Automatic Measurement of Loop Gain Based on Pseudorandom Binary Sequence CO2 Stimulation.

Objective: Measurement of loop gain in patients with obstructive sleep apnea (OSA) is of great importance for determining the cause of OSA and realizing precision medicine. In this study, automatic measurement of loop gain is carried out during wakefulness based on the pseudorandom binary sequence (PRBS) CO₂ stimulation method.

Methods: A respiratory data acquisition platform is designed and constructed to automate the processes of gas configuration, ventilatory stimulation with CO₂ and data acquisition. The respiratory data are substituted into the model of the ventilatory control system for parameter identification, and the loop gain values are calculated and then compared with the apnea-hypopnea index (AHI) measured in a hypoxia chamber.

Results: A positive correlation is found between loop gain and AHI measured in the hypoxia chamber, with the linear correlation coefficient of approximately 0.65.

Conclusion: The feasibility of automatic measurement of loop gain using the respiratory data acquisition platform based on the PRBS CO₂ stimulation method is validated, and the measured loop gain values can be used to assess the stability of ventilatory control.

Significance: This study provides an automated, rapid, and instrumented solution for loop gain measurement, laying the foundation for wide-scale clinical application of the PRBS CO₂ stimulation method.