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Biomedical subjects

S Guzzetti

Publications and source records attributed to S Guzzetti.

At least 19 recordsLinked to original sources
PubMed2001

Heart rate variability in chronic heart failure.

The analysis of heart rate variability (HRV) provides information about autonomic cardiovascular control in healthy subjects. In the past 15 years, several articles have been published regarding HRV and chronic heart failure (CHF). The results of these papers substantially demonstrated that HRV is significantly different in CHF patients compared to controls. Moreover, some variables derived from HRV analysis showed significant independent prognostic capacity. In particular, the reduction of variance (expressed as SDNN) and low-frequency spectral component of HRV (ranging from 0.03 to 0.15 Hz) seem related to an increased mortality in CHF. Nevertheless, these variables are not yet considered in clinical practice. A better understanding of the physiopathological basis of the reported alterations of HRV in CHF patients is required in order to permit its use as a clinical tool for prognosis and tailored therapy in individual CHF patients.

Chronic Disease↗
PubMed2001

Entropy, entropy rate, and pattern classification as tools to typify complexity in short heart period variability series.

An integrated approach to the complexity analysis of short heart period variability series (approximately 300 cardiac beats) is proposed and applied to healthy subjects during the sympathetic activation induced by head-up tilt and during the driving action produced by controlled respiration (10, 15, and 20 breaths/min, CR10, CR15, and CR20 respectively). The approach relies on: 1) the calculation of Shannon entropy (SE) of the distribution of patterns lasting three beats; 2) the calculation of a regularity index based on an entropy rate (i.e., the conditional entropy); 3) the classification of frequent deterministic patterns (FDPs) lasting three beats. A redundancy reduction criterion is proposed to group FDPs in four categories according to the number and type or of heart period changes: a) no variation (0V); b) one variation (1V); and c) two like variations (2LV); 4) two unlike variations (2UV). We found that: 1) the SE decreased during tilt due to the increased percentage of missing patterns; 2) the regularity index increased during tilt and CR10 as patterns followed each other according to a more repetitive scheme; and 3) during CR10, SE and regularity index were not redundant as the regularity index significantly decreased while SE remained unchanged. Concerning pattern analysis we found that: a) at rest mainly three classes (0V, 1V, and 2LV) were detected; b) 0V patterns were more likely during tilt; c) 1V and 2LV patterns were more frequent during CR10; and d) 2UV patterns were more likely during CR20. The proposed approach based on quantification of complexity allows a full characterization of heart period dynamics and the identification of experimental conditions known to differently perturb cardiovascular regulation.

Analysis of Variance↗
PubMed2001

[Heart rate variability].

In 1981 a study on heart rate variability (HRV) and on the neural control of the heart was published in Science. Since then, the number of papers concerning this topic has increased exponentially. Some aspects of the relationship between HRV and the neural control of the cardiovascular system are now clear, for example: a decreased SDNN (a measure of variance) during a period of 24 hours is a well established independent negative prognostic factor after acute myocardial infarction and in chronic heart failure patients. Moreover, an increased sympathetic modulation elicited by standard laboratory maneuvers determines an increased power of the low frequency (LF) spectral component (0.03-0.15 Hz), expressed in normalized units. Nevertheless, the interpretation of the oscillatory components present in HRV, particularly in pathophysiological conditions, is far from being clear. The influence of several neurohumoral circuits can induce various changes in HRV according to different physiological or pathological conditions. A new approach to the study of HRV called "information domain" might help to obtain some more information about HRV. Furthermore, in the future, HRV analysis might be useful when deciding on the best pharmacological combination for the individual patient and for the probabilistic prediction of acute cardiac events.

Heart Rate↗
PubMed2000

Linear and non-linear 24 h heart rate variability in chronic heart failure.

It has recently been demonstrated that SDNN of heart rate variability (HRV) is a useful independent prognostic tool in chronic heart failure (CHF). The purpose of the present study was to evaluate if spectral and non-linear analysis of 24-h HRV, considered markers of autonomic cardiac modulation, contain independent prognostic information in CHF patients. Twenty normal subjects and thirty consecutive outpatients with clinically stable CHF were studied for 2 years. Periods of 300 R-R intervals were analyzed from Holter recordings. The power spectral analysis, the slope of the linear relationship between log-power versus log-frequency (1/f), and the complexity content (using corrected conditional entropy; CCE) of the R-R series were calculated. The normalized power of the low frequency spectral component (LF) and the 1/f slope were significantly lower in patients compared to controls (respectively 30.1 +/- 3.0 vs. 48.6 +/- 3.4 and -1.27 +/- 0.04 vs. -1.08 +/- 0.05; P < 0.05). Moreover, the patients who died during the study presented a reduced LF (20.9 +/- 4.1 vs. 35.5 +/- 3.5 nu; P < 0.05) and a steeper 1/f slope (-1.40 +/- 0.09 vs. -1.21 +/- 0.04 nuts, P < 0.05) compared to survivors. These results remained significant in a logistic model including heart rate and SDNN. The information content present in spectral and non-linear analysis of HRV in CHF patients has prognostic relevance independently from the time domain measures of HRV. In particular, the reduction of LF power seems the best indicator among those considered.

Aged↗
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

Information domain analysis of cardiovascular variability signals: evaluation of regularity, synchronisation and co-ordination.

A unifying general approach to measure regularity, synchronisation and co-ordination is proposed. This approach is based on conditional entropy and is specifically designed to deal with a small amount of data (a few hundred samples). Quantitative and reliable indexes of regularity, synchronisation and co-ordination (ranging from 0 to 1) are derived in a domain (i.e. the information domain) different from time and frequency domains. The method is applied to evaluate regularity, synchronisation and co-ordination among cardiovascular beat-to-beat variability signals during sympathetic activation induced by head-up tilt (T), during the perturbing action produced by controlled respiration at 10, 15 and 20 breaths/min (CR10, CR15 and CR20), and after peripheral muscarinic blockade provoked by the administration of low and high doses of atropine (LD and HD). It is found that: (1) regularity of the RR interval series is around 0.209; (2) this increases during T, CR10 and HD; (3) the systolic arterial pressure (SAP) series is more regular (0.406) and its regularity is not affected by the specified experimental conditions; (4) the muscle sympathetic (MS) series is a complex signal (0.093) and its regularity is not influenced by HD and LD; (5) the RR interval and SAP series are significantly, though weakly, synchronised (0.093) and their coupling increases during T, CR10 and CR15; (6) the RR interval and respiration are coupled (0.152) and their coupling increases during CR10; (7) SAP and respiration are significantly synchronised (0.108) and synchronisation increases during CR10; (8) MS and respiration are uncoupled and become coupled (0.119) after HD; (9) the RR interval, SAP and respiration are significantly co-ordinated (0.118) and co-ordination increases during CR10 and CR15; (10) during HD the co-ordination among SAP, MS and the respiratory signal is larger than that among the RR interval, SAP, MS and the respiratory signal, thus indicating that the RR interval contributes towards reducing co-ordination.

Atropine↗
PubMed2000

Absence of sympathetic overactivity in Afro-Caribbean hypertensive subjects studied by heart rate variability.

Black hypertensives present a greater prevalence of left ventricular hypertrophy and an increased mortality compared to white hypertensives. Differences in sympathetic activity might contribute to explain these racial differences in hypertension. Nevertheless, previous laboratory studies did not show any increase of sympathetic activity direct to the heart in black subjects. The aim of the present study was to investigate the cardiac sympatho-vagal balance in black and white hypertensives analysing heart rate variability, during the entire 24 h. We analysed Holter recordings of 52 essential hypertensive patients, who had never received antihypertensive treatment, 26 of whom were black and 26 were white. Consecutive series of 300 beats, with 150 beats overlapped (approximately 600 series/day), were considered for the analysis in time and frequency domain. The mean 24-h value of the power of the low frequency spectral component (0.04-0.15 Hz), expressed in normalised units, ie a marker of sympathetic modulation, was significantly lower in the group of black patients compared to whites (respectively 40.0 +/- 2.1 vs 53.6 +/- 3.6 nu, P < 0.01). Similar results were observed for the LF/HF ratio, an index of the sympatho-vagal balance (respectively 4.11 +/- 0.58 vs 5.98 +/- 0.79; P < 0.05). In a multiple linear regression analysis, considering diastolic blood pressure, left ventricular mass index, race and age as independent variables, only race (P < 0.002) and age (P < 0.01) could independently predict the normalised low frequency power or the LF/HF ratio, as dependent variables. The results of this study suggest some blunting of the cardiac sympathetic neural modulation in black hypertensives compared to white hypertensives, during the entire 24 h.

Adult↗
PubMed2000

Prediction of short cardiovascular variability signals based on conditional distribution.

A new approach measuring the predictability of a process is proposed. The predictor is defined as the median of the distribution conditioned by a sequence of L - 1 previous samples (i.e., a pattern). A function referred to as the corrected mean squared predictor error is defined to prevent the perfect adequacy to the data (i.e., the decrease to zero of the prediction error), thus avoiding to divide the whole set of data in learning and test sets. This function exhibits a minimum and this minimum is taken as a measure of predictability of the series. The use of the minimization procedure avoids to fix a priori the pattern length L. This approach permits one a reliable measure of predictability on short data sequences (around 300 samples). Moreover, this method, in connection with a surrogate data approach, is useful to detect nonlinear dynamics. The analysis indicates that, in simulated and real data, predictability and nonlinearity measures provide different information. The application of this approach to the analysis of cardiovascular variability series of the heart period (RR interval) and systolic arterial pressure (SAP) shows: 1) SAP series is more predictable than RR interval series; 2) predictability of the RR interval series is larger during tilt, during controlled respiration at 10 breaths/min (bpm) and after high-dose administration of atropine; 3) SAP series is dominated by linear correlation; 4) RR interval series exhibits nonlinear dynamics during controlled respiration at 10 bpm and after low-dose administration of atropine, while it is linear during sympathetic activation produced by tilt and after peripheral parasympathetic blockade caused by high-dose administration of atropine.

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↗
PubMed1997

Individual recognition by heart rate variability of two different autonomic profiles related to posture.

BACKGROUND: Power spectrum analysis of heart rate variability (HRV) can estimate the state of sympathovagal balance modulating sinus node activity. In view of the large distribution of spectral variables, a recognition of well-defined physiological conditions has never been attempted on an individual basis. METHODS AND RESULTS: We considered 10 spectral variables extracted from short segments (200 to 500 cardiac cycles) of 350 ECG tracings recorded in normal subjects in both supine and upright positions (700 patterns). The tracings were first ordered consecutively and subsequently assigned alternatively to a training or to a test set (each consisting of 175 cases, providing 350 patterns considered to be independent). A forecasting linear method estimated a normalized activation index (ranging from -1 for supine to +1 for upright) that concentrated the information derived from spectral variables and that identified, in the test set, individual by individual, approximately 84% of corresponding body postures. CONCLUSIONS: The combined use of spectral methodology and forecasting analysis has revealed an information content embedded, per se, in a short series of RR intervals capable of recognizing, individual by individual, two different autonomic profiles related to posture.

Adolescent↗
PubMed1996

Myocardial beta adrenoceptors and left ventricular function in hypertrophic cardiomyopathy.

OBJECTIVE: To assess the relation between left ventricular function and myocardial beta adrenoceptor density. METHODS: 17 patients with hypertrophic cardiomyopathy, six with and 11 without heart failure, were studied. Left ventricular function was assessed by echocardiography, and myocardial beta adrenoceptors by positron emission tomography. Patient data were compared with those obtained in normal controls. RESULTS: Myocardial beta adrenoceptor density in the 17 patients was 7.00 (SD 1.90) pmol/g v 11.50 (2.18) pmol/g in normal controls (P < 0.01). beta Adrenoceptor density in the six patients with left ventricular failure was 5.61 (0.88) pmol/g v 7.71 (1.86) pmol/g in the 11 patients with normal ventricular function (P < 0.05), and there was a significant correlation (r = 0.52; P < 0.05) between left ventricular fractional shortening and myocardial beta adrenoceptor density. A positive correlation (r = 0.51; P < 0.05) was also found between myocardial beta adrenoceptor density and the E/A transmitral flow ratio, an index of left ventricular diastolic function. CONCLUSIONS: There is myocardial beta adrenoceptor downregulation in patients with hypertrophic cardiomyopathy with or without signs of heart failure.

Adult↗
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↗
PubMed1995

Acute hepatic and renal failure caused by Pneumocystis carinii in patients with AIDS.

Clinical and pathological findings are described in two AIDS patients with Pneumocystis carinii infection who received prophylactic treatment with nebulised pentamidine and developed unusual hepatic and renal failure. Histological examination showed clumps of P carinii massively obstructing hepatic sinuses and portal vessels in the first patient, and merular and intertubular capillaries in the second. These findings could explain the unusual clinical features, characterised by acute hepatic and renal failure.

AIDS-Related Opportunistic Infections↗
PubMed1995

A circadian perspective on myocardial ischaemia.

The non-uniform occurrence of myocardial ischaemia, with a trough at night and a peak in the morning, is at the base of the concept of a circadian distribution of coronary events. Cardiovascular variables known to influence the occurrence of ischaemia have similar rhythms, and a likely culprit could be hidden among them. Nevertheless, in many cases an identifiable trigger is lacking and the prediction of ischaemia is still elusive.

Autonomic Nervous System↗
PubMed1994

Surgical timing in aortic regurgitation: left ventricular function analysis by contractility score.

In 32 patients with aortic regurgitation, angiographic evaluation of global left ventricular performance before and after aortic valve replacement was carried out by means of a computer-analyzed contractility scoring system. A strong correlation was detected between the preoperative and postoperative contractility score. Postoperatively, the score decreased in all but 3 patients, becoming normal or near normal in 21 of 27 patients whose preoperative value had been less than 40. However, all 5 patients with a preoperative contractility score of 40 or greater exhibited a persistently elevated score after operation that indicated the presence of irreversible contractile dysfunction. Patients in groups A and B (preoperative score, 0 to 40) experienced a good surgical outcome, and at 5-year follow-up were in New York Heart Association functional class I. Patients in group C (preoperative score, > 40) altogether had a very poor surgical outcome, although they did experience a short to midterm period of symptomatic relief. It is important to offer aortic valve replacement to patients with aortic regurgitation before their chances for a good functional result are lost. The computer-analyzed contractility score may be a useful index for determining the optimal timing of operation in these patients, particularly those who show features consistent with impaired left ventricular function but are asymptomatic and who should undergo aortic valve replacement before symptoms of definitive left ventricular failure develop.

Adult↗