Calibrating Pressure — How We Make It Match Reality
Why Internal Sensor Values Rarely Reflect the Pressure
Inside Your Vascular Model
In previous articles, we discussed the physical reasons why pressure drops inside vascular models and how flow behaves in tubing, connectors, and compliant vessels. But there’s another source of discrepancy that users often overlook:
The pump says 150 mmHg — but the gauge in the model reads 100 mmHg. Who’s right?
The answer is: both readings are correct — for where they’re taken.
To understand this, you need to look not just at fluid dynamics, but also at how pressure is measured — and how we calibrate it to reflect reality.
In this week’s Tech Tuesday post, we explain:
Why internal pressure sensors don’t reflect pressure inside your model
How we calibrate Flowbox sensors using real-world data
What correction formula we use — and why it matters
How to interpret pressure values across different points in your simulation system
Where Pressure Is Measured — And Why That Matters
Like other pumps, our Flowbox pump systems NEO and NEO+ display pressure values in real time — but those values are based on internal sensors located near the pump’s outflow. These readings are:
Very useful for pump control and baseline monitoring
A consistent indicator of system behavior
Easy to read and track during use
But they do not represent the actual pressure inside your vascular model — especially if the model is:
Made of compliant (flexible) material
Connected via long or narrow tubing
Positioned downstream with valves, branches, or a region of interest (ROI)
As a result, the user might see high pressure at the pump but lower pressure in the model, and wonder why the values don’t match.
Why We Calibrate Pressure — and How We Do It
To ensure that our Flowbox pumps deliver meaningful pressure data, we calibrate each unit with external reference measuring instruments placed at a fixed distance from the pump.
During calibration, we:
Set multiple pump pressures and record internal sensor values
Measure the true pressure using a clinical-grade external pressure gauge
Plot the values to compare internal vs. actual pressure readings
Apply regression analysis (usually linear or polynomial)
Implement a correction formula in software or interpretation
This eliminates the pressure losses due to internal hydraulics and the couplings and represents the actual fluid pressure at the outlet of the pump.
Example Correction: From Internal Reading to Real Pressure
Here’s a real-world calibration dataset:
From this data, we derived a linear correction formula:
Corrected Pressure = 0.417x + 30.2
In many cases, a linear correction formula is not sufficient to calibrate the sensor to the external measured values. This requires a quadratic or more complex correction formula to be determined.
This formula can be applied in software or used by the user as a quick reference when interpreting pressure values on the pump display.
Why Pressure Differences Still Happen — Even After Calibration
Even with accurate calibration, the pressure measured inside a compliant vascular model will usually be lower than what’s displayed at the pump. This is due to:
Friction losses in tubing and connectors
Energy absorption by the vessel walls (compliance)
Changes in flow geometry inside the model
Calibration ensures your internal readings are accurate — but they still reflect the pump location, not the patient anatomy.
If you need precise pressure data inside the model, consider:
Using an inline pressure sensor near the region of interest
Recording data with external gauges for validation
Applying correction values only when relevant to your task
Takeaway
Pressure calibration is essential for meaningful simulation results — especially when training medical professionals or testing devices that rely on accurate hemodynamic conditions.
The pressure shown on your pump reflects the outlet, not the model interior
Internal sensors are useful — but must be calibrated and interpreted correctly
We calibrate every Flowbox unit using real-world data to ensure reliable readings
A simple correction formula helps translate pump display values into realistic pressures
By understanding where pressure is measured — and how it's calibrated — you can make more informed decisions in simulation, and ensure your results are as close to real physiology as possible.
In our next article, we’ll take a closer look at how to optimize flow conditions for different vascular territories, using real-world cardiac output distribution to fine-tune your stroke volume and flow rate settings.