function calculateFlowRate() {
var coInput = document.getElementById("cardiacOutput");
var hrInput = document.getElementById("heartRate");
var sepInput = document.getElementById("sep");
var resultContainer = document.getElementById("resultContainer");
var resultDisplay = document.getElementById("flowRateResult");
var co = parseFloat(coInput.value);
var hr = parseFloat(hrInput.value);
var sep = parseFloat(sepInput.value);
// Validation
if (isNaN(co) || co <= 0) {
alert("Please enter a valid Cardiac Output greater than 0.");
return;
}
if (isNaN(hr) || hr <= 0) {
alert("Please enter a valid Heart Rate greater than 0.");
return;
}
if (isNaN(sep) || sep <= 0) {
alert("Please enter a valid Ejection Period greater than 0.");
return;
}
// Calculation Logic
// Convert CO from L/min to mL/min by multiplying by 1000
var co_ml = co * 1000;
// Calculate total ejection time per minute: HR * SEP
// But the standard formula for Mean Flow (ml/s) is:
// Flow = (Cardiac Output in ml/min) / (Heart Rate * Systolic Ejection Period)
var denominator = hr * sep;
var flowRate = co_ml / denominator;
// Display Result
resultDisplay.innerHTML = flowRate.toFixed(1) + " mL/s";
resultContainer.style.display = "block";
}
Understanding Transvalvular Flow Rate Calculation
The Transvalvular Flow Rate is a critical hemodynamic parameter used primarily in cardiology to assess the severity of valvular stenosis, such as in the aortic or mitral valves. It represents the mean rate at which blood flows across a specific valve during the period the valve is open (systole for the aortic valve, diastole for the mitral valve).
This calculation is a fundamental component of the Gorlin Equation, which is the gold standard for calculating valvular surface area based on hemodynamic data obtained during cardiac catheterization or echocardiography.
The Physiology and Formula
To calculate the mean transvalvular flow rate, one must understand that blood does not flow across the valve continuously; it only flows when the valve is open. Therefore, simply dividing Cardiac Output by 60 seconds is incorrect. Instead, we must determine the flow rate specifically during the ejection period (or filling period).
Cardiac Output (CO): The volume of blood the heart pumps per minute, usually measured in Liters per minute. We convert this to milliliters by multiplying by 1000.
Heart Rate (HR): The number of heartbeats per minute.
Systolic Ejection Period (SEP) or Diastolic Filling Period (DFP): The duration in seconds of the flow across the valve per beat. For the aortic valve, this is the SEP; for the mitral valve, this is the DFP.
Clinical Significance
Accurate calculation of the transvalvular flow rate is essential for diagnosing the severity of heart valve disease:
Aortic Stenosis: In patients with aortic stenosis, the valve area is calculated by dividing the Mean Transvalvular Flow Rate by the square root of the mean pressure gradient across the valve (multiplied by the Gorlin constant). A higher flow rate with a high gradient confirms severe stenosis.
Low-Flow, Low-Gradient Stenosis: In cases of heart failure where cardiac output is low, the pressure gradient may appear artificially low. Calculating the flow rate helps distinguish between true severe stenosis and pseudo-severe stenosis.
How to Use This Calculator
This tool simplifies the math required for hemodynamic assessments.
Enter the patient's Cardiac Output (e.g., 5.0 L/min). This can be obtained via Fick method or thermodilution.
Enter the current Heart Rate (e.g., 70 bpm).
Enter the Systolic Ejection Period (SEP) or DFP. This is measured from the pressure tracing or Doppler signal, representing the time in seconds per beat that the valve is open (e.g., 0.30 seconds).
Click "Calculate" to obtain the mean flow rate in mL/s.