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Biomedical subjects

R Habib

Publications and source records attributed to R Habib.

At least 37 records · Page 2Linked to original sources
PubMed1999

Transmittance spectra and theoretical sun protection factors for a series of sunscreen-containing sun care products.

Sun care products containing sunscreens are widely used, but consumers are generally unaware of the important differences in the ability of these lotions to block exposure to the ultraviolet A (UVA) portion of the solar spectrum. The purpose of this study was to determine the transmittance spectra, with particular emphasis on the UVA portion of the spectrum, for a variety of commercially available sun care products, to determine Commission Internationale d'Eclairage (CIE) erythema effectiveness spectra and to compare these with information in the product label. The transmittance spectra for a sample of sun care products were measured spectrophotometrically. These values were convoluted with the CIE erythema action spectrum and the sunlight spectra determined for solar noon on June 21 at 0 degrees and 50 degrees N latitude to produce CIE effectiveness spectra. The UVA transmitted through the sun care products that claimed UVA protection on the bottle label varied from as little as 6% to as much as 52%. In addition, it was determined from the CIE effectiveness spectra that any erythema induced following application of the tested lotions would be caused by the UVA portion of the solar spectrum for all, but one, of the products examined. The results of this study emphasize the necessity for better guidance to the consumer as to the ability of sun care products to provide protection against UVA exposure.

Consumer Product Safety↗
PubMed1998

Hippocampal PET activations of memory encoding and retrieval: the HIPER model.

A meta-analysis of experimentally induced changes in blood flow ("activations") in positron emission tomography (PET) studies of memory has revealed an orderly functional anatomic pattern: Activations in the hippocampal region associated with episodic memory encoding are located primarily in the rostral portions of the region, whereas activations associated with episodic memory retrieval are located primarily in the caudal portions. These findings are based on an analysis of a sample of 54 "hippocampal encoding and retrieval" activations that were culled from an overall database consisting of 52 published PET studies of memory. We refer to this general pattern of rostrocaudal gradient of encoding and retrieval PET activations as the HIPER (Hippocampal Encoding/Retrieval) model. The model suggests a division of memory-related labor between the rostral and caudal portions of the hippocampal formation. Because functional anatomic pattern of encoding and retrieval activation that defines the HIPER model was unprecedented and unexpected, it is difficult to relate the model to what is already known or thought about functional neuroanatomy of episodic memory in the hippocampal regions. The model is interesting primarily because its exploration may yield fresh insights into the neural basis of human memory.

Brain Mapping↗
PubMed1998

Methylprednisolone pulse therapy in the treatment of severe forms of Schönlein-Henoch purpura nephritis.

Between 1980 and 1994, 38 children with severe forms of Schönlein-Henoch purpura glomerulonephritis were entered into a prospective study to evaluate methylprednisolone pulse therapy on the outcome of nephropathy in terms of clinical symptoms and histopathological changes. The patients were considered at risk of developing chronic renal failure when they presented with a nephrotic syndrome and/or had 50% or more crescentic glomeruli. Initial renal biopsies were obtained from all patients and revealed diffuse proliferative endocapillary glomerulonephritis in 2, focal and segmental glomerulonephritis in 4, and endo- and extracapillary glomerulonephritis in 32, 21 of whom had 50% or more glomeruli with crescents. Patients were treated with intravenous pulse methylprednisolone (3 days) followed by oral prednisone (3.5 months). At the latest follow-up, 1-16 years after initiation of therapy, 27 children had clinically recovered, 3 showed minimal urinary abnormalities, 4 persistent nephropathy, and 4 had progressed to end-stage renal failure. Sequential renal biopsies were obtained from 30 patients, 7-25 months after initiation of therapy. The clinical outcome correlated well with of the activity (hypercellularity, cellular and fibrocellular crescents, and interstitial edema with mononuclear cell infiltrates) and the chronicity (fibrous crescents, glomerular sclerosis, tubular atrophy, and interstitial fibrosis) indexes of post-therapy biopsies. Of particular interest were the post-therapy biopsies of the 18 patients who clinically recovered. They showed a significant decrease of the activity index from 5.1+/-1.1 to 0.4+/-0.8 with a decrease or even a disappearance of IgA deposits, while the chronicity index remained low (0.4+/-0.8 compared with 1.4+/-1). Although uncontrolled, our study suggests that methylprednisolone pulse therapy is effective in those patients at risk of progression of their nephropathy, especially if started early during the course of the disease before the crescents become fibrous.

Adolescent↗
PubMed1997

Brain regions differentially involved in remembering what and when: a PET study.

Recollecting a past episode involves remembering not only what happened but also when it happened. We used positron emission tomography (PET) to directly contrast the neural correlates of item and temporalorder memory. Subjects studied a list of words and were then scanned while retrieving information about what words were in the list or when they occurred within the list. Item retrieval was related to increased neural activity in medial temporal and basal forebrain regions, whereas temporal-order retrieval was associated with activations in dorsal prefrontal, cuneus/precuneus, and right posterior parietal regions. The dissociation between temporal and frontal lobe regions confirms and extends previous lesion data. The results show that temporal-order retrieval involves a network of frontal and posterior brain regions.

Adult↗
PubMed1997

Cyclosporine in the therapy of steroid-resistant idiopathic nephrotic syndrome.

Steroid-resistant nephrotic syndrome with either minimal changes or focal and segmental glomerular sclerosis on initial biopsy is a severe condition as more than 50% of patients with the disease progress to end-stage renal failure within 10 years. We recently identified a distinct form of idiopathic nephrotic syndrome with an autosomal recessive mode of inheritance and were able to map the gene on the long arm of chromosome 1. The absence of recurrence of the disease after renal transplantation suggest a primary defect in a glomerular basement membrane protein. Several reports suggest that cyclosporine is effective in a proportion of patients with steroid-resistant idiopathic nephrotic syndrome, particularly when used in combination with corticosteroids. There are also data suggesting that high doses of cyclosporine may be necessary in patients with severe hypercholesterolemia. However, cyclosporine treatment should be carefully monitored in view of the high risk of nephrotoxicity, as shown by the results of repeat renal biopsies. The beneficial role of cyclosporine in recurrent steroid-resistant nephrotic syndrome is still debated. Preliminary observations suggest that the early use of intravenous cyclosporine may be effective in these patients.

Cyclosporine↗
PubMed1996

General and specific brain regions involved in encoding and retrieval of events: what, where, and when.

Remembering an event involves not only what happened, but also where and when it occurred. We measured regional cerebral blood flow by positron emission tomography during initial encoding and subsequent retrieval of item, location, and time information. Multivariate image analysis showed that left frontal brain regions were always activated during encoding, and right superior frontal regions were always activated at retrieval. Pairwise image subtraction analyses revealed information-specific activations at (i) encoding, item information in left hippocampal, location information in right parietal, and time information in left fusiform regions; and (ii) retrieval, item in right inferior frontal and temporal, location in left frontal, and time in anterior cingulate cortices. These results point to the existence of general encoding and retrieval networks of episodic memory whose operations are augmented by unique brain areas recruited for processing specific aspects of remembered events.

Adult↗
PubMed1996

Network analysis of positron emission tomography regional cerebral blood flow data: ensemble inhibition during episodic memory retrieval.

Two important objectives in the neuroscience of memory are (1) identification of neural pathways involved in memory processes; and (2) characterization of the pattern of interactions between these pathways. Functional neuroimaging can contribute to both of these goals. Using image subtraction analysis of regional cerebral blood flow data measured with positron emission tomography, we identified brain regions that changed activity during episodic memory retrieval (visual work recognition). Relative to a baseline reading task, decreased activity was observed in bilateral prefrontal, bilateral anterior and posterior temporal, and posterior cingulate cortices. Brain regions showing increased activity were the right prefrontal (different from deactivated regions), left anterior cingulate, and left occipital cortices, and vermis of cerebellum. We then performed a network analysis with structural equation modeling to test the hypothesis that regional decreases came about through active inhibition by regions showing increased activity during retrieval. This analysis demonstrated that the influence of activated regions on deactivated regions was more negative during retrieval than during reading, confirming the inhibition hypothesis. Such confirmation could not have been made from the subtraction analysis alone because decreases can come about, at the very least, through reduction of functional influences as well as by active inhibition. The concepts of ensemble excitation and inhibition, as defined through network analysis, are introduced. We argue that is is critical to examine the combined pattern of excitatory and inhibitory influences to fully appreciate the neural basis of episodic memory.

Analysis of Variance↗
PubMed1996

Long-term (15-25 years) outcome of childhood hemolytic-uremic syndrome.

The short-term prognosis of the "typical", "post-enteropathic" form of infantile HUS is usually good, with a complete recovery of renal function. However, the extent of the renal damage observed on some biopsies may raise concern for the long-term prognosis. Therefore, we studied the outcome of 29 patients affected with classical HUS in infancy or early childhood and followed-up for 15-28 years (m = 18 yrs). Initial renal symptoms ranged from a moderate renal failure with normal diuresis to a 12-day anuria: 21 children had to be treated by peritoneal dialysis. Twenty-five patients underwent a renal biopsy shortly after recovery: lesions of glomerular thrombotic microangiopathy (TMA) were found in 14 patients, and patchy cortical necrosis was diagnosed in the other 11. At latest examination 10 patients had no renal abnormality, 12 had residual renal symptoms (hypertension in 7, proteinuria in 4 and midly reduced GFR in 1), 3 were in chronic renal failure (CRF), and 4 had reached end-stage renal failure (ESRF) 16-24 years after onset; 2 of these latter 4 had a normal GFR at 10-year examination. The long-term evolution was not correlated with the initial clinical severity but appeared well correlated with the extent of the histological damage: 10 of the 11 patients with cortical necrosis have either ESRF (4), CRF (3) or renal sequelae (3), and 4 of the 5 patients with TMA involving more than 50% of glomeruli present with moderate sequelae, whereas the 9 patients with TMA involving less than 50% of glomeruli are symptom-free or have mild sequelae. Thus, the risk of renal failure 20 years after a seemingly cured childhood HUS is not negligible, and renal histology is the best indicator of long-term prognosis.

Age of Onset↗
PubMed1995

Functional brain maps of retrieval mode and recovery of episodic information.

Positron emission tomography (PET) was used to identify brain regions associated with two component processes of episodic retrieval; those related to thinking back in subjective time (retrieval mode) and those related to actual recovery of stored information (ecphory). Healthy young subjects recognized words that had been encoded with respect to meaning or the speaker's voice. Regardless of how the information had been encoded, recognition was associated with increased activation in regions in right prefrontal cortex, left anterior cingulate, and cerebellum. These activations reflect retrieval mode. Recognition following meaning encoding was specifically associated with increased activation in left temporal cortex, and recognition following voice encoding involved regions in right orbital frontal and parahippocampal cortex. These activations reflect ecphory of differentially encoded information.

Adult↗
PubMed1995

Haemolytic uraemic syndrome: prognostic factors in children over 3 years of age.

Previous studies have shown that age at onset of primary haemolytic uraemic syndrome (HUS) is a feature of prognostic significance, the disease being of much better outcome in paediatric patients younger than 3 years than in older children. In an attempt to find an explanation for such a difference, we analysed the clinical and pathological features of 42 children over 3 years of age who presented with HUS between 1955 and 1990 in our department. On the basis of the presence of a prodromal diarrhoea, we divided our patients into two groups: 21 children presented with the diarrhoea-associated (typical or D+) form of HUS, whereas 21 had the non-diarrhoea-associated (atypical or D-) form. Of the 42 children, 20 (47.5%) progressed to end-stage renal failure. However, our study shows that age at onset of HUS is not a prognostic feature per se. The difference in outcome between children and infants is most likely related to the high incidence of the atypical subset of HUS in children over 3 years, a subset that is very uncommon in infants. The ominous features which characterise this form of the disease are: (1) the absence of a diarrhoeal prodrome, (2) normal urine output, (3) marked proteinuria, (4) hypertension, (5) the occurrence of relapses or recurrences and (6) the presence of widespread and severe arteriolar changes on renal biopsy. The poor prognosis of the atypical form of HUS warrants the use of fresh-frozen plasma infusions and/or plasma exchange as early as possible in the course of the disease.

Adolescent↗
PubMed1995

Wave speed during maximal expiratory flow and phase velocity from forced oscillations.

To test the hypothesis that pressure waves in the airways propagate at the speed obtained from maximal expiratory flow we compared wave speeds (WS) associated with flow limitation and phase velocities (PV) of oscillatory pressure waves in four excised calf tracheae for transmural pressures (Ptm) between 0 and -10 kPa. WS was calculated from static area-Ptm curves using the acoustic reflection technique. PV was determined by the forced oscillation method between 16 and 1024 Hz. WS ranged from 80 to 120 m/sec slightly increasing with decreasing Ptm. PV was relatively constant between 60 and 160 AZ with values between 170 and 310 m/sec. With decreasing Ptm, PV also increased, however, at 100 HZ it was 1.5-2.5 times higher than WS at all Ptm. In one additional trachea we found that PV decreased from approximately 200 m / sec at 7 Hz to approximately 130 m / sec at 0.23 Hz approaching WS. We suggest that VP is larger than WS because of the differences in airway wall mechanics during small-amplitude oscillations and large amplitude oscillations and large amplitude unidirectional wall motion such as a forced expiration. These results may provide an additional explanation why expiratory flow during rapid breathing or expiratory transients can exceed the maximum expiratory flow-volume envelope.

Animals↗
PubMed1994

Novelty encoding networks in the human brain: positron emission tomography data.

Data from positron emission tomography (PET) studies showed novelty activations--higher regional cerebral blood flow associated with perceiving novel rather than familiar stimuli. Regions in the right 'expanded' limbic system--hippocampal formation, parahippocampal gyrus, retrosplenial cortex, thalamus, subcallosal area, the border between cortical areas 32 and 10, anterior and inferior cingulate cortex, putamen, and medial prefrontal cortex--showed such activations for complex pictures. Because novel information is usually encoded for storage in memory, these regions can be seen as constituting components of a visual/spatial novelty encoding network. Insular, opercular and temporal regions (e.g. area 37) showed novelty activations not only for visual pictures but also for auditorily presented sentences, and can be thought of as components of a transmodal novelty encoding network.

Auditory Pathways↗
PubMed1994

Neuroanatomical correlates of retrieval in episodic memory: auditory sentence recognition.

This study used positron emission tomography (PET) to investigate the neuroanatomical correlates of remembering previously experienced events. Twelve young healthy adults listened to "old" meaningful sentences which they had studied 24 hr previously. As a control task the subjects listened to comparable "new" sentences that they had never heard before. Regional cerebral blood flow associated with each task was measured by PET scans using 15O-labeled water. Comparison (old-sentence task minus new-sentence task) of the PET images revealed an extended strip of increased blood flow in the right dorsolateral prefrontal cortex (Brodmann's areas 10, 46, and 9) and the anterior portion of area 6. Other principal regions of increased blood flow were situated around the left anterior cingulate sulcus and bilaterally in the parietal lobes (areas 7 and 40). Major decreases in blood flow were situated bilaterally in the temporal lobes (areas 21, 22, 41, and 42). A high proportion of activity changes seemed to be located in the depths of cortical sulci. Increases in blood flow are seen as reflecting the operations of a widely distributed neuronal network involving prefrontal and parietal cortical regions that subserves the conscious recollection of previously experienced events. Decreases in blood flow in the temporal auditory areas are interpreted as reflecting auditory priming. The prevalence of sulcal blood-flow changes may reflect extensive cortical gyrification; it may also indicate that memory-related processes rely on the densely packed neuropil of sulcal regions.

Adult↗
PubMed1994

Impairment of nutrient uptake in a rabbit model of gastroschisis.

Infants with gastroschisis (GS) commonly require total parenteral nutrition and prolonged hospitalization because of intestinal dysfunction resulting from dysmotility and/or malabsorption. To investigate prepartum small intestinal (SI) nutrient absorption in GS, a fetal rabbit model was surgically created on gestational day 24 (term, 31 to 33 days) in 11 time-mated New Zealand White does in each left ovarian-end fetus. Each right ovarian-end fetus served as a control (C) and was manipulated only. All does, 10 of 11 GS fetuses (91%), and 8 of 11 C fetuses (73%) survived to gestational day 30. GS fetuses had significantly reduced total body weights, SI weights, and SI lengths compared with C fetuses. Using the everted mucosal sleeve technique, the uptakes of an amino acid (proline) and a sugar (glucose) were determined. The uptakes of proline per milligram SI, proline per centimeter SI, and glucose per milligram SI were significantly impaired in GS fetuses compared with C fetuses (P < .04 by Student's paired t test). The uptake of glucose per centimeter SI was also reduced in GS fetuses, but not significantly. Uptake capacities (a measure of the entire SI's ability to absorb a given nutrient) were significantly reduced in GS fetuses compared with C fetuses (proline, 2,670 +/- 612 nmol/min/entire SI v 6,842 +/- 399 nmol/min/entire SI, P < .008 by Student's paired t test; glucose, 402 +/- 69 nmol/min/entire SI v 950 +/- 103, P < .008 by Student's paired t test).

Abdominal Muscles↗
PubMed1994

Cyclosporine in the treatment of idiopathic nephrosis.

Within the past decade, there have been numerous reports on the use of cyclosporine in idiopathic nephrosis. In this review, the results of both uncontrolled and controlled studies of the therapeutic effects of cyclosporine in steroid-sensitive/dependent idiopathic nephrosis and in steroid-resistant idiopathic nephrosis are analyzed. Cyclosporine is efficient in up to 80% of patients with steroid-sensitive/dependent idiopathic nephrosis. Most patients, however, relapse when the drug is withdrawn, thus necessitating prolonged treatments. Although cyclosporine is less efficient in patients with steroid-resistant idiopathic nephrosis, a few studies seem to indicate that this drug may be successful in some patients, especially if combined with corticosteroids. There is no evidence that cyclosporine can prevent the recurrence of nephrotic syndrome on the graft after renal transplantation. However, in patients in whom disease has recurred, high doses of cyclosporine may be effective alone or in combination with plasma exchanges. The main worrisome side effect of cyclosporine is chronic nephrotoxicity, which should be differentiated from acute or "functional" toxicity. Follow-up studies including pretreatment and posttreatment renal biopsies show a lack of correlation between structural damage and renal function, suggesting that a histologic examination of the renal parenchyma is the only reliable way of evaluating chronic cyclosporine nephrotoxicity.

Adult↗