these two metrics is essential for diagnosing arrhythmias, assessing Heart Rate Variability (HRV), and interpreting ECG strips manually.
R-R Interval Formula
The calculation relies on the fact that one minute contains 60 seconds or 60,000 milliseconds. Since heart rate is measured in Beats Per Minute (BPM), the relationship is inversely proportional.
ECG Interpretation: On standard ECG paper, small squares represent 0.04 seconds (40ms) and large squares represent 0.20 seconds (200ms). Measuring the distance between R-waves allows clinicians to calculate the exact ventricular rate.
Heart Rate Variability (HRV): This metric analyzes the variation in the time interval between heartbeats (the variation in the R-R interval). High HRV is generally a sign of good cardiovascular health and autonomic nervous system balance.
Arrhythmia Diagnosis: In conditions like Atrial Fibrillation, the R-R intervals are "irregularly irregular," meaning the calculation will yield different rates depending on which beat pair is measured.
Standard Normal Values
For a resting adult, the normal heart rate range is typically 60 to 100 BPM.
Bradycardia (< 60 BPM): R-R Interval > 1000 ms
Normal (60 – 100 BPM): R-R Interval between 600 ms and 1000 ms
Tachycardia (> 100 BPM): R-R Interval < 600 ms
Calculation Examples
Here are a few practical examples of how the conversion works:
If the R-R interval is 1000 ms (1 second), the Heart Rate is 60 BPM.
If the R-R interval is 800 ms, the Heart Rate is 75 BPM (60,000 ÷ 800).
If the Heart Rate is 120 BPM, the R-R interval is 500 ms (60,000 ÷ 120).