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Biomedical subjects

M Levy

Publications and source records attributed to M Levy.

At least 343 records · Page 19Linked to original sources
PubMed1990

Recruitment, force and fatigue characteristics of quadriceps muscles of paraplegics isometrically activated by surface functional electrical stimulation.

This study deals with the recruitment characteristics of unfatigued electrically stimulated quadriceps muscles of paraplegic subjects and with the time-dependent force output of these muscles under sustained stimulation conditions. Both these aspects of the performance of paralysed stimulated muscles were studied under isometric conditions and at different muscle lengths. The forces in the knee joint resulting from stimulation of the quadriceps were also calculated. Recruitment force curves due to a ramp-like stimulation function indicated a strong dependence on muscle length and demonstrated a sigmoid-shaped curve with three distinct regions: negligible force up to threshold stimulation intensity; rapid force increase; and levelling-off of the curve after which the force remains constant even though intensity is further increased. When normalized to the maximal force, recruitment was found to be independent of muscle length, generating a typical recruitment curve for every patient, under isometric stimulation. The peak forces were obtained at the same flexion angles previously published for normal subjects, but with much lower values. Muscle fatigue in tetanic isometric conditions, defined as the decrease in force due to sustained stimulation with fixed parameters, was found to be length dependent and to have a double exponential decay. The first is the acute force loss and is the more significant for functional purposes; the second is the more moderate and asymptotic region, in which partial force recovery in the form of bursts is observed.

Biomechanical Phenomena↗
PubMed1990

Learned changes of respiratory pump rate in response to lowered pH in Aplysia.

Respiratory pumping in the marine gastropod Aplysia is a well-characterized behavior controlled by identified neurons. The behavior is affected by stimuli such as change in ambient pH and shock. This study investigates learned changes in effects of these stimuli on rate of respiratory pumping movements. A sharp threshold exists for effects of environmental pH on respiratory pumping. Lowering the ambient pH from 7.8 to 7.0 does not affect the rate of respiratory pumping movements, but when pH is decreased further to 6.5 a large increase in pump rate is seen. Sensitizing stimuli, such as brief head shock and preexposure to pH 7.0, change the threshold so that respiratory pumping rate is increased in pH 7.0. Pairing exposure to pH 7.0 with head shock leads to pairing-specific amplification of the response in pH 7.0 alone. Pairing-specific consequences can be distinguished from sensitization only after an hour.

Acid-Base Equilibrium↗
PubMed1990

Autoantibodies in familial Mediterranean fever (recurrent polyserositis).

The presence of autoantibodies in our familial Mediterranean fever (FMF) patients was investigated using various immunological techniques. Immunofluorescence screening of 50 FMF sera revealed only one positive for antinuclear antibodies. ELISA assay and nitrocellulose filter assay revealed no difference between FMF sera and healthy controls with regard to the presence of anti-dsDNA antibodies. In Western blotting using HeLa cell extract, FMF patients' sera neither detected anti-Sm, RNP, SSA/Ro, SSB/La antibodies nor any new common band. These findings suggest that it is unlikely that FMF belongs to the family of the autoimmune 'collagen' diseases.

Adolescent↗
PubMed1990

Simple measurement of captopril in plasma by high-performance liquid chromatography with ultraviolet detection.

Captopril is an orally active inhibitor of angiotensin-converting enzyme. A rapid, accurate, and sensitive high-performance chromatography (HPLC) method is described for measuring plasma concentrations of captopril. Captopril was stabilized by forming an adduct with p-bromophenacyl bromide. This adduct was measured by HPLC using a C-18 reverse-phase column and monitoring the column effluent by ultraviolet absorption at 260 nm. The method proved to be linear in the clinical range of 10-1,000 ng/ml. The plasma levels of captopril in a young patient given a small oral dose were determined by this method.

Acetophenones↗
PubMed1990

Pharmacokinetic analysis of cloxacillin loss in children undergoing major surgery with massive bleeding.

To determine the magnitude of cloxacillin loss during surgical procedures involving significant blood loss and high fluid replacement, we compared the pharmacokinetics of cloxacillin in children during craniomaxillofacial surgery with the disposition of the drug in healthy young adult volunteers with intact circulation. Blood loss during craniofacial operations may exceed blood volume, in some cases by as much as three times. Hemodynamic replacement with electrolyte solutions and blood products, which do not contain the drug, further dilute cloxacillin concentrations. In the patients that we studied, mean drug loss was estimated at 71%. Cloxacillin concentrations in serum fell below the lower range of the MIC for Staphylococcus aureus during significant portions of the surgical procedures. Thus, the traditional dosing of cloxacillin during prolonged operations with massive blood loss is inadequate. A more frequent dosing interval or priming of all replacement fluids with the drug may be required to maintain therapeutic levels. Our findings suggest that massive blood loss is likely to have a dramatic effect on the level of any drug with a small distribution volume. If such a drug is essential to the patient's well-being (e.g., antibiotics, antiarrhythmics, and anticonvulsants), it must be replaced promptly.

Adolescent↗
PubMed1990

Urinary excretion of cGMP in response to atrial natriuretic peptide in dogs with acute pancreatitis.

Previous studies have shown that when atrial natriuretic peptide (ANF) is given to anaesthetized dogs with hypovolemic acute pancreatitis, it will produce a diuresis and natriuresis but will not elevate the glomerular filtration rate (GFR). When the same dose of peptide is given to dogs equally hypovolemic (hemorrhage) but without pancreatitis, a brisk increment in GFR occurs. GFR will, however, rise in dogs with pancreatitis in response to other peptides, such as glucagon. In these studies we assessed cGMP excretion as a marker for ANF effect in both normal anaesthetized dogs and dogs with acute experimental pancreatitis. In each group, urinary output and sodium excretion increased significantly, but GFR rose only in the control group. Urinary excretion of cGMP rose equally and dramatically in both control and experimental animals. We conclude that GFR is prevented from rising in dogs with experimental pancreatitis following ANF, but this effect does not depend on depressed cGMP generation.

Acute Disease↗
PubMed1990

Serial natriuretic response to atrial peptide in preascitic bile duct ligated dogs.

We determined if nine precirrhotic unanaesthetized dogs with chronic bile duct ligation (CBDL) responded uniformly to atrial natriuretic peptide (ANF) by infusing this peptide sequentially over 8-12 weeks at 175 ng.kg-1.min-1 and observing the natriuretic response. ANF was administered every 2 weeks post-CBDL until the 8th week and given again during the cirrhotic phase with ascites present (10-12 weeks post-CBDL). Sodium balance studies were conducted at similar time intervals. During the control period and at weeks, 2, 6, and 8 post-CBDL all dogs responded to ANF with a significant change in sodium excretion (delta UNaV, 50-240 mu equiv./min). At these times, all dogs were in sodium balance. At week 4 and during the ascitic period, heterogeneity of response to ANF was observed. In the former interval, five dogs responded (delta UNaV,75-230 mu equiv./min) and four did not, while in the latter interval, five dogs responded (delta UNaV, 50-240 mu equiv./min) and three did not (one dog died). In both time periods, there was severe urinary sodium retention (daily UNaV, 11 +/- 3 and 2 +/- 1 mequiv./day, respectively) while the dogs were ingesting 45 mequiv.Na+/day. The heterogeneity of natriuretic response was not correlated to plasma immunoreactive ANF, renin, or aldosterone levels. Plasma volume was significantly expanded from control during both intervals. We conclude that there is transient sodium retention during the 4th week post-CBDL, and that this period is associated with the heterogeneity of natriuretic response to ANF, despite the absence of ascites or edema.

Aldosterone↗
PubMed1990

Comparative effects of diuretics and atrial peptide in chronic caval dogs.

Anesthetized chronic caval dogs with ascites were given atrial natriuretic peptide (ANF) at 75 ng.kg-1.min-1 iv and were characterized as to natriuretic response [n = 21; urinary excretion rate of Na (UNaV): 28-362 mu eq/min] or lack of response (n = 14; UNaV: 0-10 mu eq/min). Sixteen normal dogs showed an increment in UNaV between 38 and 288 mu eq/min following the same dose of ANF. Both caval "responders" and "nonresponders" were equivalent with regard to pre- and post-ANF hemodynamics and renal function. When various diuretic agents (glucagon, acetazolamide, furosemide, thiazide, amiloride) were administered, equivalent natriuretic responses were obtained between both groups of caval dogs and the controls. An acute saline load (7% body wt), however, produced a greater natriuresis in controls than in caval dogs, but in this latter group the response was similar in responders and nonresponders. When six caval dogs each were initially pretreated with either amiloride or ANF, and then treated with a second agent, an additive natriuretic effect was obtained. These results suggest that tubular resistance to diuretics in caval dogs is unique to ANF, and this peptide appears to act at an additional Na transport site separate from amiloride-inhibitable channels.

Amiloride↗
PubMed1990

Physiological features of edematous dogs unresponsive to atrial natriuretic peptide.

Sodium-retaining cirrhotic and chronic caval dogs with ascites show a heterogeneous natriuretic response to atrial natriuretic factor (ANF) infusions such that half will increase their urinary excretion of sodium and half will show no natriuretic response whatsoever. In these studies we have examined several physiological variables that might discriminate between these two experimental populations. We studied 22 caval dogs (11 natriuretic responders, 11 nonresponders) and 19 cirrhotic dogs (9 responders, 10 nonresponders). After an infusion of rat ANP-(1-28), 125 ng.kg-1.min-1, differences in glomerular filtration rate, blood pressure, or urinary excretion of guanosine 3',5'-cyclic monophosphate (cGMP) could not differentiate between the two types of dogs. When the left kidney of nonresponding dogs in both the caval and cirrhotic groups was either denervated or vasodilated with acetylcholine bromide (60-80 micrograms/min), the attenuation of the natriuretic response to ANF was not reversed. Papillary plasma flow (PPF) after ANF infusion was measured by a Lillienfield technique and averaged 36 +/- 4 ml.min-1.100 g-1 in normal dogs, 10.7 +/- 0.7 ml.min-1.100 g-1 in both responding and nonresponding caval dogs, and 48.3 +/- 1.1 ml.min-1.100 g-1 for each group of cirrhotic dogs. We conclude that differences in renal perfusion, PPF, cGMP generation, or the presence of intact renal nerves cannot explain the lack of a post-ANF natriuretic response in half of caval or cirrhotic dogs. Other physiological determinants must explain the heterogeneity of natriuretic response to ANF observed in edematous dogs.

Animals↗
PubMed1990

Diseases that mimic meningitis. Analysis of 650 lumbar punctures.

A retrospective review of charts for 650 children who had lumbar puncture for suspected meningitis was undertaken to determine the characteristics of patients with and without meningitis, identify other conditions suggesting meningitis, and evaluate the predictive value of signs and symptoms of meningitis. The incidence of positive lumbar punctures increased with patient age. Younger infants did not present with classical features of meningitis. Bulging fontanel, lethargy, and irritability were nonspecific symptoms. Vomiting and headache, although not specific, proved to be more sensitive indicators of meningeal infection. Most patients with meningitis (75%) had at least one sign of meningeal irritation, but so did 25% of patients without meningitis. Brudzinski's sign was not specific. In contrast, nuchal rigidity and Kernig's sign had high predictive value. Up to age five, the diseases most often suggesting meningitis were right-sided pneumonia, gastroenteritis, otitis, tonsillitis, exanthema subitum, and urinary tract infections. Of 171 patients with febrile convulsion, one (0.5%) had bacterial meningitis and four had aseptic meningitis.

Bacterial Infections↗
PubMed1990

Home-based palliative care for children--Part 2: The benefits of an established program.

Thirty-four patients have been admitted to our palliative care program since its institution in March 1986. Five were unsuitable and were withdrawn soon after admission. Of the remainder, 22 (75.9%) had central nervous system (CNS) tumors, 5 (17.2%) had myelomeningocoele, 1 (3.45%) had an arteriovenous (AV) malformation, and 1 (3.45%) had a storage disease. Twenty-five (86.2%) have since died and 17 (68%) of these have died at home. In comparison with a similar group of 30 patients studied in a feasibility study prior to the institution of our program, patients admitted to our palliative care program were hospitalized for significantly fewer days during the terminal phase of their illness (p less than 0.05) and a significantly higher proportion died at home (p less than 0.001). Following a survey of the parents of 14 children diagnosed with CNS tumors who died while under our care, we determined that the overall level of satisfaction with the program was high compared to care provided prior to admission to the program (p less than 0.01). Components of the program deemed most satisfactory were (1) being able to care for the child at home (p less than 0.01), (2) having access to a palliative care nurse (p less than 0.05), and (3) having access to a pediatric clinical pharmacologist (p less than 0.05). The most troublesome symptoms occurring in this group of patients were pain, gastrointestinal symptoms, and seizures. Most problems were adequately managed by the parents under the supervision of the team. Eighty percent of the terminal care for these patients was provided at home.(ABSTRACT TRUNCATED AT 250 WORDS)

Central Nervous System Diseases↗
PubMed1990

Relationship between the acetylator phenotype, plasma sulfapyridine levels and adverse effects during treatment with salicylazosulfapyridine in patients with chronic bowel diseases.

We examined 122 patients with inflammatory bowel disease treated with salicylazosulfapyridine. Forty-two (34.5%) had adverse effects that led to discontinuation of therapy in 14 (11.5%). In 33 patients the effects appeared to be dose dependent. The plasma sulfapyridine levels in patients exhibiting gastrointestinal side effects were significantly higher than in patients with no adverse effects (41.0 +/- 20.3 and 23.8 +/- 14.8 micrograms/ml respectively, P less than 0.001). Plasma sulfapyridine levels were significantly higher in slow than in fast acetylators (31.5 +/- 17.1 vs. 22.2 +/- 17.1 micrograms/ml). Slow acetylators had three times as many side effects as fast acetylators; however this difference was not statistically significant.

Acetylation↗
PubMed1990

Exit-site infection during continuous and cycling peritoneal dialysis in children.

A 10-year retrospective review of pediatric patients on peritoneal dialysis showed that 50 of 83 had 132 episodes of exit-site infection (ESI). Thirty-nine episodes were purulent. The most prevalent organism was Staphylococcus aureus. Staphylococcus epidermidis was also common, usually occurring in purulent infections. Gram-negative organisms were responsible for 23 ESIs, with Pseudomonas species being the most common. Age, sex, concomitant primary disease type, length of training, dressing techniques, quality of daily dialysis technique, use of diapers, and pyelostomies did not affect the incidence of ESI. However, 40% of children with a skin infection from other sites had associated peritoneal catheter ESI. Thirty-eight episodes of ESI in 28 patients resulted in peritonitis; the main organisms involved were Staphylococcus and Pseudomonas species. Catheters were replaced in 13 patients with peritonitis, but there was no difference in the incidence of ESI before and after catheter replacement.

Catheters, Indwelling↗
PubMed1990

Factors predisposing and contributing to peritonitis during chronic peritoneal dialysis in children: a ten-year experience.

Factors contributing and predisposing to peritonitis were studied retrospectively in 83 children treated with continuous ambulatory (CAPD) or continuous cycling peritoneal dialysis (CCPD) from 1978 to 1988. Recurrent peritonitis was the most frequent complication and the major reason for peritoneal dialysis failure. Fifty patients had 171 episodes of peritonitis during the ten years and 33 remained peritonitis-free. The duration of dialysis was significantly shorter in the peritonitis-free group. The incidence of peritonitis was lower with CCPD than with CAPD. Leucopenia was not a predisposing factor nor was blood leucocytosis helpful in diagnosing peritonitis. Serum IgG was low in 33% of patients with episodes of peritonitis, but there was no correlation or predictive value in this finding. The C3 component of complement was relatively lower than the C4 but both components was relatively lower than the C4 but both components were usually in the normal range. Serum albumin was low in all patients, but lower in those with peritonitis episodes. Age, sex, primary disease, diapers, pyelostomies, dialysis training, and living conditions were not significantly associated risk factors. Sterile dressings gave no benefit over the shower technique. Patient noncompliance, upper respiratory tract infection, skin infections, and dental treatment were potential risk factors. However, peritonitis seemed to be distributed randomly among the patients.

Adolescent↗