body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
.calculator-wrapper {
background: #ffffff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 4px 15px rgba(0,0,0,0.1);
margin-bottom: 40px;
border-top: 5px solid #e74c3c;
}
.calculator-title {
text-align: center;
margin-bottom: 25px;
color: #2c3e50;
font-size: 24px;
font-weight: 700;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #555;
}
.input-group input {
width: 100%;
padding: 12px;
border: 2px solid #ddd;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.input-group input:focus {
border-color: #e74c3c;
outline: none;
}
.calc-btn {
width: 100%;
background-color: #e74c3c;
color: white;
padding: 14px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
}
.calc-btn:hover {
background-color: #c0392b;
}
.result-box {
margin-top: 25px;
padding: 20px;
background-color: #f0f4f8;
border-radius: 8px;
display: none;
border-left: 5px solid #3498db;
}
.result-item {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #ddd;
}
.result-item:last-child {
border-bottom: none;
margin-bottom: 0;
padding-bottom: 0;
}
.result-label {
font-weight: 600;
color: #555;
}
.result-value {
font-weight: 700;
color: #2c3e50;
font-size: 18px;
}
.error-msg {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
font-weight: 600;
}
.content-section {
background: #fff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
h2 {
color: #2c3e50;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
margin-top: 30px;
}
h3 {
color: #34495e;
margin-top: 25px;
}
table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
table, th, td {
border: 1px solid #ddd;
}
th, td {
padding: 12px;
text-align: left;
}
th {
background-color: #f2f2f2;
}
.formula-box {
background-color: #e8f6f3;
padding: 15px;
border-radius: 5px;
font-family: monospace;
text-align: center;
font-size: 1.2em;
margin: 20px 0;
border: 1px solid #d1f2eb;
}
function calculateRRInterval() {
var heartRateInput = document.getElementById('inputHeartRate');
var errorDiv = document.getElementById('errorMessage');
var resultDiv = document.getElementById('rrResult');
// Get value
var hr = parseFloat(heartRateInput.value);
// Reset display
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
// Validation
if (isNaN(hr) || hr <= 0) {
errorDiv.style.display = 'block';
return;
}
// Calculation Logic
// Formula: RR (ms) = 60,000 / HR (bpm)
// Formula: RR (s) = 60 / HR (bpm)
var rrMs = 60000 / hr;
var rrSec = 60 / hr;
var frequency = hr / 60; // Frequency in Hz is BPS
// Display Results
document.getElementById('resultMs').innerHTML = rrMs.toFixed(2) + " ms";
document.getElementById('resultSec').innerHTML = rrSec.toFixed(4) + " s";
document.getElementById('resultHz').innerHTML = frequency.toFixed(3) + " Hz";
resultDiv.style.display = 'block';
}
Understanding the Formula to Calculate RR Interval from Heart Rate
The RR interval is a crucial metric in cardiology and electrophysiology, representing the time elapsed between two successive R-waves of the QRS complex on an electrocardiogram (ECG). While Heart Rate (HR) measures the number of beats per minute, the RR interval measures the duration of a single cardiac cycle.
Calculating the RR interval from the heart rate is a straightforward mathematical process based on the conversion of time units. Since heart rate is expressed in beats per minute (BPM), and the RR interval is typically expressed in milliseconds (ms) or seconds (s), the formula involves dividing the time unit by the frequency of beats.
The Mathematical Formulas
Depending on the desired unit of measurement (milliseconds or seconds), use one of the following formulas:
RR (ms) = 60,000 / Heart Rate (BPM)
RR (s) = 60 / Heart Rate (BPM)
Where:
- 60,000 represents the number of milliseconds in one minute.
- 60 represents the number of seconds in one minute.
- Heart Rate is the number of beats per minute.
Example Calculations
To better understand how the formula works, consider the following examples:
Example 1: Normal Resting Heart Rate
If a patient has a heart rate of 60 BPM:
- Calculation: 60,000 / 60
- RR Interval = 1000 ms (or 1 second)
Example 2: Elevated Heart Rate (Tachycardia)
If a patient has a heart rate of 100 BPM:
- Calculation: 60,000 / 100
- RR Interval = 600 ms (or 0.6 seconds)
Example 3: Slow Heart Rate (Bradycardia)
If a patient has a heart rate of 40 BPM:
- Calculation: 60,000 / 40
- RR Interval = 1500 ms (or 1.5 seconds)
Quick Reference Table: Heart Rate to RR Interval
| Heart Rate (BPM) |
RR Interval (ms) |
RR Interval (s) |
| 40 |
1500 ms |
1.50 s |
| 50 |
1200 ms |
1.20 s |
| 60 |
1000 ms |
1.00 s |
| 70 |
857 ms |
0.86 s |
| 80 |
750 ms |
0.75 s |
| 90 |
667 ms |
0.67 s |
| 100 |
600 ms |
0.60 s |
| 120 |
500 ms |
0.50 s |
| 150 |
400 ms |
0.40 s |
Clinical Significance of the RR Interval
While the Heart Rate gives an average of beats over time, the RR interval is fundamental for analyzing Heart Rate Variability (HRV). HRV is the fluctuation in the time intervals between adjacent heartbeats.
In a healthy individual, the RR interval is not constant; it varies beat-to-beat due to the interplay between the sympathetic and parasympathetic nervous systems. A higher variability in the RR interval generally indicates better cardiovascular fitness and stress resilience, while low variability can be a marker for stress, fatigue, or underlying cardiac issues.
When correcting the QT interval for heart rate (QTc), the RR interval (measured in seconds) is the denominator in formulas such as Bazett's Formula ($QTc = QT / \sqrt{RR}$). Therefore, accurate calculation of the RR interval from the heart rate is essential for proper ECG interpretation.