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Biomedical subjects

S Cerutti

Publications and source records attributed to S Cerutti.

At least 127 records · Page 7Linked to original sources
PubMed1990

Effects of tilt and exercise on signal-averaged electrocardiogram after acute myocardial infarction.

To determine whether enhanced sympathetic activity could alter a non-invasive index of cardiac instability, we analysed the effects of 90 degrees head-up tilt and submaximal exercise stress test on high amplification signal-averaged electrocardiogram in 64 patients after acute myocardial infarction. At rest, ventricular late potentials were detected in 25% of patients, characterized by a significant prolongation of filtered QRS complex (137 +/- 3 vs 115 +/- 2 ms) and of its components smaller than 40 microV (38 +/- 2 vs 16 +/- 1 ms), as well as by a reduced root mean square voltage calculated for the terminal 40 ms of QRS complex (RMS40 voltage) (19 +/- 1 vs 75 +/- 9 microV) in comparison to patients without micropotentials. Sympathetic activation induced by tilt caused a significant increase in heart rate (from 67 +/- 3 to 79 +/- 3 beats min-1) but did not modify either the incidence of ventricular late potentials or the values of any of the signal-averaged electrocardiogram parameters considered. In 19 patients, recordings were also obtained during a submaximal bicycle exercise stress test at a heart rate of 114 +/- 4 beats min-1 and with systolic arterial blood pressure at 153 +/- 6 mmHg. No effect on signal-averaged electrocardiogram parameters was detectable during this experimental intervention. These data indicate that after myocardial infarction, sympathetic activation does not seem to modify signal-averaged electrocardiogram parameters.

Electrocardiography↗
PubMed1990

Analysis of short-term oscillations of R-R and arterial pressure in conscious dogs.

We studied the neural determinants of the second (i.e., high frequency, HF)- and third-order (i.e., low frequency, LF) spontaneous oscillations of heart period (R-R interval) and arterial pressure (AP) in conscious dogs, with the hypothesis that they might furnish quantitative markers of autonomic controlling activities. Spectral analysis of simultaneous R-R and AP variabilities quantified these oscillations that were also evaluated in units normalized by total power to focus on the balance of these two major components. At rest we observed a prevalent HF component (approximately 0.25 Hz) in R-R and AP variabilities that was synchronous with respiration. This HF component of R-R variability disappeared after atropine infusion and can be considered a marker mostly of vagal activity. When baroreceptor unloading, obtained by moderate hypotension, increased sympathetic activity the LF component increased in R-R, systolic, and diastolic AP variabilities. This increase in LF was not present after ganglionic blockade or after chronic arterial baroreceptor denervation. After chronic bilateral stellectomy, hypotension was not accompanied by an increase in LF component of R-R variability, while LF component remained in AP variability. An increase in LF component of R-R and AP variabilities was observed during transient coronary artery occlusion.

Animals↗
PubMed1990

Continuous 24-hour assessment of the neural regulation of systemic arterial pressure and RR variabilities in ambulant subjects.

In this study, we tested the hypothesis that the neural control of circulation in humans undergoes continuous but in part predictable changes throughout the day and night. Dynamic 24-hour recordings were obtained in two groups of ambulant subjects. In 18 hospitalized patients free to move, direct high-fidelity arterial pressures and electrocardiograms were recorded, and in an additional 28 nonhospitalized subjects, only electrocardiograms were obtained. Spectral analysis of systolic arterial pressure and of RR interval variabilities provided quantitative markers of sympathetic and vagal control of the sinus node and of sympathetic modulation of vasomotor tone. With this approach, the low-frequency (approximately 0.1 Hz) component of RR interval and systolic arterial pressure variabilities is considered a marker primarily of sympathetic activity, whereas the high-frequency (approximately 0.25 Hz) component of RR interval variability, related to respiration, seems to be a marker primarily of vagal activity. We observed a pronounced and consistent reduction in the markers of sympathetic activity and an increase in those of vagal activity during the night. In the invasive studies, while the subjects were still lying in bed after waking up, the markers of sympathetic activity rose rapidly and concomitantly with a simultaneous vagal withdrawal. Noninvasive studies confirmed the early morning rise of the markers of sympathetic activity and the circadian pattern of sympathovagal balance. These data indicate that the ominously increased rate of cardiovascular events in the morning hours may reflect the sudden rise of sympathetic activity and the reduction of vagal tone.

Blood Pressure↗
PubMed1989

Compressed spectral arrays for the analysis of 24-hr heart rate variability signal: enhancement of parameters and data reduction.

Heart rate variability signal in the form of an R-R interval tachogram is detected in Holter type 24-hr ECG recordings. Spectral analysis is carried out over consecutive nonoverlapping records, and the information is displayed in the form of a compressed spectral array through parametric techniques. The trends of spectral parameters such as low-frequency (LF) and high-frequency (HF) powers and central frequencies are also plotted, together with the classical mean R-R value and variance relative to each single spectrum. These parameters quantify the effect of sympatho-vagal balance on heart rate control during the 24-hr period and provide important elements for the diagnostic evaluation of various pathologies, like hypertension. A spectral compression algorithm which checks the position of the poles relative to LF and HF bands inside the unitary circle in the complex zeta-plane is also developed. Applications of this procedure are foreseen in the clinical evaluation of ambulant patients as well as in the study of physical and psychological stress.

Algorithms↗
PubMed1989

The implementation of an autoregressive model with exogenous input in a single sweep visual evoked potential analysis.

Based on a model of signal-noise interaction, we present a method for single-sweep analysis of Visual Evoked Potentials. The EEG is represented as an autoregressive process and the single-sweep VEP as a filtered version of a reference signal taken as the running average of 20 consecutive sweeps. The algorithm for model identification and filtering is an ARX (AutoRegressive with eXogenous input) which provides a fast and efficient solution by means of a least squares approach. The choice of reference signal, as well as the complexity of the model, is also discussed. A further advantage of this approach is parameter reduction: all the single-sweep information is contained in 18 model coefficients and the reference signal.

Evoked Potentials, Visual↗
PubMed1989

Spectral analysis of antepartum heart rate variability.

The present paper illustrates the basic methodological aspects of the power spectral analysis applied to fetal ECG starting from a gestational age around the 25th week of gestation until term. An abdominal ECG signal is recorded and fetal and maternal QRSs are recognised through selective digital filtering and averaging techniques. Power Spectral Density (PSD) of the discrete R-R series is then calculated through an autoregressive (AR) technique. In analogy with what happens in adult human subjects, fetuses manifest variability in correspondence to particular bands in the spectrum which are sensitive to the sympatho-vagal balance which controls many cardiovascular functions and respiration in different physiological conditions. Such a method is easily implemented on a personal computer and may be used to asses the development of the autonomic nervous system in fetuses as well as to show the physiopathological reasons which perturbate the relevant control mechanisms.

Cardiotocography↗
PubMed1989

Power spectral analysis of the heart rate of the human fetus at 26 and 36 weeks of gestation.

The fetal electrocardiogram (ECG) was recorded from the maternal abdomen together with sonographic detection of fetal states in four pregnant patients at 26 and 36 weeks of gestation. Computerised algorithms obtained a good recognition of maternal ECG and fetal ECG. The corresponding power spectral density (PSD) was estimated during epochs of quiet or breathing movements for 256 consecutive heart beats. At 36 weeks of gestation the PSD analysis showed heart rate variability components similar to an adult heart. A low frequency component was observed together with a high frequency component in the range of fetal breathing movements. This high frequency component (0.6 - 0.9 Hz) disappeared from the PSD analysis during epochs of apnea. To our knowledge this is the first demonstration of such a mechanism in the human fetus in utero. At 26 weeks no respiratory component was observed in the PSD analysis. The maturation of control mechanisms could be responsible for this difference.

Electrocardiography↗
PubMed1989

Spectral analysis of R-R and arterial pressure variabilities to assess sympatho-vagal interaction during mental stress in humans.

We tested the hypothesis that spectral analysis of the R-R interval and systolic arterial pressure variabilities allows assessment of the dynamic changes in neural control of the cardiovascular system in men undergoing mental stress testing. Mental arithmetic increased the low-frequency components of R-R and systolic arterial pressure, i.e. markers of sympathetic activity to the SA node and the vasculature, respectively; it also decreased the high frequency component of R-R variability, a marker of vagal activity. Spectral analysis of R-R and systolic arterial pressure variabilities may be used in the clinic to test the dynamic effects of mental stress on both sympathetic and vagal activities.

Adult↗
PubMed1989

Circadian changes in vascular sympathetic activity in ambulant subjects.

In 10 ambulant subjects we studied the circadian changes in sympathetic vasomotor control as assessed by the spectral power of the 0.1-Hz low-frequency component of systolic arterial pressure variability measured with a Millar phi 3F tip transducer. The low-frequency component was higher during the daytime, while the subjects were performing light physical activity, and lower during the night, thus paralleling the circadian systolic blood pressure pattern. However, the morning low-frequency rise preceded the blood pressure increase by about 3 h, suggesting that vasometer control and blood pressure control are at least partly related to different mechanisms.

Adult↗
PubMed1988

Parameter extraction from heart rate and arterial blood pressure variability signals in dogs for the validation of a physiological model.

The paper describes an automatic procedure for improving the extraction of parameters in heart rate (HR) and arterial blood pressure (ABP) beat-to-beat variability signals. Auto- and cross-spectral analysis of such signals is carried out through parametric models and the distribution of the power of the spectra and the phase relationships are compared in various physiological situations induced in the dogs via drug infusion or surgical interventions which do influence the control mechanisms of HR and ABP. This "black-box" approach allows the obtention, directly from the processing of the above-mentioned signals, of the estimation of parameters relative to cardiovascular models, as the ones described by simple equations (Windkessel and Starling laws are introduced as examples). These parameters seem to validate significantly the capability of such models to describe the physiological interactions existing between the two considered signals. Applications may be foreseen both for research and clinical purposes.

Algorithms↗
PubMed1988

Spectral analysis of heart rate variability in the assessment of autonomic diabetic neuropathy.

We studied heart rate variability in 49 uncomplicated diabetics (27 with insulin therapy; 22 with oral hypoglycemic agents) and in 40 age-matched controls. An automatic autoregressive algorithm was used to compute the power spectral density (PSD) of beat by beat RR variability derived from the surface ECG. The PSD contains two major components (a low frequency approximately 0.1 Hz (LF) and a high frequency, respiratory linked, approximately 0.25 Hz (HF] that provide, respectively, quantitative markers of sympathetic and vagal modulatory activities and of their balance. As compared to controls, in diabetics, besides a reduced RR variance at rest (2722 +/- 300 and 1436 +/- 241 ms2, respectively), we observed during passive tilt an altered response of spectral indices of sympathetic activation and vagal withdrawal, suggestive of a complex modification in the neural control activities. In addition, we compared this approach to the commonly used clinical tests score, and observed that the latter provides overall results similar to those obtained with spectral changes induced by tilt (r = 0.42; P less than 0.01). Of potential clinical importance is that the data obtained with spectral analysis appear more thoroughly quantifiable and do not require the active collaboration of the patients.

Adolescent↗
PubMed1988

Sympathetic predominance in essential hypertension: a study employing spectral analysis of heart rate variability.

In this study on 91 subjects we tested the hypothesis of an enhanced sympathetic activity in uncomplicated essential hypertension employing spectral analysis of heart rate variability. With this technique the tonic sympathetic and vagal activities and their changes are respectively assessed by the power of approximately 0.1 Hz (low frequency, LF) and approximately 0.25 Hz (respiratory linked, high frequency, HF) components of the spectrum of the beat by beat variability of RR interval. When comparing the 40 subjects with diastolic blood pressure consistently greater than 95 mmHg (hypertensives, Ht), with 35 age-matched controls (diastolic arterial pressure less than 90 mmHg, Nt), we observed that LF was greater and HF smaller in Ht as compared to Nt, thus suggesting an enhanced sympathetic activity and a reduce vagal activity in Ht. Additionally, passive tilt, which in Nt enhances LF [delta = 26 +/- 2 normalized units (nu)] and reduces HF (delta = -22 +/- 2, nu), produced smaller (P less than 0.05) changes in Ht (delta LF = 6.3 +/- 2.7 and delta HF = -7.5 +/- 2.3 nu). Furthermore, the values of LF at rest and the altered effects of tilt on LF and HF were significantly correlated with the degree of the hypertensive state. Chronic beta-adrenergic blockade (atenolol 100 mg once daily for 2 weeks, n = 13) reduced heart rate and blood pressure (from 162/103 to 136/88 mmHg) together with a significant diminution of LF and an increase of HF. Thus, spectral analysis of RR variability appears to be a convenient non-invasive technique to follow the progressive alterations in sympatho-vagal balance present in essential hypertension.

Adult↗
PubMed1988

Changes in autonomic regulation induced by physical training in mild hypertension.

The adaptive effects of physical training on cardiovascular control mechanisms were studied in 11 subjects with mild hypertension. In these subjects we assessed the gain of the heart period-systolic arterial pressure relationship in the unfit and the fit state by using 1) an open loop approach, whereby the gain is expressed by the slope of the regression of heart period as a function of systolic arterial pressure, during a phenylephrine-induced pressure rise and 2) a closed loop approach with proper simplification, whereby the gain is expressed by the index alpha, obtained through simultaneous spectral analysis of the spontaneous variabilities of heart period and systolic arterial pressure. Both methods indicated that training significantly increased the gain of the relationship between heart period and systolic arterial pressure at rest and reduced arterial pressure and increased heart period significantly. This gain was drastically reduced during bicycle exercise both in the unfit and fit state. In a second group of normotensive (n = 7; systolic pressure, 133 +/- 3 mm Hg) and hypertensive (n = 7; systolic pressure, 180 +/- 10 mm Hg) subjects undergoing 24-hour diagnostic continuous electrocardiographic and high fidelity arterial pressure monitoring, the index alpha was significantly reduced in the hypertensive group at rest. Furthermore, when analyzed continuously over the entire 24-hour period, this index underwent minute-to-minute changes with lower values during the day and higher values during the night. We propose the index alpha as a quantitative indicator of the changes in the gain of baroreceptor mechanisms occurring with physical training in mild hypertension and during a 24-hour period in ambulatory subjects.

Adult↗
PubMed1988

Automatic assessment of the interaction between respiration and heart rate variability signal.

The present paper introduces an original method of processing heart rate variability (HRV) and respiration signals as detected respectively through chest electrodes and thoracic belt in dogs under different experimental conditions. Signals are processed as time series synchronous with the occurrence of QRS complexes on ECG signal and auto and cross spectra are accordingly calculated. Two particular bands appear mainly of interest on the spectrum of HRV signal: one in correspondence with the respiration rate and another one at a lower frequency value. Values of power at these frequency bands together with coherence and phase between HRV signal and respiration complete the parameters which try to quantify a few aspects of the complex dynamic relationships between the original signals. In particular, controlled respiration in dogs was studied through the connection with an automatic ventilator, as well as the effects of drugs which interact with the neural regulatory systems (i.e. sympathetic and parasympathetic nervous system). Gain and phase relationships between heart rate variability and respiration, obtained with spectral analysis, could be used to provide a better understanding of the neural control mechanisms linking heart rate and respiration in various experimental conditions. The method described in this study is to be used both in physiological and clinical research.

Animals↗