Determination of baroreflex gain using auto-regressive moving-average analysis during spontaneous breathing

The heart rate component of the arterial baroreflex gain (BRG) was determin ed with auto-regressive moving-average (ARMA) analysis during each of spont aneous (SB) and random breathing (RB) protocols. Ten healthy subjects compl eted each breathing pattern on two different days in each of two different body positions, supine (SUP) and head-up tilt (HUT). The R-R interval, syst olic arterial pressure (SAP) and instantaneous lung volume were recorded co ntinuously. BRG was estimated from the ARMA impulse response relationship o f R-R interval to SAP and from the spontaneous sequence method. The results indicated that both the ARMA and spontaneous sequence methods were reprodu cible (r = 0.76 and r = 0.85, respectively). As expected, BRG was significa ntly less in the HUT compared to SUP position for both ARMA (mean +/- SEM; 3.5 +/- 0.3 versus 11.2 +/- 1.4 ms mmHg(-1); P<0.01) and spontaneous sequen ce analysis (10.3 +/- 0.8 versus 31.5 +/- 2.3 ms mmHg(-1); P<0.001). Howeve r, no significant difference was found between BRG during RE and SE protoco ls for either ARMA (7.9 +/- 1.4 versus 6.7 +/- 0.8 ms mmHg(-1); P = 0.27) o r spontaneous sequence methods (21.8 +/- 2.7 versus 20.0 +/- 2.1 ms mmHg(-1 ); P = 0.24). BRG was correlated during RE and SE protocols (r = 0.80; P<0. 0001). ARMA and spontaneous BRG estimates were correlated (r = 0.79; P<0.00 01), with spontaneous sequence values being consistently larger (P<0.0001). In conclusion, we have shown that ARMA-derived BRG values are reproducible and that they can be determined during SE conditions, making the ARMA meth od appropriate for use in a wider range of patients.