Effect of altering conditions of the sequence method on baroreflex sensitivity

Higher Cardiovagal Baroreflex Sensitivity Predicts Increased Pain Outcomes After Cardiothoracic Surgery

Excessive postoperative pain can lead to extended hospitalization and increased expenses, but factors that predict its severity are still unclear. Baroreceptor function could influence postoperative pain by modulating nociceptive processing and vagal-mediated anti-inflammatory reflexes. To investigate this relationship, we conducted a study with 55 patients undergoing minimally invasive cardiothoracic surgery to evaluate whether cardiovagal baroreflex sensitivity (BRS) can predict postoperative pain. We assessed the spontaneous cardiovagal BRS under resting pain-free conditions before surgery. We estimated postoperative pain outcomes with the Pain, Enjoyment, and General Activity scale and pressure pain thresholds on the first (POD1) and second (POD2) postoperative days and persistent pain 3 and 6 months after hospital discharge. We also measured circulating levels of relevant inflammatory biomarkers (C-reactive protein, albumin, cytokines) at baseline, POD1, and POD2 to assess the contribution of inflammation to the relationship between BRS and postoperative pain. Our mixed-effects model analysis showed a significant main effect of preoperative BRS on postoperative pain (P = .013). Linear regression analysis revealed a significant positive association between preoperative BRS and postoperative pain on POD2, even after adjusting for demographic, surgical, analgesic treatment, and psychological factors. Moreover, preoperative BRS was linked to pain interfering with general activity and enjoyment but not with other pain parameters (pain intensity and pressure pain thresholds). Preoperative BRS had modest associations with postoperative C-reactive protein and IL-10 levels, but they did not mediate its relationship with postoperative pain. These findings indicate that preoperative BRS can independently predict postoperative pain, which could serve as a modifiable criterion for optimizing postoperative pain management. PERSPECTIVE: This article shows that preoperative BRS predicts postoperative pain outcomes independently of the inflammatory response and pain sensitivity to noxious pressure stimulation. These results provide valuable insights into the role of baroreceptors in pain and suggest a helpful tool for improving postoperative pain management.

Induction of Day-Time Periodic Breathing is Associated With Augmented Reflex Response From Peripheral Chemoreceptors in Male Patients With Systolic Heart Failure

Spontaneous day-time periodic breathing (sPB) constitutes a common phenomenon in systolic heart failure (HF). However, it is unclear whether PB during wakefulness could be easily induced and what are the physiological and clinical correlates of patients with HF in whom PB induction is possible. Fifty male HF patients (age 60.8 ± 9.8 years, left ventricle ejection fraction 28.0 ± 7.4%) were prospectively screened and 46 enrolled. After exclusion of patients with sPB the remaining underwent trial of PB induction using mild hypoxia (stepwise addition of nitrogen gas to breathing mixture) which resulted in identification of inducible (iPB) in 51%. All patients underwent assessment of hypoxic ventilatory response (HVR) using transient hypoxia and of hypercapnic ventilatory response (HCVR) employing Read’s rebreathing method. The induction trial did not result in any adverse events and minimal SpO₂ during nitrogen administration was ∼85%. The iPB group (vs. non-inducible PB group, nPB) was characterized by greater HVR (0.90 ± 0.47 vs. 0.50 ± 0.26 L/min/%; p <0.05) but comparable HCVR (0.88 ± 0.54 vs. 0.67 ± 0.68 L/min/mmHg; p = NS) and by worse clinical and neurohormonal profile. Mean SpO₂ which induced first cycle of PB was 88.9 ± 3.7%, while in sPB mean SpO₂ preceding first spontaneous cycle of PB was 96.0 ± 2.5%. There was a reverse relationship between HVR and the relative variation of SpO₂ during induced PB (r = −0.49, p = 0.04). In summary, PB induction is feasible and safe in HF population using simple and standardized protocol employing incremental, mild hypoxia. Pathophysiology of iPB differs from sPB, as it relies mostly on overactive peripheral chemoreceptors. At the same time enhanced HVR might play a protective role against profound hypoxia during iPB.

Stand Up to Excite the Spine: Neuromuscular, Autonomic, and Cardiometabolic Responses During Motor Imagery in Standing vs. Sitting Posture

Motor imagery (MI) for health and performance strategies has gained interest in recent decades. Nevertheless, there are still no studies that have comprehensively investigated the physiological responses during MI, and no one questions the influence of low-level contraction on these responses. Thus, the aim of the present study was to investigate the neuromuscular, autonomic nervous system (ANS), and cardiometabolic changes associated with an acute bout of MI practice in sitting and standing condition. Twelve young healthy males (26.3 ± 4.4 years) participated in two experimental sessions (control vs. MI) consisting of two postural conditions (sitting vs. standing). ANS, hemodynamic and respiratory parameters, body sway parameters, and electromyography activity were continuously recorded, while neuromuscular parameters were recorded on the right triceps surae muscles before and after performing the postural conditions. While MI showed no effect on ANS, the standing posture increased the indices of sympathetic system activity and decreased those of the parasympathetic system (p < 0.05). Moreover, MI during standing induced greater spinal excitability compared to sitting posture (p < 0.05), which was accompanied with greater oxygen consumption, energy expenditure, ventilation, and lower cardiac output (p < 0.05). Asking individuals to perform MI of an isometric contraction while standing allows them to mentally focus on the motor command, not challenge balance, and produce specific cardiometabolic responses. Therefore, these results provide further evidence of posture and MI-related modulation of spinal excitability with additional autonomic and cardiometabolic responses in healthy young men.

Low ventilatory responsiveness to transient hypoxia or breath-holding predicts fast marathon performance in healthy middle-aged and older men

The aim of this study was to test the utility of haemodynamic and autonomic variables (e.g. peripheral chemoreflex sensitivity [PCheS], blood pressure variability [BPV]) for the prediction of individual performance (marathon time and VO_2max) in older men. The post-competition vasodilation and sympathetic vasomotor tone predict the marathon performance in younger men, but their prognostic relevance in older men remains unknown. The peripheral chemoreflex restrains exercise-induced vasodilation via sympathetically-mediated mechanism, what makes it a plausible candidate for the individual performance marker. 23 men aged ≥ 50 year competing in the Wroclaw Marathon underwent an evaluation of: resting haemodynamic parameters, PCheS with two methods: transient hypoxia and breath-holding test (BHT), cardiac barosensitivity, heart rate variability (HRV) and BPV, plasma renin and aldosterone, VO_2max in a cardiopulmonary exercise test (CPET). All tests were conducted twice: before and after the race, except for transient hypoxia and CPET which were performed once, before the race. Fast marathon performance and high VO_2max were correlated with: low ventilatory responsiveness to hypoxia (r =  - 0.53, r = 0.67, respectively) and pre-race BHT (r =  - 0.47, r = 0.51, respectively), (1) greater SD of beat-to-beat SBP (all p < 0.05). Fast performance was related with an enhanced pre-race vascular response to BHT (r =  - 0.59, p = 0.005). The variables found by other studies to predict the marathon performance in younger men: post-competition vasodilation, sympathetic vasomotor tone (LF-BPV) and HRV were not associated with the individual performance in our population. The results suggest that PCheS (ventilatory response) predicts individual performance (marathon time and VO_2max) in men aged ≥ 50 yeat. Although cause-effect relationship including the role of peripheral chemoreceptors in restraining the post-competition vasodilation via the sympathetic vasoconstrictor outflow may be hypothesized to underline these findings, the lack of correlation between individual performance and both, the post-competition vasodilation and the sympathetic vasomotor tone argues against such explanation. Vascular responsiveness to breath-holding appears to be of certain value for predicting individual performance in this population, however.

The nonpharmacological sequence method provides a reliable evaluation of baroreflex sensitivity in fish

The most commonly used technique to study the barostatic regulation of blood pressure in ectothermic vertebrates consists of determining the heart rate response to pharmacological manipulations of blood pressure, the so-called "Oxford method." Although well established, the Oxford method has some important limitations, such as induction of hypervolemia in small animals and undesired effects of vasoactive drugs on central and peripheral baroreflex components. As an alternative, the sequence method, which consists in the computerized evaluation of naturally-occurring baroreflex adjustments of heart rate without the need for pharmacological administrations, was developed to study baroreflexes. In the present study, we compare this sequence method with the Oxford technique in two teleost species with different life styles, and we assess the optimal software configuration for the employment of the sequence method in fish. Calculation of baroreflex gain through the sequence method was adequate and reliable when the software was configured to search for baroreflex sequences with a minimum length of three cardiac cycles with a delay of one cardiac cycle between fluctuations in mean ventral aortic blood pressure and reflex changes in pulse interval. When properly configured, the sequence and the Oxford methods yielded similar determinations of the baroreflex gain in fish.

Baroreflex sensitivity with different lags and random forests for staging cardiovascular autonomic neuropathy in subjects with diabetes

Impaired baroreflex sensitivity (BRS) may indicate cardiovascular autonomic neuropathy (CAN), which often remains undiagnosed during the initial course of diabetes mellitus. The baroreflex mechanism can be considered negative feedback because of baroreflex delay, the time delay between a change in blood pressure and the counteracting heart rate response. This work sought to analyze BRS considering lags from 1 to 10 RR intervals. We hypothesized that diabetic patients with subclinical CAN (SCAN) have a detectable delay in autonomic nervous system activity and that this would differ from patients without CAN (NCAN) and with established CAN (ECAN). In the first stage, 30 patients were included in an exploratory analysis using the Principal Component Analysis. Six indexes related to the BRS delay were proposed and considered significant for staging diabetic patients. Three indexes allowed for the differentiating of patients with and without CAN, and three indexes distinguished subjects with SCAN from subjects with NCAN or ECAN. Then, in the second stage, a random forest model was developed with 72 subjects, using the variables selected in the first stage. It was possible to detect SCAN, and to point out those subjects with the potential to change the CAN stage, allowing for the tracking of CAN progression. The model achieved a sensitivity of 96% and specificity of 100% to detect SCAN. Thus, the BRS analysis considering delayed reaction in the dynamics of heart rate variability may contribute to an accurate screening tool to staging CAN, in addition to indicating patients with most insidious disease progress.

Contribution of Baroreceptor Function to Pain Perception and Perioperative Outcomes

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain homeostasis by coordinating physiologic responses to external and internal stimuli. While it is recognized that carotid and cardiopulmonary baroreceptor reflexes modulate autonomic output to mitigate excessive fluctuations in arterial blood pressure and to maintain intravascular volume, increasing evidence suggests that baroreflex pathways also project to key regions of the central nervous system that regulate somatosensory, somatomotor, and central nervous system arousal. In addition to maintaining autonomic homeostasis, baroreceptor activity modulates the perception of pain, as well as neuroimmune, neuroendocrine, and cognitive responses to physical and psychologic stressors. This review summarizes the role that baroreceptor pathways play in modulating acute and chronic pain perception. The contribution of baroreceptor function to postoperative outcomes is also presented. Finally, methods that enhance baroreceptor function, which hold promise in improving postoperative and pain management outcomes, are presented.

Assessment of arterial baroreflex sensitivity by different computational analyses of pressure wave signals alone

BACKGROUND AND OBJECTIVE

Baroreflex sensitivity (BRS) is an important indicator of the functionality of the arterial baroreceptors, and its assessment may have major research and clinical implications. An important requirement for its quantification is the continuous recording of electrocardiography (ECG) signal, so as to extract the RR interval, in parallel with continuous beat-to-beat blood pressure recording. We aimed to accurately calculate the RR Interval from pressure wave recordings per se, namely, the Pulse Interval (PI) using various arterial pulse wave analysis algorithms and to evaluate the precision and accuracy of BRS values calculated with the PI compared to BRS values calculated with the RR Interval.

METHODS

We analyzed the open access data of the Eurobavar study, which contains a set of ECG and arterial blood pressure (BP) wave signals recorded at 11 European centers. Pressure waveforms were continuously recorded by the Finapres apparatus which uses a finger cuff. The cuff pressure around the finger is dynamically adjusted by a servo-system to equal intra-arterial pressure, thus allowing the continuous recording of beat-to-beat BP waves. RR Interval was calculated from the ECG, whereas, PI was extracted from the arterial pulse waveforms, using 4 different methods (minimum, maximum, maximum 1st derivative and intersecting tangents method). BRS values were estimated by time domain and frequency domain methods. In order to compare agreement, accuracy, precision, variability, and the association between the reference BRS using the RR Interval and the BRS values using PI, standard statistical methods (i.e. intraclass correlation coefficients, RMSE, regression analysis) and Bland-Altman methods were performed.

RESULTS

We found that analysis of pressure waves alone by frequency-based (i.e. spectral) methods, provides the most accurate results of BRS estimation compared to time-domain methods (ICC > 0.9, R > 0.9, RMSE > 0.8 ms/mmHg). Concerning the spectral method, any algorithm for PI calculation is sufficient, as all show excellent agreement with the respective RR-intervals determined by ECG time series. Only the intersecting tangents and the maximum 1st derivative methods for PI calculation produce the most accurate results in time domain BRS estimation.

CONCLUSION

BRS estimation by proper analysis of pressure wave signals alone is feasible and accurate. Further studies are needed to investigate the clinical validity and relevance of the different BRS estimations in diagnostic, prognostic and therapeutic levels.

Hypoxic tachycardia is not a result of increased respiratory activity in healthy subjects

NEW FINDINGS

What is the central question of this research? Does increased ventilation contribute to the increase in heart rate during transient exposure to hypoxia in humans? What is the main finding and its importance? Voluntary suppression of the ventilatory response to transient hypoxia does not affect the magnitude of the heart rate response to the stimulus. This indicates that hypoxic tachycardia is not secondary to hyperpnoea in humans. Better understanding of the physiology underlying the cardiovascular response to hypoxia might help in identification of new markers of elevated chemoreceptor activity, which has been proposed as a target in treatment of sympathetically mediated diseases.

ABSTRACT

Animal data suggest that hypoxic tachycardia is secondary to hyperpnoea, and for years this observation has been extrapolated to humans, despite a lack of experimental evidence. We addressed this issue in 17 volunteers aged 29 ± 7 (SD) years. A transient hypoxia test, comprising several nitrogen-breathing episodes, was performed twice in each subject. In the first test, the subject breathed spontaneously (spontaneous breathing). In the second test, the subject was repeatedly asked to adjust his or her depth and rate of breathing according to visual (real-time inspiratory flow) and auditory (metronome sound) cues, respectively (controlled breathing), to maintain respiration at the resting level during nitrogen-breathing episodes. Hypoxic responsiveness, including minute ventilation [Hyp-VI; in liters per minute per percentage of blood oxygen saturation ( S p O 2 )], tidal volume [Hyp-VT; in litres per S p O 2 ], heart rate [Hyp-HR; in beats per minute per S p O 2 ], systolic [Hyp-SBP; in millimetres of mercury per S p O 2 ] and mean blood pressure [Hyp-MAP; in millimetres of mercury per S p O 2 ] and systemic vascular resistance [Hyp-SVR; in dynes seconds (centimetres)^-5 per S p O 2 ] was calculated as the slope of the regression line relating the variable to S p O 2 , including pre- and post-hypoxic values. The Hyp-VI and Hyp-VT were reduced by 69 ± 25 and 75 ± 10%, respectively, in controlled versus spontaneous breathing (Hyp-VI, -0.30 ± 0.15 versus -0.11 ± 0.09; Hyp-VT, -0.030 ± 0.024 versus -0.007 ± 0.004; both P < 0.001). However, the cardiovascular responses did not differ between spontaneous and controlled breathing (Hyp-HR, -0.62 ± 0.24 versus -0.71 ± 0.33; Hyp-MAP, -0.43 ± 0.19 versus -0.47 ± 0.21; Hyp-SVR, 9.15 ± 5.22 versus 9.53 ± 5.57; all P ≥ 0.22), indicating that hypoxic tachycardia is not secondary to hyperpnoea. Hyp-HR was correlated with Hyp-SVR (r = -074 and -0.80 for spontaneous and controlled breathing, respectively; both P < 0.05) and resting barosensitivity assessed with the sequence technique (r = -0.60 for spontaneous breathing; P < 0.05). This might suggest that the baroreflex mechanism is involved.

Muscle sympathetic nerve responses to passive and active one-legged cycling: insights into the contributions of central command

The contribution of central command to the peripheral vasoconstrictor response during exercise has been investigated using primarily handgrip exercise. The purpose of the present study was to compare muscle sympathetic nerve activity (MSNA) responses during passive (involuntary) and active (voluntary) zero-load cycling to gain insights into the effects of central command on sympathetic outflow during dynamic exercise. Hemodynamic measurements and contralateral leg MSNA (microneurography) data were collected in 18 young healthy participants at rest and during 2 min of passive and active zero-load one-legged cycling. Arterial baroreflex control of MSNA burst occurrence and burst area were calculated separately in the time domain. Blood pressure and stroke volume increased during exercise ( P < 0.0001) but were not different between passive and active cycling ( P > 0.05). In contrast, heart rate, cardiac output, and total vascular conductance were greater during the first and second minute of active cycling ( P < 0.001). MSNA burst frequency and incidence decreased during passive and active cycling ( P < 0.0001), but no differences were detected between exercise modes ( P > 0.05). Reductions in total MSNA were attenuated during the first ( P < 0.0001) and second ( P = 0.0004) minute of active compared with passive cycling, in concert with increased MSNA burst amplitude ( P = 0.02 and P = 0.005, respectively). The sensitivity of arterial baroreflex control of MSNA burst occurrence was lower during active than passive cycling ( P = 0.01), while control of MSNA burst strength was unchanged ( P > 0.05). These results suggest that central feedforward mechanisms are involved primarily in modulating the strength, but not the occurrence, of a sympathetic burst during low-intensity dynamic leg exercise. NEW & NOTEWORTHY Muscle sympathetic nerve activity burst frequency decreased equally during passive and active cycling, but reductions in total muscle sympathetic nerve activity were attenuated during active cycling. These results suggest that central command primarily regulates the strength, not the occurrence, of a muscle sympathetic burst during low-intensity dynamic leg exercise.

Impaired Baroreflex Sensitivity after Bilateral Convulsive Seizures in Patients with Focal Epilepsy

Background

Sudden unexpected death in epilepsy (SUDEP) is probably due to an autonomic failure in the early postictal phase after bilateral convulsive seizures (BCS) in the majority of cases. The baroreflex sensitivity (BRS) is an established and reliable biomarker of autonomic function and sudden cardiac death.

Objective

To investigate whether postictal BRS depends on seizure type.

Methods

Beat-to-beat systemic blood pressure and heart rate were continuously and non-invasively recorded with the ccNexfin^® device in patients with focal epilepsy undergoing video-EEG monitoring. BRS was calculated using the sequence as well as the spectral method. A random mixed linear model was applied to analyze the influence of seizure type on BRS during three different time periods of 15-min length each (interictal, preictal, and postictal). In addition, the possible effects of other factors (hypertension, hemispheric lateralization of ictal activity, epilepsy type, body position, vigilance state) were explored. Data are given as median with interquartile range.

Results

A total of 26 seizures of 26 patients were analyzed. In BCS (n = 7), BRS significantly dropped from a preictal value of 15.0 ms/mm Hg (13.0–19.4) and an interictal value of 15.6 ms/mm Hg (12.0–20.4) to 3.1 ms/mm Hg (2.7–10.5) during the postictal period (p < 0.0001) according to the sequence method. This finding was replicated with the spectral method. In contrast, focal seizures (n = 19) did not lead to significant alterations of BRS in the postictal phase.

Conclusion

Postictal BRS depends on the seizure type and is markedly impaired after BCS. The present study provides further evidence for a disturbed autonomic function following BCS. These findings might be related to cardiovascular failure in the context of SUDEP.

Increased body fat is associated with potentiation of blood pressure response to hypoxia in healthy men: relations with insulin and leptin

Background

Increased peripheral chemosensitivity (PChS) has been proposed as mechanism underlying obesity-related sympathoactivation, with insulin and/or leptin as possible mediators. However, human data on PChS in obesity are scarce. Therefore, we explored this issue in a sample of 41 healthy men aged 30–59 years, divided according to body fat percentage (fat %) into two groups: <25 and ≥25 %.

Methods

PChS was assessed using transient hypoxia method [respiratory (PChS-MV), heart rate (PChS-HR), and blood pressure (PChS-SBP) responses were calculated]. Baroreflex sensitivity (BRS-Seq) was assessed using sequence method. Fasting plasma insulin and leptin levels were measured. Homeostatic model assessment (HOMA) was used to assess insulin sensitivity/resistance.

Results

Individuals with ≥25 % body fat demonstrated increased PChS-SBP (p < 0.01), but unchanged PChS-MV and PChS-HR (both p > 0.4). PChS-SBP was related positively with anthropometric characteristics (e.g. waist circumference, fat %), plasma insulin and HOMA (all p < 0.05), and negatively with BRS-Seq (p = 0.001), but not with plasma leptin (p = 0.27).

Conclusions

In healthy men, overweight/obesity is accompanied by augmented blood pressure response from peripheral chemoreceptors, while respiratory and heart rate responses remain unaltered. Hyperinsulinaemia and insulin resistance (but not hyperleptinaemia) are associated with augmented pressure response from chemoreceptors.

Electronic supplementary material

The online version of this article (doi:10.1007/s10286-015-0338-2) contains supplementary material, which is available to authorized users.

Age-related reflex responses from peripheral and central chemoreceptors in healthy men

Objective

The study aimed: (i) to characterize reflex responses from peripheral and central chemoreceptors in different age groups of healthy men (<50 years old vs ≥50 years old) and, (ii) to assess, within these groups, whether there is any relationship between ventilatory and hemodynamic responses from chemoreceptors and indices of autonomic nervous system (ANS).

Methods

Peripheral chemoreflex sensitivity was assessed by the transient hypoxia method and respiratory, heart rate (HR) and blood pressure responses were calculated. Central chemoreflex sensitivity was assessed by the rebreathing method and respiratory response was calculated. ANS was assessed using heart rate variability indices and baroreflex sensitivity (BRS).

Results

Sixty-seven healthy men were divided into 2 groups: <50 years (n = 38, mean age: 32 ± 10 years) and ≥50 years (n = 29, mean age: 61 ± 8 years). There were no differences in respiratory response from central and peripheral chemoreceptors between the older and younger groups of healthy males. We found a significantly different pattern of hemodynamic responses from peripheral chemoreceptors between the older and the younger groups. The former expressed attenuated HR acceleration and exaggerated blood pressure increase in response to transient hypoxia. Blunted HR response was related to reduced BRS and sympathovagal imbalance characterized by reduced vagal tone. Blood pressure responses seemed to be independent of sympathovagal balance and BRS.

Interpretation

Ageing impacts hemodynamic rather than respiratory response from chemoreceptors. Impaired arterial baroreflex and sympathovagal imbalance related to ageing may contribute to decreased heart rate response, but not to increased blood pressure response from peripheral chemoreceptors.

Circulating testosterone and estradiol, autonomic balance and baroreflex sensitivity in middle-aged and elderly men with heart failure

BACKGROUND

Heart failure (HF) is considered as a cardiogeriatric syndrome. Its fundamental pathophysiological feature is autonomic imbalance (and associated abnormalities within cardiovascular reflex control), but recent evidence suggests the involvement of deranged hormone metabolism. Both these neural and endocrine pathologies have serious clinical and prognostic consequences in patients with HF. We investigated the relations between autonomic status, baroreflex sensitivity (BRS) and hormone status in men with mild systolic HF.

METHODS

We examined 46 men with stable systolic HF (age: 62 ± 10 years, NYHA class I/II: 10/36 [22%/78%], ischemic aetiology: 72%, left ventricular ejection fraction: 32 ± 8%). Serum hormone levels (i.e. total testosterone [TT], dehydroepiandrosterone sulphate [DHEAS], oestradiol [E2], insulin-like growth factor type 1 [IGF-1] and cortisol) were assessed using immunoassays. Estimated free testosterone (eFT) was estimated using the Vermeulen's equation. Heart rate variability (HRV) was assessed in time and frequency domains, based on 10-min resting recordings. BRS was estimated using the sequence method (BRS-Seq) and the phenylephrine test (BRS-Phe).

RESULTS

Deficiencies in circulating TT, eFT, DHEAS and IGF-1 (defined as a serum hormone ≤the 10th percentile calculated for the adequate age category in the cohort of healthy men) were found in respectively 13%, 30%, 55% and 93% of men with systolic HF. Serum SHBG ≥50 nmol/L and cortisol ≥700 nmol/L characterised, respectively 44% and 29% of men with HF. In multivariable models after the adjustment for clinical variables, the following relationships were found in examined men: DHEAS and SDNN (time domain of HRV defined as a standard deviation of average R-R intervals) (β = 0.29, p = 0.03); E2 and: HRV-LF (ms(2)) (β = 0.37, p = 0.01), HRV-HF (ms2) (β = 0.44, p = 0.02) and BRS-Phe (β = 0.51, p = 0.008); TT and: HRV-HF (%) (β = 0.35, p = 0.02), HRV-LF/HF ratio (β = -0.35, p = 0.02) and BRS-Seq (β = 0.33, p = 0.04).

CONCLUSIONS

The observed associations between reduced circulating androgens, oestrogens and lower HRV and depleted BRS, irrespectively of HF severity suggest the pathophysiological links between these two mechanisms. These results constitute the premises to investigate whether the pharmacological supplementation of depleted hormones would enable to restore the autonomic balance and improve the efficacy of reflex control within the cardiovascular system in men with systolic HF.

Baroreflex sensitivity estimation by the sequence method with delayed signals

OBJECTIVE

To evaluate a modified sequence method with delayed time series for baroreflex sensitivity (BRS) estimation during supine position and orthostatism in healthy human beings.

METHODS

Nineteen clinically healthy volunteers (12 men, age 28.4 ± 6.2 years old) were included. Blood pressure recordings were obtained during supine position and orthostatism (15 min each) with a Finometer. Systolic blood pressure (SBP) and inter beat intervals (IBI) measured from all heartbeats were used to estimate BRS in both positive and negative sequences, with SBP delayed between 0 and 5 heartbeats. BRS estimations were compared by ANOVA, p < 0.05 was considered significant. Optimal recording time based on fixed BRS error estimation was calculated for each time series.

RESULTS

BRS estimation was similar between positive and negative sequences in all conditions (BRS = 12.0 ± 2.0 ms/mmHg in supine position, delay 0). BRS with no delay was similar to BRS with delays between 1 and 5 heartbeats. Compared to supine position, BRS was smaller in orthostatism in all delays (BRS = 8.0 ± 2.0 ms/mmHg with delay 0). The shortest optimal recording time with delayed time series was similar in supine position and orthostatism (4.3 ± 1.7 vs. 3.74 ± 0.07 min, respectively). Estimation error was linearly correlated to IBI, regardless of the delay.

CONCLUSION

BRS estimation with sequence method improves with delayed time series, during supine position and orthostatism. Reduced BRS estimation error and recording time from this method could benefit studies with large populations or patients with low tolerance to orthostatism.

Can baroreflex measurements with spontaneous sequence analysis be improved by also measuring breathing and by standardization of filtering strategies?

Baroreflex sensitivity (BRS) is known to be attenuated by inspiration and all the original BRS methodologies took this into account by measuring only in expiration. Spontaneous sequence analysis (SSA) is a non-invasive clinical tool widely used to estimate BRS in Man but does not take breathing into account. We have therefore modified it to test whether it too can detect inspiratory attenuation. Traditional SSA is also entangled with issues of distinguishing causal from random relationships between blood pressure and heart period and of the optimum choice of data filter settings. We have also tested whether the sequences our modified SSA rejects do behave as random relationships and show the limitations of the absence of filter standardization. SSA was performed on eupneic data from 1 h periods in 20 healthy subjects. Applying SSA traditionally produced a mean BRS of 23 ± 3 ms mmHg(-1). After modification to measure breathing, SSA detected significant inspiratory attenuation (11 ± 1 ms mmHg(-1)), and the mean expiratory BRS was significantly higher (26 ± 5 ms mmHg(-1)). Traditional SSA therefore underestimates BRS by an amount (3 ms mmHg(-1)) as big as the major physiological and clinical factors known to alter BRS. We show that the sequences rejected by SSA do behave like random associations between pressure and period. We also show the minimal effect of the r(2) filter and the biases that some pressure and heart period filters can introduce. We discuss whether SSA might be improved by standardization of filter settings and by also measuring breathing.

Factors influencing differences between invasive and spontaneous baroreflex estimates: distinct methods or different data?

Currently invasive BRS estimates are obtained with drug-induced data assuming a sigmoidal SBP-RR relationship, while spontaneous BRS estimates are obtained with non-sigmoidal estimators. In particular, the events (sequences) technique provides a spontaneous BRS estimate based on baroreflex events, BEs (baroreflex sequences, BSs). In this work, BRS estimates are compared considering that can be obtained with different estimators and evaluated in different conditions. All BRS estimates were found to be significantly correlated. In comparison with BS estimates, BE estimates from spontaneous data exhibited higher correlation with sigmoidal estimates and their differences were associated with differences in SBP levels from invasive to spontaneous condition. BE estimator evaluated in different conditions decreased the differences between BRS estimates, pointing out differences due to the use of distinct methods, and such differences were correlated with differences in SBP and RR levels from invasive to spontaneous conditions. Finally, sigmoid estimates were more correlated with BE estimates in invasive data in comparison with those evaluated from BS. In conclusion, BRS analysis from BEs provides an estimate that exhibits higher correlation and lower differences between BRS estimates from different conditions, and reflects properly the BRS physiology.

Changes in autonomic balance in patients with decompensated chronic heart failure

OBJECTIVE

In chronic heart failure (CHF) episodes of decompensation may be linked to derangements within cardiovascular reflex control. We investigated changes in autonomic tone in patients with decompensated CHF.

METHODS

We examined 17 patients with decompensated CHF (14 men, age 62 ± 2 years, LVEF 32 ± 3%) on admission and after clinical stabilization. Control group consisted of 9 patients (8 men, age 64 ± 7 years, LVEF 30 ± 7%) with stable CHF. Assessment of autonomic tone was based on 5-min ECG and blood pressure recordings using time and frequency domains of heart rate variability (HRV) and a sequence method to derive baroreflex sensitivity (BRS).

RESULTS

On admission, decompensated CHF patients had reduced HRV indices (p < 0.05) and depressed BRS (p < 0.01) as compared to those with stable CHF. After clinical stabilization (4 ± 2 days of treatment) time domain HRV indices and BRS increased (SDNN, 34.4 ± 5.4 vs. 55.8 ± 9.8 ms; RMSSD, 38.4 ± 12.0 vs. 51.1 ± 10.4 ms; BRS, 4.3 ± 0.7 vs. 7.6 ± 1.3 ms/mmHg; all p < 0.01) and became similar to those seen in stable CHF patients. Breathing with oxygen affected autonomic indices neither in decompensated nor in stable CHF patients. Eight patients developed an episode of additional CHF worsening during hospitalization, in whom the third assessment was performed on discharge. Worsening in clinical status was followed by a decrease in HRV and BRS that became similar to those noted on admission.

INTERPRETATION

HRV measures and BRS are severely deranged in the acute phase of CHF decompensation. Clinical stabilization results in an improvement of autonomic indices. However, subsequent clinical worsening adversely affects HRV and BRS.

Genetic influence on baroreflex sensitivity in normotensive young men

BACKGROUND

The dysfunction of baroreflex plays an important role in the pathogenesis of essential hypertension. Recent studies suggest that approximately 40% of the variation in baroreflex sensitivity (BRS) may be accounted for by genetic factors. However, only a few such genetic polymorphisms have been explicitly identified.

METHODS

A total of 182 normotensive young men were included in the study. They were tested for the occurrence of genotypes involving nine polymorphisms in six genes that have a role in the regulation of the cardiovascular system. BRS was calculated from the spontaneous fluctuation of systolic blood pressure (SBP) and heart interval, using a sequence method.

RESULTS

BRS was negatively correlated with body mass index (BMI), SBP, and family history of hypertension. Univariate analysis revealed that BRS is significantly associated with three of the polymorphisms studied. At the polymorphism T-786C in the endothelial nitric oxide (NO) synthase (eNOS) gene, the subjects with TT genotype had lower BRS than subjects carrying either the TC or the CC genotype. At the polymorphism of C-344T in the aldosterone synthase gene (CYP11B2), subjects with the TT genotype had higher BRS as compared to those with CC. At the polymorphism of T-58C in the bradykinin B2 receptor (B2R) gene, subjects with CC genotype had lower BRS as compared to subjects with TT. A multivariable linear regression analysis indicated that 16% of the BRS variation could be explained by these three polymorphisms.

CONCLUSIONS

Baroreflex function plays an important role in regulating blood pressure, both in the short term and in the long term. Three polymorphisms that are associated with the variation in BRS were identified in the eNOS, CYP11B2, and B2R genes, respectively; overall, they accounted for 16% of the BRS variation.

Are baroreflex events detected by invasive and non-invasive techniques coincident?

Cardiac baroreceptor sensitivity, a prognostic indicator for a range of diseases, such as myocardial infarction and stroke, may be estimated from spontaneous fluctuations of arterial blood pressure (BP) and heart rate using sequence analysis. We tested the hypothesis that BP values recorded with the non-invasive Finapres device do not always produce sequences coincident with sequences detected from central BP measurements. Finapres recordings of resting BP in the finger, ascending aorta (Millar catheter-tip transducer) and ECG were obtained from 34 patients undergoing coronary angioplasty, including 24 patients treated with betablockers. Coincidence of baroreflex sensitivity (BRS) sequences was expressed by the sensitivity of the Finapres to detect a simultaneously occurring sequence in aortic pressure. The influence of different criteria to detect and accept sequences from beat-to-beat values of systolic BP (SBP) and cardiac interval (RRi) on the Finapres sensitivity was also assessed. The Finapres was able to detect 70.7% of all three beat intra-arterial sequences when the selection criteria was based on the correlation coefficient between SBP and RRi (>0.85), but decreased to 27.5% when the P-value of the linear regression was limited to 0.05. Changing the thresholds for minimum changes in SBP and RRi also had significant effects on sensitivity, as well as in the corresponding values of BRS. Significant differences in BRS were obtained between invasive and non-invasive estimates, but there was no difference between non-invasive estimates calculated from coincident and non-coincident sequences. Non-invasive, compared with intra-arterial estimates of BRS by sequence analysis are not influenced by coincidence of sequences if acceptance of sequences is based on the correlation coefficient criteria (>0.85).

Childhood acute lymphoblastic leukemia

As cure rates in childhood acute lymphoblastic leukemia reach 80%, emphasis is increasingly placed on the accurate identification of drug-resistant cases, the elucidation of the mechanisms involved in drug resistance and the development of new therapeutic strategies targeted toward the pivotal molecular lesions. Pharmacodynamic and pharmacogenomic studies have provided rational criteria for individualizing therapy to enhance efficacy and reduce acute toxicity and late sequelae. Currently, assessment of the early response to treatment by measurement of minimal residual disease (MRD) is the most powerful independent prognostic indicator. MRD is affected by both the drug sensitivity of leukemic cells and the pharmacodynamic and pharmacogenetic properties of the host cells. Rapid advances in biotechnology and bioinformatics should ultimately facilitate the development of molecular diagnostic assays that can be used to optimize antileukemic therapy and elucidate the mechanisms of leukemogenesis. In the interim, prospective clinical trials have provided valuable clues that are further increasing the cure rate of childhood acute lymphoblastic leukemia.