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Biomedical subjects

D M Schwartz

Publications and source records attributed to D M Schwartz.

At least 37 records · Page 2Linked to original sources
PubMed1997

Depiction of pulmonary emboli with spiral CT: optimization of display window settings in a porcine model.

PURPOSE: To determine optimal spiral computed tomographic (CT) image display for depiction of pulmonary emboli (PE). MATERIALS AND METHODS: Autologous PE detected in 10 pigs with contrast material-enhanced spiral CT were displayed with six display window settings (standard mediastinal window and five modified windows referenced to attenuation values in pulmonary artery [PA] branches). The thrombus gray level and gray level contrast and separability of PE versus those of the local PA branch were computed for each window setting; results were compared with repeated measured analysis of variance. RESULTS: Of 114 PE detected pathologically, 28 were visible with spiral CT. Two of the 28 PE were not detectable with standard mediastinal windows. Statistically significantly improved gray level contrast and separability were noted with modified windows referenced to the second-order PA branch and the local PA branch than with the standard mediastinal and other modified window settings (P < .05). However, thrombus gray level was statistically significantly higher with the standard mediastinal window (P < .05). CONCLUSION: PE are best depicted as filling defects when displayed with a modified window referenced to the right or left main PA attenuation. Standard mediastinal windows are useful for identifying vessels that are occluded completely with PE.

Acute Disease↗
PubMed1997

Influence of nitrous oxide on posterior tibial nerve cortical somatosensory evoked potentials.

The suppressive effect of the halogenated inhalation anesthesia on cortical somatosensory evoked potentials (cSSEPs) has been well documented. Less studied and appreciated is the effect of nitrous oxide often with a narcotic as an alternative to a potent agent for spinal cord monitoring. This study sought to define more clearly the influence of nitrous oxide on cSSEPs elicited to posterior tibial nerve stimulation. A secondary purpose was to demonstrate the advantage of a total intravenous propofol anesthesia in facilitating uncompromised large-amplitude cSSEPs. Fifty adult patients undergoing anterior cervical discectomy served as the study sample. Brainstem and cortical posterior tibial nerve SSEPs were recorded under two independent anesthesia conditions, namely, nitrous oxide and propofol. Results demonstrated a significant amplitude reduction and latency prolongation with the nitrous oxide versus propofol protocol. cSSEP amplitude with propofol was, on the average, approximately two times larger than that with nitrous oxide. Based on these findings, the use of nitrous-oxide anesthesia is not recommended when limited to monitoring cSSEPs that are already amplitude compromised secondary to existing spinal cord disease.

Adult↗
PubMed1997

Corneal endothelial hyaluronidase: a role in anterior chamber hyaluronic acid catabolism.

The possible role of the human corneal endothelium in the turnover of anterior chamber hyaluronic acid (HA) was investigated. Hyaluronidase, an endoglycosidase that degrades HA and other glycosaminoglycans, is thought to play a role in HA homeostasis. The presence of hyaluronidase in the corneal endothelium was demonstrated immunohistochemically in sections from normal adult human cornea. Additionally, by using a modified enzyme-linked immunosorbent assay-like assay, active hyaluronidase was detected in the supernatant from primary culture human corneal endothelial cells. The optimal activity for the corneal endothelial hyaluronidase was in the acid range (pH 4.0), similar to previously isolated lysosomal hyaluronidase. Further immunohistochemistry showed that the corneal endothelial cells also express CD44, the receptor for HA, which would allow endocytosis of HA. Human corneal endothelial hyaluronidase may play a role in normal anterior segment HA metabolism and in the degradation of highly concentrated HA used as a visco-elastic.

Adult↗
PubMed1996

Guarded microvitreoretinal blade.

During vitreoretinal surgery, the microvitreoretinal blade may be misdirected and injure operating room personnel. A sheated, retractable blade has been developed to reduce the likelihood of such injuries. In the blade's retracted position, a safety feature prevents inadvertent exposure of the sharp blade. This device may have its greatest utility in operating on patients with cytomegalovirus retinitis who require either retinal reattachment surgery or placement of a ganciclovir implant.

Cytomegalovirus Retinitis↗
PubMed1996

Human vitreous hyaluronidase: isolation and characterization.

PURPOSE: Hyaluronic acid (HA) is the predominant glycosaminoglycan (GAG) of the human vitreous. Interaction of this HA with vitreous collagen is important for maintaining gel structure. The mechanism of HA homeostasis in the vitreous is incompletely understood. The aim of this study was to determine whether hyaluronidase, an endoglycosidase that degrades HA, was present in human vitreous. METHODS: Vitreous samples were collected from post-mortem eye bank specimens and from non-hemorrhagic, non-inflamed biopsy specimens. Vitreous hyaluronidase was purified by a series of column chromatographic steps, and its activity was measured by an ELISA-like assay and by substrate gel electrophoresis through and HA-impregnated gel. The purified hyaluronidase was also analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and by Western blotting. RESULTS: Hyaluronidase activity was detected in vitreous samples from both post-mortem and biopsy specimens. The enzyme was most active at acid pH, but demonstrated significant activity at neutral pH. The partially purified enzyme migrated as a 59 kDa protein on SDS-PAGE, and a single band on Western blots. CONCLUSIONS: Hyaluronidase is present in the human vitreous. Thus, hyaluronidase may be involved in HA catabolism in the vitreous and may play a role in determining its gel structure.

Blotting, Western↗
PubMed1996

Efficacy of spinal cord monitoring in scoliosis surgery in patients with cerebral palsy.

Although spinal cord monitoring is recommended during scoliosis surgery, a review from Rancho Los Amigos Medical Center stated that they were only able to obtain reproducible tracings in 53% of cerebral palsy patients. To ascertain that monitoring is both feasible and reliable in these patients, we reviewed the records of 34 consecutive patients with cerebral palsy who had scoliosis surgery at our institution. Spinal cord function was monitored by recording peripheral nerve, cervical/brainstem, and cortical somatosensory evoked potentials to posterior tibial nerve stimulation. Reproducible tracings were achieved in 31 of the 34 patients. Significant intraoperative changes were recorded in 12 of the 31 monitored patients, usually related to and requiring some modifications of the instrumentation. We conclude that with careful technique, spinal cord monitoring using cervical/brainstem somatosensory evoked potentials can be reliably achieved in most patients with cerebral palsy undergoing scoliosis surgery.

Adolescent↗
PubMed1996

Influence of rigid spinal instrumentation on the neurogenic motor evoked potential.

Three case reports are presented to illustrate how placement of spinal instrumentation obliterates previously normal neurogenic motor evoked potentials (NMEPs) elicited by transosseous electrical stimulation. This results in an unacceptably high false-positive rate for NMEP recordings during scoliosis surgery. The loss of the NMEPs was attributed to shunting of electrical current from JO5 spinous process stimulating needles through the metal rod to ground, thus preventing adequate stimulation to the spinal cord. A modification of the transosseous technique with epidural stimulation to improve test reliability is described.

Adolescent↗
PubMed1995

A sensitive and specific polymerase chain reaction-based assay for the diagnosis of cytomegalovirus retinitis.

PURPOSE: To develop a sensitive and specific laboratory assay for the diagnosis of cytomegalovirus retinitis. METHOD: We used a polymerase chain reaction-based assay for detection of cytomegalovirus DNA in vitreous samples. We attempted to detect cytomegalovirus DNA in 19 vitreous samples from patients with the acquired immunodeficiency syndrome (AIDS) who had untreated cytomegalovirus retinitis and in 40 vitreous samples from patients with AIDS who had been treated with systemic ganciclovir or foscarnet, or both. We also attempted to detect cytomegalovirus DNA in vitreous samples from 54 immunocompetent patients, including 32 with retinal detachment or macular hole, 11 with vitreous inflammation, and 11 with vitreous hemorrhage. Additionally, we attempted to detect cytomegalovirus DNA in 15 vitreous samples from patients with AIDS who had vitreoretinal inflammation not caused by cytomegalovirus. RESULTS: Cytomegalovirus DNA was detected in 18 of 19 eyes with untreated cytomegalovirus retinitis. We detected cytomegalovirus DNA in 19 of 40 vitreous samples from patients with previously treated cytomegalovirus retinitis. Cytomegalovirus DNA was not detected in any of 69 patients who did not have a clinical diagnosis of cytomegalovirus retinitis. Thus, the assay had an estimated sensitivity of 95% in detecting untreated cytomegalovirus retinitis and a sensitivity of 48% in detecting cytomegalovirus retinitis that had been treated with systemic ganciclovir or foscarnet, or both. The assay did not give false-positive results in patients with vitreous hemorrhage or vitreous inflammation. Most important, the assay did not give false-positive results in AIDS patients with vitreous inflammation from causes other than cytomegalovirus retinitis. CONCLUSION: We have developed a sensitive and specific diagnostic assay that will assist in the diagnosis of cytomegalovirus retinitis.

AIDS-Related Opportunistic Infections↗
PubMed1990

Management of traumatic hemorrhagic retinal detachment with pars plana vitrectomy.

Traumatic hemorrhagic retinal detachment may prevent successful visual rehabilitation of eyes with severe posterior segment injury. We managed 19 consecutive cases of traumatic hemorrhagic retinal detachment with pars plana vitrectomy, scleral buckling, and fluid-gas exchange, with or without internal drainage of subretinal hemorrhage. We based our approach on the amount of subretinal hemorrhage present and the location of associated retinal breaks. Internal drainage of subretinal hemorrhage was performed in 16 eyes to allow adequate retinopexy to hemorrhagically elevated retinal breaks (9 eyes), to remove massive subretinal hemorrhage (4 eyes), and to allow intraoperative reattachment when the retina exhibited bullous retinal detachment (3 eyes). Overall, with a minimum of 6 months of follow-up, anatomic reattachment was achieved in 13 (68%) of 19 eyes, and functional success (visual acuity 5/200 or better) was achieved in 6 (32%) of 19 eyes. Anatomic failure resulted from proliferative vitreoretinopathy (4 eyes) and globe atrophy (2 eyes). Drainage of subretinal blood appeared to be beneficial for hemorrhagically elevated retinal tears to allow adequate retinopexy and may help to accomplish long-term anatomic attachment in eyes with massive subretinal hemorrhage or bullous retinal detachment.

Adolescent↗
PubMed1990

Delayed sensorineural hearing loss following uncomplicated neurovascular decompression of the trigeminal root entry zone.

Trigeminal neuralgia (tic douloureux) is a condition characterized by intense, unilateral paroxysmal facial pain caused by an abnormality of the root entry zone of the trigeminal nerve. For patients with intractable pain unrelated to a pathologic process who fail to respond to conventional medical management, the microvascular decompression (MVD) is the operation of choice. Conductive or sensorineural hearing loss due either to stretching of the eighth nerve or hemotympanum during the operation is among the possible sequelae of MVD. We report on a perplexing case of delayed sensorineural hearing loss following uneventful microvascular decompression for trigeminal neuralgia that included intraoperative evoked potential monitoring.

Adult↗
PubMed1989

Intraoperative monitoring of brainstem auditory evoked potentials following emergency evacuation of a cerebellar vascular malformation.

This case report highlights the use and value of monitoring the auditory brainstem response during emergency neurosurgery. The prompt on-line changes in the auditory brainstem response after evacuation of a cerebellar arteriovenous malformation provided objective evidence of improved brainstem function, which aided in the management of this patient's disorder.

Adult↗
PubMed1989

Auditory brain stem responses in preterm infants: evidence of peripheral maturity.

This study explored further the relationship between peripheral and central auditory maturation on the basis of the auditory brain stem response. Auditory brain stem responses were recorded in preterm infants and adults to rarefaction and condensation click stimuli transduced through insert Tubephones. Infant recordings presented a triphasic waveform preceding wave I similar to that of the cochlear receptor potentials seen with adults during electrocochleography. Wave I latency and amplitude were found to be equivalent to those of adult subjects. Moreover, neither latency nor amplitude variability among infant wave I responses was found to be any greater than adults. Latencies of waves III and V, however, exhibited the expected differences relative to the adult comparison group. When the indirect evidence of cochlear receptor potentials in the infant are viewed adjacent to the observations that their ABR wave I latency, amplitude, and variability were entirely consistent with those of young adults, the data lend strong support for peripheral auditory electromaturity. These data are discussed relative to previously published reports of prolonged wave I latency in the infant which was attributed either to middle ear effects or immaturity of the cochlea and first order VIIIth nerve neurons.

Adult↗
PubMed1988

Inter- and intraclonal variability of polypeptides synthesized in a rat hepatoma cell line. Quantitative two-dimensional gel analysis.

To examine the degree of clonal heterogeneity in the synthesis of polypeptides in neoplastic cells, single-cell subclones from the rat hepatoma cell line H4-II-E were isolated. Polypeptides from the clones were resolved on high resolution two-dimensional polyacrylamide gels (PAGE), and quantitatively analyzed with a computerized two-dimensional PAGE analysis system developed in this laboratory. Only four qualitatively different spots were found which were synthesized in one of the subclones in four out of five experiments. In contrast, 5-20% of the spots showed statistically significant quantitative differences when any one subclone was compared to any other. These differences were generally quite small, averaging about 1.5-fold in intensity, although variations of fourfold or more were observed. Different cultures of the same subclone showed quantitative differences of the same order as seen in different subclones, indicating that this variability was primarily intraclonal in nature, i.e. associated with the cultures rather than the subclones. The distribution of quantitatively variable spots indicates that 50% or more of the polypeptides in these cells may display intraclonal variability. Similar results were obtained with a second set of subclones derived from these primary ones. Time course studies were conducted where cells were maintained continuously for 12 weeks, with samples taken for two-dimensional PAGE analysis once a week. The fraction of polypeptides that vary significantly generally increased with time between sampling points. Experiments with independent cultures grown in parallel indicate that about 4% of this variability can be correlated to the age of the culture media, although the majority appears due to uncontrolled and/or random differences that arise between cultures. These results indicate that independent cultures quickly develop detectable quantitative differences in the expression of a large fraction of their polypeptides. These differences cannot, at present, be associated with the observable biology of the cells and probably reflect time-associated variations in the balance of cellular macromolecular synthesis which arise in tissue culture cells.

Animals↗
PubMed1988

Reference threshold sound-pressure levels for the TDH-50 and ER-3A earphones.

Reference threshold sound-pressure levels were established for a new insert earphone, the ER-3A tubephone, and for the TDH-50 earphone. In test-retest comparisons, the tubephone produced estimates of auditory threshold as reliable as the thresholds produced by the supraaural earphone. Reference thresholds were developed for the two earphones from data contributed by three laboratories. While the TDH-50 data are in good agreement with the provisional ANSI 6-cc coupler reference levels (ASHA, 1982), the ER-3A data are at variance with the manufacturer's provisional recommendation for 2-cc coupler reference thresholds for frequencies below 1 kHz. The differences are attributed to physiologic noise that masked the lower frequency thresholds.

Acoustic Stimulation↗
PubMed1987

Neurodiagnostic audiology: contemporary perspectives.

This paper reviews the principals of clinical epidemiology as they relate to diagnostic audiology including the problems associated with the test battery approach. The paper also presents a philosophical discussion as to the influence of disease prevalence on diagnostic testing protocols in different clinical environments.

Hearing Tests↗