Heinz Rüdiger

The trigonometric regressive spectral analysis—a method for mapping of beat-to-beat recorded cardiovascular parameters on to frequency domain in comparison with Fourier transformation

Heart rate and peripheral blood pressure as physiological recorded vegetative parameters are very often rhythmically investigated with the Fourier Transformation (FT). In contrast to the original use of FT these parameters are still stochastic with overlaying rhythmical structures. The R-R intervals as independent variables of time are not equidistant. The mathematical structure for the spectral decomposition is critically analysed. The purpose of this article is the presentation of a mathematical method, considering both the statistical and rhythmical features of such time series. On the basis of trigonometric regressions, this method is presented to eliminate the equidistance problems, arising with the usage of FT, by a new mathematical approach. This method computes more precisely the spectral power especially in the VLF range (0.003-0.04 Hz) than FT, because this method of trigonometric regression does not perform a frequency quantization. This method has been used and successfully tested for the analysis of peripheral blood pressure and R-R intervals including an effective reduction of input data.

Spontaneous baroreflex sensitivity in children and young adults calculated in the time and frequency domain.

Spontaneous baroreflex receptor sensitivity (BRS) was calculated in 22 healthy normotensive children and young adults (age 14 +/- 5 years) using the sequence technique (time domain) and the alpha-coefficient or the gain of the transfer function between coherent oscillations (frequency domain). BRS estimated by the sequence technique (median: 16.7 ms/mm Hg) was significantly higher than BRS calculated from the gain of the transfer function using all frequencies (median: 13.0 ms/mm Hg; p = 0.009). However, there was a high correlation between these methods (r = 0.92). The reproducibility coefficient (RC) was high for all methods, but the coefficient of variability (VC) was best for the sequence technique and the gain of the transfer function, but significantly worse for the estimates of the alpha-coefficient in the low or high frequency band. The differentiation between increasing or decreasing blood pressure (BP) ramps did not give further information showing the same BRS values. The best BRS estimates will be achieved by using three consecutive beats without lag by the sequence technique and by using only frequencies with a proven correlation of BP and pulse interval (PI) and then calculating the gain of the transfer function using coherent oscillations.

Baroreflex Sensitivity and Power Spectral Analysis During Autonomic Testing in Different Extrapyramidal Syndromes

Autonomic dysfunction has been frequently demonstrated in patients with extrapyramidal diseases by cardiovascular autonomic testing. In addition to classical testing, we applied the more detailed baroreflex and spectral analysis on three traditional cardiovascular tests in this study to get additional information on autonomic outflow. We recorded continuously blood pressure, electrocardiogram, and respiration in 35 patients with multiple system atrophy, 32 patients with progressive supranuclear palsy, 46 patients with idiopathic Parkinsons disease and in 27 corresponding healthy subjects during cardiovascular autonomic testing (metronomic breathing, Valsalva manoeuvre, head‐up tilt). Baroreflex and spectral analyses were performed by using trigonometric regressive spectral analysis between and during the manoeuvres. Consistent with previous interpretations, our data showed an increase of sympathetic activity in head‐up tilt and Valsalva test in healthy controls. This sympathetic activity was significantly decreased in patients with typical and atypical Parkinson syndromes. Significant modulation of baroreflex activity could be observed especially during metronomic breathing; again it was significantly lower in all patient groups. Baroreflex and spectral parameters could not only differentiate between patients and healthy controls, but also differentiate between clinically symptomatic (with autonomic dysfunction as eg. orthostatic hypotension) and asymptomatic patients. In conclusion, our approach allows the evaluation of autonomic variability during short and nonstationary periods of time and may constitute a useful advance in the assessment of autonomic function in both physiological and pathological conditions.

Autonomic blood pressure control in children and adolescents with type 1 diabetes mellitus

Introduction:  Increased daytime blood pressure and reduced nocturnal dipping can already be found in children with type 1 diabetes mellitus. We hypothesized that impaired baroreflex sensitivity can cause this abnormal blood pressure behavior in children and adolescents with type 1 diabetes, reflecting an early stage of diabetic autonomic neuropathy.

Determination of baroreflex sensitivity during the modified Oxford maneuver by trigonometric regressive spectral analysis.

Background Differences in spontaneous and drug-induced baroreflex sensitivity (BRS) have been attributed to its different operating ranges. The current study attempted to compare BRS estimates during cardiovascular steady-state and pharmacologically stimulation using an innovative algorithm for dynamic determination of baroreflex gain. Methodology/Principal Findings Forty-five volunteers underwent the modified Oxford maneuver in supine and 60° tilted position with blood pressure and heart rate being continuously recorded. Drug-induced BRS-estimates were calculated from data obtained by bolus injections of nitroprusside and phenylephrine. Spontaneous indices were derived from data obtained during rest (stationary) and under pharmacological stimulation (non-stationary) using the algorithm of trigonometric regressive spectral analysis (TRS). Spontaneous and drug-induced BRS values were significantly correlated and display directionally similar changes under different situations. Using the Bland-Altman method, systematic differences between spontaneous and drug-induced estimates were found and revealed that the discrepancy can be as large as the gain itself. Fixed bias was not evident with ordinary least products regression. The correlation and agreement between the estimates increased significantly when BRS was calculated by TRS in non-stationary mode during the drug injection period. TRS-BRS significantly increased during phenylephrine and decreased under nitroprusside. Conclusions/Significance The TRS analysis provides a reliable, non-invasive assessment of human BRS not only under static steady state conditions, but also during pharmacological perturbation of the cardiovascular system.

Trigonometric Regressive Spectral Analysis Reliably Maps Dynamic Changes in Baroreflex Sensitivity and Autonomic Tone: The Effect of Gender and Age

Background The assessment of baroreflex sensitivity (BRS) has emerged as prognostic tool in cardiology. Although available computer-assisted methods, measuring spontaneous fluctuations of heart rate and blood pressure in the time and frequency domain are easily applicable, they do not allow for quantification of BRS during cardiovascular adaption processes. This, however, seems an essential criterion for clinical application. We evaluated a novel algorithm based on trigonometric regression regarding its ability to map dynamic changes in BRS and autonomic tone during cardiovascular provocation in relation to gender and age. Methodology/Principal Findings We continuously recorded systemic arterial pressure, electrocardiogram and respiration in 23 young subjects (25±2 years) and 22 middle-aged subjects (56±4 years) during cardiovascular autonomic testing (metronomic breathing, Valsalva manoeuvre, head-up tilt). Baroreflex- and spectral analysis was performed using the algorithm of trigonometric regressive spectral analysis. There was an age-related decline in spontaneous BRS and high frequency oscillations of RR intervals. Changes in autonomic tone evoked by cardiovascular provocation were observed as shifts in the ratio of low to high frequency oscillations of RR intervals and blood pressure. Respiration at 0.1 Hz elicited an increase in BRS while head-up tilt and Valsalva manoeuvre resulted in a downregulation of BRS. The extent of autonomic adaption was in general more pronounced in young individuals and declined stronger with age in women than in men. Conclusions/Significance The trigonometric regressive spectral analysis reliably maps age- and gender-related differences in baroreflex- and autonomic function and is able to describe adaption processes of baroreceptor circuit during cardiovascular stimulation. Hence, this novel algorithm may be a useful screening tool to detect abnormalities in cardiovascular adaption processes even when resting values appear to be normal.

Autonomic responses to stress in Black versus Caucasian Africans: The SABPA Study

Underlying mechanisms of increased pressor responses to stress in Blacks are poorly understood. Cardiovascular regulation of normotensive Black (n=43) and Caucasian (n=90) Africans was studied during a cold pressor and color-word conflict test. Autonomic evaluation was performed by spectral analysis. Higher diastolic pressor and heart rate responses to the cold pressor test were observed in Black compared to Caucasian Africans. Autonomic efferent outflow to stress was comparable between groups. Transient downregulation of baroreflex during stress was evident in Blacks but not in Caucasians. Greater diastolic pressor responses were related to a higher cardiac reactivity, a baroreflex desensitization, and higher stress perception in Black Africans. Thus, increased stress perception may facilitate cardiac and diastolic hyperreactivity, indirectly affecting baroreflex function in Black Africans.

LDL apheresis improves deranged cardiovagal modulation in hypercholesterolemic patients

OBJECTIVE Hypotensive episodes are relatively frequent adverse effects during LDL apheresis. To evaluate the impact of LDL apheresis on autonomic cardiovascular control we investigated hypercholesterolemic patients before and after a single LDL apheresis in comparison to an age-matched control group. METHODS We continuously recorded systemic arterial blood pressure, electrocardiogram and respiration in 21 hypercholesterolemic patients (57 ± 15 years) on regular LDL apheresis treatment and 22 healthy control subjects (56 ± 4 years) during cardiovascular autonomic testing (metronomic breathing, Valsalva manoeuvre, head-up tilt). Baroreflex sensitivity and frequency spectra of R-R intervals and systolic blood pressure were evaluated by trigonometric regressive spectral analysis. RESULTS Hypercholesterolemic patients had reduced resting baroreflex sensitivity and high-frequency power of heart rate variability compared to controls. Consequently, there was a sympathetic predominance of heart rate modulation reflected by increased ratio of low-to-high frequency power of R-R intervals. Cardiovascular stimulation failed to adequately activate baroreflex mechanisms before LDL apheresis. After LDL apheresis, the parasympathetic response to cardiovascular stimulation improved and sympathetic outflow to peripheral vasculature was reduced. Baroreflex sensitivity remained low. CONCLUSION Hypercholesterolemic patients on regular LDL apheresis treatment have significant autonomic dysfunction. A single LDL apheresis does not evoke sympathetic overactivation but improved deranged cardiovagal heart rate modulation in hypercholesterolemia.

Regular lipoprotein apheresis maintains residual cardiovascular and microvascular function in patients with advanced atherosclerotic disease

OBJECTIVE To determine whether previously demonstrated beneficial short-term effects on cardiovascular function in regular users of lipoprotein apheresis would be sustainable over time. METHODS Regular users of lipoprotein apheresis (n = 17) were studied between February 2009 and July 2010. All patients were examined for endothelial and autonomic function at baseline and at one year of regular treatment. Microvascular function was determined by flicker-induced vasodilation of retinal vessels using the Dynamic Vessel Analyzer. Autonomic regulation of blood pressure and heart rate upon cardiovascular perturbation by deep breathing at 0.1 Hz and orthostatic challenge was evaluated by trigonometric regressive spectral analysis. RESULTS The acute improvement of cardiovagal function and venular endothelial function seen after a single lipoprotein apheresis was not evident at one year of regular treatment. However, baroreflex sensitivity showed an improved recovery after orthostatic challenge as compared to baseline measurements. Initially compromised autonomic and microvascular function had not further deteriorated at one year of regular lipoprotein apheresis treatment. CONCLUSION In patients with advanced atherosclerotic disease regular lipoprotein apheresis treatment maintains residual cardiovascular functioning over time.

Acute hyperlipidemia but not hyperhomocysteinemia impairs reflex regulation of the cardiovascular system

BACKGROUND Elevated circulating lipids and homocysteine may affect autonomic cardiovascular function by decreasing baroreflex sensitivity (BRS) and cardiovagal outflow and by increasing sympathetic drive. METHODS To test this hypothesis 25 clinically healthy men (mean age 24 ± 2 years) received 500 ml whipping cream (30% fat) and 0.1 g/kg l-methionine, respectively, at intervals of one week apart to induce hyperlipidemia and hyperhomocysteinemia, respectively. Cardiovascular parameters and endothelial function were assessed before and 2 h after the fat load and before and 4 h after the methionine load, respectively. Cardiovascular responses to sublingual application of a nitrovasodilator and a beta-agonist were also determined. RESULTS Hyperlipidemia elicited a significant decline in BRS and an increase in heart rate and sympathetic drive. Reductions in BRS were associated with changes in total cholesterol but not with triglycerides or endothelial function. Autonomic and hemodynamic variables remained unaltered during transient hyperhomocysteinemia although there was a trend to lower BRS. Autonomic and hemodynamic responses to pharmacological vasodilation and beta-adrenoceptor stimulation were preserved under both conditions. CONCLUSIONS These data provide experimental support for the concept that acute hyperlipidemia but not hyperhomocysteinemia impairs reflex regulation of the circulatory system.