function calculateRR() {
var hrInput = document.getElementById('hrInput');
var hrValue = parseFloat(hrInput.value);
var errorMsg = document.getElementById('hrError');
var resultsDiv = document.getElementById('resultsDisplay');
// Input Validation
if (isNaN(hrValue) || hrValue <= 0) {
errorMsg.style.display = 'block';
resultsDiv.style.display = 'none';
return;
} else {
errorMsg.style.display = 'none';
}
// Calculations
// RR (ms) = 60,000 / BPM
var rrMs = 60000 / hrValue;
// RR (s) = 60 / BPM
var rrSec = 60 / hrValue;
// Frequency (Hz) is roughly equivalent to BPM / 60
var freqHz = hrValue / 60;
// Display Results
document.getElementById('resMs').innerHTML = rrMs.toFixed(2) + ' ms';
document.getElementById('resSec').innerHTML = rrSec.toFixed(4) + ' s';
document.getElementById('resHz').innerHTML = freqHz.toFixed(3) + ' Hz';
resultsDiv.style.display = 'block';
}
function resetCalculator() {
document.getElementById('hrInput').value = '';
document.getElementById('resultsDisplay').style.display = 'none';
document.getElementById('hrError').style.display = 'none';
}
Understanding RR Intervals and Heart Rate
The RR interval is a critical metric in cardiology and physiology, representing the time elapsed between two successive R-waves of the QRS signal on an electrocardiogram (ECG). While Heart Rate (HR) measures the number of beats per minute, the RR interval measures the duration of one specific cardiac cycle.
This calculator assists medical professionals, researchers, and athletes in converting standard Heart Rate (BPM) into the precise time duration of the cardiac cycle in milliseconds (ms) or seconds (s).
The Conversion Formula
The relationship between Heart Rate and the RR Interval is inversely proportional. As heart rate increases, the time between beats (RR Interval) decreases. The mathematical formulas used in this calculator are:
60,000 represents the number of milliseconds in one minute.
60 represents the number of seconds in one minute.
BPM is the Beats Per Minute.
Why Calculate RR Interval?
While BPM provides a general overview of cardiac activity, the RR interval is essential for more detailed analysis:
Heart Rate Variability (HRV): HRV analysis relies entirely on the variation of RR intervals (often termed NN intervals for normal beats) rather than average BPM. High variability in RR intervals generally indicates a healthy autonomic nervous system.
ECG Interpretation: Cardiologists measure the distance between R peaks on rhythm strips to determine regularity and calculate exact rates for arrhythmias.
Corrected QT Interval (QTc): To calculate the QTc, which assesses the risk of ventricular arrhythmias, one must first know the RR interval (often derived from heart rate) to correct the QT interval for the heart rate.
Common RR Interval Values
Below is a reference table showing the relationship between common Heart Rates and their corresponding RR Intervals.
Heart Rate (BPM)
RR Interval (ms)
RR Interval (seconds)
Condition
40
1500 ms
1.50 s
Bradycardia (Slow)
60
1000 ms
1.00 s
Normal Resting (Low)
75
800 ms
0.80 s
Normal Resting (Avg)
100
600 ms
0.60 s
Normal / Tachycardia Border
150
400 ms
0.40 s
Exercise / Tachycardia
200
300 ms
0.30 s
Peak Exercise
Clinical Note
It is important to note that this calculator assumes a regular rhythm. In a physiological setting, the heart rate changes constantly, meaning the RR interval varies from beat to beat. This calculator provides the average RR interval for a given instantaneous Heart Rate.
For calculating QTc (Corrected QT Interval), the RR interval is typically measured in seconds. If you are using formulas like Bazett's or Fridericia's, ensure you use the value in seconds (e.g., 0.8s) rather than milliseconds (e.g., 800ms).