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C Cogliati

Publications and source records attributed to C Cogliati.

At least 19 recordsLinked to original sources
PubMed2004

Automatic classification of interference patterns in driven event series: application to single sympathetic neuron discharge forced by mechanical ventilation.

This study proposes a method for the automatic classification of nonlinear interactions between a strictly periodical event series modelling the activity of an exogenous oscillator working at a fixed and well-known rate and an event series modelling the activity of a self-sustained oscillator forced by the exogenous one. The method is based on a combination of several well-known tools (probability density function of the cyclic relative phase, probability density function of the count of forced events per forcing cycle, conditional entropy of the cyclic relative phase sequence and a surrogate data approach). Classification is reached via a sequence of easily applicable decision rules, thus rendering classification virtually user-independent and fully reproducible. The method classifies four types of dynamics: full uncoupling, quasiperiodicity, phase locking and aperiodicity. In the case of phase locking, the coupling ratio (i.e. n: m) and the strength of the coupling are calculated. The method, validated on simulations of simple and complex phase-locking dynamics corrupted by different levels of noise, is applied to data derived from one anesthetized and artificially ventilated rat to classify the nonlinear interactions between mechanical ventilation and: (1) the discharges of two (contemporaneously recorded) single postganglionic sympathetic neurons innervating the caudal ventral artery in the tail and (2) arterial blood pressure. Under central apnea, the activity of the underlying sympathetic oscillators is perturbed by means of five different lung inflation rates (0.58, 0.64, 0.76, 0.95, 1.99 Hz). While ventilation and arterial pressure are fully uncoupled, ventilation is capable of phase locking sympathetic discharges, thus producing 40% of phase-locked patterns (one case of 2:5, 1:1, 3:2 and 2:2) and 40% of aperiodic dynamics. In the case of phase-locked patterns, the coupling strength is low, thus demonstrating that this pattern is sliding. Non-stationary interactions are observed in 20% of cases. The two discharges behave differently, suggesting the presence of a population of sympathetic oscillators working at different frequencies.

Adrenergic Fibers↗
PubMed2001

Sympathetic rhythms and cardiovascular oscillations.

Spectral analysis of heart rate and arterial pressure variabilities is a powerful noninvasive tool, which is increasingly used to infer alterations of cardiovascular autonomic regulation in a variety of physiological and pathophysiological conditions, such as hypertension, myocardial infarction and congestive heart failure. A most important methodological issue to properly interpret the results obtained by the spectral analysis of cardiovascular variability signals is represented by the attribution of neurophysiological correlates to these spectral components. In this regard, recent applications of spectral techniques to the evaluation of the oscillatory properties of sympathetic efferent activity in animals, as well as in humans, offer a new approach to a better understanding of the relationship between cardiovascular oscillations and autonomic regulation.

Blood Pressure↗
PubMed2001

[Spectral analysis of muscle sympathetic nerve activity in man].

Recent applications of frequency domain analysis to the variability of muscle sympathetic nerve activity (MSNA) have improved the comprehension of the relationship between cardiovascular oscillations and the autonomic nervous system. It has been observed that spectral analysis of MSNA is characterized by two major oscillatory components at low (LF) and high (HF) frequencies, similar to those detectable in the variability of cardiovascular signals. Pharmacological and non-pharmacological studies have shown that, at least within the physiological range, the two MSNA rhythms show a reciprocal behavior, similar to that already observed for cardiovascular oscillations. The oscillatory pattern of MSNA provides non-redundant but complementary information with respect to the time domain measures of MSNA (burst rate and amplitude) since it has been shown that completely different spectral profiles may be derived from various MSNA recordings. On the other hand, the latter are instead comparable in terms of mass activity. Due to the intrinsic characteristics of the signal, which represents the direct outflow of the central neural structures of the cardiovascular autonomic nervous system, this approach can be considered as a unique window over the central organization of excitatory and inhibitory neural mechanisms responsible for the genesis and the regulation of cardiovascular oscillations.

Electrophysiology↗
PubMed2000

Comparison of low-dose dobutamine ventriculography with low-dose dobutamine echocardiography for predicting regional improvement in left ventricular function after coronary artery bypass grafting.

The demonstration of a contractile reserve during low-dose dobutamine echocardiography (LDDE) identifies viable myocardium and predicts recovery of left ventricular (LV) function after myocardial revascularization in patients with chronic coronary artery disease. However, a technically difficult transthoracic visualization may limit the use of LDDE, thus requiring an alternative diagnostic procedure. The present study compares LDDE with low-dose dobutamine ventriculography (LDDV) in predicting an improvement in regional LV function after surgical revascularization. We studied 18 patients with coronary artery disease and LV dysfunction who were to undergo coronary artery bypass grafting. Preoperatively, all patients were evaluated for the presence of viable myocardium using LDDE and LDDV. Follow-up echocardiography at rest and left ventriculography were performed 4 months after successful revascularization to assess recovery of LV function. The sensitivity and specificity of LDDE to identify dysfunctional segments capable of recovering function were 63% and 71%, respectively, with a diagnostic accuracy of 68%. The sensitivity, specificity, and diagnostic accuracy of LDDE improved to 81%, 72%, and 76% when patients with optimal transthoracic evaluation were selected, whereas they were 30%, 77%, and 57%, respectively, in those who underwent suboptimal evaluation. The sensitivity, specificity, and diagnostic accuracy of LDDV were 66%, 75%, and 71%, respectively, with no difference in subgroups of patients. This study demonstrates that LDDV can be considered a useful technique for identifying the presence of myocardial viability and may provide an advantage over LDDE in patients with suboptimal echocardiographic visualization.

Aged↗
PubMed2000

Detection of low- and high-frequency rhythms in the variability of skin sympathetic nerve activity.

Spectral analysis of skin blood flow has demonstrated low-frequency (LF, 0.03-0.15 Hz) and high-frequency (HF, 0.15-0.40 Hz) oscillations, similar to oscillations in R-R interval, systolic pressure, and muscle sympathetic nerve activity (MSNA). It is not known whether the oscillatory profile of skin blood flow is secondary to oscillations in arterial pressure or to oscillations in skin sympathetic nerve activity (SSNA). MSNA and SSNA differ markedly with regard to control mechanisms and morphology. MSNA contains vasoconstrictor fibers directed to muscle vasculature, closely regulated by baroreceptors. SSNA contains both vasomotor and sudomotor fibers, differentially responding to arousals and thermal stimuli. Nevertheless, MSNA and SSNA share certain common characteristics. We tested the hypothesis that LF and HF oscillatory components are evident in SSNA, similar to the oscillatory components present in MSNA. We studied 18 healthy normal subjects and obtained sequential measurements of MSNA and SSNA from the peroneal nerve during supine rest. Measurements were also obtained of the electrocardiogram, beat-by-beat blood pressure (Finapres), and respiration. Spectral analysis showed LF and HF oscillations in MSNA, coherent with similar oscillations in both R-R interval and systolic pressure. The HF oscillation of MSNA was coherent with respiration. Similarly, LF and HF spectral components were evident in SSNA variability, coherent with corresponding variability components of R-R interval and systolic pressure. HF oscillations of SSNA were coherent with respiration. Thus our data suggest that these oscillations may be fundamental characteristics shared by MSNA and SSNA, possibly reflecting common central mechanisms regulating sympathetic outflows subserving different regions and functions.

Adult↗
PubMed2000

Effects of spinal section and of positive-feedback excitatory reflex on sympathetic and heart rate variability.

The sympathetic outflow appears to be capable of displaying a rhythmicity synchronous with cardiovascular Mayer's waves even after spinal section. To test the hypothesis that spinal sympathetic low frequency (LF) oscillation can be enhanced during sympathetic excitation, we recorded cardiac sympathetic nerve activity (SNA), R-R interval, arterial pressure, and ventilation in 9 unanesthetized decerebrate-vagotomized cats before and after C1 spinal section. LF and high frequency (HF) components were detected in the variability of SNA, R-R interval, and systolic arterial pressure both before and after spinal section. In this latter condition, a significant coherence between LF(SNA) and LF(R-R) was present in 5 animals, whereas HF(SNA) and HF(R-R) were correlated in 4 animals. During an excitatory sympathetic spinal reflex elicited by aortic constriction, the efferent sympathetic firing was markedly enhanced (from 7+/-2 to 33+/-7 spikes/s); concomitantly, the powers of both LF(SNA) and HF(SNA) were also increased. Coherence between LF(SNA) and LF(R-R) became significant in all cases, whereas HF(SNA) and HF(R-R) became correlated in 6 animals. In 3 animals, the reflex sympathetic excitation was no longer elicitable after interrupting a vast contingent of sympathetic afferents by means of thoracic dorsal root section. We report for the first time that LF and HF oscillations are detectable in SNA, R-R interval, and systolic arterial pressure variabilities of decerebrate-vagotomized spinal cats and that an excitatory spinal reflex is capable of increasing the power of both SNA spectral components.

Animals↗
PubMed1998

Central vagotonic effects of atropine modulate spectral oscillations of sympathetic nerve activity.

BACKGROUND: Low-dose atropine causes bradycardia either by acting on the sinoatrial node or by its effects on central muscarinic receptors increasing vagal activity. Any central muscarinic effects of high-dose atropine on RR interval are masked by peripheral muscarinic blockade at the sinoatrial node, which causes tachycardia. Effects of central parasympathetic activation on sympathetic activity are not known. METHODS AND RESULTS: Using power spectral analysis of RR interval, intra-arterial blood pressure, respiration, and muscle sympathetic nerve activity (MSNA), we examined the effects of both low (2 microgram/kg IV) and high (15 microgram/kg IV) doses of atropine. After low-dose atropine, RR increased by 9+/-1% (P<0.0001), the low-frequency (LF) component (in normalized units, NU) of RR variability decreased by -32+/-8%, and the high-frequency (HF)NU component increased (+74+/-19%); hence, LF/HF of RR variability fell by 52+/-10% (all P<0.01). Although overall MSNA did not change, LFNU of MSNA decreased (-15+/-5%), HFNU of MSNA increased (+31+/-3%), and LF/HF of MSNA fell (-41+/-8%) (all P<0.01). After high-dose atropine, LFNU of MSNA decreased (-17+/-12%), HFNU of MSNA increased (+22+/-3%), and LF/HF of MSNA fell (-51+/-21%) (all P<0.02). CONCLUSIONS: Increasing central parasympathetic activity with low-dose atropine is associated with an increase in the HF and a decrease in the LF oscillations of both RR interval and MSNA variability. High-dose atropine similarly induces an increase in the HF and a decrease in the LF components of MSNA variability. Thus, central parasympathetic activation is able to modulate the oscillatory characteristics of sympathetic nerve traffic to peripheral blood vessels.

Adult↗
PubMed1998

Altered cardiovascular variability in obstructive sleep apnea.

BACKGROUND: Altered cardiovascular variability is a prognostic indicator for cardiovascular events. Patients with obstructive sleep apnea (OSA) are at an increased risk for cardiovascular disease. We tested the hypothesis that OSA is accompanied by alterations in cardiovascular variability, even in the absence of overt cardiovascular disease. METHODS AND RESULTS: Spectral analysis of variability of muscle sympathetic nerve activity, RR interval, and blood pressure were obtained during undisturbed supine rest in 15 patients with moderate-to-severe OSA, 18 patients with mild OSA, and 16 healthy control subjects in whom sleep disordered breathing was excluded by complete overnight polysomnography. Patients with OSA were newly diagnosed, never treated for OSA, and free of any other known diseases. Patients with moderate-to-severe OSA had shorter RR intervals (793+/-27 ms) and increased sympathetic burst frequency (49+/-4 bursts/min) compared with control subjects (947+/-42 ms; 24+/-3 bursts/min; P=0.008 and P<0.001, respectively). In these patients, total variance of RR was reduced (P=0.01) and spectral analysis of RR variability showed an increase in low frequency normalized units, a decrease in high frequency normalized units, and an increase in the ratio of low to high frequency (all P<0.05). Even though blood pressure was similar to that of the control subjects, blood pressure variance in patients with moderate-to-severe OSA was more than double the variance in control subjects (P=0.01). Patients with mild OSA also had a reduction in RR variance (P=0.02) in the absence of any significant difference in absolute RR interval. For all patients with OSA, linear regression showed a positive correlation (r=0.40; P=0.02) between sleep apnea severity and blood pressure variance. CONCLUSIONS: Cardiovascular variability is altered in patients with OSA. This alteration is evident even in the absence of hypertension, heart failure, or other disease states and may be linked to the severity of OSA. Abnormalities in cardiovascular variability may be implicated in the subsequent development of overt cardiovascular disease in patients with OSA.

Adult↗
PubMed1998

Evidence for a central origin of the low-frequency oscillation in RR-interval variability.

BACKGROUND: Short-term variability of RR interval and blood pressure occurs predominantly at low frequency (LF; approximately 0.1 Hz) and high frequency (approximately 0.25 Hz). The arterial baroreflex is thought to be the predominant determinant of the LF component of RR variability. Patients with severe congestive heart failure (CHF) have an attenuated or absent LF oscillation in RR variability. The left ventricular assist device (LVAD) offers a unique possibility for analysis of spectral oscillations in RR interval independent of any effects of blood pressure that influence these oscillations via the baroreflex. METHODS AND RESULTS: We performed spectral analysis of RR, blood pressure, and respiration in 2 patients with CHF before and after LVAD implantation. LF components of the RR-interval and blood pressure variability were absent in both CHF patients before LVAD implantation. After LVAD implantation, spectral analysis of the RR interval showed restoration of a clear and predominant LF oscillation in the native hearts of both patients, with no such oscillation evident in the blood pressure profile. CONCLUSIONS: During total circulatory support with the LVAD, the LF oscillation in RR interval of the native heart, absent in CHF, is restored. This LF oscillation in RR interval occurs in the absence of LF oscillations in blood pressure and thus is unlikely to be explained by baroreflex mechanisms. Hence, the absence of LF oscillation in the RR interval in CHF is functional and is reversible by LVAD circulation. The presence of a predominant LF oscillation in RR interval independent of any oscillation in blood pressure suggests that the LF oscillation is a fundamental property of central autonomic outflow.

Adult↗
PubMed1998

Myocardial beta-adrenergic and muscarinic receptor density in cardiac pressure or volume overload.

Decreased myocardial beta-adrenergic receptor density has been demonstrated in experimental and clinical models of cardiac disease. Nevertheless, the individual role played by pressure or volume overload in determining the receptor downregulation has never been described in humans. Moreover, no data have been reported about the reversibility of the downregulation after non-pharmacological improvement of cardiac function. In the present study, we measured the myocardial beta-adrenergic and muscarinic receptor density, using an autoradiographic method, in 14 patients with cardiac pressure overload (aortic stenosis) and in five patients with cardiac volume overload (aortic regurgitation). Five patients with aortic stenosis were studied again six months after successful valve replacement. A significant lower density of beta-adrenergic receptors was observed in patients with a chronic pressure overload compared to those with a chronic volume overload (20+/-2 and 28+/-2 fmol/mg protein, respectively P<0.05). No significant differences were found between the two groups regarding beta-adrenoceptor sub-types proportion and muscarinic receptor density. Six months after successful aortic valve replacement, we observed a significant upregulation of the beta-adrenoceptor density (delta 29+/-9 fmol/mg protein P<0.05). In conclusion, these observations indicate that: (a) the type of left ventricle haemodynamic overload may be a quantitative determinant factor in the myocardial beta-adrenoceptor downregulation; (b) the reduction of a pathological cardiac load leads to an upregulation of these receptors.

Adult↗
PubMed1998

Measuring regularity by means of a corrected conditional entropy in sympathetic outflow.

A new method for measuring the regularity of a process over short data sequences is reported. This method is based on the definition of a new function (the corrected conditional entropy) and on the extraction of its minimum. This value is taken as an index in the information domain quantifying the regularity of the process. The corrected conditional entropy is designed to decrease in relation to the regularity of the process (like other estimates of the entropy rate), but it is able to increase when no robust statistic can be performed as a result of a limited amount of available samples. As a consequence of the minimisation procedure, the proposed index is obtained without an a-priori definition of the pattern length (i.e. of the embedding dimension of the reconstructed phase space). The method is validated on simulations and applied to beat-to-beat sequences of the sympathetic discharge obtained from decerebrate artificially ventilated cats. At control, regular, both quasiperiodic and periodic (locked to ventilation) dynamics are observed. During the sympathetic activation induced by inferior vena cava occlusion, the presence of phase-locked patterns and the increase in regularity of the sympathetic discharge evidence an augmented coupling between the sympathetic discharge and ventilation. The reduction of complexity of the neural control obtained by spinalization decreases the regularity in the sympathetic outflow, thus pointing to a weaker coupling between the sympathetic discharge and ventilation.

Animals↗
PubMed1996

Non-linear dynamics and chaotic indices in heart rate variability of normal subjects and heart-transplanted patients.

OBJECTIVES: Heart rate variability (HRV) is characterised by a variety of linear, non-linear, periodical and non-periodical oscillations. The aim of the present study was mainly to investigate the role played by neural mechanisms in determining non-linear and non-periodical components. METHODS: Analysis was performed in 7 recently heart transplanted patients and in 7 controls of similar age whose HRV signal was collected during 24 h. Parameters that quantify non-linear dynamic behaviour, in a time series, were calculated. We first assessed the specific non-linear nature of the time series by a test on surrogate data after Fourier phase randomization. Furthermore, the D2 correlation dimension, K2 Kolmogorov entropy, and H self-similarity exponent of the signal were estimated. From this last parameter, the dimension D = 1/H can be obtained. In order to assess whether the dynamics of the system are compatible with chaotic characteristics, the entire spectrum of Lyapunov exponents was calculated. We used return maps to graphically represent the non-linear and non-periodical behaviours in patients and controls. RESULTS: Surrogate data suggest that the HRV time courses have unique non-linear characteristics. D2, K2 and 1/H parameters were significantly lower in transplanted subjects than in controls. Positivity of the first Lyapunov exponent indicates divergence of trajectories in state-space. Furthermore, the display of return maps on projections obtained after Singular Value Decomposition, especially in low-complexity data (as in transplanted patients), shows a structure which is suggestive of a strange attractor. These findings support the hypothesis that chaotic dynamics underlie HRV. CONCLUSION: These results indicate that non-linear dynamics are likely to be present in HRV control mechanisms, giving rise to complex and qualitatively different behaviours. System complexity decreases in transplanted patients and this may be related to loss of the neural modulation of heart rate.

Adult↗
PubMed1995

Sympathetic predominance followed by functional denervation in the progression of chronic heart failure.

Using spectral analysis of heart rate and systolic arterial pressure variabilities, the study was set up to evaluate cardiovascular efferent autonomic modulation in patients with different degrees of chronic heart failure. We studied 30 patients with stable chronic heart failure and 15 controls of similar age. ECG, arterial blood pressure and respiratory signal were recorded at rest, during controlled respiration and during passive head-up tilting. R-R interval periods of 256-512 were analysed. Routine 2D echocardiogram and Doppler studies were also carried out. As expected, we found a decrease in the mean and variance of R-R intervals in patients with sever heart failure. In New York Heart Association (NYHA) class II patients, the power spectral pattern of R-R variability was characterized by the predominance of the low frequency component (72 +/- 3 nu), considered a marker of sympathetic activity, and by its unresponsiveness to tilting. Patients in NYHA class III also presented blunted changes in spectral components during tilting. A drastic decrease in the variance of R-R intervals (191 +/- 58 vs 1056 +/- 149 ms2 in controls) and an almost complete absence of the low frequency spectral component (8 +/- 3 nu) were present in patients in NYHA class IV. Controlled respiration, which in normal subjects decreased the low frequency component, induced changes that blunted progressively as heart failure increased. These data suggest that autonomic neural modulation and cardiovascular response to neural activity differ at different stages of the disease.

Analysis of Variance↗
PubMed1994

Influences of neural mechanisms on heart period and arterial pressure variabilities in quadriplegic patients.

The heart period (R-R) variability power spectrum presents two components, at low (LF; approximately 0.10 Hz) and high (approximately 0.25 Hz) frequencies, whose reciprocal powers appear to furnish an index of sympathovagal interaction modulating heart rate. In addition, the LF component of the systolic arterial pressure variability spectrum furnishes a marker of sympathetic modulation of vasomotor activity. The contribution of spinal and supraspinal neural circuits to the genesis of these rhythmic oscillatory components remains largely unsettled. Therefore we performed spectral analysis of R-R and systolic arterial pressure variabilities in 15 chronic neurologically complete quadriplegic patients (QP) and in 15 control subjects during resting conditions, controlled respiration, and head-up tilt. At rest, in seven QP the LF component was undetectable in both cardiovascular variability spectra; in two QP this component was present only in R-R variability spectrum, whereas the remaining six showed a significantly reduced LF in both signals. In QP, the LF component, when present, underwent paradoxical changes with respect to controls, decreasing during tilt and increasing during controlled respiration. In five QP in whom the recording session was repeated after 6 mo, a significant increase in LF was observed in both variability spectra. These data confirm the finding that a disconnection of sympathetic outflow from supraspinal centers can cause the disappearance of the LF spectral component. However, LF presence in some QP supports the hypothesis of a spinal rhythmicity likely to be modulated by the afferent sympathetic activity.

Adolescent↗