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.

Gap junctions promote synchronous activities in a network of inhibitory interneurons.

By using a single compartment biophysical model of a fast spiking interneuron the synchronization properties of a pair of cells, coupled by electrical and inhibitory synapses, are investigated. The inhibitory and excitatory synaptic couplings are modeled in order to reproduce the experimental time course of the corresponding currents. It is shown that increasing the conductance value of the electrical synapses enhances the synchronization between the spike trains of the two cells. Moreover, increasing either the decay time constant of the inhibitory current or the firing frequency of the cells favours the emergence of synchronous discharges.

Sciatic nerve block with lateral popliteal approach for hallux vagus correction. Comparison between 0.5% bupivacaine and 0.75% ropivacaine.

AIM: In this study the authors compared the clinical profile of 2 local anesthetic drugs in the sciatic nerve block used during hallux valgus correction, a surgical procedure known to be post-operatively extremely painful. Since hallux valgus correction is painful post-operatively, many attempts have been tried to ensure a long-lasting analgesia. Block of the sciatic nerve appears to be the right choice balancing ease to performance, satisfaction of the patient and duration of action. METHODS: The authors investigated the use of 20 ml of 0.5% bupivacaine or 0.75% ropivacaine regarding the speed of onset, quality and length of duration of sciatic nerve block performed with a lateral popliteal approach. Sixty ASA I-III patients (aged 19-73 years) were enrolled in this trial. Written informed consent was asked and obtained. A 20 G 50 mm Teflon coated Crawford needle, delivering 0.5 mA at 2 Hz, was used to locate and block the sciatic nerve in the popliteal fossa with a lateral approach. RESULTS: Patients in the ropivacaine group required about 13 minutes to achieve a complete block and about 16 minutes were needed in the bupivacaine group for the anesthesia to be complete. The length of analgesia was 16 h for the ropivacaine group and 13 h for the bupivacaine group. This kind of approach to block the sciatic nerve appeared to the authors to be very easy to perform, with the patient lying in a natural position. Surgical anesthesia required less than 30 min in both groups to be ready, while the ropivacaine group had a longer length of analgesia compared to the bupivacaine group. CONCLUSIONS: Patient satisfaction was high in both groups.

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).

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.

The use of remifentanil for bloodless surgical field during vertebral disc resection.

BACKGROUND: A short hospital stay is nowadays desirable and affordable for a wide range of surgical pathology, respecting safety of care and home discharge. In the present study, the Authors investigated the use of TIVA with propofol/remifentanil during microsurgical vertebral disc resection to maintain a controlled vascular hypotension for bloodless surgical field aiming to reduce the operating time and consequently recovery room length of stay and morbility related to anaesthesia. METHODS: The study took place in a 300 bed Orthopaedics hospital over a period of 3 months and 50 ASA I-II patients were enrolled in this trial; further data are presented for comparison of 50 ASA I-II patients homogeneous for age and sex to the studied population, operated under a standard TIVA with propofol and boluses of fentanyl. Duration of anaesthesia and surgery, time for awakening after cessation of TIVA, incidence of postoperative nausea and vomiting (PONV), amount and quality of postoperative analgesia, length of stay in the recovery room are reported in statistical presentation. RESULTS: Time of surgery and anaesthesia were reduced in the remifentanil group compared with the fentanyl group, thanks to an easily reachable and durable state of controlled hypotension in the first group without the use of any other drug. The recovery profile was shorter in the remifentanil group the drug being rapidly metabolised by plasma cholinesterase. CONCLUSIONS: No difference occurred between the two groups regarding quality and amount of postoperative analgesia, while PONV presented more in the fentanyl group and shivering more in the remifentanil group.

0.25% levo-bupivacaine for interscalene block during shoulder surgery. A survey on 20 patients.

BACKGROUND: Interscalene brachial plexus block (ISB) is an alternative procedure to general anaesthesia for shoulder surgery, and consents the anaesthetist to easily control postoperative pain that, indeed, is known to be intense and often requires strong analgesic administration. The introduction of regional anaesthesia for this type of surgery, contributed to the relief of acute postoperative pain occurring in the recovery room since the analgesic effects of block persist for several hours after surgery depending upon the selected drug. The aim of this study was to determine the effects of 40 ml of 0.25% levo-bupivacaine, a local anaesthetic derived from the racemic mixture of bupivacaine, on the speed of onset, quality and duration of ISB. METHODS: Twenty adult ASA I-II patients, undergoing shoulder surgery for various pathologies, were enrolled in this study. All patients were examined before surgery and were given a full explanation; written informed consent was asked for and obtained. ISB was placed with the classic Winnie approach and the plexus was localised by means of a 40 mm, 22G Teflon(R) coated needle connected to an electro neural stimulator distributing 0.5 mA at 2 Hz. Once twitching was observed, 16 ml of 0.25% levo-bupivacaine were injected on shoulder lift, 12 ml on forearm abduction and 12 ml on forearm adduction. Monitoring: the time elapsing from last injection to loss of sensibility of pin-prick on the shoulder area, degree of motor block expressed on a 4 points scale, surgery time, as well as total time of analgesia were recorded for statistical analysis. STATISTICS: data were analysed at the STATISTICS Department of the University of Messina (Italy) and results are expressed as means and standard deviations. RESULTS: Eighteen patients were operated under ISB and light sedation while 2 patients were scheduled for interscalene block plus deep sedation, the position being very discomforting and surgery supposed to last more than 60 min (shoulder arthroscopy). Less than 9 min were required for the block to be complete with satisfactory muscle relaxation, optimal intraoperative anaesthetic condition and more than 13 hours of postoperative analgesia occurred. CONCLUSIONS: Levobupivacaine is a newly developed local anaesthetic derived from a bupivacaine racemic mixture from which the right isomer has been eliminated. Levo-bupivacaine, compared to racemic mixture, is acknowledged to be less cardiotoxic, faster at equal dosage, and ensures a longer analgesic interval. Zero point twenty-five percent concentration was preferred in this study in order to inject large volumes (40 ml) with a minimal anaesthetic amount (100 mg), resulting in short time for obtaining loss of sensibility, optimal intraoperative conditions and long lasting block with adequate postoperative analgesia.

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.

Nonlinear activity of identified Lymnaea neurons.

Two long-lasting discharges of action potentials were recorded from a buccal cell of the pond snail, respectively, before and after superfusing the preparation with low-calcium solution. The corresponding sequences of interspike intervals were then analysed by the nonlinear prediction methods. The results yield evidence of a small but clear nonlinearity only in the second of analysed tachograms. This finding is evaluated and discussed.

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.

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.

Interleukin-12 and interleukin-10 production by mononuclear phagocytic cells from breast cancer patients.

Interleukin-10 (IL-10) and Interleukin 12 (IL-12) generation may be regulated by a complex monocyte and macrophage-derived cytokine network and an impairment of the immune system can be observed in neoplastic disease. In this study, we examined the production of these cytokines by phagocytic cells, obtained from breast cancer (BCa)-bearing patients. Our results suggest that an increased IL-10 formation may represent an important regulatory pathway of IL-12 production by BCa mononuclear cells. In this report, we show that mononuclear cells of patients affected by breast cancer have a defective IL-12 production capability while generating higher amounts of IL-10.

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.

[Clinical study of residual function and recurrence in patients undergoing partial thyroidectomy for euthyroid nodular goiter]. / Studio clinico della funzione residua e delle recidive in pazienti operati di tiroidectomia parziale per struma nodulare eutiroideo.

The different surgical options for the treatment of non toxic nodular goiter led the Authors to study the residual thyroid function following conservative surgery (subtotal thyroidectomy, lobectomy and enucleation). Follow-up showed an overall recurrence rate of 49%, with a higher rate after lobectomy and enucleation than after subtotal thyroidectomy. On the other hand, subclinical hypothyroidism was higher in patients who underwent subtotal thyroidectomy. No significative correlation was found between high plasmatic levels of TSH and recurrences.

In vitro effects of lithium chloride on TNF alpha and IL-6 production by monocytes from breast cancer patients.

It is well known that lithium chloride (LiCl) is able to trigger human monocytes to release tumor necrosis factor alpha (TNF alpha). In this study we have evaluated the in vitro effect of LiCl on TNF alpha and interleukin-6 (IL-6) release by monocytes from patients affected by non-metastatic (BCa/M0) and metastatic breast cancer (BCa/M1), preincubated with autologous serum (sPt). Our data demonstrate that monocytes from cancer patients (BCa) treated with LiCl released lower amounts of TNF alpha compared to those from healthy donors (HD). Preincubation in autologous serum (sPt) impaired TNF alpha production by monocytes from BCa with LiCl. On the contrary, our data indicate that IL-6 production by monocytes treated was not impaired. Moreover, the results obtained from the same cells, preincubated in sPt and treated with LiCl, indicate that serum factors may synergize with LiCl treatment in releasing IL-6.

[Esophageal leiomyoma: ultrasonographic endoscopic diagnosis]. / Leiomioma dell'esofago: diagnosi ecoendoscopica.

Leiomyoma is the most frequent benign neoplasia of the esophagus. It is generally diagnosed, accidentally during a radiologic examination (filling defect with clear and regular margins) or endoscopically (sessile, hemispheric, covered by pink mucosa). Recently, to the above conventional exams, endoscopic ultrasonography has been added allowing to identify the single layers of the esophageal wall, thus furnishing useful informations on the morpho-structural characteristics of the leiomyoma. From October '94 to May '96, at the Endoscopy Service of the Institute of Oncology of the University of Messina, 12 patients, 8 males and 4 females, ranging from 39 to 69 years of age (median age 55.4) underwent EUS for suspect leiomyoma. An Olympus EU-M20 echoendoscope was used with a radial scan transducer of 12 Mhz. In 8 patients the leiomyoma was located in the III mid-esophagus, while in 4 patients the III inferior portion was interested. The Authors observed lesions ranging in size from 0.5 to 2.5 cm. In their experience, a suspect of leiomyoma represents a good indication for an endoscopic ultrasonography, which shows high sensitivity and specificity.

Dynamics of the neural discharge in snail neurons.

Spike trains recorded under weak sinusoidal driving from central neurons of Lymnaea stagnalis appear quite irregular and envisage the possibility of an underlying chaotic process. Therefore, the sequences of interspike intervals are analyzed in the framework of non-linear dynamics. Since, for several reasons, these sequences are rather short, the analysis is performed by using methods of non-linear forecasting. To reject the null hypothesis that the original time series is a realization of a linear stochastic process with the same autocorrelation function, the results obtained on the original data are compared with those from surrogate data sets. Some 'non-linear' predictability occurs only in narrow regions of the space of stimulus parameters and the frequency of perturbation is critical in determining it. Moreover, it is shown that such behavior can be qualitatively mimicked by the FitzHugh-Nagumo model driven by a weak sinusoidal signal plus noise. It is argued that the narrowness of the non-linear predictability regions renders quite unlikely the detection of deterministic dynamics in the activity of these neurons.

Dynamics of analog-to-frequency transduction in sensory receptors.

We analyze the analog-to-frequency transduction by sensory neurons in vivo. Spatially extended neural models are made to fire by applying the stimulus to the membrane potential at the boundary of the trigger zone. The membrane property that provides a broad dynamical range of frequency is a prolonged hyperpolarizing afterpotential. In support of this PDE model, we study the stimulus-dependent location of pulse-initiation in crayfish stretch receptors Ringham (1971).

Ring wave solutions of a n+1-dimensional Sine-Gordon model.

The dynamical properties of the ring wave solutions of the model psi(tt)- nabla (n) (2)psi+sin psi+ varepsilon sin (psi/2)+alphapsi(t)=0 (00, alpha=0 (or alpha>0) the return effect of the ring wave does not occur only for well defined values of varepsilon. It will be shown numerically that the dissipative perturbation alphapsi(t) (alpha>0) stabilizes both the velocity and the wave profile of the ring wave when the return effect does not occur. (c) 1997 American Institute of Physics.