Convert the time interval between pressure peaks into Beats Per Minute (BPM).
Seconds (s)
Milliseconds (ms)
How to Calculate Heart Rate from a Pressure-Time Graph
A pressure-time graph, often seen in arterial line monitoring or hemodynamics studies, displays the fluctuation of blood pressure over time. The peaks on this graph represent systole (the contraction phase of the heart). To find the heart rate, you must measure the duration of one complete cardiac cycle.
The Formula
Heart rate is the number of beats that occur in 60 seconds. If you know the time between two consecutive peaks (the R-R interval equivalent in pressure waveforms), the formula is:
BPM = 60 / Interval (in seconds)
Or, if measuring in milliseconds:
BPM = 60,000 / Interval (in milliseconds)
Step-by-Step Calculation Guide
Identify Two Peaks: Locate two consecutive systolic peaks on the pressure-time graph.
Determine Time: Look at the horizontal (X) axis to find the time at Peak A and the time at Peak B.
Calculate ΔT: Subtract the time of Peak A from Peak B (ΔT = T2 – T1). This is your beat-to-beat interval.
Apply Formula: Divide 60 by your ΔT value to get the Beats Per Minute.
Practical Example
Imagine a pressure-time graph where the first peak occurs at 1.2 seconds and the following peak occurs at 2.0 seconds.
Interval: 2.0s – 1.2s = 0.8 seconds.
Calculation: 60 / 0.8 = 75.
Result: The heart rate is 75 BPM.
Common Time Intervals and Heart Rates
Interval (Seconds)
Heart Rate (BPM)
0.60s
100 BPM
0.85s
70.5 BPM
1.00s
60 BPM
1.20s
50 BPM
function calculateBPM() {
var intervalValue = document.getElementById('peakInterval').value;
var unit = document.getElementById('timeUnit').value;
var resultDiv = document.getElementById('heartRateResult');
var resultText = document.getElementById('resultText');
if (intervalValue === "" || intervalValue <= 0) {
alert("Please enter a valid positive time interval.");
return;
}
var interval = parseFloat(intervalValue);
var bpm;
if (unit === "seconds") {
bpm = 60 / interval;
} else {
// milliseconds
bpm = 60000 / interval;
}
var status = "";
if (bpm 100) {
status = " (Tachycardia range)";
} else {
status = " (Normal resting range)";
}
resultDiv.style.display = "block";
resultText.innerHTML = "Calculated Heart Rate: " + bpm.toFixed(2) + " BPM" + status + "";
// Scroll to result
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}