Calculate perfusion index (PI) as a percentage from the pulsatile (AC) and nonpulsatile (DC) signals, or find AC or DC from a known PI.
Perfusion Index Formula
The perfusion index is the ratio of the pulsatile signal to the nonpulsatile signal, expressed as a percentage. Choose the value to solve for, then enter the other two values.
- PI = perfusion index, expressed as a percent
- AC = pulsatile signal, caused by arterial pulse changes
- DC = nonpulsatile signal, caused by tissue, venous blood, and steady light absorption
The signal values can be entered in µV, mV, or V when both amplitudes use the same compatible infrared signal and scaling. The calculator converts signal inputs to µV before applying the formula, then converts the answer back to the unit you selected.
- To calculate perfusion index: enter the pulsatile signal and nonpulsatile signal.
- To calculate nonpulsatile signal: enter the perfusion index and pulsatile signal.
- To calculate pulsatile signal: enter the perfusion index and nonpulsatile signal.
Perfusion Index Interpretation Limits
Pulse-oximeter perfusion index is a device-derived pulsatile-to-nonpulsatile signal ratio at the sensor site. It is not a universal measure of organ perfusion, cardiac output, or vascular disease. Compare values only under the same device, sensor site, and measurement conditions and follow the manufacturer’s documentation; no universal clinical bands are assigned here.
Signal Unit Conversions
| Unit | Equivalent in µV | Use in calculator |
|---|---|---|
| 1 µV | 1 µV | Base signal unit |
| 1 mV | 1,000 µV | Converted before calculation |
| 1 V | 1,000,000 µV | Converted before calculation |
Example Problems
Example 1: Calculate perfusion index
You have a pulsatile signal of 40 µV and a nonpulsatile signal of 2,000 µV.
The perfusion index is 2%.
Example 2: Calculate pulsatile signal
You have a perfusion index of 1.5% and a nonpulsatile signal of 3 mV.
First convert 3 mV to µV:
Then calculate the pulsatile signal:
The pulsatile signal is 45 µV.
FAQ
What does perfusion index measure?
Perfusion index measures the strength of the pulsatile blood flow signal compared with the nonpulsatile background signal. In pulse oximetry, it is often used as an indicator of pulse signal strength at the sensor site.
Is a higher perfusion index always better?
A higher perfusion index usually means the sensor is detecting a stronger pulse signal. It does not always mean better overall circulation or better health. Sensor placement, body temperature, movement, and device type can all change the value.
Why does each mode require two values?
The perfusion index equation has three variables: PI, AC, and DC. Select the value you want to calculate, then enter the other two. DC must be positive. Solving DC requires positive PI and AC; zero PI and zero AC do not determine a unique DC value.
