Modulation of the postural effects of cognitive load by hypnotizability.

Aim of the experiment was to study whether cognitive load affects postural control more in low (Lows) than in highly hypnotizable (Highs) subjects due to the latter's greater attentional abilities. Standing Highs and Lows underwent an experimental session (closed eyes) consisting of a basal condition and of mental computation in an easy (stable support) and a difficult (unstable support) postural condition. Variability [standard deviation (SD)] and complexity [sample entropy (SampEn)] of the movement of the centre of pressure (CoP), its mean velocity (Velocity), the area swept by the CoP (Area) and the ratio between the CoP trajectory length and area [length for surface (LFS)] were measured. Few hypnotizability-related differences were detected (reduction in the Highs' SD and increases in the Lows' LFS in the difficult postural condition). Thus, the hypnotizability-related postural differences observed in previous studies during sensory alteration could not be accounted mainly by attentional abilities.

Long- and short-time analysis of heartbeat sequences: correlation with mortality risk in congestive heart failure patients.

We analyze RR heartbeat sequences with a dynamic model that satisfactorily reproduces both the long- and the short-time statistical properties of heart beating. These properties are expressed quantitatively by means of two significant parameters, the scaling delta concerning the asymptotic effects of long-range correlation, and the quantity 1-pi establishing the amount of uncorrelated fluctuations. We find a correlation between the position in the phase space (delta, pi) of patients with congestive heart failure and their mortality risk.

Detection of nonlinearity in the healthy heart rhythm.

Sequences of interbeat intervals from two groups of subjects, 24 in relaxed and 10 in sleeping condition were analyzed by the nonlinear predictor method as well as by a method, proposed recently, able to directly estimate the time series nonlinearity. The nonlinear predictability of the R-R intervals is tested by using surrogate data. The results obtained with both methods show that nearly all the sequences exhibit a statistically meaningful degree of nonlinearity. This raises the question whether such nonlinearity encodes information about the physiological condition of the examined subjects.

Heart rate and blood pressure response to short-term head-down bed rest: a nonlinear approach.

Although it is well-known that prolonged exposure to microgravity environment such as in space travel results in derangements of orthostasis, recent evidence suggests that even short-term exposure may have similar effects and parallels such common examples as prolonged bed rest. Whereas spectral analysis of heart rate and systolic blood pressure have been unable to detect changes, we hypothesized that nonlinear indexes may be better able to uncover such perturbations. Eighteen healthy subjects were exposed to 4-hour head-down tilt, and of these, 4 exhibited fainting. Two nonlinear indexes, mutual information and recurrence quantification were used to analyze the data. Only recurrence quantification was able to detect a "decoupling" of heart rate and systolic blood pressure at rest using discriminant analysis (p < 0.05). These results suggest that orthostatic intolerance may be due to a decoupling of heart rate from systolic blood pressure reflexive activity occurring at rest.

An efficient unsupervised fetal QRS complex detection from abdominal maternal ECG.

Non-invasive fetal heart rate is of great relevance in clinical practice to monitor fetal health state during pregnancy. To date, however, despite significant advances in the field of electrocardiography, the analysis of abdominal fetal ECG is considered a challenging problem for biomedical and signal processing communities. This is mainly due to the low signal-to-noise ratio of fetal ECG and difficulties in cancellation of maternal QRS complexes, motion and electromyographic artefacts. In this paper we present an efficient unsupervised algorithm for fetal QRS complex detection from abdominal multichannel signal recordings combining ICA and maternal ECG cancelling, which outperforms each single method. The signal is first pre-processed to remove impulsive artefacts, baseline wandering and power line interference. The following steps are then applied: maternal ECG extraction through independent component analysis (ICA); maternal QRS detection; maternal ECG cancelling through weighted singular value decomposition; enhancing of fetal ECG through ICA and fetal QRS detection. We participated in the Physionet/Computing in Cardiology Challenge 2013, obtaining the top official scores of the challenge (among 53 teams of participants) of event 1 and event 2 concerning fetal heart rate and fetal interbeat intervals estimation section. The developed algorithms are released as open-source on the Physionet website.

Watching neutral and threatening movies: subjective experience and autonomic responses in subjects with different hypnotizability levels.

Subjects with high hypnotizability scores (Highs) have been considered more prone to experience negative affect and more vulnerable to its autonomic effects with respect to low hypnotizable individuals (Lows). The aim of the study was to analyze the subjective experience, tonic skin conductance (SC), respiratory frequency (RF), heart rate (HR) and heart rate variability (HRV) of healthy Highs and Lows during a long-lasting, emotionally neutral task (Session R, 46 subjects) and a moderately threatening one (Session T, 35 subjects). At the end of the relaxing Session R, all participants reported an increased relaxation. At the end of the threatening Session T, only 20 subjects reported a decreased relaxation (effective T: eT subsample). Highs and Lows of this subsample reported a similarly reduced relaxation and showed a similarly increased skin conductance. HR and HRV did not differ between the two sessions and between Highs and Lows. Among the subjects not reporting decreased relaxation at the end of Session T (ineffective T: iT subsample, n=15), relaxation was deeper and associated with lower skin conductance in Highs, although HR and HRV did not differ between Highs and Lows. All together, the results do not support the hypothesis of higher proneness of Highs to experience negative affect and to exhibit the autonomic correlates of negative emotion.

A minimal model for the respiratory sinus arrhythmia.

The cardiac and respiratory rhythms in humans are known to be coupled by several mechanisms. In particular, the first rhythm is deeply modulated by the second. In this report we propose a simple operational model for heart rate variability which, taking such modulation into account, reproduces the main features of some experimental sequences of RR intervals recorded from healthy subjects in the resting condition. Also, peer analysis of the model performance allows us to answer the question whether the observed behaviour should be ascribed to phase synchronisation of the heart beating to the respiratory rhythm. Lastly, the changes of the model activity brought about by changing its relevant parameters are analysed and discussed.

Heart rate variability in subjects with different hypnotic susceptibility receiving nociceptive stimulation and suggestions of analgesia.

The aim of the present study was to investigate the possible hypnotizability-related modulation of heart activity during nociceptive stimulation (pressor pain) and during nociceptive stimulation associated with the suggestion of analgesia in not hypnotized healthy individuals with a high (Highs) and a low (Lows) hypnotic susceptibility. ECG and respirogram were recorded. Standard time and frequency domain indexes were evaluated, together with the sd1 and sd2 values of the Poincaré plot over the RR series. Results showed self reports of analgesia in Highs and a significant increase of the respiratory frequency during stimulation in both groups. Very few significant differences between groups and among conditions were detected for mean RR and heart rate variability (HRV) through spectral analysis. and through the Poincaré indexes evaluation. On the contrary, a promising approach seems to be the study of the correlations among standard and Poincaré variables. In particular, different changes in (or even lost of) correlations were enlightened in Highs and Lows, suggesting a different modulation of RR in the two groups, probably due to the very low frequency components of HRV. Different roles of sympathetic and parasympathetic activities during stimulation can be suggested.

Effect of 4 hours HD -6 degrees on heart rate variability in symptomatic and non symptomatic subjects.

Orthostatic intolerance is the most serious symptom of cardiovascular deconditioning induced by microgravity exposure. In fact the neural control mechanisms of the cardiovascular system are significantly affected by this condition. Non-invasive measurement of Heart Rate Variability (HRV) have been used as a valuable tool to characterize the ability of neuroendocrine regulatory systems to modulate the cardiovascular function by analyzing the spontaneous fluctuations of arterial pressure and heart period on a beat-to-beat basis. Concerning this, conflicting results have been reported on the heart rate and blood pressure variability responses during exposure to microgravity. These differences seem to be due to different experimental designs used. Moreover, the different behavior of normal subjects in response to orthostatic stress after HD, i.e. Symptomatic (S) or Non Symptomatic (NS), could play some roles in producing these discrepancies. Therefore the aim of the present study was to examine BP and HR variability before and after 4 hours of HD in two groups of normal subjects with and without symptoms of orthostatic intolerance to orthostatic stress.

[The quantitative cineangiography. Part II. Computerized analysis of the left ventricular volumes in man (author's transl)]. / Cineangiografia quantitativa. Parte II: Analisi computerizzata del volume ventricolare sinistro nell'uomo.

The values of left ventricular volumes (EDV and ESV) were determined in 35 patients with various heart diseases by computerized reading technique utilizying both the area-length and the slice methods. The data thus obtained were compared both with those derived manually and with those obtained following injection of 113mIn into the left ventricle and monitoring by external counting the dilution curve. Good agreement among the data obtained by the various methods was found. It appears, then, in the clinical practice, the computerized method has definite advantages over the others since it allows quick determination of the data and therefore examination of multiple frames.

[Quantitative cineangiography. Part I. Computerized volumetry of ventricular models (author's transl)]. / Cineangiografia quantitativa. Parte I. Volumetria computerizzata di modelli ventricolari.

A computerized system for cineangiograms analysis is described. Each selected frame is displayed by a TV camera on a TV monitor, allowing the physician to draw the left ventricular contour using a light-pen. The coordinates of selected points are sent to a small size digital computer to be processed. The processing techniques are outlined, while particular evidence is given to the operating procedure. Left ventricular volume is evaluated using both area-length and slice methods. Results obtained on models yield an estimation of the accuracy of the volume measurements.

Head-down bed rest reduces the breathing rate short-term variability in subjects with orthostatic intolerance.

Orthostatic intolerance is the most serious symptom of cardiovascular deconditioning induced by microgravity. We have showed that in symptomatic subjects the baroreflex control of sinus node is affected by short term simulated microgravity. At present the influence of the respiration on the cardiovascular system in this condition is not clear. The aim of the present study was to examine the behaviour of the Breathing Rate (BR) in 5 Non-Symptomatic (NS) and 3 Symptomatic (S) subjects before and after 4 hours of head-down bed rest (HD).

Mutual information detects a decreased interdependence between RR and SAP in orthostatic intolerance after microgravity condition.

Orthostatic intolerance is the most serious symptom of cardiovascular deconditioning induced by microgravity. However, the exact mechanisms underlying these alterations have not been completely clarified. Several methods for studying the time series of systolic arterial pressure and RR interval have been proposed both in the time and in the frequency domain. However, these methods did not produce definitive results. In fact heart rate and arterial pressure show a complex pattern of global variability which is likely due to non linear feedback which involves the autonomic nervous system and to "stochastic" influences. Aim of this study was to evaluate the degree of interdependence between the mechanisms responsible for the variability of SAP and RR signals in subjects exposed to head down (HD). This quantification was achieved by using Mutual Information (MI).

Average magnitude of heartbeat fluctuations in healthy subjects after exposure to 4 hours head down bed rest.

Orthostatic intolerance, induced by microgravity exposure, has been hypothesized to be related to a disorder of the autonomic control of the cardiovascular system. Non-invasive measurement of Heart Rate Variability (HRV) have been used as a valuable tool to characterize the ability of the autonomic system to modulate the cardiovascular function by analyzing the spontaneous fluctuations of arterial pressure and heart period on a beat-to-beat basis. Concerning this, conflicting results have been reported on the heart rate and blood pressure variability responses during exposure to microG. These differences seem to be due to different experimental designes used. Moreover, the different behavior of normal subjects in response to orthostatic stress after HD, i.e. Symptomatic (S) or Non Symptomatic (NS), could play some role in producing these discrepancies [correction of dicrepancies]. In this study we suggest the analysis of "magnitude" or "volatility" as a new method to study HRV variability. The volatility is a measure of the beat-to-beat excursion capability of the heart, regardless to its direction (positive or negative): the higher the volatility, the greater the excursion. The aim of the present study was to examine R-R volatility before and after 4 hours of HD -6 degrees in normal subjects.

Effect of aging on responses to autonomic cardiovascular tests.

Cardiovascular deconditioning (CD) and orthostatic intolerance represent some of the major disturbances experienced by astronauts returning on Earth after micro-G exposure. The orthostatic intolerance observed in crew members after space missions has been hypothesized to be related to a disorder of the autonomic control of the cardiovascular system. There is evidence that advanced acing itself may alter the cardiovascular mechanism that underlie the CD. Due to involvement of elderly subjects in space flights it is mandatory to verify how age affects the cardiovascular autonomic neural regulation. In order to assess age-related differences in autonomic cardiovascular regulation our aim is to analyze the cardiovascular responses to 3 different autonomic tests that explore baroreceptor (tilt and deep breathing) and non-baroreceptor (isometric exercise) afferent pathways, in two goups of normal subjects characterized by significant different age.