Looking for a precursor of spontaneous Sleep Slow Oscillations in human sleep: The role of the sigma activity.

Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation between cellular downstates and upstates), and sleep spindles, paradigmatic EEG markers of thalamic rhythm, are two hallmarks of sleeping brain. Selective thalamic lesions are reportedly associated to reductions of spindle activity and its spectrum ~14 Hz (sigma), and to alterations of SSO features. This apparent, parallel behavior suggests that thalamo-cortical entrainment favors cortical bistability. Here we investigate temporally-causal associations between thalamic sigma activity and shape, topology, and dynamics of SSOs. We recorded sleep EEG and studied whether spatio-temporal variability of SSO amplitude, negative slope (synchronization in downstate falling) and detection rate are driven by cortical-sigma-activity expression (12-18Hz), in 3 consecutive 1s-EEG-epochs preceding each SSO event (Baselines). We analyzed: (i) spatial variability, comparing maps of baseline sigma power and of SSO features, averaged over the first sleep cycle; (ii) event-by-event shape variability, computing for each electrode correlations between baseline sigma power and amplitude/slope of related SSOs; (iii) event-by-event spreading variability, comparing baseline sigma power in electrodes showing an SSO event with the homologous ones, spared by the event. The scalp distribution of baseline sigma power mirrored those of SSO amplitude and slope; event-by-event variability in baseline sigma power was associated with that in SSO amplitude in fronto-central areas; within each SSO event, electrodes involved in cortical bistability presented higher baseline sigma activity than those free of SSO. In conclusion, spatio-temporal variability of thalamocortical entrainment, measured by background sigma activity, is a reliable estimate of the cortical proneness to bistability.

Psycho-physiological tele-monitoring of human operators in commercial diving: The Life Support System in the SUONO project.

Sea-diving operations for monitoring or intervention are carried out by highly-specialized divers called Certified Commercial Divers (CCD). CCDs operate under highly demanding working conditions in extreme and hazardous environments. Every day consists of an 8 hours' shift. To avoid decompression problems the remaining 16 hours are spent in a hyperbaric environment located aboard the surface vessel or on the platform. These operating conditions require the design of a technologically-advanced device for tele-monitoring, to maximize CCDs' safety. Here we describe a proposal for monitoring and supporting CCDs during operations. We design a dedicated Life Support System (LSS), that captures real-time, vital (heart rate, respiratory rate, accelerometry, etc) and stress-related (heart-rate variability) signals from operators to transmit them to dedicated servers via telematic protocols. LSS is equipped with protocols for tele-medicine/tele-consultation. Our system is being developed within the research project SUONO (Safe Underwater OperatioNs in Oceans).

Innovative approach to interpret the variability of biomarkers after ultra-endurance exercise: the multifactorial analysis.

AIMS: We assessed the inter-relationship that exists between variations of different biochemical and hematological parameters following strenuous endurance exercise in Ironmen by using multiple factor analysis (MFA). MFA was used to estimate the associations among groups of parameters in order to identify concurrent changes in many different biochemical variables. MATERIALS & METHODS: In total, 14 Ironman athletes were followed before and early after a race. MFA was applied to the parameters that showed a significant variation after the race, as we previously described in detail. Specifically, MFA standardizes data in each group and calculates the global axes (GAs), which are the linear combination of original parameters that maximize the global data variance. RESULTS: MFA identified three global axes (GAs) as significant, explaining approximately 62% of the global data variance. The first GA contained NT-proBNP, IL-1ra, IL-6, IL-8 and the oxidative index. The second and third GAs included calcium, creatinine, potassium, uric acid, hemoglobin, hematocrit and glucose. Analysis of the first two GAs showed that changes in the oxidative index were associated with variations in IL-8 and NT-proBNP. CONCLUSION: Among all the variables considered, MFA evidenced a close relationship between variations in oxidative stress, IL-8 and NT-proBNP, which may have a meaning in the mechanisms related to the physiological response after strenuous acute exercise.

How stressful are 105 days of isolation? Sleep EEG patterns and tonic cortisol in healthy volunteers simulating manned flight to Mars.

Spaceflights "environment" negatively affects sleep and its functions. Among the different causes promoting sleep alterations, such as circadian rhythms disruption and microgravity, stress is of great interest also for earth-based sleep medicine. This study aims to evaluate the relationships between stress related to social/environmental confinement and sleep in six healthy volunteers involved in the simulation of human flight to Mars (MARS500). Volunteers were sealed in a spaceship simulator for 105 days and studied at 5 specific time-points of the simulation period. Sleep EEG, urinary cortisol (24 h preceding sleep EEG recording) and subjectively perceived stress levels were collected. Cognitive abilities and emotional state were evaluated before and after the simulation. Sleep EEG parameters in the time (latency, duration) and frequency (power and hemispheric lateralization) domains were evaluated. Neither cognitive and emotional functions alterations nor abnormal stress levels were found. Higher cortisol levels were associated to: (i) decrease of sleep duration, increase of arousals, and shortening of REM latency; (ii) reduction of delta power and enhancement of sigma and beta in NREM N3; and (iii) left lateralization of delta activity (NREM and REM) and right lateralization of beta activity (NREM). Stressful conditions, even with cortisol fluctuations in the normal range, alter sleep structure and sleep EEG spectral content, mirroring pathological conditions such as primary insomnia or insomnia associated to depression. Correlations between cortisol fluctuations and sleep changes suggest a covert risk for developing allostatic load, and thus the need to develop ad-hoc countermeasures for preventing sleep alterations in long lasting manned space missions.

Disentangling different functional roles of evoked K-complex components: Mapping the sleeping brain while quenching sensory processing.

During non-REM sleep the largest EEG response evoked by sensory stimulation is the K-complex (eKC), composed of an initial positive bump (P200) followed by a bistable cortical response: a giant negative deflection (N550) and a large positive one (P900), respectively reflecting down states and up states of < 1 Hz oscillations.Sensory-modality-independent topology of N550 and P900, with maximal detection rate on fronto-central areas, has been consistently reported, suggesting that sensory inputs arise to the cortex avoiding specific primary sensory areas. However, these studies neglected latencies of all KC components as a function of electrode sites.Our aim is to identify, component by component, which topological/dynamical properties of eKCs depend on stimulus modality and which are mainly related to local cortical properties. We measured temporal and morphological features of acoustic, tactile and visual eKCs to disentangle specific sensory excitatory activities from aspecific responses due to local proneness to bistability, measured by means of the N550 descending steepness (synchronization in falling into down state).While confirming the sensory-modality independence of N550 and P900 topology with maximal detection rate in fronto-central areas, four main original results emerge from this study: (i) the topology of P200 latency depends on the sensory modality with earliest waves in the stimulation-related primary sensory areas; (ii) P200 rapidly travels as a cortical excitation; (iii) P200-like excitations when KCs are not evoked are detected over the scalp with significantly smaller amplitudes in fronto-central areas, compared to eKC P200s; and (iv) N550 latency mirrors its mean local steepness which is a function of topological proneness to bistability.From these results we can describe the emergence N550/P900 complex as the interplay between a waxing P200 cortical travel and higher fronto-central proneness to bistability.In conclusion, eKCs exhibit a physiological dichotomy: P200 acts as a traveling cortical excitation whose function is to induce the bistable cortical response (N550/P900), which in turn is crucial for maintaining sleep and unconsciousness.

Brain responses to emotional stimuli during breath holding and hypoxia: an approach based on the independent component analysis.

Voluntary breath holding represents a physiological model of hypoxia. It consists of two phases of oxygen saturation dynamics: an initial slow decrease (normoxic phase) followed by a rapid drop (hypoxic phase) during which transitory neurological symptoms as well as slight impairment of integrated cerebral functions, such as emotional processing, can occur. This study investigated how breath holding affects emotional processing. To this aim we characterized the modulation of event-related potentials (ERPs) evoked by emotional-laden pictures as a function of breath holding time course. We recorded ERPs during free breathing and breath holding performed in air by elite apnea divers. We modeled brain responses during free breathing with four independent components distributed over different brain areas derived by an approach based on the independent component analysis (ICASSO). We described ERP changes during breath holding by estimating amplitude scaling and time shifting of the same components (component adaptation analysis). Component 1 included the main EEG features of emotional processing, had a posterior localization and did not change during breath holding; component 2, localized over temporo-frontal regions, was present only in unpleasant stimuli responses and decreased during breath holding, with no differences between breath holding phases; component 3, localized on the fronto-central midline regions, showed phase-independent breath holding decreases; component 4, quite widespread but with frontal prevalence, decreased in parallel with the hypoxic trend. The spatial localization of these components was compatible with a set of processing modules that affects the automatic and intentional controls of attention. The reduction of unpleasant-related ERP components suggests that the evaluation of aversive and/or possibly dangerous situations might be altered during breath holding.

Cardiac function and oxygen saturation during maximal breath-holding in air and during whole-body surface immersion.

INTRODUCTION: The magnitude of the oxygen-sparing effect induced by the diving response in humans is still under debate. We wished to compare cardiovascular changes during maximal breath-holding (BH) in air and during whole-body immersion at the surface in a group of BH divers. METHODS: Twenty-one divers performed a maximal static apnea in air or during whole-body immersion. Dopplerechocardiography, arterial blood pressure and haemoglobin saturation (SaO2) were obtained at the beginning of, and at 1/3, 2/3 and maximal BH time. RESULTS: BH time was on the average 3.6 ± 0.4 min, with no differences between the two conditions. SaO2 significantly decreased during BH in both conditions, but was significantly higher during immersion as compared to the dry (P = 0.04). In both conditions, BH induced a significant linear increase in right ventricular diameter (P < 0.001), left ventricular (LV) volumes (P < 0.001) and LV stroke volume (P < 0.001) but a significant linear decrease in LV ejection fraction (P = 0.033). In both conditions, Doppler diastolic parameters showed changes suggesting a constrictive/restrictive left ventricular filling pattern (i.e., an increase of early diastolic left ventricular filling velocity, P = 0.005, and a decrease in the deceleration time of early diastolic left ventricular filling. P < 0.001). CONCLUSION: BH induces progressive LV enlargement both in air and whole-body immersion, associated with reduced LV ejection fraction and progressive hindrance to diastolic filling. For a similar apnea duration, SaO2 decreased less during immersed BH, indicating an O2-sparing effect of diving, suggesting that interruption of apnea was not triggered by a threshold critical value of blood O2 desaturation.

Fragments of wake-like activity frame down-states of sleep slow oscillations in humans: new vistas for studying homeostatic processes during sleep.

During NREM sleep cortical activity corresponding to EEG fast rhythms (FRs>10 Hz) is interrupted by fragments of neural stillness (down-states), responsible for the negative peak within sleep slow oscillation (SSO). Researchers still debate whether the down-states spontaneously occur or need an initial overshoot in fluctuating activity. Herein, we studied temporally-isolated SSO in healthy subjects in order to identify two distinct EEG markers defining a putative initial up-state: i) a significant positive deflection and ii) an associated FR increase, before the negative peak. We found a positive bump preceding the down-state, which is detectable already at the cortical SSO origin site, both during N2 and N3. This early positive deflection, concurrent with a broadband activation, is characterized by an increase of sigma activity (12-18 Hz) from N2 to N3, while an opposite trend was observed for sigma activity crowning the up-state following the negative peak. Also, we found: (i) FR activations during up-states up to high gamma frequencies; (ii) depressed sigma activity in after-spindle recovery phase; and (iii) tightly coordinated activities between distinct bands (12-36 Hz, ~70 Hz, ~85 Hz and 105-125 Hz). The correlation between different bands suggested a common mechanism for sigma and gamma, and the pre-down-state activation associated with the initial bump suggested an activity ignition for down-state, whose intensity is dependent on sleep stage. In conclusion, we hypothesize that FR accompanying SSO could mark i) sleep homeostatic processes, such as the regulation/stabilization of sleep, counterbalancing the detrimental effects of continuous inputs from peripheries, and ii) neural mechanisms favoring the storage of information acquired during wakefulness.

Interactions between immune, stress-related hormonal and cardiovascular systems following strenuous physical exercise.

Physical exercise represents a eustress condition that promotes rapid coordinated adjustments in the immune, stress-related hormonal and cardiovascular systems, for maintaining homeostasis in response to increased metabolic demands. Compared to the tight multisystem coordination during exercise, evidence of between-systems cross talk in the early post exercise is still lacking. This study was aimed at identifying possible interactions between multiple systems following strenuous physical exercise (Ironman race) performed by twenty well-trained triathletes. Cardiac hemodynamics, left ventricle systolic and diastolic function and heart rate variability were measured along with plasma concentrations of immune messengers (cytokines and C-reactive protein) and stress-related hormones (catecholamines and cortisol) both 24h before and within 20 min after the race. Observed changes in antiinflammatory pathways, stress-related hormones and cardiovascular function were in line with previous findings; moreover, correlating parameters' changes (post versus pre-race) highlighted a dependence of cardiovascular function on the post-race biohumoral milieu: in particular, individual post-race variations of heart rate and diastolic function were strongly correlated with individual variations of anti-inflammatory cytokines, while individual baroreflex sensitivity changes were linked to IL-8 increase. Multiple correlations between anti-inflammatory cytokines and catecholamines were also found according with the autonomic regulation of immune function. Observed post-race cytokine and hormone levels were presumptively representative of the increases reached at the effort end while the cardiovascular parameters after the race were measured during the cardiovascular recovery; thus, results suggest that sustained strenuous exercise produced a stereotyped cardiovascular early recovery, whose speed could be conditioned by the immune and stress-related hormonal milieu.

Thalamic contribution to Sleep Slow Oscillation features in humans: a single case cross sectional EEG study in Fatal Familial Insomnia.

OBJECTIVE: Studying the thalamic role in the cortical expression of the Sleep Slow Oscillation (SSO) in humans by comparing SSO features in a case of Fatal Familial Insomnia (FFI) and a group of controls. METHODS: We characterize SSOs in a 51-year-old male with FFI carrying the D178N mutation and the methionine/methionine homozygosity at the polymorphic 129 codon of the PRNP gene and in eight gender and age-matched healthy controls. Polysomnographic (21 EEG electrodes, two consecutive nights) and volumetric- (Diffusion tensor imaging Magnetic Resonance Imaging DTI MRI) evaluations were carried out for the patient in the middle course of the disease (five months after the onset of insomnia; disease duration: 10 months). We measured a set of features describing each SSO event: the wave shape, the event-origin location, the number and the location of all waves belonging to the event, and the grouping of spindle activity as a function of the SSO phase. RESULTS: We found that the FFI individual showed a marked reduction of SSO event rate and wave morphological alterations as well as a significant reduction in grouping spindle activity, especially in frontal areas. These alterations paralleled DTI changes in the thalamus and the cingulate cortex. CONCLUSIONS: This work gives a quantitative picture of spontaneous SSO activity during the NREM sleep of a FFI individual. The results suggest that a thalamic neurodegeneration specifically alters the cortical expression of the SSO. This characterization also provides indications about cortico-thalamic interplays in SSO activity in humans.

Mind-body relationships in elite apnea divers during breath holding: a study of autonomic responses to acute hypoxemia.

The mental control of ventilation with all associated phenomena, from relaxation to modulation of emotions, from cardiovascular to metabolic adaptations, constitutes a psychophysiological condition characterizing voluntary breath-holding (BH). BH induces several autonomic responses, involving both autonomic cardiovascular and cutaneous pathways, whose characterization is the main aim of this study. Electrocardiogram and skin conductance (SC) recordings were collected from 14 elite divers during three conditions: free breathing (FB), normoxic phase of BH (NPBH) and hypoxic phase of BH (HPBH). Thus, we compared a set of features describing signal dynamics between the three experimental conditions: from heart rate variability (HRV) features (in time and frequency-domains and by using nonlinear methods) to rate and shape of spontaneous SC responses (SCRs). The main result of the study rises by applying a Factor Analysis to the subset of features significantly changed in the two BH phases. Indeed, the Factor Analysis allowed to uncover the structure of latent factors which modeled the autonomic response: a factor describing the autonomic balance (AB), one the information increase rate (IIR), and a latter the central nervous system driver (CNSD). The BH did not disrupt the FB factorial structure, and only few features moved among factors. Factor Analysis indicates that during BH (1) only the SC described the emotional output, (2) the sympathetic tone on heart did not change, (3) the dynamics of interbeats intervals showed an increase of long-range correlation that anticipates the HPBH, followed by a drop to a random behavior. In conclusion, data show that the autonomic control on heart rate and SC are differentially modulated during BH, which could be related to a more pronounced effect on emotional control induced by the mental training to BH.

The dynamics of EEG gamma responses to unpleasant visual stimuli: from local activity to functional connectivity.

Many electroencephalographic (EEG) studies on the cortical dynamics induced by unpleasant picture viewing demonstrated the modulation of event-related potentials (ERPs) components as a function of valence and the increase of gamma band responses to emotional stimuli; while only a few studies investigated phase synchronization phenomena such as inter-trial or between regions phase locking of gamma responses to emotional stimulation. The aim of this study was to provide a complete description of the cortical dynamics induced by unpleasant and neutral pictures viewing, from the ERP averages to gamma rhythm modulation, and its phase synchronization. Gamma rhythm modulation was estimated by the event-related synchronization (ERS) approach, and phase synchrony between trials and between cortical regions was studied by extending the phase-locking statistics (PLS) approach. Consistent with previous literature, an increase in P300 and late positive potential and an increase in gamma activity during viewing of unpleasant pictures as compared to neutral ones were found. No inter-trial synchronization was evoked by the stimuli, whereas widespread phase locking between sites was identified. In particular, differences in gamma synchronization between unpleasant and neutral stimuli were found. Specifically, at early (0-250 ms) lags from stimulus onset, in the 38-45 Hz gamma interval, stronger inter-site synchronizations for the unpleasant stimuli, even though quite widespread across the scalp, mainly involved the interhemispheric synchronization between temporal and frontal regions. In contrast, in the 30-37 Hz gamma interval, stronger synchronizations for the responses to neutral trials were found in the 500-750 time interval, mainly involving the temporo-parietal regions. These findings suggest that the full elaboration of unpleasant stimuli requires a tight interhemispheric communication between temporal and frontal regions that is realized by means of phase synchronization at about 40 Hz. In addition, in contrast with the idea of a broadband modulation of high-frequency activity by cognitive/emotional stimuli, the present findings i.e. stronger BRS responses to either emotional or neutral trials at specific frequency and time range, indicate that specific intervals of gamma activity could be each primarily involved in a specific aspect of stimulus processing.

ErpICASSO: a tool for reliability estimates of independent components in EEG event-related analysis.

Independent component analysis and blind source separation methods are steadily gaining popularity for separating individual brain and non-brain source signals mixed by volume conduction in electroencephalographic data. Despite the advancements on these techniques, determining the number of embedded sources and their reliability are still open issues. In particular to date no method takes into account trial-to-trial variability in order to provide a reliability measure of independent components extracted in Event Related Potentials (ERPs) studies. In this work we present ErpICASSO, a new method which modifies a data-driven approach named ICASSO for the analysis of trials (epochs). In addition to ICASSO the method enables the user to estimate the number of embedded sources, and provides a quality index of each extracted ERP component by combining trial-to-trial bootstrapping and CCA projection. We applied ErpICASSO on ERPs recorded from 14 subjects presented with unpleasant and neutral pictures. We separated potentials putatively related to different systems and identified the four primary ERP independent sources. Standing on the confidence interval estimated by ErpICASSO, we were able to compare the components between neutral and unpleasant conditions. ErpICASSO yielded encouraging results, thus providing the scientific community with a useful tool for ICA signal processing whenever dealing with trials recorded in different conditions.

Evaluation of latent links between irritable bowel syndrome and sleep quality.

AIM: To examine the links between quality of sleep and the severity of intestinal symptoms in irritable bowel syndrome (IBS). METHODS: One hundred and forty-two outpatients (110 female, 32 male) who met the Rome III criteria for IBS with no psychiatric comorbidity were consecutively enrolled in this study. Data on age, body mass index (BMI), and a set of life-habit variables were recorded, and IBS symptoms and sleep quality were evaluated using the questionnaires IBS Symptom Severity Score (IBS-SSS) and Pittsburgh Sleep Quality Index (PSQI). The association between severity of IBS and sleep disturbances was evaluated by comparing the global IBS-SSS and PSQI score (Pearson's correlation and Fisher's exact test) and then analyzing the individual items of the IBS-SSS and PSQI questionnaires by a unitary bowel-sleep model based on item response theory (IRT). RESULTS: IBS-SSS ranged from mild to severe (120-470). The global PSQI score ranged from 1 to 17 (median 5), and 60 patients were found to be poor sleepers (PSQI > 5). The correlation between the global IBS-SSS and PSQI score indicated a weak association (r = 0.2 and 95% CI: -0.03 to 0.35, P < 0.05), which becomes stronger using our unitary model. Indeed, the IBS and sleep disturbances severities, estimated as latent variables, resulted significantly high intra-subject correlation (posterior mean of r = 0.45 and 95% CI: 0.17 to 0.70, P < 0.05). Moreover, the correlations between patient features (age, sex, BMI, daily coffee and alcohol intake) and IBS and sleep disturbances were also analyzed through our unitary model. Age was a significant regressor, with patients ≤ 50 years old showing more severe bowel disturbances (posterior mean = -0.38, P < 0.05) and less severe sleep disturbances (posterior mean = 0.49, P < 0.05) than older patients. Higher daily coffee intake was correlated with a lower severity of bowel disturbances (posterior mean = -0.31, P < 0.05). Sex (female) and daily alcohol intake (modest) were correlated with less severe sleep disturbances. CONCLUSION: The unitary bowel-sleep model based on IRT revealed a strong positive correlation between the severity of IBS symptoms and sleep disturbances.

Early subclinical increase in pulmonary water content in athletes performing sustained heavy exercise at sea level: ultrasound lung comet-tail evidence.

Whether prolonged strenuous exercise performed by athletes at sea level can produce interstitial pulmonary edema is under debate. Chest sonography allows to estimate extravascular lung water, creating ultrasound lung comet-tail (ULC) artifacts. The aim of the study was to determine whether pulmonary water content increases in Ironmen (n = 31) during race at sea level and its correlation with cardiopulmonary function and systemic proinflammatory and cardiac biohumoral markers. A multiple factor analysis approach was used to determine the relations between systemic modifications and ULCs by assessing correlations among variables and groups of variables showing significant pre-post changes. All athletes were asymptomatic for cough and dyspnea at rest and after the race. Immediately after the race, a score of more than five comet tail artifacts, the threshold for a significant detection, was present in 23 athletes (74%; 16.3 ± 11.2; P < 0.01 ULC after the race vs. rest) but decreased 12 h after the end of the race (13 athletes; 42%; 6.3 ± 8.0; P < 0.01 vs. soon after the race). Multiple factor analysis showed significant correlations between ULCs and cardiac-related variables and NH(2)-terminal pro-brain natriuretic peptide. Healthy athletes developed subclinical increase in pulmonary water content immediately after an Ironman race at sea level, as shown by the increased number of ULCs related to cardiac changes occurring during exercise. Hemodynamic changes are one of several potential factors contributing to the mechanisms of ULCs.

Telematic integration of health data: a practicable contribution.

The patients' clinical and healthcare data should virtually be available everywhere, both to provide a more efficient and effective medical approach to their pathologies, as well as to make public healthcare decision makers able to verify the efficacy and efficiency of the adopted healthcare processes. Unfortunately, customised solutions adopted by many local Health Information Systems in Italy make it difficult to share the stored data outside their own environment. In the last years, worldwide initiatives have aimed to overcome such sharing limitation. An important issue during the passage towards standardised, integrated information systems is the possible loss of previously collected data. The herein presented project realises a suitable architecture able to guarantee reliable, automatic, user-transparent storing and retrieval of information from both modern and legacy systems. The technical and management solutions provided by the project avoid data loss and overlapping, and allow data integration and organisation suitable for data-mining and data-warehousing analysis.

Post-dive ultrasound detection of gas in the liver of rats and scuba divers.

In a previous study, we obtained histologic documentation of liver gas embolism in the rat model of rapid decompression. The aim of the study was to assess in the same model occurrence and time course of liver embolism using 2-D ultrasound imaging, and to explore by this means putative liver gas embolism in recreational scuba divers. Following 42 min compression at 7 ATA breathing air and 12 min decompression, eight surviving female rats were anesthetized and the liver imaged by ultrasound at 20 min intervals up to 120 min. A significant enhancement of echo signal was recorded from 60 to 120 min as compared to earlier post-decompression times. Enzymatic markers of liver damage (AST, ALT, and GGT) increased significantly at 24 h upon decompression. Twelve healthy experienced divers were studied basally and at 15-min intervals up to 60 min following a 30-min scuba dive at 30 msw depth. At 30 min upon surfacing echo images showed significant signal enhancement that progressed and reached plateau at 45 and 60 min. Total bilirubin at 24 h increased significantly (p = 0.02) with respect to basal values although within the reference range. In conclusion, 2-D ultrasound liver imaging allowed detection of gas embolism in the rat and defined the time course of gas accumulation. Its application to scuba divers revealed liver gas accumulation in all subjects in the absence of clear-cut evidence of liver damage or of any symptom. The clinical significance of our findings remains to be investigated.

Advanced instrumentation for research in diving and hyperbaric medicine.

Improving the safety of diving and increasing knowledge about the adaptation of the human body to underwater and hyperbaric environment require specifically developed underwater instrumentation for physiological measurements. In fact, none of the routine clinical devices for health control is suitable for in-water and/or under-pressure operation. The present paper addresses novel technological acquisitions and the development of three dedicated devices: * an underwater data logger for recording O2 saturation (reflective pulsoxymetry), two-channel ECG, depth and temperature; * an underwater blood pressure meter based on the oscillometric method; and * an underwater echography system. Moreover, examples of recordings are presented and discussed.

Complex intermittency blurred by noise: theory and application to neural dynamics.

We propose a model for the passage between metastable states of mind dynamics. As changing points we use the rapid transition processes simultaneously detectable in EEG signals related to different cortical areas. Our model consists of a non-Poissonian intermittent process, which signals that the brain is in a condition of complexity, upon which a Poisson process is superimposed. We provide an analytical solution for the waiting-time distribution for the model, which is well obeyed by physiological data. Although the role of the Poisson process remains unexplained, the model is able to reproduce many behaviors reported in literature, although they seem contradictory.

Gas embolization of the liver in a rat model of rapid decompression.

Occurrence of liver gas embolism after rapid decompression was assessed in 31 female rats that were decompressed in 12 min after 42 min of compression at 7 ATA (protocol A). Sixteen rats died after decompression (group I). Of the surviving rats, seven were killed at 3 h (group II), and eight at 24 h (group III). In group I, bubbles were visible in the right heart, aortic arch, liver, and mesenteric veins and on the intestinal surface. Histology showed perilobular microcavities in sinusoids, interstitial spaces, and hepatocytes. In group II, liver gas was visible in two rats. Perilobular vacuolization and significant plasma aminotransferase increase were present. In group III, liver edema was evident at gross examination in all cases. Histology showed perilobular cell swelling, vacuolization, or hydropic degeneration. Compared with basal, enzymatic markers of liver damage increased significantly. An additional 14 rats were decompressed twice (protocol B). Overall mortality was 93%. In addition to diffuse hydropic degeneration, centrilobular necrosis was frequently observed after the second decompression. Additionally, 10 rats were exposed to three decompression sessions (protocol C) with doubled decompression time. Their mortality rate decreased to 20%, but enzymatic markers still increased in surviving rats compared with predecompression, and perilobular cell swelling and vacuolization were present in five rats. Study challenges were 1) liver is not part of the pathophysiology of decompression in the existing paradigm, and 2) although significant cellular necrosis was observed in few animals, zonal or diffuse hepatocellular damage associated with liver dysfunction was frequently demonstrated. Liver participation in human decompression sickness should be looked for and clinically evaluated.