Comparison of standard autonomic tests and power spectral analysis in normal adults.

Standard autonomic measures [heart rate response to deep breathing (HR[DB]), systolic blood pressure response to orthostatic load, the 30:15 ratio, and the Valsalva ratio (VR)] and spectral measures of the heart rate (HR) and the arterial blood pressure (ABP) (MF: mid-frequency band at 0.05-0.15 Hz; HF: high-frequency band at 0.15-0.33 Hz) were performed in 50 healthy subjects. The supine HR-HF and the tilt ABP-MF were taken as indicators of parasympathetic and sympathetic outflow, respectively. The transfer function magnitude of HR related to the ABP in the mid-frequency band estimated the baroreflex sensitivity. The HR[DB] and the 30:15 ratio were correlated with the parasympathetic spectral measure, and the VR was, surprisingly, only correlated with the sympathetic spectral measure. Significant baroreflex contribution was only evident for the 30:15 ratio. The spectral HR data were highly correlated with their corresponding spectral data of ABP. These results provide insights into autonomic regulation, but further studies on both basic physiological mechanisms of these methods and their clinical value have to be performed before a broad application can be recommended.