Biomedical subjects

N R Mehta

Publications and source records attributed to N R Mehta.

At least 19 recordsLinked to original sources

PubMed2004

Anti-ganglioside antibody-mediated neuronal cytotoxicity and its protection by intravenous immunoglobulin: implications for immune neuropathies.

Antibodies against GD1a, GM1 and related gangliosides are frequently present in patients with the motor variant of Guillain-Barré syndrome (GBS), and their pathological role in this variant of GBS is now widely accepted. However, two basic issues related to anti-ganglioside antibody-mediated neural injury are not completely resolved: (i) some anti-ganglioside antibodies can cross-react with glycoproteins and therefore the nature of antigens targeted by these antibodies is not well established; and (ii) although pathological studies suggest that complement activation occurs in GBS, experimental data for the role of complement remain inconclusive. To address these issues, we developed and characterized a simple anti-ganglioside antibody-mediated cytotoxicity assay. Our results demonstrate first, that both GBS sera containing anti-ganglioside antibodies and monoclonal anti-ganglioside antibodies cause neuronal cell lysis by targeting specific cell surface gangliosides, and secondly, that this cell lysis is complement dependent. In this assay, the GD1a cell membrane pool appears to be more susceptible to anti-ganglioside antibody-mediated injury than the GM1 pool. Further, human intravenous immunoglobulin (i.v.Ig), now a standard treatment for GBS, significantly decreased cytotoxicity in this assay. Our data indicate that the mechanisms of i.v.Ig-mediated protection in this assay include anti-idiotypic antibodies and downregulation of complement activation. This simple cytotoxicity assay can potentially be used for screening of (i) pathogenic anti-ganglioside antibodies in patients with immune-mediated neuropathies; and (ii) new/experimental therapies to prevent anti-ganglioside antibody-mediated neural injury.

Animals↗

PubMed2001

Gastric proteolysis in preterm infants fed mother's milk or formula.

Gastric proteolysis is assumed to be low in the newborn (Britton & Koldovsky 1989). Postprandial pepsin output is significantly lower in preterm infants than adults, 589 vs. 3352U/kg, respectively (Armand et al. 1995, 1996). We now report on gastric proteolysis in preterm infants (gestation age, 29 weeks; postnatal age, 5-6 weeks) gavage-fed mother's milk or preemie formula. The data show that a) the nonprotein component is higher in human milk than formula, b) net proteolysis amounts to 15% of protein, c) gastric proteolysis is lower than lipolysis and, contrary to the latter, is not enhanced by milk feeding (Armand et al. 1996). We suggest that stomach pH, enzyme output, and food structure are the reasons for differences in gastric digestion of protein and fat in infants.

Aging↗

PubMed2001

Forensic issues in pain: review of current practice.

Forensic activity in pain practice is reviewed with reference to the differing roles of the pain clinician and the independent expert. Ethical guidelines and recommendations for assessment, documentation, record review, and court testimony are discussed. Specific issues include the assessment of disability and impairment, malingering, and application of the Daubert standard in forensic pain practice. Examples of case law are reviewed for civil liability and CRPS, malpractice with opioid prescribing, and practice issues in a correctional setting.

Journal Article↗

PubMed2000

Different effects of nocturnal parafunction on the masticatory system: the Weak Link Theory.

It is proposed that damage to the masticatory system from intense parafunction can be assessed more accurately by the Weak Link Theory. The theory predicts that the more intense and the more prolonged the forces, the more the tendency of damage to either. 1. the periodontal tissue; 2. the teeth; or 3. the orofacial structures. To test the theory, 22 subjects were selected based on reports of nocturnal bruxism. Each was assessed for masticatory system breakdown on the Russell Periodontal Index, the Helkimo Dysfunction Index, and a Tooth Wear Index. A Bruxcore (Forgione, A. 1974 J Dent Res 53:127) was used to obtain an objective score of bruxism. Five of eleven subjects with mild bruxism scored high on only one index. Significantly more subjects (ten of eleven) with moderate to severe bruxism scored high on one index only.

Female↗

PubMed2000

Energy requirements derived from total energy expenditure and energy deposition during the first 2 y of life.

BACKGROUND: Current recommendations for energy intake of children are derived from observed intakes. Deriving energy requirements on the basis of energy expenditure and deposition is scientifically more rational than is using the observational approach and is now possible with data on total energy expenditure (TEE), growth, and body composition. OBJECTIVES: The objectives of this study were 1) to define energy requirements during the first 2 y of life on the basis of TEE and energy deposition; 2) to test effects of sex, age, and feeding mode on energy requirements; and 3) to determine physical activity. DESIGN: TEE, sleeping metabolic rate, anthropometry, and body composition were measured in 76 infants. TEE was measured with doubly labeled water, sleeping metabolic rate with respiratory calorimetry, and body composition with a multicomponent model. RESULTS: Total energy requirements were 2.23, 2.59, 2.97, 3. 38, 3.72, and 4.15 MJ/d at 3, 6, 9, 12, 18, and 24 mo, respectively. Energy deposition (in MJ/d) decreased significantly over time (P: = 0.001) and was lower in breast-fed than in formula-fed infants (P: = 0.01). Energy requirements were approximately 80% of current recommendations. Energy requirements differed by age (P: = 0.001), feeding group (P: = 0.03), and sex (P: = 0.03). Adjusted for weight or fat-free mass and fat mass, energy requirements still differed by feeding group but not by age or sex. Temperament and motor development did not affect TEE. CONCLUSION: The TEE and energy-deposition data of these healthy, thriving children provide strong evidence that current recommendations for energy intake in the first 2 y of life should be revised.

Anthropometry↗

PubMed2000

Physiologic variations in dural venous sinus flow on phase-contrast MR imaging.

OBJECTIVE: Our study quantifies normal physiologic variations of dural sinus flow using phase-contrast MR imaging. SUBJECTS AND METHODS: Fifteen volunteers were imaged using nontriggered and triggered phase-contrast MR venography of the superior sagittal and transverse sinuses. Triggered scans were obtained during regular breathing; nontriggered scans were obtained during regular breathing, breath-holding, deep inspiratory breath-holding, and deep expiratory breath-holding. Analysis of variance, Bonferroni method, and Dunn post hoc analysis were used to determine any significant differences in the mean flow and velocity between the different breathing maneuvers. A paired t test was used to compare flow between sinuses during regular breathing. RESULTS: Deep inspiratory breath-holding and deep expiratory breath-holding resulted in a significant decrease in blood flow and velocity in all dural sinuses compared with regular breathing. During deep inspiratory breath-holding, blood flow decreased 30.8% in the superior sagittal sinus, 19.7% in the left transverse sinus, and 19.1% in the right transverse sinus. Similarly, during deep expiratory breath-holding, blood flow decreased 30.2% in the superior sagittal sinus, 20.8% in the left transverse sinus, and 20.3% in the right transverse sinus. The sum of the flow in the transverse sinuses was significantly greater than in the sagittal sinus. Normal pulsatility of dural sinus blood velocity was also characterized for all measured sinuses. CONCLUSION: Characterization of variations in dural sinus velocity and flow as a function of the cardiac cycle and breathing maneuvers, using phase-contrast MR imaging, may help separate physiologic from pathologic changes of flow resulting from conditions that influence the cerebrovascular circulation.

Adult↗

PubMed1999

Dynamic T1-weighted spin-echo MR imaging: the role of digital subtraction in the demonstration of enhancing brain lesions.

We compared subtracted and non-subtracted images obtained from a contrast-enhanced dynamic T1-weighted spin echo (SE) magnetic resonance (MR) technique for the demonstration of enhancing brain lesions with and without associated hemorrhage. Thirty-four patients with enhancing brain lesions or subacute parenchymal hematomas were imaged using a contrast-enhanced dynamic T1-weighted SE MR technique modified by a keyhole scheme. On-line digital subtraction was performed. Non-subtracted and subtracted dynamic scans were compared for conspicuity and contrast-to-noise ratios (CNRs) of enhancing brain lesions. The presence and pattern of enhancement in the subacute parenchymal hematomas were evaluated on the subtracted images. In all, 47 enhancing brain lesions were detected on both the non-subtracted and the subtracted images. The enhancing brain lesions were more conspicuous on the subtracted images (P < 0.05). There was an increase in CNRs of the enhancing lesions on the subtracted images compared with the non-subtracted ones (P < 0.001). Seventeen subacute parenchymal hematomas were detected on the non-subtracted images. The subtracted images demonstrated enhancement in 15 hematomas (8 rim enhancement only/7 both nodular and rim enhancement). Digital subtraction in contrast-enhanced dynamic T1-weighted SE MR imaging is helpful in demonstrating enhancing brain lesions with and without associated hemorrhage.

Aged↗

PubMed1999

Protective function of human milk: the milk fat globule.

Human milk contains many components that protect the newborn against infection at a time when the infant's own defense mechanisms are poorly developed. Fat is one of the major nutrients in human milk. The fat is contained within milk fat globules composed of a core of triglyceride and a membrane consisting of phospholipids, cholesterol, proteins, and glycoproteins. Both the membrane and the core components can provide protection against microorganisms. The major protective membrane glycoproteins, mucin, and lactadherin are resistant to conditions in the newborn's stomach and maintain their structure and function even at low pH and in the presence of the proteolytic enzyme pepsin. The core triglycerides upon hydrolysis by digestive lipases (especially gastric lipase, which is well developed in the newborn) produce free fatty acids and monoglycerides, amphiphylic substances able to lyse enveloped viruses, bacteria, and protozoa. Therefore, in addition to its nutritional value, the fat in human milk has a major protective function.

Anti-Bacterial Agents↗

PubMed1999

The effect of vertical dimension and mandibular position on isometric strength of the cervical flexors.

This study compared the peak isometric strength of the cervical flexors in deep bite temporomandibular dysfunction (TMD) patients while biting in four bite positions: habitual occlusion, edge-to-edge, lateral shift and retruded. These values were then compared to those of the same subjects' bite positions elevated to a functional criterion (maximum isometric strength of the deltoid muscles). The mean height increase was 2.4 mm with a range of 1.5-3.8 mm. Fifteen of eighteen deep bite subjects met an inclusionary criterion, at least 13.3 Newtons (N) stronger cervical muscle strength with mandible relaxed open than habitual bite. Peak strength biting edge-to-edge was significantly greater than biting in habitual occlusion. Strength was found to increase significantly when biting in each of four mandibular positions when the bite was elevated to the functional criterion. The greatest strength was obtained from elevated habitual and edge-to-edge positions. The findings are of clinical significance, suggesting that cervical muscle isometric strength is affected by bite position and vertical dimension of occlusion. The results suggest that when biting, individuals with deep bite may be functioning at about 60% of their potential cervical flexor, isometric strength. The interaction between occlusal position, vertical dimension and cervical muscle function suggests a craniomandibular-cervical masticatory system.

Adult↗

PubMed1998

Milk fat globule glycoproteins in human milk and in gastric aspirates of mother's milk-fed preterm infants.

Human milk fat globule (HMFG) glycoproteins can prevent infections by microorganisms in breast-fed infants; the MUC-1 mucin inhibits binding of S-fimbriated Escherichia coli to buccal mucosa, and lactadherin may prevent symptomatic rotavirus infections. In this study, the survival of these HMFG glycoproteins in the stomach of human milk-fed preterm infants (gestational age = 27.5 +/- 0.4 wk) was assessed, and levels in their mothers' milk determined, using specific RIAs. Butyrophilin, a major component of HMFG membrane that has no demonstrated antimicrobial activity, was studied for comparison. The levels of mucin, lactadherin, and butyrophilin in 41 milk samples of 20 mothers were 729 +/- 75, 93 +/- 10, and 41 +/- 3 microg/mL, respectively. Mucin and lactadherin were significantly higher in early milk samples (<15 d postpartum) than in later milk samples (15-90 d postpartum), whereas butyrophilin showed no such difference. Significant amounts of mucin and lactadherin were found in almost all gastric aspirates of human milk-fed infants, even 4 h after feeding (mucin, 270 +/- 30 microg/mL; lactadherin, 23.2 +/- 4.4 microg/mL), whereas butyrophilin was rapidly degraded in the majority of aspirates. Western blot analysis demonstrated that the immunoreactive mucin, lactadherin, and butyrophilin in the milk-fed gastric aspirates had the expected native molecular weights. Mucin and lactadherin survived at all gastric pH values, whereas butyrophilin was found only at pH > 4. Neither lactadherin nor butyrophilin were detected in gastric aspirates of formula-fed infants (gestational age = 27.8 +/- 0.5 wk), whereas the very low level of mucin (9.1 +/- 1.1 microg/mL) in this group is presumably cross-reacting gastric mucin. These results demonstrate that two HMFG glycoproteins implicated in prevention of infection, MUC-1 mucin and lactadherin, survive and maintain their integrity in the stomachs of human milk-fed preterm infants.

Anti-Infective Agents↗

PubMed1997

Effect of increased maxillo-mandibular relationship on isometric strength in TMD patients with loss of vertical dimension of occlusion.

The effect on isometric strength of the shoulders and limbs while biting in habitual occlusion, on a bite-elevating appliance and on a placebo appliance was analyzed. Twenty female volunteer patients, presenting with temporomandibular pain dysfunction syndrome and obvious loss of vertical dimension, served as subjects. All were weaker to the manual application of the isometric Deltoid Press (IDP) when biting, as opposed to maintaining the mandible in an unsupported rest position. Two intraoral appliances were fabricated for each subject: a bite-elevating appliance (BEA) set by a functional criterion of peak strength to the IDP and a placebo appliance which did not interfere with occlusion but was "set" with a mock IDP procedure. Testing was carried out by the Neuromuscular Research Testing Laboratory of the Neurology Department of Tufts New England Medical Center. Testing was independent of the dentist who fabricated and set the appliances. A standard neuromuscular test with the Maximal Voluntary Isometric Contraction apparatus was used to assess strength of right and left shoulder, elbow and knee flexion and extension as is routinely performed with all neuromuscular disease patients. Twelve strength tests were carried out for each of three conditions: 1. Baseline-biting in habitual occlusion; 2. Elevated-biting on the BEA; and 3. Placebo-biting with the placebo appliance inserted. The order of conditions 2 and 3 was counterbalanced without knowledge of the subjects. Twelve repeated measures ANOVAs (each subject as their own control) were conducted for each of the 12 strength measures. All F-tests indicated a significant main effect for treatment differences (p < 0.0001). Mean strength biting on the BEA was consistantly greater (p < 0.001) than Baseline or Placebo strength. Baseline and Placebo condition were equivalent. These findings confirmed previous observations at this TMD Center: individuals with loss of vertical dimension of occlusion respond to a bite raising appliance by increased isometric-strength.

Analysis of Variance↗

PubMed1996

The relationship between jaw posture and muscular strength in sports dentistry: a reappraisal.

From the late 1970s until the early 1990s, there have been several reports of improved appendage muscle strength and athletic performance. Much of the criticism of using a mouthguard alone or in conjunction with a splint, such as a mandibular orthopedic repositioning appliance (MORA), to enhance athletic performance has been aimed at study designs, controls, periods of time, double blindness, and the placebo effect. Although it would appear that designing a study which pleases both clinician and researcher would be a difficult task, studies have been performed that do meet the "gold standard." The results favor the premise that jaw repositioning can enhance appendage muscular strength and athletic performance. Studies performed during the mid-1980s, and to which the scientific community refers to continually, on closer examination are flawed.

Bite Force↗

PubMed1996

Effect of human milk or formula on gastric function and fat digestion in the premature infant.

The effect of diet, human milk or formula, on gastric function (lipase and pepsin activity, pH, and volume) and intragastric digestion of fat was assessed in 28 appropriate for gestational age preterm infants (gestational age, 28.9 +/- 1.4, 29.1 +/- 0.9, 29.5 +/- 0.6 wk; birth weight, 1.00 +/- 0.14 to 1.18 +/- 0.07 kg). The infants were fed either human milk (n = 11), SMA Super Preemie formula (n = 9), or Similac, Special Care formula (n = 8). Fasting and postprandial activity of digestive enzymes, pH, and gastric volume (measured before or during 50 min after gavage feeding) did not differ as a function of diet among the three groups of infants. Gastric lipase output, 23.1 +/- 5.1, 28.3 +/- 6.6, and 22.5 +/- 6.4 (U/kg of body weight) in human milk-, SMA SP-, or Similac SC-fed infants was comparable to the gastric lipase output of healthy adults fed a high fat diet (22.6 +/- 3.0). Pepsin output was, however, significantly lower (597 +/- 77, 743 +/- 97, and 639 +/- 142 U/kg of body weight) in human milk-, SMA SP-, and Similac SC-fed infants) than in healthy adults (3352 +/- 753 U/kg). The hydrolysis of dietary fat was 1.7-2.5-fold higher (p < 0.01) in human milk-fed infants than in infants fed either formula. We conclude that differences in type of feeding, i.e. different fatty acid profiles (long chain or medium chain triglycerides), different emulsions (natural or artificial), and different fat particle sizes do not affect the level of activity of gastric enzymes. However, the triglyceride within milk fat globules appears to be more accessible to gastric lipase than that within formula fat particles. We suggest that the contribution of gastric lipase to overall fat digestion might be greater in the newborn (a period of pancreatic insufficiency) than in the adult.

Dietary Fats↗

PubMed1995

Clinical study of location and reproducibility of three mandibular positions in relation to body posture and muscle function.

Clinical studies have confirmed the adequate reproducibility of both centric occlusion and centric relation when used as reference positions during treatment; however, the reproducibility of the neuromuscular position has been found inadequate. This study evaluated the location and reproducibility of these three mandibular positions in relation to body posture, sitting and supine, and bilateral muscle activity before and after the insertion of a flat mandibular positioning device equilibrated to balance the muscle functions, as shown by two electromyography biofeedback instruments. Intraoral recordings were made in 11 young subjects with complete natural dentition. Acrylic resin clutches that supported a screw point in the maxillary arch and painted glass in the mandibular arch were used and positioned not to interfere with the occlusion. The distances of the screw scratch from two of the edges of the painted glass were used to measure the anteroposterior and mediolateral locations with a micrometer. The reproducibility was evaluated by measuring the scratch surface by measuring the weight of the print cutouts made from photographs of the scratches taken with a stereoscope. The location and reproducibility of centric occlusion and centric relation were not affected by body posture. A more precise posterior neuromuscular position was obtained in the supine position. The insertion of a mandibular positioning device did not affect centric occlusion but gave a more precise centric relation. Neuromuscular position became as precise as centric occlusion and was located anteroposteriorly between centric occlusion and centric relation.

Acrylic Resins↗

PubMed1995

Whole-body irradiation transiently diminishes the adrenocorticotropin response to recombinant human interleukin-1 alpha.

Recombinant human interleukin-1 alpha (rhIL-1 alpha) has significant potential as a radioprotector and/or treatment for radiation-induced hematopoietic injury. Both IL-1 and whole-body ionizing irradiation acutely stimulate the hypothalamic-pituitary-adrenal axis. We therefore assessed the interaction of whole-body irradiation and rhIL-1 alpha in altering the functioning of the axis in mice. Specifically, we determined the adrenocorticotropin (ACTH) and corticosterone responses to rhIL-1 alpha administered just before and hours to days after whole-body or sham irradiation. Our results indicate that whole-body irradiation does not potentiate the rhIL-1 alpha-induced increase in ACTH levels at the doses used. In fact, the rhIL-1 alpha-induced increase in plasma ACTH is transiently impaired when the cytokine is administered 5 h after, but not 1 h before, exposure to whole-body irradiation. The ACTH response may be inhibited by elevated corticosterone levels after whole-body irradiation, or by other radiation-induced effects on the pituitary gland and hypothalamus.

Adrenalectomy↗

PubMed1995

Relationship of muscular strength to jaw posture in sports dentistry.

From the late 1970s until the early 1990s there have been several reports of improved appendage muscle strength and athletic performance. Much of the criticism of using a mouthguard alone or in conjunction with a splint, such as a mandibular orthopedic repositioning appliance (MORA), to enhance athletic performance has been aimed at study designs, controls, periods of time, double blindness and the placebo effect. Although it would appear that designing a study that would please both clinician and researcher would be a difficult task, studies have been performed that do meet the "gold standard"; and the results favor the premise that jaw repositioning can enhance appendage muscular strength and athletic performance. Previous studies performed in the mid-1980s, and to which the scientific community refers to continually, on closer examination are flawed.

Dentistry↗

PubMed1994

Systemically administered histamine H1 and H2 receptor antagonists do not block the ACTH response to bacterial lipopolysaccharide and interleukin-1.

The administration of lipopolysaccharide (LPS) results in the activation of the hypothalamic-pituitary-adrenal axis (HPAA). We recently reported that the participation and interaction of LPS-induced proinflammatory cytokines were obligatory for the stimulation of adrenocorticotropic hormone (ACTH) release by LPS. LPS and LPS-derived cytokines also stimulate the release of histamine (HA). HA is a known hypothalamic neurotransmitter and activates the HPAA. Therefore, to elucidate the role of HA in LPS- and cytokine-induced ACTH release, we evaluated the effects of several HA H1 and H2 receptor antagonists on the ACTH response to LPS, recombinant human interleukin-1 alpha (rhIL-1 alpha) and HA in mice. Although all 3 of the H1 receptor antagonists administered (mepyramine (MEP), diphenhydramine (DPH) or promethazine (PMZ) were able to block the 10-min ACTH response to HA, only PMZ (a less selective H1 receptor antagonist than MEP) was able to reduce the LPS- or rhIL-1 alpha-induced ACTH responses. Ranitidine, a powerful and selective H2 receptor antagonist, had little effect on the LPS- and rhIL-1 alpha-induced ACTH responses, while metiamide (MET), a much less potent first-generation H2 receptor antagonist, substantially diminished ACTH release. The greater effectiveness of PMZ, in contrast to MEP or DPH, probably relates to the ability of phenothiazine derivatives to inhibit non-HA-dependent pathways involved in the stimulation of the HPAA by cytokines; the same may be true of MET.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1992

Strength and bite, Part 2: Testing isometric strength using a MORA set to a functional criterion.

The effect on isometric strength of biting on three intraoral devices and habitual occlusion was analyzed. Only subjects who showed a relative weakness to the Isometric Deltoid Press (IDP) when biting as opposed to maintaining the mandible in an unsupported rest position were included in the study. Both in the original 35 subjects and the 23 subjects returning on the second day, performance wearing the appliance set by a functional criterion of peak strength (locking) to the IDP was significantly greater than wearing a placebo appliance and a bite raising appliance that deflected the mandible 1 mm to the left. Strength biting on the appliance set by a functional criterion was significantly greater than all these conditions. Strength biting in habitual trials that were matched with the deflection condition was found to be significantly greater than that biting in the placebo condition. It was concluded that a relationship does exist between bite and isometric strength. Previous speculation about the role of placebo effect was not substantiated by the data gathered in this experiment.

Adolescent↗