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Biomedical subjects

L Gray

Publications and source records attributed to L Gray.

At least 109 records · Page 6Linked to original sources
PubMed1993

Developmental changes in chickens' masked thresholds.

Masked thresholds were estimated at four frequencies (.25, .5, 1, and 2 kHz) in three levels of broadband noise (approximately 0, 10, and 20 dB/Hz) in over 100 chickens at 0 and 4 days of age. An adaptive procedure was based on delays in ongoing peeps that occurred when chicks heard the tones over the background noise. Masked thresholds decreased an average of 1 dB per day immediately after birth. This increasing sensitivity is more likely due to nonsensory factors, similar to distraction masking reported in human neonates, than to improving frequency resolution. Masked thresholds in these neonates are otherwise affected by spectrum level and frequency in the same way as the responses of mature subjects: thresholds increase by nearly 1 dB for each dB of increase in the spectrum level of the masker, and by approximately 3 dB for each octave of frequency. Thus, although elevated by some nonsensory effect, masked thresholds in newborn chicks are similar to those in humans.

Animals↗
PubMed1993

False-positive MRI detection of recurrent or metastatic pediatric infratentorial tumors.

Gadolinium-DTPA enhanced MRI is the modality of choice when imaging central nervous system infratentorial tumors in the pediatric population. The detection of a new enhancing lesion following initiation of therapy is typically considered pathognomonic for recurrent or metastatic tumor. We report two pediatric patients with infratentorial central nervous system tumors who demonstrated new areas of enhancement with gadolinium-DTPA enhanced MRI following initiation of multimodality therapy. Both patients had surgical biopsy of the new lesions with histologic review failing to demonstrate viable tumor. These studies suggest caution in considering new enhancing lesions detected by MRI in a child with a brain tumor pathognomonic for new sites of active tumor.

Astrocytoma↗
PubMed1993

Simultaneous masking in newborn chickens.

Simultaneous masking was used to investigate the development of frequency analysis in newborn animals. The ability of young chickens to detect a tone in the presence of a second tone was measured. In the first experiment data were collected with a 500-Hz masker presented at 15 or 25 dB above absolute threshold. Signals to be detected varied up to an octave from the masker (+/- 1/9, +/- 2/9, +/- 1/3, +/- 2/3, and -1 octave). Receiver operating characteristics (ROCs) were constructed from delays in ongoing peeps that occur when chicks detect the presence of the signal over the masker. Psychometric functions were fit by probit analysis using areas under these ROCs. Amounts of masking were estimated by the degree to which psychometric functions were shifted toward the right by the presence of the masker. There is no developmental change in these masking patterns, corroborating recent data from human infants. Masking was shown in a second experiment to be similar at a higher frequency (given intensities corrected for improving absolute thresholds). In conclusion, masking patterns derived from chicks' peeps are like those from adult humans. Frequency analysis, as measured by simultaneous masking, appears to be mature in chickens at hatching.

Acoustic Stimulation↗
PubMed1993

Laparoscopic placement of a percutaneous endoscopic gastrostomy (PEG) feeding tube.

Patients may have abnormal anatomic relationships between the stomach and adjacent organs, particularly when there is a history of abdominal surgery and adhesion formation. Routine placement of a percutaneous endoscopic gastrostomy tube can then be unsafe and result in inadvertent colon perforation, small bowel enterotomy, or injury to other structures. Described herein is a 94-year-old malnourished male in whom the colon lay directly anterior to the greater curvature of the stomach. A new technique was devised--laparoscopically-directed PEG placement--which proved to be a safer alternative approach in this patient.

Aged↗
PubMed1993

Disturbed fluid and electrolyte homoeostasis following dehydration in elderly people.

Disturbances in homoeostatic capacity are typical of the ageing process. Changes in the neuroendocrine controls of salt and water homoeostasis with age make elderly people more susceptible to fluid and electrolyte disturbances such as dehydration and overhydration. Not only do elderly subjects show reduced thirst and water intake following dehydration, but their kidneys are less able to retain water. This reduced thirst and water intake is not dependent on palatability of the liquids offered as the amounts drunk are no different if water alone or a variety of beverages are offered to healthy elderly dehydrated men. It is of interest that the arginine vasopressin (AVP) response to dehydration is maintained in elderly subjects, indicating that their reduced renal water retentive capacity is due to relative renal resistance to vasopressin. The mechanism underlying the reduced thirst is unclear. Dehydration causes plasma hypertonicity and reduced extracellular fluid (ECF) volume, both of which stimulate thirst and AVP secretion. Elderly subjects show deficits in sensing the reduced ECF volume through reduced low and high pressure baroreceptor sensitivity. In contrast, while the AVP responses to hypertonicity are maintained, the thirst responses seem to be reduced. It seems unlikely that the primary sensing 'osmoreceptor' neurons in the hypothalamus leading to AVP secretion or thirst would be differentially affected by age. Therefore the thirst deficit may result from changes with age in the more poorly defined pathways that bring thirst to consciousness. Following rehydration, thirst and AVP secretion are inhibited in young individuals thus avoiding overhydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Effects of drinking on thirst and vasopressin in dehydrated elderly men.

Inhibition of dehydration-induced arginine vasopressin (AVP) secretion and thirst depends on removal of osmotic and hemodynamic stimuli as well as on preabsorptive oropharyngeal factors that reduce thirst and AVP secretion on drinking before correction of the water deficits. Plasma atrial natriuretic peptide (ANP) levels may also change with drinking. Therefore, the thirst and plasma responses to oral water loads (10 ml/kg) in 10 healthy old (64-76 yr) and young (20-32 yr) 24-h water-deprived men were investigated. After 24-h water deprivation plasma sodium, osmolality, and AVP were increased similarly in both groups (P < 0.001). Plasma ANP levels fell after dehydration similarly in both groups (P < 0.05) but were always higher in the older group (P < 0.05). However, although thirst increased in both groups (P < 0.05), this was significantly less in the elderly (P < 0.05). After the water load, thirst was reduced in both groups throughout the study (P < 0.05). However, plasma AVP fell immediately after drinking only in the young group and rose to postdeprivation levels after 15 min. Plasma AVP was not different from postdeprivation throughout in the old group and after 15 min in the young group presumably because the water load was insufficient to replace their water deficits. In the young group only, plasma ANP rose to 182 +/- 43% of postdeprivation levels at 3 min after drinking (P < 0.05). These results demonstrate reduced oropharyngeal inhibition of AVP secretion after drinking in healthy elderly men but maintained inhibition of thirst.

Adult↗
PubMed1993

Mesenrhombencephalitis: MR findings in nine patients.

OBJECTIVE: Mesenrhombencephalitis is a serious form of brainstem inflammation predominantly involving the deep and vital portions of the brain, that is, the mesencephalon (midbrain) and rhombencephalon (pons, medulla). Mesenrhombencephalitis is difficult to diagnose on the basis of clinical and laboratory findings alone, and access to this portion of the brain for surgical biopsy carries high morbidity. We describe the MR appearance of mesenrhombencephalitis and correlate the imaging findings with clinical information. MATERIALS AND METHODS: Unenhanced and contrast-enhanced MR images of nine patients with mesenrhombencephalitis were reviewed retrospectively and correlated with clinical, laboratory, and pathologic data. The patients were categorized according to the cause of the disease: three had herpes simplex, one had Listeria monocytogenes, and five had mesenrhombencephalitis of undetermined cause. The three patients with clinical and MR evidence of herpes simplex mesenrhombencephalitis (one confirmed by brain biopsy) were comatose at presentation, with cranial nerve abnormalities in two and seizures in one. One patient with L. monocytogenes (established by blood culture) had cranial nerve palsies, fever, and pain in the ear. Five additional patients had headache (three), fever (three), nausea and vomiting (four), cranial nerve palsies (three), coma (two), and hyporeflexia (one) or hyperreflexia (four). Brain biopsy performed in two patients revealed chronic inflammation of unspecified cause; in one, it was compatible with viral encephalitis. RESULTS: MR images in three patients with herpes simplex mesenrhombencephalitis showed T2 signal hyperintensity in the midbrain (two), pons (one), medulla (one), and temporal lobes (three). Parenchymal foci of hemorrhage (methemoglobin, one patient) and leptomeningeal enhancement (one patient) were identified in the temporal lobes. T2-weighted MR images in one patient with L. monocytogenes showed signal hyperintensity in the brainstem, vermis, midbrain, and internal capsules. On T1-weighted images, low signal was present in these areas, which enhanced with paramagnetic contrast agents. In the remaining five patients, T2-weighted MR images showed patchy signal hyperintensity in the pons, medulla, and thalamus in three each and in the midbrain and temporal lobes in one each. T1-weighted MR images showed normal findings (two) or signal hypointensity in the thalamus and pons in one patient each. Areas of leptomeningeal and parenchymal enhancement were identified in one patient each. Brainstem swelling was seen in three patients, one of whom had petechial hemorrhage in the pons and hydrocephalus. CONCLUSION: Mesenrhombencephalitis is a serious illness that is diagnosed by a combination of imaging, clinical, laboratory, and pathologic studies. MR imaging may be crucial to the early diagnosis of this illness, and radiologists must be familiar with this uncommon entity and its MR findings in order to make timely diagnoses and facilitate treatment.

Adult↗
PubMed1993

FDG-PET in differentiating lymphoma from nonmalignant central nervous system lesions in patients with AIDS.

Structural imaging studies such as CT or MRI are not able to accurately differentiate infectious from malignant cerebral lesions in patients with AIDS. We studied 11 individuals with AIDS and central nervous system (CNS) lesions with 18F-fluoro-2-deoxyglucose (FDG) and positron emission tomography (PET). FDG-PET was able to accurately differentiate between a malignant (lymphoma) and nonmalignant etiology for the CNS lesions. Both qualitative visual inspection of the images as well as semiquantitative analysis using count ratios was performed and revealed similar results. FDG-PET may be useful in the management of AIDS patients with CNS lesions since high FDG uptake most likely represents a malignant process which should be biopsied for confirmation rather than treated presumptively as infectious.

AIDS-Related Opportunistic Infections↗
PubMed1992

Phase III clinical evaluation of gadoteridol injection: experience in pediatric neuro-oncologic MR imaging.

Twenty-two pediatric patients with known CNS neoplasms underwent magnetic resonance (MR) imaging before and after intravenous injection of 0.1 mmol/kg gadoteridol injection as part of a Phase IIIB open label multicenter clinical trial. Intravenous administration of this neutral, nonionic contrast agent was found to be safe in children. No clinically relevant changes in vital signs or laboratory values (including complete blood count, blood chemistry, serum electrolytes, thyroid and metabolic panel and clotting function) were attributed to the administration of gadoteridol injection. There were no systemic complaints. The imaging characteristics of gadoteridol in pediatric CNS disease appeared similar to those of gadopentetate dimeglumine. Contrast enhancement was present in 17 of 22 patients (77%). The administration of gadoteridol injection provided additional clinically relevant information including improved visualization and delineation of the primary lesion, detection of additional lesions, determination of tumor recurrence and narrowing the list of differential considerations in all 17 enhancing studies as well as in 2 of 5 studies without signal intensity enhancement. The very low toxicity, inherent to this nonionic low osmolal paramagnetic contrast formulation may allow administration of increased doses at increased infusion rates for an increased number of indications with improved sensitivity.

Adolescent↗
PubMed1992

Aspiration after stroke: lesion analysis by brain MRI.

Aspiration is a common problem following stroke, resulting in feeding difficulties and aspiration pneumonia. Despite past studies using clinical assessments and computed tomographic (CT) scans of the head, the correlation of stroke location with aspiration remains unclear. Since brain magnetic resonance imaging is more sensitive than CT for many stroke types, we have correlated MRI lesions with aspiration in patients who have sustained a stroke. We selected patients with acute stroke who underwent brain MRI and a swallowing evaluation. Aspiration was present in 21 of 38 patients (55%). Patients with just small vessel infarcts had a significantly lower occurrence of aspiration (3 of 14, 21%) compared to those with both large- and small-vessel infarcts (15 of 20, 75%, p = 0.002). Multivariate analysis of several specific brain areas failed to identify a significant association between stroke location and the occurrence of aspiration. These findings suggest that patients who have experienced stroke should be individually evaluated for swallowing dysfunction regardless of stroke location or size, since even small-vessel strokes can be associated with aspiration in greater than 20% of cases.

Adult↗
PubMed1992

Multidimensional scaling of head and neck metastases.

A mathematical analysis, called multidimensional scaling, was applied to two sets of data on metastases from head and neck cancers. The analysis places lymph nodes in an imaginary space (here termed a 'nodalgram') such that distances between nodal clusters are proportional to differences in the occurrence of tumor metastases. Two-dimensional scaling explains 93% of the variance in clinical data from 1008 patients and 91% of the variance in pathological data from a different set of 415 patients. These independent results are closely correlated, and both explain vastly more of the data than expected by chance. The dimensions of the nodalgram are not related to anatomical coordinates of the nodes, suggesting that a representation of these structures in an abstract space explains the spread of cancers better than an analysis of spread in real space. Surprisingly, a plot of the extent to which metastases from different primary sites spread along the nodalgram dimensions is closely related to the normal anatomical locations of the primaries. This shows that although the nodalgram may be difficult to interpret, it must have some biological significance. In conclusion, multidimensional scaling successfully quantifies a pattern in the spread of head and neck cancers.

Algorithms↗
PubMed1992

An auditory psychometric function from newborn chicks.

This study shows how the hearing of newborn chicks can be quantified with receiver operating characteristics (ROCs). A detailed auditory psychometric function was constructed from areas under ROCs, derived from delays in ongoing vocalizations elicited by pulsing pure tones. Over 20,000 delays were analyzed from 160 birds tested at four frequencies (0.25-2 kHz), eight intensities (-3 to 18 dB above estimated threshold), and two ages (0 and 4 days posthatch). Areas under these ROCs increase in an S-shaped function over intensity, as expected. Maximum responsiveness at approximately 75% correct shows that these neonates never achieve the near-perfect performance of mature listeners. Thresholds appear best estimated by the level required for 65% correct. Results replicate previous findings, showing that thresholds mature at low frequencies before high. Although there is no simple way to alleviate decreasing responsiveness caused by habituation over trials, improved performance results from presenting different frequencies, but only in the younger birds, and primarily with louder stimuli.

Animals↗
PubMed1992

Absorption and lymphatic transport of peroxidized lipids by rat small intestine in vivo: role of mucosal GSH.

The absorption and lymphatic transport of peroxidized MaxEPA fish oil was studied using the lymph fistula rat to determine the role of mucosal glutathione (GSH) in intestinal metabolism of luminal lipid hydroperoxides. Decreasing intestinal GSH concentrations with buthionine sulfoximine (BSO, 1.15 +/- 0.20 nmol/g), diethyl maleate (DEM, 0.93 +/- 0.26 nmol/g), phorone (1.46 +/- 0.14 nmol/g), or 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, 1.54 +/- 0.18 nmol/g) compared with control (2.60 +/- 0.38 nmol/g) resulted in higher luminal recovery of the infused lipid hydroperoxide (% of infused dose): BSO (87.8 +/- 4.8%), DEM (86.1 +/- 1.3%), phorone (78.1 +/- 2.1%), and BCNU (71.7 +/- 4.8%) compared with control (52.8 +/- 4.3%). These results suggest that decreased elimination of luminal peroxidized lipids is associated with decreased tissue GSH. Treatment of rats with BSO, DEM, phorone, or BCNU resulted in dramatic increases in appearance of peroxidized lipids in lymph over 6-h lipid infusion (54.7 +/- 3.7, 57.7 +/- 4.6, 46.4 +/- 2.7, and 42.1 +/- 3.9 nmol, respectively) compared with control (20.5 +/- 3.4 nmol). The results are consistent with decreased intracellular metabolism of absorbed hydroperoxides and enhanced transport into lymph under GSH-deficient conditions. The current findings suggest that the function of the mucosal GSH peroxidase/oxidized glutathione (GSSG) reductase system may play an important role in intestinal handling of luminal lipid hydroperoxides. A compromised function of this detoxication mechanism in GSH-deficient states can significantly alter the metabolic fate of dietary peroxidized lipids.

Absorption↗
PubMed1992

An investigation of the relationship between free radical activity and vitamin C metabolism in elderly diabetic subjects with retinopathy.

Abnormalities of both free radical activity and ascorbic acid metabolism have been documented in diabetes, but their biological basis is unclear and their relationship unstudied in any detail. This study was designed to compare changes in antioxidant status and free radical reactions in a group of elderly diabetic patients (with and without retinopathy) with those in a group of age-matched control subjects. No significant differences in thiobarbituric acid (TBA) reactivity, red cell glutathione (GSH) concentrations or diene conjugates (DC) between patients and controls were seen despite significant depletion of ascorbic acid in patients with diabetes, especially in those with retinopathy. The results emphasise the present-day difficulties of measuring free radical activity and demonstrate a marked abnormality in ascorbic acid metabolism in diabetes.

Aged↗
PubMed1992

Stroke with negative brain magnetic resonance imaging.

BACKGROUND AND PURPOSE: Magnetic resonance imaging (MRI) of the brain is replacing computed tomography in the diagnostic evaluation of acute ischemic strokes. Past studies have suggested that MRI may not visualize all acute strokes, but few clinical details were included. To better understand the clinical characteristics of strokes not detected by MRI, we collected and reviewed case histories of several patients with acute stroke who had negative MRI scans. METHODS: Patients with a clinical diagnosis of stroke and negative brain MRI scans were ascertained from hospital records dating from 1989 to mid-1991. Patients with transient ischemic attacks, postictal paralysis, functional examinations, central nervous system infections, other nonstroke diagnoses, or equivocal findings were excluded. The MRI scans were performed with a GE Signa 1.5-T magnet in an axial plane (spin-echo repetition time/echo time: 500 msec/20 msec; 2,500 msec, 30 msec/80 msec). One patient received contrast material. RESULTS: We identified seven patients with clinically diagnosed ischemic stroke and negative brain MRI scan. Six of seven patients were scanned within 7 days of symptom onset and two patients within 24 hours. One patient was scanned 3 months after symptom onset. The strokes not detected by MRI were clinically localized to the cortex (n = 3), brain stem (n = 3), and subcortical/lacunar area (n = 1). One patient underwent two MRI scans, one with gadolinium. CONCLUSIONS: These cases, while selected, illustrate some potential limitations of MRI for diagnosing stroke.

Aged↗
PubMed1992

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part III. Reliability of a standardized MRI evaluation of Alzheimer's disease.

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD) has developed procedures for standardized imaging and reporting of magnetic resonance (MR) findings in Alzheimer's disease (AD) for use by neuroradiologists in multiple medical centers using a variety of MR equipment and field strengths. After initial pretesting, we revised the protocol, expanded the summary rating scale to seven points, and added more illustrations. Fourteen participating neuroradiologists evaluated 28 MR scans of elderly patients, giving us the basis for judging interrater agreement. We obtained acceptable intraclass correlations (greater than 0.79) for rating the size of the lateral and third ventricles and the temporal horn. Less satisfactory intraclass correlations occurred when rating other areas, including (1) global atrophy of the brain (0.70); (2) dilatation of the sulci of the temporal lobe (0.66); (3) frequency, location, and severity of white matter lesions (0.77); (4) sylvian fissure enlargement (0.70); and (5) cerebral sulcal dilatation (0.64). We also saw considerable variation in the reporting of cortical and lacunar infarcts. Despite careful design of the rating methodology and readings by experienced neuroradiologists, we did not find satisfactory interrater agreement for interpreting MR findings in elderly subjects. These findings may explain the difficulties encountered in applying similar subjective rating techniques that meet with success at one institution to multicenter studies. More objective and reproducible procedures are needed for interpretation of neuroimaging findings of AD in multicenter studies.

Alzheimer Disease↗
PubMed1992

The paperless essay: one way to teach writing and computer skills in medical school.

We designed an assignment for first-year medical students that included instruction in writing and in computer use, two important subjects that are usually neglected in the traditional curriculum. As part of a neuroscience course, students wrote an essay using a word processor and submitted it to the instructor via the campus computer network. If requested by the instructor, the students submitted a revision of their essays without a grade penalty. As a result of completing the assignment, students learned the importance of revision and were stimulated to learn more about computers. With only slight modification of medical school courses, faculty can place more emphasis on writing skills and computer literacy.

Computer Literacy↗