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Biomedical subjects

G Hamel

Publications and source records attributed to G Hamel.

At least 19 recordsLinked to original sources
PubMed1994

Management of fluid overload in infants by tidal peritoneal dialysis: is there a benefit compared with continuous cycling peritoneal dialysis?

Dialysed infants are sometimes characterized by a hyperpermeable peritoneal state. In this situation decreasing dwell time and/or increasing dialysate tonicity are usually proposed to achieve adequate ultrafiltration (UF). We have investigated UF capacity under different peritoneal dialysis modalities in three infants. UF was not obtained with isotonic continuous ambulatory peritoneal dialysis (CAPD), and was only achieved with short dwell times and hypertonic CAPD. For the prescription of automated peritoneal dialysis, a shorter dwell time of hourly sequences is needed, which consequently decreases the phosphate diffusion time. Continuous cycling peritoneal dialysis with sequences of 1 h allowed efficient UF [UF/glucose absorption (UF/G) 4.2 +/- 0.9] but the dialysate/plasma (D/P) phosphate ratio was low (0.47 +/- 0.12). In contrast, tidal peritoneal dialysis gave a better UF/G ratio (6.8 +/- 0.7) without a decrease in the D/P phosphate ratio (0.64 +/- 0.18).

Body Fluids↗
PubMed1994

Specific developmental profiles of lysosomal and brush border enzymuria in the human.

Various enzymatic urinary activities have been proposed to assess renal proximal tubule damage in children, including neonates. Nevertheless comprehensive knowledge on the developmental aspects of physiological enzymuria is limited, particularly with regard to lysosomal and brush border enzymuria. Urinary activities of two lysosomal enzymes, N-acetyl-beta-D-glucosaminidase (NAG) and beta-galactosidase (GAL), and of two brush border enzymes, alanine aminopeptidase (AAG) and gamma-glutamyltransferase (GGT) were comparatively investigated in normal prematures (n = 28), term neonates (n = 52), infants aged less than 2 years (n = 19) and children (n = 33), and compared to urinary excretion of beta 2-microglobulin (B2M). Enzymatic activities were assayed using either spectrophotometrical (NAG, AAP, GGT) fluorimetrical (GAL) or radioimmunological (B2M) methods, and were related to urinary creatinine excretion. Developmental profiles of both the studied lysosomal enzymes and of B2M were similarly characterized with significantly decreasing values from prematures (NAG 9.29 +/- 1.44, GAL 2.26 +/- 0.26 IU/mmol creatinine, indicated as mean +/- SEM) to term neonates (6,94 +/- 0.58 and 1.76 +/- 0.15 IU/mmol creatinine, respectively) and older infants and children. Lysosomal enzymatic urinary activities correlated linearly with a coefficient of r = 0.75, (p < 0.05), while correlations between each lysosomal enzymatic activity and B2M urinary excretion were weaker.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylglucosaminidase↗
PubMed1994

Optimization of CCPD prescription in children using peritoneal equilibration test.

Continuous cycling peritoneal dialysis (CCPD) is automatically performed by a cycler as a repetition several times per session of the same programmed exchange. We have investigated the efficiency, in terms of ultrafiltration (UF) capacity and solute clearance (phosphate), of an adapted (optimized) CCPD versus a conventional CCPD. Adapted CCPD was performed manually in order to allow a combination of short dwell times (optimal ultrafiltration) and long dwell times (optimal purification). The ratio of ultrafiltration over glucose absorbed (UF/G) was higher with adapted CCPD (5.7 +/- 0.8) compared with conventional CCPD (4.8 +/- 1.3). Phosphate purification was also enhanced with adapted CCPD (0.21 +/- 0.05 versus 0.16 +/- 0.05 mL/min/kg). These results confirm the usefulness of the concept of adapted CCPD with variable dwell times for optimization of peritoneal dialysis performances in children.

Absorption↗
PubMed1993

Genetic amniocentesis: a six-years experience in an isolated region of northeastern Quebec (Canada).

The indications, results and outcomes of 508 genetic amniocenteses performed during a 6-years period in Saguenay-Lac-St-Jean (SLSJ), a geographically isolated region of Quebec were reviewed. The geographical distribution of the residences showed that women living in urban communities were more likely to have an amniocentesis than those coming from rural communities. Advanced maternal age was the most frequent indication (62%) while a family history of hereditary disease was an indication in 9%, which is higher than in other published series. The rate of abnormal results in SLSJ was similar to those obtained in other series except for the rate found in amniocenteses done for hereditary diseases (4.3% versus 17.4-45.5%). All the pregnancies for which an abnormal result, but balanced translocations, was found were interrupted or ended spontaneously.

Adolescent↗
PubMed1992

Phosphate dialytic removal: enhancement of phosphate cellular clearance by biofiltration (with acetate-free buffer dialysate).

Phosphate dialytic removal (PDR) depends in part on the type (acetate or bicarbonate) and the concentration of the buffer dialysate. Plasma phosphate reduction or PDR during a dialysis treatment is the algebraic sum, of phosphate cellular flux (removal or captation) and of phosphate tissular precipitation. High bicarbonate levels induce an intracellular shift of phosphate, thus not available for dialytic removal. On the contrary, acidosis prevents P shifting into the intracellular space, thus more P is available for dialytic removal. In order to evaluate cellular phosphate sequestration (CPS) we tested PDR in a crossover study. Three children were dialyzed (18 sessions) successively using either biofiltration with free buffer dialysate and a constant bicarbonate fluid infusion rate (BF) or using sequential biofiltration (SBF) with an initial controlled acidosis period realized by bicarbonate reinjection fluid rate modelling. PDR was higher in SBF (32 +/- 4 mmol/session) than in BF (24 +/- 6 mmol/session). SBF seemed to be efficient against CPS; it clearly demonstrates that bicarbonate modelling is a promising dialytic approach to enhance PDR. The real clinical relevance of these biological results needs clinical long-term evaluation.

Adolescent↗
PubMed1991

Solute equilibration curves, crossing time for urea and glucose during peritoneal dialysis: a function of age in children.

Glucose is absorbed from the dialysate more rapidly in younger than in older children on CAPD leading to a relatively early loss of ultrafiltration during dwell time. In order to assess peritoneal permeability and in term to prescribe optimal management of CAPD, we tested peritoneal equilibration curves (EC) for urea and glucose, especially the crossing time point of these two ECs. Baseline values were obtained from 8 patients divided in two groups by age at start of CAPD: group I (N = 4) mean age 1 year 6 months, mean body weight 8.25 +/- 3.17 kg, group II (N = 4) mean age 12 years 6 months, mean body weight 33.5 +/- 1.5 kg. The crossing time point is earlier in group I (49 +/- 14 min) than in group II (101 +/- 20 min) (p less than 0.001). Followup of each patient, during a mean time of 20 months in group I and 23 months in group II, establishes that the curves crossing time point for each patient remains stable.

Age Factors↗
PubMed1991

[Double profile dialysis: ultrafiltration and sodium variable description and clinical validation in the child].

Despite significant technical improvements (bicarbonate dialysate, volumetric ultrafiltration control) high intradialytic ultrafiltration is troublesome in children, specially in the proportion of patients presenting a normal or low blood pressure even with overweight. We used, in this group of children (overhydratated without vascular repercution) a modelling of both sodium and ultrafiltration during dialysis, in order to achieve dry body weight without increasing session time despite hypotension risks. The usefulness and practicability of sodium and ultrafiltration modelling together during dialysis in children is analysed in a short time study (for plasma volume changes calculation) and in a long term follow up study over a year (for clinical tolerance). Today, we reserve this form of dialysis only for a single session needed by overhydratation (more than 5% of dry body weight) in order to achieve dry body weight maintaining dialysis session time constant without increasing side effects (hypotension).

Blood↗
PubMed1990

A reactor permitting injection and sampling for steady state studies of enzymatic reactions at high pressure: tests with aspartate transcarbamylase.

A high pressure reactor for steady state studies of enzymes is described. It allows injection, stirring, and sampling without release of the pressure (up to at least 400 MPa). Thus, either substrate or enzyme can be injected to initiate an enzyme-catalyzed reaction whose progress can then be followed by measurements on samples taken from the reactor. The dead time of sampling is 10-15 s, which allows reactions with pseudo-first-order rate constants smaller than about 1 min-1 to be monitored. It can be used for any enzymatic reaction; unlike previously described high pressure apparatus, it is not limited to the study of enzymes whose activity can be directly followed by spectrophotometry. The use and reliability of this reactor is demonstrated by tests with aspartate transcarbamylase. The activity of this enzyme is enhanced by pressures of the order of 120 MPa.

Aspartate Carbamoyltransferase↗
PubMed1989

Beta-2-microglobulin in hemodiafiltered children: long-term efficiency follow-up.

Data of beta 2-microglobulin (beta 2M) levels are not well known in hemodialyzed children. We analyzed 28 children, all maintained on thrice weekly hemodiafiltration (HDF) with highly permeable membrane (mean age 8 years 7 months, mean time on dialysis 32 months). beta 2M is significantly elevated: 34 + 8.5 mg/l without differences for sex but correlated to residual urinary volume. The kinetics of beta 2M removal during HDF with different dialysis membranes (polysulfone, polyacrylonitrile), and with the same membrane (polysulfone) used in diffusive (hemodialysis), in convective (hemofiltration) and in diffusive and convective (HDF) modes reveals that polysulfone membranes in HDF mode allow the greatest beta 2M serum level drop over dialysis session time (-60 +/- 12%). Five children, anuric, mean time on dialysis 75 months (65-94), chronically on thrice weekly (3 x 3 h) HDF with first polyacrylonitrile then polysulfone membranes are investigated regarding beta 2M levels and amyloidosis risks. Despite the high removal rate of beta 2M with these dialytic modes, beta 2M serum levels do not decrease during this five-year study. High beta 2M serum extraction seems to be compensated by high beta 2M cell generation. Further investigation is necessary for the explanation of the presumed high beta 2M generation rate in the HDF with polysulfone membranes before recommendation of safe long-term use of such highly permeable membranes for prevention of amyloidosis risks in dialytic patients.

Adolescent↗
PubMed1987

Human auditory steady-state evoked potentials during selective attention.

The human auditory steady-state evoked potentials were examined during several different tasks requiring attention. Both Fourier analysis and signal averaging were used to measure the responses at stimulus rates between 37 and 41/sec. There was no effect of attention on the amplitude and phase of the steady-state evoked potentials when subjects either counted successive increments in stimulus intensity or read a book. In a dichotic listening task, there were clear changes in the late transient evoked potentials with selective attention but no changes in the steady-state responses. Furthermore, the steady-state potentials recorded during reading were not different from those obtained while the subjects were selectively attending to the auditory stimuli in one ear. There is therefore no evidence that the auditory steady-state responses are affected by attention.

Adult↗
PubMed1986

Human auditory steady state responses: effects of intensity and frequency.

Human auditory steady state responses were recorded in 41 normal subjects and 22 patients with hearing loss. The effect of intensity on the responses at different tonal frequencies was assessed using the sweep technique. The amplitude of the responses increases and the phase delay decreases with increasing intensity. Both the amplitude and the phase delay are smaller for high frequency tone bursts. Notched noise decreases the amplitude of the response by a factor of two but does not affect the phase of the responses. Thresholds were estimated in waking subjects using two techniques: intensity sweeps analyzed by linear regressions, and fixed intensities analyzed by Hotelling's T2 test. Frequency-specific thresholds obtained with notched noise were less variable and more accurate with the fixed intensity technique. In patients with sensorineural hearing loss the amplitude increased more with increasing intensity above threshold than in patients with conductive hearing loss.

Adult↗
PubMed1985

Selective culture of neurons from rat cerebral cortex: morphological characterization, glutamate uptake and related enzymes during maturation in various culture media.

Dissociated cerebral cortex of fetal rat was grown in a serum-free, chemically defined medium (CDM) (containing insulin, progesterone, estradiol, transferrin, putrescine, selenium and 15 mM KCl) and compared with cultures grown in a medium containing 20% fetal calf serum (SCM). Neurons survived well using either medium, but in the serum-free medium the cellular population was exclusively neuronal (at 96%), while glial cells began to proliferate after one week in the SCM. The various cellular morphologies are described in the present report and the presence of immunological markers characteristic of neurons was investigated. Autoradiographic experiments have been performed after incubation with various putative neurotransmitters and we have shown the presence of a strikingly high proportion of glutamatergic neurons in these cultures. Glutamate high affinity uptake was also greatly increased in neuronal cultures maintained in a CDM compared to a SCM, especially in young cultures. The development of different enzymes involved in the metabolism of glutamate was also studied; the specific activity of glutaminase increased in culture and was found to be higher in a CDM than in a SCM, while the inverse was true for glutamine synthetase. The relative proportion of both enzymes in neurons compared to glial cells was opposite, as neuronal cultures had higher levels of glutaminase and glial cultures were enriched in glutamine synthetase activity. It seems that the proportion of glutamate-neurons increases when cultured in a CDM compared to a SCM and we suggest that this culture procedure may provide a purely neuronal population enriched in mature glutamatergic neurons. It may thus be useful for future in vitro studies on glutamate and GABA metabolism in neurons.

Animals↗
PubMed1982

Rapid immunochemical determination of plasma fibronectin with a centrifugal analyzer.

We report a turbidimetric procedure, using commercially available reagents, for the determination of plasma fibronectin with an unmodified centrifugal analyser. Fixed-time kinetic readings at 340 nm were taken at 60 and 720 s. A wide range of concentration (up to 1000 mg/l) can be measured. Precision and accuracy were quite acceptable. Correlation with radial immunodiffusion was satisfactory. This automated procedure, simple and rapid, allows extensive studies of fibronectin in various diseases.

Autoanalysis↗
PubMed1979

Brainstem evoked potentials to tonepips in notched noise.

Notched noise can be used to mask the frequency spread of acoustic energy in the brief tonepips that are used to elicit brainstem evoked potentials. Brainstem responses to tonepips and notched noise can therefore be used to evaluate auditory thresholds at particular frequencies. These thresholds are more frequency-specific than those obtained using tonepips alone, and are accurate to within 20 dB of the conventional audiometric thresholds.

Acoustic Stimulation↗