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M Weiss

Publications and source records attributed to M Weiss.

At least 73 records · Page 4Linked to original sources

New class of eigenstates in generic hamiltonian systems

In mixed systems, besides regular and chaotic states, there are states supported by the chaotic region mainly living in the vicinity of the hierarchy of regular islands. We show that the fraction of these hierarchical states scales as Planck's over 2pi(alpha) and we relate the exponent alpha = 1-1/gamma to the decay of the classical staying probability P(t) approximately t(-gamma). This is numerically confirmed for the kicked rotor by studying the influence of hierarchical states on eigenfunction and level statistics.

Journal Article↗

Author reply

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Journal Article↗

Effect of estrogen replacement therapy on speed of sound at multiple skeletal sites.

OBJECTIVES: To evaluate the effect of estrogen replacement therapy (ERT) on postmenopausal bone loss by multi-site ultrasound measurement. METHODS: A cross-sectional comparison of postmenopausal women, ERT users and non-users. The two study groups were enrolled for the reference database collection for the Sunlight Omnisense (Omnisense) and were matched by years since menopause. Speed of sound (SOS) was measured at the distal radius (RAD), mid-shaft tibia (TIB), fifth metatarsus (MTR) and proximal phalanx (PLX). RESULTS: 143 ERT users for 5.2+/-3.6 years were compared with 139 ERT non-users (age: 57.0+/-5.3 and 57.5+/-5.5, respectively). Both groups were 7.1+/-5.0 years since menopause. SOS, expressed in T-score units, was higher at the RAD in ERT users as compared to ERT non-users (-0.55+/-1.30 and -1.36+/-1.60, respectively, P<0.0001), and at the TIB (-0.73+/-1.34 and -1.28+/-1.45, respectively, P=0. 003). Same trend was observed at the MTR and PLX, but not statistically significant because of fewer observations. In early post menopause period, the ERT-non users RAD data shows an annual SOS decrease of 0.17 versus annual increase of 0.12 T-score units (P=0.037). Similar effect is observed at the TIB, though not statistically significant (non-users decrease of 0.20 vs. users increase of 0.08 T-score units/year, P=0.086). CONCLUSIONS: SOS measurements by Omnisense at multiple skeletal sites support the ERT protective effect on bone.

Aged↗

Neuronal expression of Fos protein in the hypothalamus of rats with heart failure.

We sought to identify the areas that have altered neuronal activity within the hypothalamus of rats with heart failure (HF) by mapping neuronal staining of c-Fos protein (Fos) 6-8 weeks following coronary artery ligation (HF group; n=17) or sham surgery (sham-operated control group, n=15). Fos-like immunoreactivity was observed in the paraventricular nucleus (PVN), supraoptic nucleus (SON), median preoptic nucleus (MnPO), anterior hypothalamus (AH) and posterior hypothalamus (PH) using a standard ABC immunocytochemical protocol. The rats in the HF group displayed infarcts averaging 34+/-2% of the outer circumference and 41+/-1% of the inner circumference of the left ventricular wall. Sham-operated control rats had no observable damage to the myocardium. Rats with chronic heart failure (n=5) but no manipulation (no surgery) had a similar number of Fos-staining cells in PVN SON, MnPO, AH and PH compared to sham-operated rats. Acute surgery for isolation of vagus nerves and anesthesia for 90 min increased the number of Fos positive cells in PVN, SON and MnPO of both sham-operated rats and rats with HF. Furthermore, rats with heart failure (n=5) had significantly higher number of Fos-staining cells in PVN (four times), SON (4.5 times) and MnPO (1.5 times) compared to sham-operated rats after acute surgery for isolation of the vagus. The number of Fos-staining cells remained unaltered in AH and PH in both groups of rats. However, in a third series of experiments vagotomy reduced the number of Fos-staining cells in the PVN, SON or MnPO of rats with HF (n=5) to those observed in sham-operated vagotomized rats. This study shows that: (1) there is augmented neuronal activity as indicated by increased number of Fos staining neurons in the PVN, SON and MnPO due to acute surgical stress in rats with HF, and (2) vagal afferents are responsible for the increased neuronal activity in PVN, SON and MnPO of rats with HF during acute surgical stress. These data support the conclusion that vasopressin producing neurons and autonomic areas within the hypothalamus influenced by vagal afferents are activated during HF and are sensitive to 'acute surgical stress' and may contribute to the elevated levels of vasopressin and sympatho-excitation commonly observed in heart failure.

Animals↗

[Clinical value of scintigraphy for gastrointestinal bleeding. Experiences in a large community hospital].

BACKGROUND AND OBJECTIVE: In the majority of cases of gastrointestinal bleeding the site and cause can be determined by gastroscope. If this is unsuccessful, radiological and nuclear-medical tests are available. This study was undertaken to determine the value of scintigraphy in diagnosing of the site of gastrointestinal bleeding. PATIENTS AND METHODS: The data on 155 patients who, between 1984 and 1988, had undergone 161 scintigraphies (with 99mTc-labelled erythrocytes, 5 with 99mTc-Sn colloid) were retrospectively analysed. The results were compared with other diagnostic tests that had been performed, with the definitive diagnosis and, where applicable, the findings at surgery. RESULTS: 78 scintigrams (47%) provided positive results. The site of bleeding had been demonstrated ca. 20 hours after the diagnostic studies had begun. In 47 of the cases the diagnosis was confirmed by additional tests. The intestine was the most common site of bleeding. Localization of the source of bleeding by scintigraphy and other diagnostic tests succeeded in 34 cases, with a 82% concordance between the tests. No bleeding was demonstrated in 88 scintigrams (53%), including all those done with Sn-colloid. In 13 cases the final diagnosis suggested that there had been no previous bleeding and in 43 cases the source of bleeding could not be determined. In 32 scintigraphically negative cases the source of bleeding was demonstrated by other tests. But only 2 of the 13 angiograms and none of the 33 double-contrast studies of the small intestine gave positive results. Among the total number of cases in which bleeding was demonstrated, scintigraphy had a sensitivity of 71%. CONCLUSION: Because of the long duration of observation, scintigraphy with 99mTc-labelled erythrocytes proved superior to other diagnostic tests in the demonstration of the bleeding. By localizing the source of bleeding in a definite part of the gastrointestinal tract, scintigraphy points the way to choosing other diagnostic methods or treatment. If the initial endoscopy has failed, scintigraphy, a method of low invasiveness, should be included when further tests are planned.

Angiography↗

Commentary: using the convection-dispersion model and transit time density functions in the analysis of organ distribution kinetics.

The convection-dispersion model and its extended form have been used to describe solute disposition in organs and to predict hepatic availabilities. A range of empirical transit-time density functions has also been used for a similar purpose. The use of the dispersion model with mixed boundary conditions and transit-time density functions has been queried recently by Hisaka and Sugiyama in this journal. We suggest that, consistent with soil science and chemical engineering literature, the mixed boundary conditions are appropriate providing concentrations are defined in terms of flux to ensure continuity at the boundaries and mass balance. It is suggested that the use of the inverse Gaussian or other functions as empirical transit-time densities is independent of any boundary condition consideration. The mixed boundary condition solutions of the convection-dispersion model are the easiest to use when linear kinetics applies. In contrast, the closed conditions are easier to apply in a numerical analysis of nonlinear disposition of solutes in organs. We therefore argue that the use of hepatic elimination models should be based on pragmatic considerations, giving emphasis to using the simplest or easiest solution that will give a sufficiently accurate prediction of hepatic pharmacokinetics for a particular application.

Algorithms↗

Difficult airway management: comparison of the Bullard laryngoscope with the video-optical intubation stylet.

PURPOSE: To evaluate, whether the video-optical intubation stylet (VOIS) was more successful for difficult tracheal intubation than the Bullard laryngoscope (BL). METHODS: An intubation mannequin head was modified so that, using a Macintosh blade size 3, only the epiglottis was visible at direct laryngoscopy, representing a grade III laryngoscopic view. Forty anesthesiologists attempted tracheal intubation using each technique. Tracheal intubation with the Bullard laryngoscope was performed using the attached non-malleable intubating stylet preloaded with an endotracheal tube. The video-optical intubation stylet inserted into an endotracheal tube was used with direct laryngoscopy. During conventional laryngoscopy, the video-view from the stylet tip allowed the tracheal tube to be guided behind the epiglottis into the trachea. Ten attempts with each technique were performed by each anesthesiologist in randomized order. Intubation time, and failed intubation (> 60 sec/esophageal intubation) were recorded. The operators assessed the degree of difficulty of each method using a Likert-scale. RESULTS: Mean intubation time (19.2+/-4.5 sec for the BL and 18.8+/-4.6 sec for the VOIS) was almost the identical. The video-optical intubation stylet was associated with fewer failed intubations (8 vs. 41; P<0.005) and had a lower degree of difficulty (1.7+/-0.65 for the VOIS and 2.6+/-0.74 for the BL; P<0.0001). No correlation was found between the anesthesiologist's experience and mean intubation time, estimated degree of difficulty or number of unsuccessful intubation. CONCLUSION: The video-optical intubation stylet was a more effective and simpler intubation device to facilitate difficult tracheal intubation than the Bullard laryngoscope.

Epiglottis↗

Video-intuboscopic monitoring of tracheal intubation in pediatric patients.

PURPOSE: To evaluate the efficacy of video-intuboscopic monitoring during orotracheal intubation in a pediatric anesthesia teaching unit. METHODS: In 100 pediatric patients direct laryngoscopy performed by residents or nurse anesthetists was monitored on a video display using a flexible, ultralight video-endoscopic system (O.D. 2.8 mm/length 1.8 m) within the endotracheal tube (ETT). Best direct laryngoscopic view was assessed by the intubator. The instructor observed the intubation procedure on the video display and noted number of intubation attempts, best laryngoscopic monitor view, tube passage through the larynx and final tube position. If required he gave instructions or corrections. After removal of the laryngoscope, tracheal tube position was adjusted using the monitor view. Difficulties attributed to the fibreoptic endoscope during intubation and removal from the ETT were recorded. RESULTS: The trachea was successfully intubated at the first attempt in all patients. The supervisor detected one esophageal and 12 endobronchial intubations that were immediately corrected before starting ventilation. Final visualized endotracheal tube adjustment above the carina was possible in all patients except in one with copious tracheal secretions. Compared with direct laryngoscopy the video display provided an improved view of the vocal cords during intubation. In six patients direct laryngoscopy was difficult but the tracheas were intubated using the monitor view. No difficulties with the equipment were encountered except that the black coated endoscope compromised recognition of the black ETT depth-markings in small tubes. CONCLUSIONS: Video-intuboscopic monitoring is a useful monitor of tracheal intubation. "The improved view of the cords may provide assistance during difficult laryngoscopy.

Adolescent↗

Syringe size and flow rate affect drug delivery from syringe pumps.

PURPOSE: To evaluate the effect of syringe size and infusion rate on drug delivery after vertical displacement of syringe pumps. METHODS: Four syringes (10 ml, 20 ml, 30 ml, 50 ml) were studied at three infusion speeds (2 ml x hr(-1), 1 ml x hr(-1) and 0.5 ml x hr(-1)). Fluid delivery was measured gravimetrically using an electronic balance. Aspiration volume (amount of fluid retracted into the syringe-infusion line assembly) and zero-drug delivery time (time between the lowering of the syringe pump and reattainment of the initial weight) were determined after lowering the syringe pump 130 cm or 50 cm. Then, infusion bolus was measured after elevating the pump to its initial position. Syringe compliance was calculated from the occlusion release bolus at an occlusion pressure of 300 mmHg. RESULTS: Zero-drug delivery time, aspiration volume and infusion bolus increased with syringe size (P < 0.0001). At 0.5 ml x hr(-1), a zero-drug delivery time of 29.7 +/- 0.6 min was recorded for the 50 ml syringe and 5.5 +/- 0.15 min for the 10 ml syringe. As infusion rates increased, zero-drug delivery times decreased following a 1/x ratio. Zero-drug delivery time highly correlated with calculated syringe compliance (Pearson's r = 0.97, P < 0.001), which was closely related to syringe plunger area (R2 = 0.93, P < 0.001). CONCLUSIONS: Vertical displacement of syringe pumps causes flow irregularities which correlate directly with syringe size and indirectly with infusion rate. Extreme vertical maneuvering of syringe pumps should be avoided. Infusion rates > or = 1 ml x hr(-1) and low-compliant, small syringes are recommended when highly concentrated drugs are administered.

Humans↗

[Tropisetron for prevention of nausea and vomiting in children undergoing tonsillectomy and/or adenoidectomy].

BACKGROUND: Postoperative nausea and vomiting (PONV) after tonsillectomy is a common problem in children. Tropisetron is a new 5HT3 receptor antagonist and is successfully used in paediatric patients receiving cancer therapy. The aim of the study was to assess efficacy and safety of a single intravenous dose of tropisetron for prevention of PONV in paediatric patients at risk for postoperative vomiting. METHODS: In a randomised, double-blind, placebo-controlled trial, we studied 98 children aged 2-12 years undergoing tonsillectomy or adenotonsillectomy. Patients received placebo or tropisetron 0.1 mg (= 0.1 ml)/kg body weight immediately after induction of anesthesia. A standard general anesthetic technique (Sevoflurane/N2O/O2 without neuromuscular blockers or opioids) was used. Perioperative vital signs, grade of sedation and episodes of postoperative nausea and vomiting were recorded. RESULTS: No vomiting episodes occurred in 65.3% of the tropisetron treated patients compared to 34.7% of the placebo group (p = 0.0024). Only 10.2% of the tropisetron treated patients vomited more than 3 times compared to 22.4% of the control patients (p = 0.0004). The need for antiemetic rescue medication was significantly lower in the study group (10.4%) compared to 28.6% (p = 0.025). No significant adverse effects of the study medication were shown. CONCLUSION: A single intravenous prophylactic dose of tropisetron effectively reduces the incidence of PONV during the first 24 postoperative hours after tonsillectomy and/or adenoidectomy. Because of the low incidence of adverse effects, the prophylactic use of tropisetron seems to be safe and justified in paediatric surgical patients at high risk for postoperative vomiting.

Adenoidectomy↗

[The effect of air within the infusion syringe on drug delivery of syringe pump infusion systems] .

Application of highly concentrated short-acting vasoactive drugs in the critically ill patient requires precisely working syringe pump systems for continuous intravenous drug delivery. We performed a bench study to investigate the consequences of small amounts of air entrapped within a 50-ml infusion syringe. In particular we studied the effect of entrapped air on drug delivery after moderate vertical displacement of the pump by 50 cm (e.g. in preparation for transport) and the effect on the time required to trigger the pressure alarm after occlusion of the infusion line. At a flow rate of 1 ml/h, lowering the syringe pump prolonged the zero-drug delivery time from (mean +/- SD) 4.1 +/- 0.8 min (without air) to 6.2 +/- 0.9 (with 1 ml air) and to 13.1 +/- 0.9 min (with 2 ml of air, p < 0.001 for all comparisons). Entrapping of 2 ml of air within the syringe resulted in a 2.6-fold prolongation of the occlusion alarm time after accidental occlusion of the infusion line and a 3-fold increase of the resulting infusion bolus after occlusion. Enclosed air within infusion syringes considerably affects the syringe compliance. It increases the susceptibility of constant drug delivery to vertical displacement of syringe pumps and impairs the occlusion alarm function. Therefore, any air in syringe of infusion pump systems should be carefully removed. To avoid infusion boluses of short-acting vasoactive drugs after accidental occlusions, the occluded infusion line should be released to ambient pressure first.

Air↗

Influence of infusion line compliance on drug delivery rate during acute line loop formation.

OBJECTIVE: To determine whether infusion line compliance contributes to irregular drug delivery during vertical displacement of syringe pumps. DESIGN: Five different commercially available infusion lines were studied at infusion rates of 0.5, 1.0, and 1.5 ml/h. Zero drug delivery time was measured after acute line loop formation (70 cm) using an electronic balance. Compliance of each infusion line was calculated using a pressure transducer and measurement of the occlusion release bolus at 300 mmHg occlusion pressure. Finally, the influence of infusion line compliance on drug delivery during acute lowering of the syringe pump was studied using low- and high-compliance infusion lines. RESULTS: Acute line loop formation resulted in zero drug delivery time from 5.1 +/- 1.5 to 44.0 +/- 6.8 s at flow rates of 0.5 ml/h. Increased flow rates significantly reduced loop-induced flow variability. A close correlation was found between zero drug delivery time and calculated infusion line compliance at 0.5 ml/h (linear regression R2 = 0.79). Lowering of the syringe pump 50 cm prolonged zero drug delivery time from 295.8 +/- 20.7 s with the low-compliance tube to 463.3 +/- 24.0 s with the high-compliance infusion line. CONCLUSIONS: Infusion line compliance contributes to irregular drug delivery associated with vertical displacement of syringe pumps. Siphoning of the infusion line during patient care should be avoided, and flow rates of 1 ml/h or higher are recommended. Low-compliance infusion lines are indicated whenever highly short-acting vasoactive drugs at low delivery rates are administered.

Child↗

Reference database for bone speed of sound measurement by a novel quantitative multi-site ultrasound device.

The nonuniform skeletal involvement in osteoporosis argues for multi-site evaluation. The Sunlight Omnisense (Sunlight Ultrasound Technologies, Israel) is a multi-site device that measures speed of sound (SOS) at the appendicular skeleton. We report the reference database for SOS at the radius (RAD), tibia (TIB), metatarsus (MTR) and phalanx (PLX). The database was obtained from 1521 healthy Israeli women (age 20-90 years) out of 2051 respondents. SOS was determined in 97.6% of the participants at the PLX, 96.4% at the TIB, 93.6% at the RAD and 85.1% at the MTR; it was not measurable in 0.5%. Short-term coefficient of variation was lowest at the RAD and always less than 1%. Maximal SOS was noted at 35-45 years of age in three of the sites (RAD 4169 m/s, MTR 3663 m/s, PLX 4047 m/s, respectively) but 10 years earlier at the TIB (3939 m/s). In the perimenopausal period (age 46-55 years), SOS was always lower in post- as compared with premenopausal women (p<0.05). Immediately following the menopause, SOS annually declined close to the short-term CV: 16, 34, 37 and 13 m/s at the RAD, PLX, MTR and TIB, respectively. The average age-stratified SOS values at various measurement sites were highly correlated at the population level (0.96-0.99), but less so at the individual level (0.40-0.57). Therefore, multi-site SOS measurements are better than single-site assessment. After 79 years of age, the average T-score at the RAD and PLX was <--2.5. This is similar to that of dual-energy X-ray absorptiometry (DXA)-determined spine bone mineral density (BMD) and somewhat lower than hip BMD. Equivalent T-score curves obtained by percentile adjustment of SOS at various sites to that of the RAD (at age group 60-69 years) reveal convergence and indicate that 52-68% of women older than 79 years are osteoporotic. In conclusion, multi-site peripheral SOS measurements reveal age-dependent bone changes with a high degree of measurement precision and indicate a prevalence of osteoporosis similar to that obtained by DXA.

Adult↗

Discrimination of proximal hip fracture by quantitative ultrasound measurement at the radius.

Osteoporosis is a disease that culminates in fragility fractures and, therefore, imposes major burden on the health economy. In dealing with this worldwide condition, it is prudent to use a reliable, inexpensive, portable diagnostic means that does not use ionizing radiation and is capable of measuring bone properties at several sites. Recently, a quantitative ultrasound device (Omnisense) that measures speed of sound (SOS) at multiple skeletal sites was introduced. The Omnisense combines the 'axial transmission' mode and the critical angle concept. Preliminary reports suggested that of the different skeletal sites measured by this device, the distal third of the radius is the preferred measurement site for osteoporosis. In this cross-sectional study, SOS was determined at the radius using Omnisense in 50 hip-fractured elderly women (group F, age 76.1 +/- 6.0 years), 130 elderly controls (group NF, age 71.5 +/- 5.2 years) and 185 young healthy controls (group YH, age 40.6 +/- 3.0 years). Actual SOS was significantly lower in group F compared with group NF (p = 0.0001). Whereas SOS T-scores calculated for each woman and stratified into age subgroups within each of the study groups indicate decline from -2.22 to -3.56 in group F and from -1.56 to -3.17 in group NF, there was an increase from -0.02 to 0.03 in group YH. Age- and BMI-adjusted logistic regression for hip fracture discrimination indicated an area under the receiver operating characteristic curve for hip fracture of 0.79 (95% CI, 0.73-0.86; p = 0.005) and an odds ratio of 1.92 (95% CI, 1.22-3.02; p = 0.005). We conclude that SOS measured at the radius by Omnisense discriminates subjects with hip fracture. from controls. Prospective studies are needed to support the role of Omnisense in assessing the risk of hip fracture.

Adult↗

Generation of antibodies directed against the low-immunogenic peptide-toxins microcystin-LR/RR and nodularin.

The preparation of antibodies against the liver toxin microcystin, as described here, is of major importance for its detection and purification in food and water, and for a therapeutic approach to neutralize the toxin by passive immunization. Microcystin-LR (MLR) and microcystin-RR (MRR) were purified from cyanobacterial cell materials by extraction, Sephadex LH-20-, ODS silica gel-, ionic exchange and RP-HPLC-chromatography. In order to reduce the toxicity for parenteral administration, microcystins were coupled by the carbodiimide method to poly-L-lysine (PLL(50.000)). Mice and rabbits were immunized with the conjugates in the presence of two lipopeptide immunoadjuvants (P(3)CSK(4) and P(3)CS-T(h)). High MLR-specific antibody levels were observed after parenteral coadministration of antigen and lipopeptides, whereas no anti-MLR antibodies were obtained with free microcystin or the microcystin-PLL(50.000)-conjugate in the absence of lipopeptide. In oral immunization, coadministration of antigen and adjuvants resulted in an accelerated development of anti MLR-specific antibodies and high antibody levels. Using the antisera, we could detect different microcystins and nodularin down to a concentration range of 10-50 ng/ml by a competitive inhibition ELISA; detection of microcystins in crude cell preparations was also possible. Furthermore, microcystins from different sources could be detected and discriminated from cyclic cyanopeptolines.

Administration, Oral↗

Gender and the stigma of onchocercal skin disease in Africa.

This paper reports results from a multicenter study of gender differences in the stigma associated with onchocercal skin disease (OSD) in five African sites: Cameroon, Ghana, Nigeria (Awka and Ibadan) and Uganda. The studies used a common protocol to compare affected and unaffected respondents, that is, men and women with onchodermatitis in highly endemic areas and respondents from communities with low endemicity or no onchocerciasis. The methods were both quantitative and qualitative, allowing for the comparison of stigma scores and people's verbal descriptions of their experiences and attitudes. Questions to the unaffected were asked after providing them with photographs and short descriptions (vignettes) depicting typical cases. We found that stigma was expressed more openly by the unaffected, who perceived OSD as something foreign or removed from themselves, whereas the affected tended to deny that they experienced stigma as a result of the condition. Gender differences in stigma scores were not significantly different for men and women, but qualitative data revealed that stigma was experienced differently by men and women, and that men and women were affected by it in distinctive ways. Men were more concerned about the impact of the disease on sexual performance and economic prospects, whereas women expressed more concern about physical appearance and life chances, especially marriage. Similar trends were found in the different sites in the responses of affected and unaffected respondents, and differences between them, despite geographical and cultural variations.

Adult↗

Kinetics of propranolol uptake in muscle, skin, and fat of the isolated perfused rat hindlimb.

The tissue distribution kinetics of a highly bound solute, propranolol, was investigated in a heterogeneous organ, the isolated perfused limb, using the impulse-response technique and destructive sampling. The propranolol concentration in muscle, skin, and fat as well as in outflow perfusate was measured up to 30 min after injection. The resulting data were analysed assuming (1) vascular, muscle, skin and fat compartments as well mixed (compartmental model) and (2) using a distributed-in-space model which accounts for the noninstantaneous intravascular mixing and tissue distribution processes but consists only of a vascular and extravascular phase (two-phase model). The compartmental model adequately described propranolol concentration-time data in the three tissue compartments and the outflow concentration-time curve (except of the early mixing phase). In contrast, the two-phase model better described the outflow concentration-time curve but is limited in accounting only for the distribution kinetics in the dominant tissue, the muscle. The two-phase model well described the time course of propranolol concentration in muscle tissue, with parameter estimates similar to those obtained with the compartmental model. The results suggest, first that the uptake kinetics of propranolol into skin and fat cannot be analysed on the basis of outflow data alone and, second that the assumption of well-mixed compartments is a valid approximation from a practical point of view (as, e.g., in physiological based pharmacokinetic modelling). The steady-state distribution volumes of skin and fat were only 16 and 4%, respectively, of that of muscle tissue (16.7 ml), with higher partition coefficient in fat (6.36) than in skin (2.64) and muscle (2.79).

Adipose Tissue↗