Objective Power spectral analysis of heart rate variability is used clinically to assess cardiac autonomic function. High frequency power is related to respiratory sinus arrhythmia and therefore to parasympathetic cardiovagal tone. The relationship of low frequency (LF) power to cardiac sympathetic tone is less clear. We reported previously that LF power may reflect baroreflex function; however, in the previous study LF power was not adjusted for possible influences of respiration. In this study we assessed relationships of LF power, including respiration-adjusted LF power (LFa) using the ANSAR ANX 3.0 device, with cardiac sympathetic innervation and baroreflex function in chronic autonomic failure patients who either had or did not have neuroimaging evidence of cardiac sympathetic denervation. Methods Values for LF power with patients seated at baseline and during the Valsalva maneuver were compared between groups with low or normal myocardial concentrations of 6-[18F]fluorodopamine-derived radioactivity. Baroreflex-cardiovagal gain (BRS) was calculated from the slope of cardiac interbeat interval vs. systolic pressure during the Valsalva maneuver with subjects supine. Results Individual values for LF and LFa were unrelated to myocardial 6-[18F]fluorodopamine-derived radioactivity. During both sitting rest and the Valsalva maneuver the logs of LF and LFa correlated positively with the log of BRS (r=0.61, p=0.0005; r=0.47, p=0.009; r=0.69, p<0.0001; r=0.60, p=0.0006). Patients with low BRS (≤3 msec/mm Hg) had low LF and LFa regardless of the status of cardiac innervation. Conclusion LF and LFa reflect baroreflex function independently of cardiac sympathetic innervation.

LF power reflects baroreflex function, not cardiac sympathetic innervation.

Abstract-Supine hypertension occurs commonly in primary chronic autonomic failure. This study explored whether supine hypertension in this setting is associated with orthostatic hypotension (OH), and if so, what mechanisms might underlie this association. Supine and upright blood pressures, hemodynamic responses to the Valsalva maneuver, baroreflex-cardiovagal gain, and plasma norepinephrine (NE) levels were measured in pure autonomic failure (PAF), multiple-system atrophy (MSA) with or without OH, and Parkinson's disease (PD) with or without OH. Controls included age-matched, healthy volunteers and patients with essential hypertension or those referred for dysautonomia. Baroreflex-cardiovagal gain was calculated from the relation between the interbeat interval and systolic pressure during the Valsalva maneuver. PAF, MSA with OH, and PD with OH all featured supine hypertension, which was equivalent in severity to that in essential hypertension, regardless of fludrocortisone treatment. Among patients with PD or MSA, those with OH had higher mean arterial pressure during supine rest (109Ϯ3 mm Hg) than did those lacking OH (96Ϯ3 mm Hg, Pϭ0.002). Baroreflex-cardiovagal gain and orthostatic increments in plasma NE levels were markedly decreased in all 3 groups with OH. Among patients with PD or MSA, those with OH had much lower mean baroreflex-cardiovagal gain (0.74Ϯ0.10 ms/mm Hg) than did those lacking OH (3.13Ϯ0.72 ms/mm Hg, Pϭ0.0002). In PAF, supine hypertension is linked to both OH and low baroreflex-cardiovagal gain. The finding of lower plasma NE levels in patients with than without supine hypertension suggests involvement of pressor mechanisms independent of the sympathetic nervous system. Key Words: hypertension, essential Ⅲ hypotension Ⅲ Parkinson's disease Ⅲ autonomic nervous system Ⅲ sympathetic nervous system Ⅲ norepinephrine P rimary chronic autonomic failure has been classified clinically into 3 forms: pure autonomic failure (PAF), multiple-system atrophy (MSA), and autonomic failure in the setting of Parkinson's disease (PD). 1 All 3 forms typically include orthostatic hypotension (OH), wherein reflexive increases in sympathetic neurocirculatory tone fail to compensate adequately for decreased venous return to the heart.Patients with primary chronic autonomic failure also often have supine hypertension. 2 Because of widespread use of the salt-retaining steroid fludrocortisone to treat OH and literature documenting increases in blood pressure secondary to mineralocorticoid administration, 3,4 supine hypertension in primary chronic autonomic failure might be a side effect of treating the OH and not part of the disease; however, supine hypertension has been reported in a substantial proportion of untreated patients. 5 Analogously, levodopa is a mainstay in the treatment of PD, and based on literature that levodopa produces OH, 6 OH in PD might be a side effect of treating the movement disorder and not part of the disease; however, OH occurs in at least some patients with PD who are off or have never been ...