Baroreflex analysis in diabetes mellitus: linear and nonlinear approaches

Advanced Cross-Correlation Function Application to Identify Arterial Baroreflex Sensitivity Variations From Healthy to Diabetes Mellitus

Diabetes mellitus (DM) is a chronic disease characterized by elevated blood glucose levels, which leads over time to serious damage to the heart, blood vessels, eyes, kidneys, and nerves. DM is of two types–types 1 or 2. In type 1, there is a problem with insulin secretion, and in type 2–insulin resistance. About 463 million people worldwide have diabetes, and 80% of the majority live in low- and middle-income countries, and 1.5 million deaths are directly attributed to diabetes each year. Autonomic neuropathy (AN) is one of the common diabetic complications, leading to failure in blood pressure (BP) control and causing cardiovascular disease. Therefore, early detection of AN becomes crucial to optimize treatment. We propose an advanced cross-correlation function (ACCF) between BP and heart rate with suitable threshold parameters to analyze and detect early changes in baroreflex sensitivity (BRS) in DM with AN (DM+). We studied heart rate (HR) and systolic BP responses during tilt in 16 patients with diabetes mellitus only (DM−), 19 diabetes mellitus with autonomic dysfunction (DM+), and 10 healthy subjects. The ACCF analysis revealed that the healthy and DM groups had different filtered percentages of significant maximum cross-correlation function (CCF) value (p < 0.05), and the maximum CCF value after thresholds was significantly reduced during tilt in the DM+ group (p < 0.05). The maximum CCF index, a parameter for the phase between HR and BP, separated the healthy group from the DM groups (p < 0.05). Due to the maximum CCF index in DM groups being located in the positive range and significantly different from healthy ones, it could be speculated that BRS dysfunction in DM and AN could cause a phase change from lead to lag. ACCF could detect and separate DM+ from DM groups. This fact could represent an advantage of the ACCF algorithm. A common cross-correlation analysis was not easy to distinguish between DM− and DM+. This pilot study demonstrates that ACCF analysis with suitable threshold parameters could explore hidden changes in baroreflex control in DM+ and DM−. Furthermore, the superiority of this ACCF algorithm is useful in distinguishing whether AN is present or not in DM.

Interplay between baroreflex sensitivity, obesity and related cardiometabolic risk factors (Review)

The baroreflex represents a rapid negative feedback system implicated in blood pressure regulation, which aims to prevent blood pressure variations by regulating peripheral vascular tone and cardiac output. The aim of the present review was to highlight the association between baroreflex sensitivity (BRS) and obesity, including factors associated with obesity, such as metabolic syndrome, hypertension, cardiovascular disease and diabetes. For the present review, a literature search was conducted using the PubMed database until August 21, 2021. The searched terms included ‘baroreflex’, and other terms such as ‘sensitivity’, ‘obesity’, ‘metabolic syndrome’, ‘hypertension’, ‘diabetes’, ‘gender’, ‘aging’, ‘children’, ‘adolescents’, ‘physical activity’, ‘bariatric surgery’, ‘autonomous nervous system’ and ‘cardiometabolic risk factors’. Obesity and its related metabolic disorders can influence baroreflex functionality and decrease BRS, mostly by potentiating sympathetic nervous system activity. Obesity induces inflammation, which can increase sympathetic system activity and lead to a higher incidence of cardiovascular events. Obesity also represents an important risk factor for hypertension through numerous mechanisms; in this setting, dysfunctional baroreceptors are not able to protect against constantly elevated blood pressure. Furthermore, diabetes mellitus and oxidative stress result in deterioration of BRS, whereas aging is also generally related to reduced cardiovagal BRS. Differences in BRS have also been observed between men and women, and overall cardiovagal BRS in healthy women is less intense compared with that in men. BRS appears lower in children with obesity compared with that in children of a healthy weight. Notably, physical exercise can increase BRS in both hypertensive and normotensive subjects, and BRS can also be significantly improved following bariatric surgery and weight loss. In conclusion, obesity and its related metabolic disorders may influence baroreflex functionality and decrease BRS, and baroreceptors cannot protect against the constantly elevated blood pressure in obesity. However, following bariatric surgery and weight loss, BRS can be significantly improved. The present review summarizes the role of obesity and related metabolic risk factors in BRS, providing details on possible mechanisms and shedding light on their interplay leading to autonomic neuropathy.

Status of nutrition and cardiovascular system in children from the south Moravian region of the Czech Republic: a pilot study

Nutritional status, its assessment and its influence on numerous diseases is currently still being discussed. The aim of this study was to determine the current state of nutrition by various research methods in school children. Also, to verify the accuracy of body mass index (BMI) determination in school environment and to compare the nutritional status in two different types of school. We used a quantitative questionnaire method in 64 children from schools in the South Moravian Region. We have verified the weight and height measurement in the same group by sophisticated instruments. We have determined the basic parameters of the cardiovascular system (non-invasive continuously blood pressure recording; mutual spectral analysis for estimation of baroreflex sensitivity; applanation tonometry and cardiac polygraphy for arterial stiffness evaluation). The indicative questionnaire method encountered a problem with the weight of almost 40 % of the population approached - both obesity (14.3 %) and malnutrition (25.2 %). Cardiovascular parameters were in physiological range for the given age categories. We found increased values in BMI, % of body fat and heart rate in children from countryside type of school, respectively. We concluded that obesity/malnutrition are both common phenomena in the children population in the Czech Republic.

Application of a Speedy Modified Entropy Method in Assessing the Complexity of Baroreflex Sensitivity for Age-Controlled Healthy and Diabetic Subjects

The percussion entropy index (PEI_orginal) was recently introduced to assess the complexity of baroreflex sensitivity. This study aimed to investigate the ability of a speedy modified PEI (i.e., PEI_NEW) application to distinguish among age-controlled subjects with or without diabetes. This was carried out using simultaneous photo-plethysmo-graphy (PPG) pulse amplitude series and the R wave-to-R wave interval (RRI) series acquired from healthy subjects (Group 1, number = 42), subjects diagnosed as having diabetes mellitus type 2 with satisfactory blood sugar control (Group 2, number = 38), and type 2 diabetic patients with poor blood sugar control (Group 3, number = 35). Results from PEI_orginal and multiscale cross-approximate entropy (MCAE) were also addressed with the same datasets for comparison. The results show that optimal prolongation between the amplitude series and RRI series could be delayed by one to three heartbeat cycles for Group 2, and one to four heartbeat cycles for Group 3 patients. Group 1 subjects only had prolongation for one heartbeat cycle. This study not only demonstrates the sensitivity of PEI_NEW and PEI_orginal in differentiating between Groups 2 and 3 compared with MCAE, highlighting the feasibility of using percussion entropy applications in autonomic nervous function assessments, it also shows that PEI_NEW can considerably reduce the computational time required for such processes.

Importance of cardiovascular examination in patients with multiple lentigines: two cases of LEOPARD syndrome with hypertrophic cardiomyopathy

Introduction LEOPARD syndrome is a rare genetic disorder characterised by lentigines, electrocardiographic conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth and sensorineural deafness. Clinical manifestations are often mild, which may result in difficult and late diagnosis. Cardiac involvement may have a significant impact on the prognosis, however, appearance of severe abnormalities such as hypertrophic cardiomyopathy usually precedes the occurrence of multiple lentigines and may be asymptomatic. Case presentation We report two cases of LEOPARD syndrome with hypertrophic cardiomyopathy in a 10-year-old girl and an 18-year-old boy. In both cases, multiple lentigines, ocular hypertelorism and growth retardation were present. The first patient was followed up at the paediatric cardiology clinic due to the risk of progression of septal hypertrophy and pressure gradient across the left ventricular outflow tract, the second patient underwent surgery for a moderate obstruction of the left ventricular outflow tract with uncomplicated post-operative follow-up. Conclusion In both presented patients, hypertrophic cardiomyopathy was clinically silent and the murmur over the precordium was the sole cardiac abnormality revealed during routine visit. A detailed cardiologic examination should be considered in the patients with suspicion of LEOPARD syndrome since the ventricular hypertrophy is thought to precede the occurrence of lentigines and progress over time.

Study of impaired cardiovascular and respiratory coupling during orthostatic stress based on joint symbolic dynamics

The present study investigates the instantaneous coupling among the cardiac, vascular, and respiratory systems, using the heart rate, respiration, and systolic and diastolic blood pressure variability in 12 healthy and 16 vasovagal syncope female subjects during a head-up tilt (HUT) testing protocol at 70° This study contributes to the coupling analysis by using a nonlinear joint symbolic dynamics (JSD) in a high-temporal resolution scheme, based on 5 min segments of the time series that are shifted every minute. For each segment, a bivariate JSD matrix was constructed to obtain global and local coupling indices in accordance to Shannon's entropy and the probability of occurrence of various bivariate words, respectively. The novel approach revealed important findings in the coupling dynamics of the systems, thus allowing the detection of group differences during the early orthostatic phase, and during the HUT test, before the occurrence of any pre-syncopal symptoms. In patients, the global indices indicated a significant decrease of cardiovascular coupling, starting at 10 min after the tilt-up, manifested by reduced baroreflex sensitivity and cardiorespiratory coupling that was initiated 8 min after the onset of the orthostatic phase (OP). A decreased autonomic control on cardiovascular-respiratory couplings was further evidenced by increased alterations of the JSD indices during the OP compared to the supine position in patients compared to controls. Furthermore, findings based on local indices demonstrated that female patients showed reductions and disengagements in cardiovascular (p < 0.001) and cardiorespiratory (p < 0.01) couplings, as early as the first 5 min and during the complete OP.

System dynamics of active and passive postural changes: Insights from principal dynamic modes analysis of baroreflex loop

The baroreflex being a key modulator of cardiovascular control ensures adequate blood pressure regulation under orthostatic stress which otherwise may cause severe hypotension. Contrary to conventional baroreflex sensitivity indices derived across a-priori traditional frequency bands, the present study is aimed at proposing new indices for the assessment of baroreflex drive which follows active (supine to stand-up) and passive (supine to head-up tilt) postural changes. To achieve this, a novel system identification approach of principal dynamic modes (PDM) was utilized to extract data-adaptive frequency components of closed-loop interactions between beat-to-beat interval and systolic blood pressure recorded from 10 healthy humans. We observed that the gain of low-pass global PDM of cardiac arm (:feedback reflex loop, mediated by pressure sensors to adjust heart rate in response to arterial blood pressure), and 0.2 Hz global PDM of mechanical arm (:feed-forward pathways, originating changes in arterial blood pressure in response to heart rate variations) may function as potential markers to distinguish active and passive orthostatic tests in healthy subjects.

Baroreflex Coupling Assessed by Cross-Compression Entropy

Estimating interactions between physiological systems is an important challenge in modern biomedical research. Here, we explore a new concept for quantifying information common in two time series by cross-compressibility. Cross-compression entropy (CCE) exploits the ZIP data compression algorithm extended to bivariate data analysis. First, time series are transformed into symbol vectors. Symbols of the target time series are coded by the symbols of the source series. Uncoupled and linearly coupled surrogates were derived from cardiovascular recordings of 36 healthy controls obtained during rest to demonstrate suitability of this method for assessing physiological coupling. CCE at rest was compared to that of isometric handgrip exercise. Finally, spontaneous baroreflex interaction assessed by CCE_BRS was compared between 21 patients suffering from acute schizophrenia and 21 matched controls. The CCE_BRS of original time series was significantly higher than in uncoupled surrogates in 89% of the subjects and higher than in linearly coupled surrogates in 47% of the subjects. Handgrip exercise led to sympathetic activation and vagal inhibition accompanied by reduced baroreflex sensitivity. CCE_BRS decreased from 0.553 ± 0.030 at rest to 0.514 ± 0.035 during exercise (p < 0.001). In acute schizophrenia, heart rate, and blood pressure were elevated. Heart rate variability indicated a change of sympathovagal balance. The CCE_BRS of patients with schizophrenia was reduced compared to healthy controls (0.546 ± 0.042 vs. 0.507 ± 0.046, p < 0.01) and revealed a decrease of blood pressure influence on heart rate in patients with schizophrenia. Our results indicate that CCE is suitable for the investigation of linear and non-linear coupling in cardiovascular time series. CCE can quantify causal interactions in short, noisy and non-stationary physiological time series.

Dependency Structures in Differentially Coded Cardiovascular Time Series

Objectives. This paper analyses temporal dependency in the time series recorded from aging rats, the healthy ones and those with early developed hypertension. The aim is to explore effects of age and hypertension on mutual sample relationship along the time axis. Methods. A copula method is applied to raw and to differentially coded signals. The latter ones were additionally binary encoded for a joint conditional entropy application. The signals were recorded from freely moving male Wistar rats and from spontaneous hypertensive rats, aged 3 months and 12 months. Results. The highest level of comonotonic behavior of pulse interval with respect to systolic blood pressure is observed at time lags τ = 0, 3, and 4, while a strong counter-monotonic behavior occurs at time lags τ = 1 and 2. Conclusion. Dynamic range of aging rats is considerably reduced in hypertensive groups. Conditional entropy of systolic blood pressure signal, compared to unconditional, shows an increased level of discrepancy, except for a time lag 1, where the equality is preserved in spite of the memory of differential coder. The antiparallel streams play an important role at single beat time lag.

Baroreflex Sensitivity in Children and Adolescents: Physiology, Hypertension, Obesity, Diabetes Mellitus

The increased prevalence of obesity in children and its complications have led to a greater interest in studying baroreflex sensitivity (BRS) in children. This review of BRS in children and adolescents includes subtopics on: 1. Resting values of BRS and their reproducibility, 2. Genetics of BRS, 3. The role of a primarily low BRS and obesity in the development of hypertension, and 4. Association of diabetes mellitus, BRS, and obesity. The conclusions specific to this age follow from this review: 1. The mean heart rate (HR) influences the measurement of BRS. Since the mean HR decreases during adolescence, HR should be taken into account. 2. A genetic dependency of BRS was found. 3. Low BRS values may precede pathological blood-pressure elevation in children with white-coat hypertension. We hypothesize that low BRS plays an active role in the emergence of hypertension in youth. A contribution of obesity to the development of hypertension was also found. We hypothesize that both factors, a primarily low BRS and obesity, are partially independent risk factors for hypertension in youths. 4. In diabetics, a low BRS compared to healthy children can be associated with insulin resistance. A reversibility of the BRS values could be possible after weight loss.

Orthostatic stress causes immediately increased blood pressure variability in women with vasovagal syncope

The cardiovascular and respiratory autonomic nervous regulation has been studied mainly by hemodynamic responses during different physical stressors. In this study, dynamics of autonomic response to an orthostatic challenge was investigated by hemodynamic variables and by diverse linear and nonlinear indices calculated from time series of beat-to-beat intervals (BBI), respiratory cycle duration (RESP), systolic (SYS) and diastolic (DIA) blood pressure. This study included 16 young female patients (SYN) with vasovagal syncope and 12 age-matched female controls (CON). The subjects were enrolled in a head-up tilt (HUT) test, breathing normally, including 5min of baseline (BL, supine position) and 18min of 70° orthostatic phase (OP). To increase the time resolution of the analysis the time series were segmented in five-minute overlapping windows with a shift of 1min. Hemodynamic parameters did not show any statistical differences between SYN and CON. Time domain linear analysis revealed increased respiratory frequency and increased blood pressure variability (BPV) in patients during OP meaning increased sympathetic activity and vagal withdrawal. Frequency domain analysis confirmed a predominance of sympathetic tone by steadily increased values of low over high frequency power in BBI and of low frequency power in SYS and DIA in patients during OP. The nonlinear analysis by symbolic dynamics seemed to be highly suitable for differentiation of SYN and CON in the early beginning of OP, i.e., 5min after tilt-up. In particular the index SYS_plvar3 showed less patterns of low variability in patients reflecting a steadily increase in both BPV and sympathetic activity. The proposed dynamical analysis could lead to a better understanding of the temporal underlying mechanisms in healthy subjects and patients under orthostatic stress.

A percentile-based coarse graining approach is helpful in symbolizing heart rate variability during graded head-up tilt

Coarse graining of physiological time series such as the cardiac interbeat interval series by means of a symbolic transformation retains information about dynamical properties of the underlying system and complements standard measures of heart rate variability. The transformations of the original time series to the coarse grained symbolic series usually lead to a non-uniform occurrence of the different symbols, i.e. some symbols appear more often than others influencing the results of the subsequent symbolic series analysis. Here, we defined a transformation procedure to assure that each symbol appears with equal probability using a short alphabet {0,1,2,3} and a long alphabet {0,1,2,3,4,5}. The procedure was applied to the cardiac interbeat interval series RRi of 17 healthy subjects obtained during graded head-up tilt testing. The symbolic dynamics is analyzed by means of the occurrence of short sequences (`words') of length 3. The occurrence of words is grouped according to words without variations of the symbols (0V%), one variation (1V%), two like variations (2LV%) and two unlike variations (2UV%). Linear regression analysis with respect to tilt angle showed that for the short alphabet 0V% increased with increasing tilt angle whereas 1V%, 2LV% and 2UV% decreased. For the long alphabet 0V%, and 1V% increased with increasing tilt angle whereas 2LV% and 2UV% decreased. These results were slightly better compared to the results from non-uniform symbolic transformations reflecting the deviation from the mean. In conclusion, the symbolic transformation assuring the appearance of symbols with equal probability is capable of reflecting changes of the cardiac autonomic nervous system during graded head-up tilt. Furthermore, the transformation is independent of the time series' distribution.

An alternative approach to approximate entropy threshold value (r) selection: application to heart rate variability and systolic blood pressure variability under postural challenge

This study presents an alternative approach to approximate entropy (ApEn) threshold value (r) selection. There are two limitations of traditional ApEn algorithm: (1) the occurrence of undefined conditional probability (CPu) where no template match is found and (2) use of a crisp tolerance (radius) threshold 'r'. To overcome these limitations, CPu is substituted with optimum bias setting ɛ opt which is found by varying ɛ from (1/N - m) to 1 in the increments of 0.05, where N is the length of the series and m is the embedding dimension. Furthermore, an alternative approach for selection of r based on binning the distance values obtained by template matching to calculate ApEnbin is presented. It is observed that ApEnmax, ApEnchon and ApEnbin converge for ɛ opt = 0.6 in 50 realizations (n = 50) of random number series of N = 300. Similar analysis suggests ɛ opt = 0.65 and ɛ opt = 0.45 for 50 realizations each of fractional Brownian motion and MIX(P) series (Lu et al. in J Clin Monit Comput 22(1):23-29, 2008). ɛ opt = 0.5 is suggested for heart rate variability (HRV) and systolic blood pressure variability (SBPV) signals obtained from 50 young healthy subjects under supine and upright position. It is observed that (1) ApEnbin of HRV is lower than SBPV, (2) ApEnbin of HRV increases from supine to upright due to vagal inhibition and (3) ApEnbin of BPV decreases from supine to upright due to sympathetic activation. Moreover, merit of ApEnbin is that it provides an alternative to the cumbersome ApEnmax procedure.

Joint symbolic dynamics for the assessment of cardiovascular and cardiorespiratory interactions

Beat-to-beat variations in heart period provide information on cardiovascular control and are closely linked to variations in arterial pressure and respiration. Joint symbolic analysis of heart period, systolic arterial pressure and respiration allows for a simple description of their shared short-term dynamics that are governed by cardiac baroreflex control and cardiorespiratory coupling. In this review, we discuss methodology and research applications. Studies suggest that analysis of joint symbolic dynamics provides a powerful tool for identifying physiological and pathophysiological changes in cardiovascular and cardiorespiratory control.

From the First Spectral Analysis of Blood Pressure Variability in the World to the Present Time: Contribution of the Department of Physiology of the Faculty of Medicine, Masaryk University, Brno

The review shows the significance of blood pressure regulation studies conducted during several decades at the Department of Physiology, Faculty of Medicine, Masaryk University, Brno. Continuous non-invasive blood pressure measurement was first introduced and patented here and, with the obtained data, the first spectral analysis of blood pressure was performed. This method was used in many different physiological studies on the relationship of blood pressure regulation to circulatory parameters, breathing, and baroreflex sensitivity. The article deals with studies on risk stratification of sudden cardiac death according to decreased baroreflex sensitivity, 24-hour heart rate variability, the amount of extrasystoles and late potentials. Importance of the new method of determination of one summation risk index is described here. A summary of the new conception of the relationship between low baroreflex sensitivity and hypertension is presented. Here, not only pathological changes of the vessel wall but also increased sympathetic activity and genetic predisposition play a role. Importance of studies conducted in young adults is highlighted, as inherited BRS decrease contributes to earlier blood pressure increase in the young. This research is highly topical, since prevention of hypertension in childhood is possible. Recent studies are dedicated to blood pressure regulation in young diabetics.

Diagnostic significance of a mild decrease of baroreflex sensitivity with respect to heart rate in type 1 diabetes mellitus

Decreased baroreflex sensitivity is an early sign of autonomic dysfunction in patients with type-1 diabetes mellitus. We evaluated the repeatability of a mild baroreflex sensitivity decrease in diabetics with respect to their heart rate. Finger blood pressure was continuously recorded in 14 young diabetics without clinical signs of autonomic dysfunction and in 14 age-matched controls for 42 min. The recordings were divided into 3-min segments, and the mean inter-beat interval (IBI), baroreflex sensitivity in ms/mm Hg (BRS) and mHz/mm Hg (BRSf) were determined in each segment. These values fluctuated in each subject within 42 min and therefore coefficients of repeatability were calculated for all subjects. Diabetics compared with controls had a decreased mean BRS (p=0.05), a tendency to a shortened IBI (p=0.08), and a decreased BRSf (p=0.17). IBI correlated with BRS in diabetics (p=0.03); this correlation was at p=0.12 in the controls. BRSf was IBI independent (controls: p=0.81, diabetics: p=0.29). We conclude that BRS is partially dependent on mean IBI. Thus, BRS reflects not only an impairment of the quick baroreflex responses of IBI to blood pressure changes, but also a change of the tonic sympathetic and parasympathetic heart rate control. This is of significance during mild changes of BRS. Therefore, an examination of the BRSf index is highly recommended, because this examination improves the diagnostic value of the measurement, particularly in cases of early signs of autonomic dysfunction.

Spectral Peak Frequency in Low-Frequency Band in Cross Spectra of Blood Pressure and Heart Rate Fluctuations in Young Type 1 Diabetic Patients

In this study we tested whether joint evaluation of the frequency (fcs) at which maxima of power in the cross-spectra between the variability in systolic blood pressure and inter-beat intervals in the range of 0.06-0.12 Hz occur together with the quantification of baroreflex sensitivity (BRS) may improve early detection of autonomic dysfunction in type 1 diabetes mellitus (T1DM). We measured 14 T1DM patients (age 20.3-24.2 years, DM duration 10.4-14.2 years, without any signs of autonomic neuropathy) and 14 age-matched controls (Co). Finger arterial blood pressure was continuously recorded by Finapres for one hour. BRS and fcs were determined by the spectral method. Receiver-operating curves (ROC) were calculated for fcs, BRS, and a combination of both factors determined as F(z)=1/(1+exp(-z)), z=3.09–0.013*BRS–0.027*fcs. T1DM had significantly lower fcs than Co (T1DM: 88.8±6.7 vs. Co: 93.7±3.8 mHz; p<0.05), and a tendency towards lower BRS compared to Co (T1DM: 10.3±4.4 vs. Co: 14.6±7.1 ms/mm Hg; p=0.06). The ROC for Fz showed the highest sensitivity and specificity (71.4 % and 71.4 %) in comparison with BRS (64.3 % and 71.4 %) or fcs (64.3 % and 64.3 %). The presented method of evaluation of BRS and fcs forming an integrated factor Fz could provide further improvement in the risk stratification of diabetic patients.

Long-term neuropeptide Y administration in the periphery induces abnormal baroreflex sensitivity and obesity in rats

Neuropeptide Y (NPY) is an important neuronal element involved in cardiovascular regulation. Since elevated plasma levels of NPY have been observed in numerous pathological situations, this study aimed to determine whether long-term elevated plasma concentrations of NPY could result in aberrant baroreflex sensitivity. Mini-osmotic pump containing NPY (85 μg per 30 days) was subcutaneously implanted between scapulae in male rats for 4 months. The rats treated with NPY showed the following characters compared with control group: (1) attenuated heart rate responding to the increases in mean arterial blood pressure (MABP) induced by phenylephrine, but enhanced heart rate responding to the decreases in MABP induced by sodium nitroprusside; (2) decreased protein levels of substance P (SP) and GluR2, while increased the expression of γ-aminobutyric acid A receptor (GABA(A)R) in brainstem; (3) abdominal obesity indicated by increased body weight and accumulated fat mass in peritoneal cavity; (4) significant increases in total cholesterol, triglycerides, and low density lipoprotein levels in the periphery. These findings indicate that long-term NPY administration in the periphery leads to abnormal baroreflex sensitivity due, at least in part, to the down-regulated expression of SP/GluR2 and elevated expression of GABA(A)R in both protein and RNA levels, which indicate the alternations in glutamate function and GABA action in the nucleus tractus solitarii in NPY-treated rats. Furthermore, long-term NPY administration results in abdominal obesity and dyslipidemia.

Assessment of the dynamic interactions between heart rate and arterial pressure by the cross time-frequency analysis

In this study, a framework for the characterization of the dynamic interactions between RR variability (RRV) and systolic arterial pressure variability (SAPV) is proposed. The methodology accounts for the intrinsic non-stationarity of the cardiovascular system and includes the assessment of both the strength and the prevalent direction of local coupling. The smoothed pseudo-Wigner-Ville distribution (SPWVD) is used to estimate the time-frequency (TF) power, coherence, and phase-difference spectra with fine TF resolution. The interactions between the signals are quantified by time-varying indices, including the local coupling, phase differences, time delay, and baroreflex sensitivity (BRS). Every index is extracted from a specific TF region, localized by combining information from the different spectra. In 14 healthy subjects, a head-up tilt provoked an abrupt decrease in the cardiovascular coupling; a rapid change in the phase difference (from 0.37 ± 0.23 to -0.27 ± 0.22 rad) and time delay (from 0.26 ± 0.14 to -0.16 ± 0.16 s) in the high-frequency band; and a decrease in the BRS (from 23.72 ± 7.66 to 6.92 ± 2.51 ms mmHg(-1)). In the low-frequency range, during a head-up tilt, restoration of the baseline level of cardiovascular coupling took about 2 min and SAPV preceded RRV by about 0.85 s during the whole test. The analysis of the Eurobavar data set, which includes subjects with intact as well as impaired baroreflex, showed that the presented methodology represents an improved TF generalization of traditional time-invariant methodologies and can reveal dysfunctions in subjects with baroreflex impairment. Additionally, the results also suggest the use of non-stationary signal-processing techniques to analyze signals recorded under conditions that are usually supposed to be stationary.

Delayed effect of blood pressure fluctuations on heart rate in patients with end-stage kidney disease

The time delay of the baroreflex may be affected by decreased autonomic activity in uremia. To assess the magnitude and the time delay of heart rate response in patients with end-stage renal disease, continuous beat-to-beat intervals (IBI) and systolic blood pressure (SBP) recordings were monitored in hemodialysis (HD) patients (n = 72), in patients after renal transplantation (TX) (n = 41) and in age-matched controls (C) (n = 34). A 2-term prediction model was computed, in which each IBI change was represented as a function of SBP difference values of two immediately preceding beats. Baroreflex slope and the frequency domain variables low frequency (LF) α index, phase shift, and lag time were also calculated. b₁ coefficient, representing the dependence of IBI difference with the first previous SBP difference was lower in HD than in Cs, but increased after TX. b₁ correlated with age, baroreflex slope, and LF α, and b₂ (the 2nd term), with both the phase shift between SBP and IBI and lag time. The latter was lower in Cs than in HD or transplanted patients. These findings show that the time delay of the heart rate response to SBP variations is increased in renal insufficiency. The prolonged delay may contribute to the circulatory instability in uremic patients.