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Biomedical subjects

S Cerutti

Publications and source records attributed to S Cerutti.

At least 109 records · Page 6Linked to original sources
PubMed1992

The dynamic behaviour of the evoked magnetoencephalogram detected through parametric identification.

A single trial technique has been used for the analysis of neuromagnetic signals. This method, applied to evoked magnetoencephalograms, permitted us to evaluate the dynamics of brain responses under repetitive somatosensory stimulation. Two different phenomena have been investigated: synchronized spontaneous activity (SSA), elicited by bursts of stimuli at a given frequency; and somatosensory evoked fields (SEF), the transient response to a single stimulus. A transient period of adaptation of the SSA response to the particular stimulation paradigm is reported at specific stimulation frequencies; no significant decrease of the response amplitude even after 300 repetitions is observed. The amplitudes of single SEFs also appear to be constant. Possible physiological implications of the SSA response parameters studied (amplitude, frequency and decay time), and a preliminary discussion of the relationship between SEF and SSA, are presented.

Brain↗
PubMed1992

Spectral analysis of sympathetic discharge, R-R interval and systolic arterial pressure in decerebrate cats.

In 19 decerebrate and artificially ventilated cats, we analyzed, with a power spectral methodology, the variability simultaneously present in R-R interval and in thoracic preganglionic sympathetic outflow. R-R interval was characterized, as already described in humans and other experimental preparations, by two rhythmic components occurring at a frequency of about 0.1 Hz (low-frequency, LF) and at one corresponding to respiratory rate (high-frequency, HF) which, in these experiments, was set at 0.32 Hz. Two similar rhythmic components were also present in the sympathetic discharge. Arterial pressure changes were produced by aorta or vena cava flow obstruction in order to produce reflex responses in sympathetic activity. Reflex sympathetic excitations induced an increase in the LF component of both R-R interval and sympathetic discharge variabilities, while the HF components were simultaneously reduced. In contrast, reflex sympathetic inhibitions were accompanied by a decrease in LF components of both variability signals, while the HF components were simultaneously increased. A significant and positive correlation was found between changes in impulse activity and the amplitude of LF component of either R-R interval or sympathetic discharge variabilities. These data support the hypothesis that the low-frequency component of R-R variability can be used as a marker of sympathetic modulation.

Animals↗
PubMed1992

[Modification of the sympatho-vagal interaction in mitral valve prolapse syndrome. Evaluation of heart rate variability by spectrum analysis].

To determine whether clinical manifestations in patients with mitral valve prolapse (MVP) are associated with altered sympatho-vagal tone, 46 patients (mean age 27 +/- 6, range 20-45 years; 18 males and 28 females) were studied by power spectrum analysis of RR variability. Patients were divided in 2 groups, according to echocardiographic criteria: Group A: 11 patients with classical MVP; Group B: 35 patients with non classical MVP. These patients were compared with 30 healthy subjects (Group C) well matched for age, body surface area and heart rate. Our findings indicate that at rest there is a significant difference in the high-frequency component between Group A and Group C. Similarly, during the increase in sympathetic activity induced by 70 degrees head-up tilt all groups showed an increase in the low-frequency component, that was more evident in Group A. The data generated from our laboratory suggest that mitral regurgitation (Group A) is a probable cause of vagal tone increase and that there is an adaptive long-term mechanism towards sympathetic conditions. In addition, probably the normalization, demonstrable by the effect of sympathetic activity in tilt, can mask a dysfunction that may be differently evoked.

Adult↗
PubMed1991

Assessment of the neural control of the circulation during psychological stress.

In this study, we used spectral analysis of short-term R-R and systolic arterial pressure (SAP) variabilities to estimate the changes in neural control of the circulation produced by psychological stress. The 0.1 Hz low-frequency (LF) component of R-R and SAP variabilities provided a quantitative index of the sympathetic activity controlling heart rate and vasomotion. Conversely the high-frequency (HF) respiratory component of R-R variability provided an index of vagal tone. In conscious dogs we used the seemingly stressful situation of being accompanied for the first time to the experimental laboratory as a stimulus. In human subjects we used mental arithmetic. In both cases LF of R-R and SAP variabilities increased significantly suggesting enhanced sympathetic activity both to the SA node and the vasculature. In man, the index alpha, a measure of the overall gain of baroreceptor mechanisms, was found to be reduced during mental arithmetic. Spectral analysis of cardiovascular variabilities thus suggests that in man and in conscious dogs psychological challenges induce a profound re-arrangement of neural control of the circulation, which appears to be characterised by sympathetic predominance and which can be monitored by this technique.

Adult↗
PubMed1991

Analysis of the neuromagnetic data on the frequency responsivity of the human brain: a progress report.

The study of the responsivity of the human brain at different rates of sensory stimulation has provided several pieces of information on brain functionality. The new analysis technique used in this study permits us to investigate the dynamics of these responses and to obtain a larger amount of statistical data to allow for fine frequency discrimination. This allows us to suggest, for example, phase locked systems as models for synchronisable spontaneous activity. Absence of subject fatigue during the repetition of the stimulation paradigm, as well as the presence of a 'learning period' characterised by transient dynamics of the responses, are also discussed.

Acoustic Stimulation↗
PubMed1991

Signal averaging of pre- and post-extrasystolic beats in patients with ventricular arrhythmias.

To evaluate the effects of premature ventricular beats on the impulse conduction of adjacent sinus cycles, we compared the high amplification signal-averaged electrocardiogram parameters of the pre- and post-extrasystolic beats with those of the remaining sinus cycle. According to the duration of filtered QRS (fQRS), to the voltage of root mean square of the terminal 40 ms (RMS 40) and to the duration of low amplitude terminal components of the sinus cycles, ventricular late potentials were detected in nine out of 29 subjects. Patients with an abnormal signal-averaged electrocardiogram exhibited a longer fQRS (146 +/- 6 versus 116 +/- 2 ms), a reduced RMS40 voltage (18 +/- 2 versus 80 +/- 10 microV) and a prolonged duration of less than 40 microV components (42 +/- 4 versus 17 +/- 2 ms). Analysis of the pre-extrasystolic beats did not reveal any significant variation in the above parameters, showing a mean difference of 0.44 +/- 2.4 ms; 0.02 +/- 1.14 microV; 1 +/- 1.9 ms and of -1.45 +/- 1.02 ms; 3.5 +/- 8.6 microV; -0.7 +/- 0.84 ms respectively, for patients with and without ventricular late potentials. In addition, no significant variation was observed when the post-extrasystolic beats were considered. These results indicate that the sinus cycles adjacent to premature ventricular discharges do not present variations of signal-averaged electrocardiogram parameters that may suggest an influence of the ectopic beats on their intramyocardial impulse propagation.

Adult↗
PubMed1991

Altered pattern of circadian neural control of heart period in mild hypertension.

We addressed the problem of the circadian changes in neural control of heart period in ambulant hypertensive subjects. A running spectral analysis of R-R variability from Holter tapes provided markers of sympathetic, i.e. low-frequency component (LF) almost equal to 0.10 Hz, and vagal, i.e. high-frequency component (HF) almost equal to 0.25 Hz, controlling activities for the 24-h period of the recording. Significant circadian differences were observed in LF between the two groups of subjects: during night-time rest (0300-0400 h), LF was greater in hypertensives than in normotensives (56 +/- 2 and 48 +/- 2 nu, respectively; P less than 0.05). Furthermore, the difference between daytime and night-time LF values was progressively reduced with increasing severity of the hypertensive state, as assessed by resting arterial pressure levels. Spectral analysis of R-R variability suggests that essential hypertension may be characterized by a reduced day-night oscillation in sympathetic activity than can be quantified non-invasively using this approach.

Adult↗
PubMed1991

A model for the cortico-cortical neural interaction in multisensory-evoked potentials.

This paper addresses the methodological problem of enhancing selective responses from the central nervous system when two (or more) different sensorial stimuli are simultaneously presented to the subject. In particular, contemporaneous visual and somato-sensory stimulation is considered and a model of signal and noise interaction is developed for the processing of the evoked responses. An ARXX parametric model (AutoRegressive with two eXogenous inputs) is introduced and a least squares algorithm is used to determine the selective response of the two neural systems from the overall evoked response. Such an analysis may be also carried out on a sweep-by-sweep basis. Applications of this method are the following ones: i) modeling of multisensory potentials; ii) description of facilitation or defacilitation phenomena in multitasking experiments; iii) analysis of cortico-cortical neural interactions.

Algorithms↗
PubMed1991

Cardiovascular neural regulation explored in the frequency domain.

A consistent link appears to exist between predominance of vagal or sympathetic activity and predominance of HF or LF oscillations, respectively: RR variability contains both of these rhythms, and their relative powers appear to subserve a reciprocal relation like that commonly found in sympathovagal balance. In this respect, it is our opinion that rhythms and neural components always interact, just like flexor and extensor tones or excitatory and inhibitory cardiovascular reflexes, and that it is misleading to separately consider vagal and sympathetic modulations of heart rate. In humans and experimental animals, functional states likely to be accompanied by an increased sympathetic activity are characterized by a shift of the LF-HF balance in favor of the LF component; the opposite occurs during presumed increases in vagal activity. In addition, LF oscillation evaluated from SAP variability appears to be a convenient marker of the sympathetic modulation of vasomotor activity. Although based on indirect markers, the exploration in the frequency domain of cardiovascular neural regulation might disclose a unitary vision hard to reach through the assemblage of more specific but fragmented pieces of information.

Animals↗
PubMed1991

Sympathovagal interaction during mental stress. A study using spectral analysis of heart rate variability in healthy control subjects and patients with a prior myocardial infarction.

We tested the hypothesis that psychological stress testing in the clinical laboratory provokes changes in the sympathetic and vagal activities regulating heart rate that can be assessed noninvasively using spectral analysis of RR variability. To account for the effects on respiration produced by talking, this study was performed with two different procedures: the I.K.T. (i.e., a computer-controlled mental task that is performed in silence and does not entail human confrontation) and a stressful interview. Finally, we assessed whether ischemic heart disease modifies the spectral changes induced by psychological stress by comparing a group of healthy subjects (age, 38 +/- 2 years) with a group of patients (age, 52 +/- 3 years) recovering from 1-month-old myocardial infarctions. The findings indicate that psychological stress induced marked changes in the sympathovagal balance, which moved toward sympathetic predominance. The low-frequency component of RR variability, a marker of sympathetic activity, increased from 58 +/- 5 normalized units (NU) to 68 +/- 3 NU with the I.K.T. and to 76 +/- 3 NU with the interview. This increase was absent in the group of post-myocardial infarction patients. However, arterial pressure increased significantly in both groups of subjects. The possibility of age playing an important role in determining the differences observed was disproved by the findings of a marked increase in low frequency with mental stimuli in an additional group of borderline hypertensive subjects with ages (55 +/- 2 years) comparable to those of post-myocardial infarction patients.

Adult↗
PubMed1990

The influence of exercise intensity on the power spectrum of heart rate variability.

The power spectral analysis of R-R interval variability (RRV) has been estimated by means of an autoregressive method in seven sedentary males at rest, during steady-state cycle exercise at 21 percent maximal oxygen uptake (%VO2max), SEM 2%, 49% VO2max, SEM 2% and 70% VO2max, SEM 2% and during recovery. The RRV, i.e. the absolute power of the spectrum, decreased 10, 100 and 500 times in the three exercise intensities, returning to resting value during recovery. In the RRV power spectrum three components have been identified: (1) high frequency peak (HF), central frequency about 0.24 Hz at rest and recovery, and 0.28 Hz, SEM 0.02, 0.37 Hz, SEM 0.03 and 0.48 Hz, SEM 0.06 during the three exercise intensities, respectively; (2) low frequency peak (LF), central frequency about 0.1 Hz independent of the metabolic state; (3) very low frequency component (VLF), less than 0.05 Hz, no peak observed. The HF peak power, as a percentage of the total power (HF%), averaged 16%, SEM 5% at rest and did not change during exercise, whereas during recovery it decreased to 5%-10%. The LF% and VLF% were about 50% and 35% at rest and during low exercise intensity, respectively. At higher intensities, LF% decreased to 16% and VLF% increased to 70%. During recovery a return to resting values occurred. The HF component may reflect the increased respiratory rate and the LF peak changes the resetting of the baroreceptor reflex with exercise. The hypothesis is made that VLF fluctuations in heart rate might be partially mediated by the sympathetic system.

Adult↗
PubMed1990

Spectral analysis of heart rate variability signal and respiration in diabetic subjects.

The paper deals with methods of processing ECG and respiration signals which aim at detecting parameters whose values may be correlated to normal and diabetic subjects with or without cardiovascular autonomic neuropathy (CAN). Beat-to-beat R-R duration values of the ECG and discrete series of respiration are obtained from original signals using a recognition algorithm. Power spectrum analysis (autospectra, cross-spectra and coherence via autoregressive modelling) is carried out on segments of about 200 consecutive cardiac cycles. Spectral parameters of the R-R variability signal are obtained as follows: total power, powers of low-frequency (LF) and high-frequency (HF) components, power of the signal which is (or is not) coherent with respiration, in absolute or in percentage values. The experimental protocol considers 40 diabetic patients (21 of whom have diabetic neuropathy) and 14 normals in three different conditions: resting, standing and controlled respiration. The developed spectral parameters seem sensitive enough to differentiate between normal and pathological subjects. These parameters may constitute a quantitative means to be added to the classical diabetic tests for the diagnosis of cardiovascular autonomic neuropathy.

Adult↗
PubMed1990

Spectral analysis of short-term heart rate variability in diabetic patients.

Spectral analysis of short term R-R variability estimated by autoregressive modelling is a recently developed method for the evaluation of cardiovascular autonomic function. This new test also allows to study the interaction on heart rate variability of parasympathetic and sympathetic system. The sensitivity of the method for detection of cardiovascular autonomic neuropathy has been evaluated in a group of diabetic patients in comparison with the sensitivity of a battery of the most commonly used cardiovascular autonomic tests (deep-breathing, lying-to-standing, Valsalva Manoeuvre, postural hypotension and hand grip). Spectral analysis of heart rate variability resulted in a very sensitive method for early detection of diabetic autonomic neuropathy, about one-fourth of diabetic patients with normal traditional cardiovascular autonomic tests had abnormal results at spectral analysis. Both sympathetic and vagal control of heart rate resulted alterated in diabetic autonomic neuropathy.

Adult↗
PubMed1990

Spectral analysis of sympathetic discharge in decerebrate cats.

To evaluate if the 0.1-Hz low-frequency oscillations of R-R interval are a reflection of rhythmical pattern of discharge of the sympathetic outflow, we analysed in 10 decerebrate cats heart rate and cardiac sympathetic efferent discharge variability. A predominant low-frequency component was present in both signals, thus suggesting that the 0.1-Hz rhythm indeed reflects a rhythmical pattern of discharge of sympathetic outflow.

Animals↗