Flow Rate Increase Calculator (ml/min/mmHg)
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Flow Conductance Calculator (ml/min/mmHg)
Initial Pressure (P1) in mmHg
Initial Flow Rate (Q1) in ml/min
Final Pressure (P2) in mmHg
Final Flow Rate (Q2) in ml/min
Calculate Flow Increase Ratio
Pressure Change (ΔP): 0 mmHg
Flow Rate Change (ΔQ): 0 ml/min
Ratio: 0 ml/min/mmHg
*This value represents the Hydraulic Conductance (Slope).
How to Calculate the Increase in Flow Rate in ml/min/mmHg
In fluid dynamics, physiology, and biomedical engineering, calculating the relationship between flow rate and pressure is essential for understanding the efficiency of a system. The metric ml/min/mmHg represents Hydraulic Conductance , which measures how much the flow rate increases for every unit increase in pressure (mmHg).
The Concept of Flow Conductance
Flow rate ($Q$) and pressure ($P$) are related through the resistance ($R$) of the vessel or pipe. According to the fluid dynamics equivalent of Ohm's Law:
Q = ΔP / R
However, when we want to express how "easy" it is for fluid to flow through the system, we use Conductance ($C$), which is the reciprocal of resistance ($1/R$). The unit ml/min/mmHg specifically asks for the slope of the pressure-flow relationship.
Calculation Formula
To calculate the increase in flow rate per mmHg, you need two data points: an initial state ($P_1, Q_1$) and a final state ($P_2, Q_2$). The formula is:
Ratio (C) = (Q₂ – Q₁) / (P₂ – P₁)
Where:
Q₂ – Q₁ represents the change in flow rate ($\Delta Q$) in ml/min.P₂ – P₁ represents the change in pressure ($\Delta P$) in mmHg.The result is the conductance expressed in ml/min/mmHg.
Example Calculation
Imagine a scenario in a dialysis machine or a blood vessel study:
Initial Pressure ($P_1$) = 80 mmHg, Initial Flow ($Q_1$) = 100 ml/min.
Pressure is increased to ($P_2$) = 120 mmHg, and Flow increases to ($Q_2$) = 180 ml/min.
Step 1: Calculate flow change ($\Delta Q$) = 180 – 100 = 80 ml/min.Step 2: Calculate pressure change ($\Delta P$) = 120 – 80 = 40 mmHg.Step 3: Divide $\Delta Q$ by $\Delta P$ = 80 / 40 = 2.0 ml/min/mmHg .
This means for every 1 mmHg increase in pressure, the flow rate increases by 2 ml/min.
Applications
This calculation is widely used in:
Hemodynamics: Assessing vascular compliance and vessel stiffness.Medical Infusions: Determining catheter flow rates relative to pressure bags.Filtration Systems: Calculating membrane permeability or flux.
function calculateFlowRatio() {
// Get input values
var p1 = document.getElementById('initialPressure').value;
var q1 = document.getElementById('initialFlow').value;
var p2 = document.getElementById('finalPressure').value;
var q2 = document.getElementById('finalFlow').value;
var errorMsg = document.getElementById('errorMsg');
var resultBox = document.getElementById('resultBox');
// Reset error state
errorMsg.style.display = 'none';
resultBox.style.display = 'none';
// Validation
if (p1 === " || q1 === " || p2 === " || q2 === ") {
errorMsg.innerText = "Please fill in all fields to calculate the ratio.";
errorMsg.style.display = 'block';
return;
}
// Parse numbers
var valP1 = parseFloat(p1);
var valQ1 = parseFloat(q1);
var valP2 = parseFloat(p2);
var valQ2 = parseFloat(q2);
// Check for non-numeric inputs
if (isNaN(valP1) || isNaN(valQ1) || isNaN(valP2) || isNaN(valQ2)) {
errorMsg.innerText = "Please enter valid numeric values.";
errorMsg.style.display = 'block';
return;
}
// Calculate deltas
var deltaP = valP2 – valP1;
var deltaQ = valQ2 – valQ1;
// Check for division by zero (Zero pressure change)
if (deltaP === 0) {
errorMsg.innerText = "The change in pressure (ΔP) cannot be zero.";
errorMsg.style.display = 'block';
return;
}
// Calculate Ratio (Conductance)
var ratio = deltaQ / deltaP;
// Display results
document.getElementById('deltaPressure').innerText = deltaP.toFixed(2);
document.getElementById('deltaFlow').innerText = deltaQ.toFixed(2);
document.getElementById('flowRatio').innerText = ratio.toFixed(4);
resultBox.style.display = 'block';
}