IMPROVING ESTIMATION OF CARDIAC VAGAL TONE DURING SPONTANEOUS BREATHING USING A PACED BREATHING CALIBRATION

Respiratory sinus arrhythmia (RSA) is a commonly employed non-invasive measure of cardiac vagal control. It has been demonstrated that respiratory parameters such as tidal volume and respiratory fre-quency can change RSA without altering tonic vagal activity. Thus, within-individual comparisons of cardiac vagal control across different behavioral tasks might benefit from an adjustment for respiratory confounds. We tested an adjustment method using transfer function analysis and paced breathing at 3 different respiratory frequencies as the basis for regressing out respiratory related RSA changes in a task where breathing was not controlled. Electrocardiogram and calibrated respiration were recorded with the LifeShirt system from 15 young adult participants. Time series of RR intervals and lung volume change were computed and the respiration-to-RR-interval transfer-function magnitude (RSA-TF, in ms/liter