Reduction in ventilatory response to CO2 with relaxation feedback during CO2 rebreathing for ventilator patients

Background: Previous studies have shown that relaxation biofeedback reduced the amount of time spent receiving ventilation for difficult-to-wean patients. Objective: The present study was begun to test the hypothesis that the underlying mechanism of biofeedback ventilator weaning was the reduction of neural respiratory drive (NRD). Design: Prospective. Setting: Pulmonary Medicine division in a Veterans Affairs hospital and the St. Louis Regional Medical Center. Subjects: Twenty-four patients who were receiving mechanical ventilation were randomly assigned to either the biofeedback group or the control group. Intervention: Respiratory relaxation feedback (RFB) was administered while a single variable, PaCO2, was inputted to the respiratory control system and the output was measured. While rebreathing 7% CO2/93% O-2, the biofeedback group received a CO2 trial session and a CO2 RFB session, and the control group received a CO2 trial session and a CO2 no-feedback (NFB) session. Measurements and results: There was a significant (p < 0.05) reduction in respiratory and EEG parameters for the RFB group at maximal end-tidal CO2 (mean [+/- SE]; 70 +/- 0.2 mm Hg) between the CO2 trial and the CO2 RFB session compared to the control group where there was no significant difference between the results of the CO2 trial and the CO2 NFB session. The mean values for the CO2 trial and CO2 RFB session for the biofeedback group were as follows: occlusion pressure 0.1 s from the onset of inspiration, 8.42 +/- 1.08 and 6.48 +/- 0.78 cm H2O (which reflects NRD), respectively; minute inspiratory ventilation, 15.84 +/- 0.81 and 13.91 +/- 0.72 L/min, respectively; mean inspiratory flow, 670 +/- 2.28 and 581 +/- 35 mL/s, respectively; respiration rate, 32 +/- 2.28 and 31.2 +/- 2.58 breaths/min, respectively; and chest background electromyography, 4.89 +/- 0.71 and 3.54 +/- 0.54 muV, respectively. The mean electroencephalograph outputs for the CO2 trial and CO2 RFB session for the biofeedback group were as follows: mean EEG frequency, 14.78 +/- 0.98 and 13.06 +/- 0.59 Hz, respectively; and beta EEG power, 3.1 +/- 0.03 and 2.39 +/- 0.19, muV(2), respectively; and gamma EEG power, 2.96 +/- 0.34 and 2.24 +/- 0.24 muV(2), respectively. Conclusion: We conclude that the decrease in respiratory parameters reflecting NRD induced by RFB represents a key mechanism for the previously demonstrated effectiveness of biofeedback in reducing weaning time from mechanical ventilation.