Oscillatory patterns in sympathetic neural discharge and cardiovascular variables during orthostatic stimulus

Background-We tested the hypothesis that a common oscillatory pattern might characterize the rhythmic discharge of muscle sympathetic nerve activity ( MSNA) and the spontaneous variability of heart rate and systolic arterial p ressure (SAP) during a physiological increase of sympathetic activity induc ed by the head-up tilt maneuver. Methods and Results-Ten healthy subjects underwent continuous recordings of EGG, intra-arterial pressure, respiratory activity, central venous pressur e. and MSNA, both in the recumbent position and during 75 degrees head-up t ilt. Venous samplings for catecholamine assessment were obtained at rest an d during the fifth minute of tilt, Spectrum and cross-spectrum analyses of R-R interval, SAP, and MSNA variabilities and of respiratory activity provi ded the low (LF, 0.1 Hz) and high frequency (HF, 0.27 Hz) rhythmic componen ts of each signal and assessed their linear relationships. Compared with th e recumbent position. tilt reduced central venous pressure, but blood press ure was unchanged. Heart rate, MSNA, and plasma epinephrine and norepinephr ine levels increased, suggesting a marked enhancement of overall sympatheti c activity. During tilt, LFMSNA increased compared with the level in the su pine position; this mirrored similar changes observed in the LF components of R-R interval and SAP variabilities, The increase of LFMSNA was proportio nal to the amount of the sympathetic discharge. The coupling between LF com ponents of MSNA and R-R interval and SAP variabilities was enhanced during tilt compared with rest. Conclusions-During the sympathetic activation induced by tilt, a similar os cillatory pattern based on an increased LF rhythmicity characterized the sp ontaneous variability of neural sympathetic discharge, R-R interval, and ar terial pressure.