Biomedical subjects

Y Sivan

Publications and source records attributed to Y Sivan.

At least 19 recordsLinked to original sources

PubMed2006

Waves in nonlinear lattices: ultrashort optical pulses and Bose-Einstein condensates.

The nonlinear Schrödinger equation i (partial differential)(z)A(z,x,t)+(inverted Delta)(2)(x,t)A+[1+m(kappax)]|A|2A=0 models the propagation of ultrashort laser pulses in a planar waveguide for which the Kerr nonlinearity varies along the transverse coordinate x, and also the evolution of 2D Bose-Einstein condensates in which the scattering length varies in one dimension. Stability of bound states depends on the value of kappa=beamwidth/lattice period. Wide (kappa>>1) and kappa=O(1) bound states centered at a maximum of m(x) are unstable, as they violate the slope condition. Bound states centered at a minimum of m(x) violate the spectral condition, resulting in a drift instability. Thus, a nonlinear lattice can only stabilize narrow bound states centered at a maximum of m(x). Even in that case, the stability region is so small that these bound states are "mathematically stable" but "physically unstable."

Journal Article↗

PubMed2006

Interaction-induced localization of anomalously diffracting nonlinear waves.

We study experimentally the interactions between normal solitons and tilted beams in glass waveguide arrays. We find that as a tilted beam, traversing away from a normally propagating soliton, coincides with the self-defocusing regime of the array, it can be refocused and routed back into any of the intermediate sites due to the interaction, as a function of the initial phase difference. Numerically, distinct parameter regimes exhibiting this behavior of the interaction are identified.

Journal Article↗

PubMed2001

Melatonin production in healthy infants: evidence for seasonal variations.

The objective of this study was to determine the normal range of nocturnal urinary excretion of the major melatonin metabolite, 6-sulfatoxymelatonin (6SMT) in a large sample of healthy full-term infants (8 and 16 wk old) and assess whether the endogenous production of melatonin changes with season. 6SMT was assessed in urine samples extracted from disposable diapers removed from full-term, 8- (n = 317) and 16-wk-old (n = 93) infants over the nocturnal period (19:00-08:00 h). In addition, 6SMT was assessed in 8-wk-old (n = 35) healthy infants over the entire 24-h period. 6SMT was determined by an ELISA assay. 6SMT excretion at 8 wk of age exhibited diurnal variations with (mean +/- SD) 61 +/- 18% of the daily production excreted during the nocturnal period regardless of season. The nocturnal 6SMT values in the entire cohort (at 8 as well as 16 wk of age) were found to significantly depart from normal distribution (Kolmogorov-Smirnov test). A normal distribution was obtained using a natural base logarithmic (ln) transformation of the data. The normal range (2.5-97.5 percentile of the ln 6SMT excretion per night) was thus defined as 4.66-8.64 (106-5646 ng/night) for 8-wk-old and 5.19-9.67 (180-15,820 ng/night) for 16-wk-old infants. A significant effect of the month of birth on 6SMT production at the age of 8 wk was found (ANOVA, p < 0.002) with maximal levels produced by infants born in June (summer solstice) and minimal excretion in infants born in December (winter solstice). Short-photoperiod-born infants excreted on average about threefold less 6SMT compared with long-photoperiod-born infants (t test, p = 0. 01). The seasonal variations were no longer present at 16 wk of age. No effect of breast-feeding at the time of sampling on seasonality of 6SMT was found. Normal ranges for the nocturnal urinary excretion of 6SMT in full-term infants at 8 and 16 wk of age are defined. This enables the evaluation of nocturnal 6SMT excretion as a prognostic and diagnostic factor for child development. The strong effect of season on the normal excretion of nocturnal 6SMT at 8 but not 16 wk of age suggests prenatal influence of the photoperiod on the ontogeny of melatonin.

Analysis of Variance↗

PubMed2000

Hyper-releasability of mast cells in family members of infants with sudden infant death syndrome and apparent life-threatening events.

BACKGROUND: An allergic reaction with increased degranulation of mast cells has been suggested as a possible mechanism in sudden infant death syndrome (SIDS). STUDY DESIGN: Mast cell releasability was assessed in 2 study groups: A, 22 subjects, 16 first-degree relatives of infants who had had an apparent life-threatening event (ALTE) and 6 infants after ALTE and B, 46 first-degree relatives of SIDS cases. These groups were compared with 71 members of an age-matched control group. In each subject the skin wheal and flare reactions were measured after an intradermal injection of 0.02 mL of each of the following substances dissolved in phenol-saline solution: histamine 0.0001 mg/mL, histamine 0.001 mg/mL, codeine 0.5 mg/mL, codeine 1 mg/mL, compound 48/80 0.05 mg/mL, compound 48/80 0. 1 mg/mL, and phenol-saline solution. The size of wheal and flare skin reaction was assessed by computerized planimetry after the shape of the cutaneous response was copied onto a paper. RESULTS: The wheal and flare skin reaction to each of the substances was significantly larger in the 2 study groups compared with the control group (P <.05) except for the wheal reaction to compound 48/80 0.1 mg/mL, codeine 0.5 mg/mL, and histamine in both concentrations for group A and the wheal reaction to codeine 1 mg/mL and histamine in both concentrations for group B. All individuals with increased reaction belonged to 3 (50%) of 6 families with ALTE history and to 8 (73%) of 11 families with SIDS history. CONCLUSIONS: Increased mast cell hyper-releasability and degranulation take place in family members of some SIDS and ALTE cases and in some infants with ALTE, supporting a possible role for an immunologic mechanism in the pathophysiology of these entities.

Adult↗

PubMed2000

Low melatonin production in infants with a life-threatening event.

This study compares the urinary excretion of the main melatonin metabolite, 6-sulfatoxymelatonin (6SMT), in infants who have and have not experienced a life-threatening event (ALTE). 6SMT was assessed in the following groups of infants: 15 infants with ALTE for whom home monitoring had been recommended, 15 infants who had had an abrupt cyanotic apneic event but did not require mouth-to-mouth resuscitation, 15 siblings of those who had died from sudden infant death syndrome (SIDS), and 35 age-matched healthy comparison infants. All 80 infants were between 48 and 58 weeks of postconceptional age. On a double-blind basis, the total amount of 6SMT excreted over 24 hours and the diurnal rhythm in the rate of 6SMT excretion were assessed using urine samples taken from disposable diapers (nappies). The mean daily excretion of 6SMT was significantly lower in the ALTE (1,588 ng/24 hour) than in the comparison infants (3,961 ng/24 hour). No such difference was found between the infants with a cyanotic apneic event (3,268 ng/24 hour) and the SIDS siblings (2,962 ng/24 hour). The diurnal 6SMT rhythms in the ALTE infants were characterized by lower 24-hour mean and amplitude values, whereas the time of peak and nadir excretion rates (07:15 to 08:45 hours and 14:45 to 16:15 hours respectively) was similar in all four infant groups. Follow-up of the ALTE infants, performed 6 to 8 weeks later (59 to 66 weeks of postconceptional age), revealed that 6SMT excretion increased in all of them, suggesting a delayed ontogeny rather than permanent deficiency of melatonin production in ALTE.

Acute Disease↗

PubMed2000

Repeat computed tomographic scan within 24-48 hours of admission in children with moderate and severe head trauma.

OBJECTIVE: To asses the yield and contribution of a routine predetermined repeat head computed tomographic (CT) scan within 24-36 hrs in pediatric patients with moderate to severe head trauma. DESIGN: Records review. SETTING: Five pediatric intensive care units. PATIENTS: We reviewed the charts of 173 consecutive pediatric patients with moderate to severe head trauma (Glasgow Coma Scale score of < or = 11) that survived the first 24 hrs after being admitted to five Israeli trauma centers. Clinical data collected included status at admission, at the time between the first and second CT scans, and after the second scan. Head details of the first, second, and, if performed, third CT scan were collected. Treatment strategy during each period was recorded, including any change in treatment after each CT scan. MEASUREMENTS AND MAIN RESULTS: A total of 47 (27%) of the second CT scans showed new lesions including six intracranial hemorrhages, 17 cases of worsening brain edema, and 18 newly diagnosed brain contusions. However, none of these findings necessitated surgical intervention or any change in therapy. Of the 67 patients who underwent a third CT scan, two cases required surgical intervention because of new findings in the third CT. CONCLUSIONS: A second routine prescheduled head CT scan within 24-36 hrs after admission in pediatric patients with moderate to severe head trauma is unlikely to yield any change in therapy. Clinically and intracranial pressure-oriented CT scan may better select and diagnose patients who require changes in therapy, including surgery. Studies aimed to determine the ideal timing for the second are warranted.

Adolescent↗

PubMed2000

Immunologic response to a single dose of tetanus toxoid in older people.

OBJECTIVES: Several studies have demonstrated that a large percentage of older people are inadequately immunized against tetanus. The aim of this study was to assess the immunity against tetanus in a group of individuals aged 69 and older and to examine the immune response to a single dose of tetanus toxoid. DESIGN: A convenience sample of 115 residents of a large retirement home, aged 69 and older, was studied. After a blood sample for anti-tetanus antibody titer, a single dose of tetanus toxoid vaccine was administered. Repeat titers were obtained 6 weeks after the vaccination and analyzed by ELISA assay. Antibody levels equal to or greater than 0.1 IU/mL were considered protective. RESULTS: Sixty-seven of 115 (58.3%) individuals had adequate antibody titers. Those individuals who reported having been vaccinated with tetanus toxoid in the past were more likely to be immunized adequately compared with those who reported having never been vaccinated (66.7% vs 39.3%, P = .02). After vaccination, 34 of 46 (73.9%) individuals with inadequate antibody titers became seropositive. Those who remained seronegative had mean prevaccination antibody titers significantly lower than those who seroconverted. Sixteen of 17 (94.1%) persons who reported having been vaccinated in the past and were found to be seronegative developed adequate antibody titers following vaccination, compared with only nine of 16 (56.2%) who reported never having been vaccinated (P = .04). There was no association between seroconversion rate and age, sex, underlying diseases, and army service. CONCLUSIONS: Most individuals will develop an adequate anti-tetanus antibody titer following administration of a single dose of tetanus vaccine. A history of past immunization is a good predictor of becoming adequately immunized. It is important that physicians follow the current recommendations for adult immunization and initiate campaigns to ensure that the older population is protected against tetanus.

Aged↗

PubMed2000

Duration of home monitoring for infants discharged with apnea of prematurity.

Sixty-four preterm infants with apnea of prematurity (AOP) discharged with cardiorespiratory home monitoring (HM) were prospectively followed. For each monitor alarm the parents recorded the occurrence of apnea, bradycardia or color change, and the type of assistance provided. The mean gestational age at birth was 28.8 (26-34) weeks, and the mean birth weight was 1,180 (730-2,390) g. The parents of 61/64 infants (95%) reported a total of 185 true AOPs with a mean of 3 (1-12) events/infant. The mean postconceptional age (PCA) at the last apnea was 41.0 (37-44) weeks. In 80%, AOP terminated between 40 and 44 weeks PCA. There was no correlation between the degree of prematurity and the PCA of the last apnea. We conclude that in preterm infants with AOP discharged with HM, HM may be discontinued at 45 weeks PCA.

Apnea↗

PubMed2000

Reaching the diagnosis of cystic fibrosis--the limits of the spectrum.

BACKGROUND: Cystic fibrosis is the most common life-limiting autosomal recessive genetic disorder in Caucasians. Typically it is a multisystem disease diagnosed by increased chloride levels on sweat testing, with mortality due mainly to progressive respiratory disease. The clinical spectrum of CF has recently been much expanded. Genetic testing for mutant CF transmembrane regulator has revealed atypical cases where sweat test results are borderline or normal. In other patients, genetic mutations cannot be identified but abnormal CFTR function is shown using nasal potential difference measurement. OBJECTIVES: To highlight the diagnostic and therapeutic dilemmas in cases of atypical cystic fibrosis. METHODS: We reviewed patients with atypical CF and widely varying phenotype who are managed at Schneider Children's Medical Center of Israel. RESULTS: Two patients had severe lung disease but little expression in other organs. Accurate diagnosis was essential to enable aggressive therapy in a specialized center. Four other patients are in excellent general health but have symptoms limited to male infertility, heat exhaustion, pancreatitis or transient liver dysfunction, while lung disease is minimal. For these patients, careful counseling is needed to avoid unnecessary upheaval, inappropriately aggressive management, and the psychosocial implications of a CF diagnosis. These dilemmas have increased considerably in our center, as in others worldwide. CONCLUSION: It is our obligation as clinicians--at the level of both primary physician and referral center--to maintain an ever higher index of suspicion for CF, tempered by a rational program of counseling and management appropriate to the individual.

Adult↗

PubMed1999

Real-time PC-based system for dynamic beat-to-beat QT-RR analysis.

A real-time analysis (RTA) system, based on a personal computer with a digital signal processor card (DSP) was developed. The system extracts and saves the QT and RR intervals from an incoming ECG signal sampled at 1 kHz. The method of defining the QT and RR intervals is based on performing multiple cross-correlations that enables rejection of artifacts from the analysis. The relationship between the RR and the QT intervals is found using the following general formula QT(i) cRR(i)(i-1). Linear regression is performed on the logarithms of QT and RR measurements obtained to estimate a constant (a = logc) and a slope (b), reflecting the dynamic change of the QT intervals. Having these two values, the dynamic QT extrapolated to a heart period of 1 s (QTcd) was calculated. The system also performs spectral analysis of the intervals and dynamic QT-RR relation analysis. The system was evaluated on recordings from 10 infants aged 4 to 24 weeks. The QT/RR computerized measuring device used in the present study answers to the requirements for precise dynamic beat-to-beat QT measurement. Its sampling rate is high and can achieve a real millisecond-precision without the need of interpolation methods. The measurements are performed on-line, at the time of the actual recording. Results appear immediately and a measure of dynamic QT behavior can be easily obtained within minutes. The computerized system with the dynamic QT-RR measurements may provide a simple and accurate tool for testing drug treatment and effects of other interventions for cardiac disorders and arrhythmia risk.

Electrocardiography↗

PubMed1997

Treatment of loculated pleural effusion with intrapleural urokinase in children.

BACKGROUND/PURPOSE: The use of fibrinolytic agents such as urokinase and streptokinase has been reported in cases of empyema in adults. In pediatric patients the experience is, however, very limited. METHODS: A series of seven consecutive children who had loculated pleural effusion that did not respond to drainage and antibiotics is reported. RESULTS: In all cases, the effusion was found to be multiloculated. Urokinase (UK) instillation through the already existing chest tube was started. A dose of 100,000 U of UK diluted in 100 mL of normal saline was instilled through the chest tube, which was clamped for 12 hours and then was left open for another 12 hours. In six of seven children, the treatment was terminated after complete or almost complete resolution was attained. This was achieved within 5 treatment days (mean, 3.3). There was one failure which was attributed to relatively late initiation of treatment. No complications were observed. CONCLUSIONS: The authors conclude that intrapleural administration of UK is a safe and efficient method of treatment in cases of loculated pleural effusions in children. UK instillation to the intrapleural space should be considered early before initiating surgical intervention. Starting intrapleural UK treatment should not be delayed.

Child↗

PubMed1997

Home monitoring for infants at high risk for the sudden infant death syndrome.

The rate of sudden infant death syndrome (SIDS) In Israel is relatively low (0.5-0.9:1,000). Home cardiorespiratory monitoring (HM) is an accepted practice in infants at high risk for SIDS. We report our experience with 261 infants who were referred to our SIDS prevention program. They included: 52 preterm infants with apneas and bradycardias, 83 SIDS siblings (3 twins), 22 infants of drug-addicted mothers, and 104 infants after an idiopathic apparent life-threatening event (ALTE). HM was performed in 40 of 52 preterms, 38 of 83 SIDS siblings, all 22 infants of addicted mothers and 67 of 104 post-ALTE. All received 24 h/day medical and technical backup as well as emotional support, and were closely followed until 15 months of age. None of the 261 infants died. Five infants experienced six ALTEs that required resuscitative measures; another 28 infants had monitor alarms judged as real by the caregivers. The average duration of HM was 3.2 months (range 1-7). In 8 of 167 cases the parents stopped HM earlier than recommended, and in 34 of 167 cases (20%), parents continued HM beyond the time when discontinuation was recommended by the medical personnel. Among the caregivers, 85% found HM to be reassuring and stated that it helped them to conduct a normal life. We suggest that in our population, HM may have a favorable effect on family life. With close backup and support, most families will benefit from HM and will gain reassurance that will enable them to conduct normal life.

Home Care Services↗

PubMed1996

Screening obstructive sleep apnoea syndrome by home videotape recording in children.

Overnight polysomnography (PSG) has been used to diagnose and assess the severity of obstructive sleep apnoea syndrome (OSAS) in children. The aim of this study was to determine whether home video-recording of children during sleep may be used for screening OSAS. In 58 children suspected of having OSAS, PSG results were compared with the corresponding analyses of 30 min video-recordings of each child sleeping at home. The video-recordings were evaluated by: 1) overall investigator's clinical judgement; and 2) a scoring system based on noisy breathing, movements, walking episodes, apnoea, chest retractions and mouth breathing. PSG results were highly correlated with the video test results, with agreement in 49 out of 58 (84%). In 36 of the 58 children, the PSG was abnormal compared with 41 out of 58 abnormal video tests. The sensitivity of the overall investigator judgement of video test was 94% (34 out of 36) and the specificity 68% (15 out of 22). Video scores > 10 were highly predictive of OSAS, whilst scores < 5 were associated with normality. Using a stepwise logistic regression analysis, each of the scoring variables was tested against the PSG results and an equation was formulated for predicting PSG by the video test. The equation predicted PSG results in 49 out of 58 (84%) cases. Thirty minutes of home video-recordings during sleep is a reliable screening method for obstructive sleep apnoea syndrome in children. This technique may, thus, improve patient selection for polysomnography.

Algorithms↗

PubMed1996

Flow limitation in anesthetized rhesus monkeys: a comparison of rapid thoracoabdominal compression and forced deflation techniques.

Rapid thoracoabdominal compression (RTC) and forced deflation (FD) allow the examination of maximal expiratory flow-volume (MEFV) curves in animals and human infants unable to generate a voluntary maximal expiratory maneuver. We compared flows generated by these two techniques and by constructing isovolume pressure-flow (IVPF) curves examined each method's potential to produce flow limitation. RTC and FD were performed in seven intubated rhesus monkeys from +40 cm H2O inspiratory pressure with deflation pressures ranging from -20 to -100 cm H2O and jacket pressures from +20 to +100 cm H2O (arms outside jacket). We also performed RTC maneuvers in all monkeys with the arms inside the jacket at +100 cm H2O jacket pressure. Maximal expiratory flows achieved by FD and RTC were analyzed at isovolume points. Both techniques produced flow limitation conditions over the last 25% of the MEFV curve. Individual IVPF curves generated by the two techniques demonstrated remarkable differences in shape and flow rates. Maximal transpulmonary pressures achieved with FD were higher than those with RTC in this experiment. Negative effort dependence was observed with higher deflation pressures in the majority of the monkeys. Flows achieved by RTC with the arms in were lower than those achieved with the arms out when compared at identical pressure gradients. We conclude that the difference in expiratory flow rates at isovolume-pressure points is most likely related to different effects on the behavior of intrapulmonary airways and choke point characteristics by the two techniques.

Animals↗

PubMed1994

Measurement of high lung volumes by nitrogen washout method.

Studies on human infants suggested that thoracic gas volume (TGV) measured at end exhalation may not depict the true TGV and may differ from TGV measured from a series of higher lung volumes and corrected for the volume added. This was explained by gas trapping. If true, we should expect the discrepancy to be more pronounced when functional residual capacity (FRC) and higher lung volumes are measured by gas dilution techniques. We studied lung volumes above FRC by the nitrogen washout technique in 12 spontaneously breathing rhesus monkeys (5.0-11.3 kg wt; 42 compared measurements). Lung volumes directly measured were compared with preset lung volumes achieved by artificial inflation of the lungs above FRC with known volumes of air (100-260 ml). Measured lung volume strongly correlated with and was not significantly different from present lung volume (P = 0.05; r = 0.996). The difference between measured and preset lung volume was 0-5% in 41 of 42 cases [1 +/- 0.4% (SE)]. The direction of the difference was unpredictable; in 22 of 42 cases the measured volume was larger than the preset volume, but in 17 of 42 cases it was smaller. The difference was not affected by the volume of gas artificially inflated into the lungs. We conclude that, overall, lung volumes above FRC can be reliably measured by the nitrogen washout technique and that FRC measurements by this method reasonably reflect true FRC.

Animals↗

PubMed1992

Autosomal dominant congenital laryngomalacia.

A family is presented in which congenital stridor due to laryngomalacia was evident in 9 individuals through 3 generations. This report confirms the autosomal dominant transmission of at least one type of laryngomalacia.

Adult↗

PubMed1992

Estimation of arterial carbon dioxide by end-tidal and transcutaneous PCO2 measurements in ventilated children.

Simultaneous measurements of arterial, end-tidal, and transcutaneous carbon dioxide (PaCO2, PetCO2, PtcCO2, respectively) were obtained in 134 children receiving mechanical ventilation (ages, 2 days to 16 years; mean, 2.5 years). The mean +/- SD PetCO2 bias (PaCO2 - PetCO2) was 3.4 +/- 6.6 mmHg. When the PetCO2 bias was plotted against the PaO2/PAO2 ratio, a change in the scatter was obvious at about 0.3. The PetCO2 bias for patients with PaO2/PAO2 under 0.3 was 7.8 +/- 7.3 mmHg compared to 0 +/- 3.4 in patients with PaO2/PAO2 above 0.3 (P less than 0.001). PetCO2 differed significantly from PaCO2 (P less than 0.001) only for patients with PaO2/PAO2 under 0.3. The slope (PaCO2 versus PetCO2) for these patients was 1.59, while the slope for patients with PaO2/PAO2 above 0.3 coincided with the line of identity (1.00). The mean +/- SD PtcCO2 bias (PaCO2 - PtcCO2) was -1.3 +/- 7.2 mmHg. Skin perfusion was recorded at the area close to the transcutaneous CO2 monitor electrode and was defined as normal when capillary refill was below 3 seconds. The PtcCO2 bias for patients with normal skin perfusion was -0.2 +/- 5.4 mmHg (P = 0.73) compared to -4.1 +/- 9.9 for patients with decreased skin perfusion (P = 0.01). The slope of PtcCO2 against PaCO2 was closer to identity in patients with normal skin perfusion (1.17) than in patients where it was decreased (slope, 1.40). We suggest that PaCO2 estimation by both PetCO2 and PtcCO2 is sufficiently precise and reliable for clinical use in critically ill children. Certain limitations stem from the nature of the techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Sudden infant death syndrome in the Tel Aviv and Petah Tikva districts.

We studied the epidemiology and incidence of the sudden infant death syndrome (SIDS) in the Tel Aviv and Petah Tikva districts during the period April 1980 to March 1983. Sixty-nine infants were diagnosed as SIDS and 38 of them had autopsies. Four cases were excluded because their autopsy revealed other diagnoses. When calculating for 24,183 live births per year during the study period, the rate of SIDS was found to be 0.47-0.90:1,000 live births. Other epidemiologic characteristics were: female:male [corrected] ratio 1:1.3; peak incidence at 2-4 months age, with 80% before age 6 months; increased incidence during the autumn and winter months (85% of SIDS cases); and highest incidence between midnight and 8:00 AM (84% of SIDS cases). None of the infants had a history of a previous apparent life-threatening event. Birthweight of infants who died of SIDS was not significantly different from that in the general population. No statistical relation to DTP (diphtheria, tetanus, pertussis) vaccination was found. Half the cases had mild respiratory illness during the week that preceded the sudden death. The incidence of parental cigarette smoking was higher than in the general population (56.5% vs. 36-53%; P less than 0.005) as well as the incidence of maternal smoking during pregnancy. We conclude that the incidence of SIDS in Israel is relatively low. The epidemiologic characteristics of SIDS in Israel are very similar to the presentation of the syndrome in other countries.

Age Factors↗