Concomitant hypertension, bradycardia, and loss of transcranial electric motor evoked potentials during pedicle hook removal: report of a case

Neurophysiologic monitors in the form of transcranial electric motor evoked potentials (tceMEPs) and somatosensory evoked potentials (SSEPs) have become widely used modalities to monitor spinal cord function during major orthopedic spine procedures. In combination with invasive and non-invasive clinical monitoring and an anesthesia information management system (AIMS), we promptly recognized an acute change in hemodynamic and neurophysiologic parameters, managed intraoperative spinal cord contusion, and successfully minimized iatrogenic injury to the spinal cord during corrective spine surgery.

Expression of reverse cholesterol transport proteins ATP-binding cassette A1 (ABCA1) and scavenger receptor BI (SR-BI) in the retina and retinal pigment epithelium

AIMS

Excessive lipid accumulation in Bruch's membrane (BrM) is a hallmark of ageing, the major risk factor for age-related macular degeneration (AMD). Retinal pigment epithelial (RPE) cells may utilise reverse cholesterol transport (RCT) activity to move lipid into BrM, mediated through ATP-binding cassette A1 (ABCA1) and scavenger receptor BI (SR-BI).

METHODS

ABCA1 expression was assessed by reverse transcription polymerase chain reaction (RT-PCR) and western blotting of human RPE cell extracts. Lipid transport assays were performed using radiolabelled photoreceptor outer segments (POS). ABCA1 and SR-BI expression was examined in normal mouse eyes by immunofluorescence staining. BrMs of ABCA1 and SR-BI heterozygous mice were examined microscopically.

RESULTS

Human RPE cells expressed ABCA1 mRNA and protein. The ABCA1 and SR-BI inhibitor glyburide (also known as glibenclamide) abolished basal transport of POS-derived lipids in RPE cells in the presence of high-density lipoprotein. Mouse retina and RPE expressed ABCA1 and SR-BI. SR-BI was highly expressed in RPE. BrMs were significantly thickened in SR-BI heterozygous mice, but not in ABCA1 heterozygous mice.

CONCLUSION

RPE cells express ABCA1 and SR-BI. This implies a significant role for SR-BI and ABCA1 in lipid transport and RCT in the retina and RPE.

High density lipoprotein mediated lipid efflux from retinal pigment epithelial cells in culture

BACKGROUND/AIM

[corrected] The transport of radiolabelled photoreceptor outer segments (POS) lipids was investigated by cultured retinal pigment epithelial cells (RPE). Phagocytosis of POS by the RPE is essential to maintain the health and function of the photoreceptors in vivo. POS are phagocytised at the apical cell surface of RPE cells. Phagocytised POS lipids may be either recycled to the photoreceptors for reincorporation into new POS or they may be transported to the basolateral surface for efflux into the circulation.

RESULTS

The authors have demonstrated that high density lipoprotein (HDL) stimulates efflux of radiolabelled lipids, of POS origin, from the basal surface of RPE cells in culture. Effluxed lipids bind preferentially to HDL species of low and high molecular weight. Effluxed radiolabelled phosphotidyl choline was the major phospholipid bound to HDL, with lesser amounts of phosphatidyl ethanolamine, phosphatidyl inosotol. Effluxed radiolabelled triglycerides, cholesterol, and cholesterol esters also bound to HDL. Lipid free apolipoprotein A-I (apoA-I) and apoA-I containing vesicles also stimulate lipid efflux.

CONCLUSION

The findings suggest a role for HDL and apoA-I in regulating lipid and cholesterol transport from RPE cells that may influence the pathological lipid accumulation associated with age related macular degeneration.

Saxitoxin: an anesthetic of the deepithelialized rabbit cornea

PURPOSE

The aim of the current study was to define the efficacy of saxitoxin as a corneal anesthetic in rabbits after mechanical corneal abrasion and photorefractive keratectomy (PRK).

METHODS

Twelve Dutch belted rabbits were given a single 1.2-microg dose of saxitoxin or vehicle after mechanical abrasion of the cornea. Corneal sensation was evaluated hourly for 6 hours. A second group of 12 Dutch belted rabbits was given a 1.2-microg dose of saxitoxin or vehicle every 5 hours for 30 hours after PRK. Corneal sensation was evaluated after 5, 10, 15, 20, 25, and 30 hours. Pachometry was performed before PRK and again after the epithelial defects had healed. The rate of epithelial defect closure was assessed by measuring the epithelial defect size 25, 42, 65, 88, and 113 hours after PRK.

RESULTS

A dose of 1.2 microg of saxitoxin given every 5 hours produced continuous corneal anesthesia after PRK. There was no difference in the rate of wound healing between eyes treated with saxitoxin and vehicle. There was no difference in the degree of wound healing, as measured by pachometry, between eyes treated with saxitoxin and vehicle. There were no apparent ocular or systemic toxic effects from saxitoxin administration.

CONCLUSION

At a dose of 1.2 microg, saxitoxin is a safe, effective, long-acting corneal anesthetic in rabbits after PRK.

Post implantation adjustable intraocular lenses

To eliminate persistent refractive errors after cataract and phakic IOL surgery, photosensitive silicone IOLs have been developed. These IOL formulations enable precise laser adjustment of IOL power to correct spherical and toric errors post-operatively, after wound and IOL stabilization. Initial experience with these laser adjustable IOLs indicate excellent biocompatability and adjustability of more than five diopters.

Expression of CD44 isoforms in cultured human trabecular meshwork cells

PURPOSE

To determine the expression of CD44 isoforms in cultured human trabecular meshwork (HTM) and to discuss their possible relationship with outflow facility.

METHODS

CD44 isoform expression in cultured HTM was qualitatively examined using immunohistochemistry and RT-PCR analysis.

RESULTS

Immunohistochemistry of cultured HTM showed intense staining with a CD44s antibody, and with antibodies against CD44 exon 7, exon 11-12 and exon 14. By RT-PCR, at least three isoforms of CD44 were expressed in HTM: CD44s, CD44v-III and CD44v-I.

CONCLUSIONS

At least three isoforms of CD44 are expressed in the HTM. CD44 may play a role in binding and turnover of hyaluronic acid in the trabecular meshwork, thereby regulating outflow facility.

Prevention of positional brachial plexopathy during surgical correction of scoliosis

Continuous intraoperative monitoring of spinal cord function using somatosensory evoked potentials (SSEP) has gained nearly universal acceptance as a reliable and sensitive method for detecting and possibly preventing neurologic injury during surgical correction of spinal deformities. In several reports, spinal cord injury was identified successfully based on changes in SSEP response characteristics, specifically amplitude and latency. Less well documented and used, however, is monitoring of peripheral nerve function with SSEPs to identify and prevent the neurologic sequelae of prolonged prone positioning on a spinal frame. The authors describe a patient who underwent surgical removal of spinal instrumentation but was not monitored. A brachial plexopathy developed in this patient from pressure on the axilla exerted by a Relton-Hall positioning frame during spinal surgery. In addition, data are presented from 15 of 500 consecutive pediatric patients who underwent surgical correction of scoliosis between 1993 and 1997 with whom intermittent monitoring of ulnar nerve SSEPs was used successfully to identify impending brachial plexopathy, a complication of prone positioning. A statistically significant reduction in ulnar nerve SSEP amplitude was observed in 18 limbs of the 500 patients (3.6%) reviewed. Repositioning the arm(s) or shoulders resulted in nearly immediate improvement of SSEP amplitude, and all awoke without signs of brachial plexopathy. This complication can be avoided by monitoring SSEPs to ulnar nerve stimulation for patients placed in the prone position during spinal surgery.

An economic analysis of interventions for diabetes

The objective of this article is to stratify interventions for diabetes according to their economic impact. We conducted a review of the literature to select articles that performed a cost-benefit analysis for 17 widely practiced interventions for diabetes. A scale for categorizing interventions according to their economic impact was defined. The 17 interventions were classified as follows: 1) clearly cost-saving, 2) clearly cost-effective, 3) possibly cost-effective, 4) non-cost-effective, or 5) unclear. Clearly cost-saving interventions included eye care and pre-conception care. Clearly cost-effective interventions included nephropathy prevention in type 1 diabetes and improved glycemic control. Possibly cost-effective interventions included nephropathy prevention in type 2 diabetes and self-management training. Non-cost-effective interventions were not identified. Interventions with unclear economic impact included case management, medical nutrition therapy, self-monitoring of blood glucose, foot care, blood pressure control, blood lipid control, smoking cessation, exercise, weight loss, HbA1c measurement, influenza vaccination, and pneumococcus vaccination. Widely practiced interventions for patients with diabetes can be clearly cost-saving and clearly cost-effective. These practices are attractive from both a medical and an economic perspective.

The human fetal retinal pigment epithelium: A target tissue for thyroid hormones

Thyroid hormone (T(3)) has previously been shown to regulate visual function in experimental animals and humans. To determine if T(3) exerts direct effects on retinal function, cultured human fetal retinal pigment epithelial (RPE) cells were tested for the presence of thyroid hormone receptors (TRs) and T(3) responses. Using TR-isoform-specific reverse-transcriptase polymerase chain reaction techniques, mRNA was detected for alpha1, alpha2 and beta1 TR isoforms. Immunohistochemistry using a polyclonal antibody that simultaneously recognizes alpha1, alpha2 and beta1 TRs showed nuclear staining of the fetal RPE. Specific binding of (125)I-T(3) to RPE cell nuclear extracts was detected, and Scatchard analysis revealed a K(d) of 110 pM. To determine if RPE cells can respond to T(3), hyaluronic acid (HA) levels in cell culture media were measured after 2, 4 or 6 days of growth in medium containing 10(-7) M T(3). T(3) inhibited accumulation of HA in the cell culture medium of RPE cells. This effect was not evident at 2 days, but at 4 days there was 42.8% less HA in cell culture medium of RPE cells grown in 10(-7) M T(3) (p < 0.01, t test). The effect persisted through 6 days, when there was 46.3% less HA in cell culture medium of RPE cells grown in 10(-7) M T(3) (p < 0.001, t test). The data indicate that human fetal RPE cells are a direct target for thyroid hormones.

Evaluation of compensation filters in pedal radiographs

Compensation filters allow increased visibility of detail in chest, shoulder, spine, hip, knee, and foot radiographs. This study examines use of an anatomic compensation filter to improve imaging in pedal radiographs. Anteroposterior radiographs were obtained of 25 cadaveric feet at two settings with and without the compensation filter. Densitometer readings were taken at ten forefoot anatomic sites. The compensation filter produced statistically significant reductions in densitometer readings at all anatomic sites and at both radiographic settings. Filtration improved imagery of bony structures, provided excellent soft-tissue visualization, and lowered patient exposure.

Visual and anatomic outcomes associated with posterior segment complications after ganciclovir implant procedures in patients with AIDS and cytomegalovirus retinitis

PURPOSE

To determine anatomic and visual acuity outcomes of posterior segment complications after ganciclovir implant surgery.

METHODS

We reviewed the medical records of 63 patients with acquired immunodeficiency syndrome who had active cytomegalovirus retinitis in 82 eyes and who underwent 110 consecutive ganciclovir implant procedures. Preoperative and postoperative visual acuity, type of postoperative complication, treatment, and lines of visual acuity change were determined.

RESULTS

Thirty-eight eyes of 19 patients had bilateral ganciclovir implant procedures, and 25 eyes of 19 patients underwent two or more ganciclovir implant procedures. Thirteen (12%) of 110 ganciclovir implant procedures developed posterior segment complications: rhegmatogenous retinal detachment in six, vitreous hemorrhage in four, endophthalmitis in two, and cystoid macular edema with epiretinal membrane in one. Treatment included pars plana vitrectomy with silicone oil in two cases and without silicone oil in three cases, scleral buckling in one, intravitreal antibiotic injection in two, and laser photocoagulation in two. Overall, median visual acuity was 20/25 preoperatively. Median follow-up was 6 months for all eyes and 7 months for eyes with complications. Postoperative median visual acuity was 20/25 for eyes without complications vs 20/40 at 1 month, 20/60 at 3 and 6 months, and 20/100 at 12 months in eyes with complications (P < .001). More eyes with than without complications lost 2 or more lines of visual acuity (P < .001).

CONCLUSION

Postoperative complications occurred in 12% of the ganciclovir implant procedures and were associated with decreased visual acuity despite treatment.

Human trabecular meshwork cells as a thyroid hormone target tissue: presence of functional thyroid hormone receptors

PURPOSE

To determine whether human trabecular meshwork cells (HTM) are a potential target tissue for thyroid hormone (3,3',5-triiodothyronine, T3).

METHODS

Cultured HTM were assayed for the presence of thyroid hormone receptors (TRs) and retinoid X receptors (RXRs) by reverse-transcriptase polymerase chain reaction (RT-PCR) to detected TR and RXR mRNA, and by immunohistochemistry to detect nuclear TR and RXR proteins. Functionality of the TR was determined by analysis of 125I-T3 binding affinity and capacity in HTM nuclear extracts. Effects of T3 on modulation of hyaluronic acid (HA) levels in HTM were measured as a function of dose and duration of T3 administration.

RESULTS

Analysis of RT-PCR and immunohistochemistry demonstrated that cultured HTM expressed TRalpha1, TRalpha2, and TRbeta1 but not TRbeta2; and RXRalpha but not RXRbeta and RXRgamma isoforms. Saturation binding and analysis of 125I-T3 to HTM nuclear extracts revealed Kd of 57 pM. The number of T3 binding sites extrapolated from a Scatchard plot was 7.3 x 10(10)/microg of HTM nuclear protein extract. T3 supplementation reduced the concentration of HA in the cell medium by 32-43% compared to cells grown in the absence of T3.

CONCLUSIONS

Cultured HTM express three TR isoforms and one RXR isoform, bind T3 with an affinity similar to that of TR in responsive cells, and modulate their HA production in response to T3. These findings indicate that the human trabecular meshwork tissue has the capacity to respond to thyroid hormones.

Tetrodotoxin: anesthetic activity in the de-epithelialized cornea

BACKGROUND

Tetrodotoxin (TTX) binds with high affinity to sodium channels and produces local anesthesia. We investigated whether TTX is an effective, long-acting corneal anesthetic in rabbits.

METHODS

After mechanical debridement of the central corneal epithelium, topical TTX (1 mM, 0.1 mM, or 0.01 mM) was applied to one eye each of 18 New Zealand White rabbits. The fellow eye of each rabbit was treated with control vehicle. Blink response to a mechanical stimulus was assessed. Blink response was also assessed every 3 h for 30 h in 6 rabbits treated with 1 mM TTX administered every 6 h. In a separate group of 12 rabbits with central epithelial debridement, the rate of epithelial healing was compared between animals treated with topical 1.0 mM TTX and animals receiving no treatment.

RESULTS

After 4 h, eyes treated with 1.0 mM and 0.1 mM TTX were anesthetic. At 6 h, five of six rabbit eyes treated with 1.0 mM TTX were still partially anesthetic. By 8 h, the mean anesthesia score for 1.0 mM TTX was approaching normal. With multiple dosing, all six rabbit eyes remained anesthetic for the duration of the experiment. There was no significant difference in the rate of re-epithelialization between eyes treated with TTX and untreated controls. There was no evidence of systemic or local toxicity from topical TTX.

CONCLUSION

In a rabbit model, TTX is a long-acting topical anesthetic that retains its effectiveness when administered repeatedly over 24 h and does not inhibit epithelial healing. It may have application in management of pain after photorefractive keratectomy.

Experimental study of tetrodotoxin, a long-acting topical anesthetic

PURPOSE

To determine the effectiveness and toxicity of tetrodotoxin for use as a long-acting topical anesthetic.

METHODS

Four groups of six rabbits each received a 40-microl aliquot of either tetrodotoxin in one of three concentrations (10 mM, 1 mM, or 0.1 mM) or proparacaine 0.5% into the inferior conjunctival cul-de-sac of one eye, with the fellow eye of each rabbit receiving 40 microl of a 60-mM, pH 4.3 sodium citrate vehicle as a control. Corneal sensation was tested for up to 8 hours after administration of drugs, and response was noted by no blink, partial blink without full eyelid closure, and full blink. Slit-lamp examination at 12 and 24 hours after administration and pachymetry before and 24 hours after administration were performed to detect corneal toxicity.

RESULTS

Rabbits receiving all three concentrations of tetrodotoxin did not demonstrate any ocular irritation, corneal thickening, or signs of systemic toxicity. At a dose of 10 mM, tetrodotoxin produced an anesthetic effect lasting up to 8 hours. At 1 mM, tetrodotoxin was an effective but shorter-acting anesthetic. At 0.1 mM, tetrodotoxin had no significant anesthetic effect. Proparacaine-treated rabbits initially were anesthetic, but this effect was largely gone by 1 hour and completely gone by 3 hours.

CONCLUSIONS

Tetrodotoxin is a long-acting topical anesthetic in the rabbit cornea. Although additional toxicity studies are required, tetrodotoxin may provide an effective, long-lasting topical anesthetic for use in pain control after corneal procedures such as photorefractive keratectomy.

Experimental use of tetrodotoxin for corneal pain after excimer laser keratectomy

PURPOSE

To determine the duration of anesthesia, effect on corneal reepithelialization, and systemic toxicity of topical tetrodotoxin (TTX) administered after excimer laser keratectomy.

METHODS

Two groups of six rabbits each underwent excimer laser keratectomy in the right eye to create a 5-mm-diameter wound, 75 mm in depth. One group then received a 40-microl aliquot of topical 1 mM TTX into the injured eye, whereas the other group received 40 microl of the sodium citrate vehicle as a control. The rabbits were treated with TTX or vehicle again at 6, 12, 18, and 24 h. Corneal sensation was tested at 3, 6, 9, 12, 15, 18, 21, 24, 30, 32, and 40 h. To determine whether TTX inhibited corneal reepithelialization, compared with vehicle-treated control eyes, the healing rate of the epithelial defect was measured.

RESULTS

Administration of TTX every 6 h for 24 h produced nearly complete anesthesia for > or = 30 h. At 32 h, 8 h after the final application of TTX, there was still significant anesthesia of the TTX-treated corneas (p = 0.0325, Wilcoxon test). Normal corneal sensation in all TTX-treated animals returned at 40 h, or 16 h after the final dose. In contrast, vehicle-treated eyes all had normal sensation for nearly the entire duration of the experiment. At 40 h, the TTX-treated eyes had slightly larger defects than vehicle-treated eyes, 7.85+/-1.74 versus 4.54+/-1.31 mm2 (p < 0.025, t test). However, at 49 h and thereafter, both groups were equally healed (p > 0.05, t test). No systemic toxicity was observed in any of the rabbits.

CONCLUSION

Topical TTX is a long-acting and nontoxic local anesthetic in a rabbit model of excimer laser keratectomy.

Aqueous hyaluronic acid concentration: comparison in pediatric and adult patients

PURPOSE

To determine if there is an age-related increase in human aqueous hyaluronic acid (HA) concentration.

METHODS

HA concentrations were measured in 102 specimens of human aqueous humour obtained during intraocular surgery. Patient age ranged from one month to 93 years. Measurement of the HA concentration in the specimens was performed by a modified ELISA-like assay using a biotinylated HA-binding peptide.

RESULTS

An approximate five-fold increase in the mean aqueous HA concentration was observed between the pediatric (0.33 microgram/ml, n = 5) and the adult patients (1.72 micrograms/ml, n = 97, p < 0.0002). Among the adult patients, however, there was a poor correlation between age and aqueous HA concentration.

CONCLUSIONS

Adult aqueous humor has a significantly higher HA concentration than aqueous obtained from pediatric patients. The source of this increase is unclear, but may be from anterior segment production of HA, or alternatively, from anterior diffusion of vitreous HA.

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.

Hyaluronan polymer size modulates intraocular pressure

To investigate whether the occasional increase in intraocular pressure that may arise following injection of sodium hyaluronan into the anterior segment during intraocular surgery is related to the polymer size of hyaluronan, controlled fragmentation of hyaluronan chains in vitro was obtained using progressive incubation with testicular hyaluronidase. The profile of molecular sizes of the hyaluronan polymers in various preparations was determined using molecular sieve column chromatography. Individual preparations were injected into six rabbit eyes and intraocular pressures were measured every one-half hour for 12 hours. Longer incubations of hyaluronan with hyaluronidase resulted in more extensive degradation with accumulation of shorter chain lengths. In the rabbit, mean intraocular pressure for 12 hours following intracameral injection of hyaluronic acid (HA) is proportional to the polymer size of HA. The occasional elevation of intraocular pressure that occurs following injection of hyaluronan during ophthalmic surgery can be avoided in part by assuring the rapid fragmentation of the large molecular size hyaluronan polymer.

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.

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.

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.

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.

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.

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.

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.

Influence of click polarity on the brain-stem auditory evoked response (BAER) revisited

Brain-stem auditory evoked responses (BAERs) were recorded both to rarefaction and condensation click stimuli in 92 normal hearers and 78 patients with varying degrees of cochlear hearing loss (N = 340 ears). Frequency distributions of rarefaction minus condensation (R - C) latency and amplitude differences revealed clinically significant polarity effects in a substantial percentage of the patients studied. Bivariate plots of R - C latency and amplitude differences versus average high frequency hearing loss (PTA 3) demonstrated that the magnitude of the R - C latency and amplitude differences also seemed to be influenced by degree of high frequency hearing loss. Results are discussed relative to the phase-locking properties of the afferent auditory nerve fibers and the possible electrodiagnostic consequences of recording the BAER either to alternating or condensation clicks.

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.

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.

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.

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.

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.

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.

Validity of acoustic reflectometry in detecting middle ear effusion

Pneumootoscopy, tympanometry, and acoustic reflectometry were performed in 256 middle-class children seen in a surburban pediatric office. The results demonstrated that relectometry, when validated by otoscopic findings, detected middle ear effusion with 88% sensitivity and 83% specificity when a cut-off of 5 linear units was used. Corresponding values for tympanometry were 87% and 77.5%. These results are in keeping with those of earlier studies on acoustic reflectometry and demonstrate the usefulness of this simple technique in detecting chronic and acute otitis media with effusion.

Induction by phenobarbital in McA-RH7777 rat hepatoma cells of a polycyclic hydrocarbon inducible cytochrome P450

The metabolism of 2-acetylaminofluorene (AAF) to its six oxidative metabolites has been used to study cytochrome P450 monooxygenase activity in two rat hepatoma cell lines, McA-RH7777 and Reuber H4-II-E. McA-RH7777 cells exhibited considerably higher basal activities than H4-II-E cells for all metabolic pathways studied. Phenobarbital induced AAF metabolite formation in McA-RH7777 cells to a similar extent as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but was only a weak inducer of these activities in H4-II-E cells. Northern blot analysis utilizing specific phenobarbital or 3-methylcholanthrene inducible cytochrome P450 cDNA probes indicated that there was at least a 10-fold increase in a 3-methylcholanthrene inducible cytochrome P450 transcript in phenobarbital treated McA-RH7777 cells. These data suggest that in this transformed cell line phenobarbital behaves as a polycyclic hydrocarbon-like inducer.

Sequential analysis of chemically induced hepatoma development in rats by two dimensional electrophoresis

Using the Solt-Farber hepatocarcinogenesis model, a large population of preneoplastic and neoplastic nodules were induced in male Fischer 344 rats. Total cellular polypeptides from normal liver and individual preneoplastic and neoplastic nodules were analyzed for both qualitative and quantitative changes using computer assisted high resolution two-dimensional electrophoresis. Approximately 800-1000 cytosolic and 1200-1400 membrane associated polypeptides were readily separated and detected using an ultrasensitive silver stain. The polypeptide patterns were remarkably similar for each tissue and only four qualitative polypeptide differences were noted. One cytosolic polypeptide, 6.8/57 (designated pl/Mr X 10(-3), and three membrane associated polypeptides, 6.25/41, 6.75/24, and 6.05/21, were expressed in both preneoplastic and neoplastic nodules but not in normal liver. No qualitative polypeptide differences were detected among the individual preneoplastic or individual neoplastic nodules or between preneoplastic and neoplastic nodules. Numerous quantitative changes in both known markers for hepatocarcinogenesis and in as yet unidentified polypeptides were noted. In particular, the Ya subunit of glutathione S-transferase B, the Yb subunit of glutathione S-transferase A, as well as the three isoelectric point variants of the Yp subunit of glutathione S-transferase P were increased 2-, 4-, and 7-fold, respectively, in preneoplastic and neoplastic nodules. Whereas DT-diaphorase was increased 2-3-fold in hyperplastic nodules as compared to normal liver, no differences in the expression of albumin were noted. Although no differences were observed in the expression of aldehyde dehydrogenase in preneoplastic and neoplastic nodules, polypeptide b (6.9/54) was shifted slightly toward the basic region in normal liver. alpha-Fetoprotein was not detected in either preneoplastic or neoplastic nodules. In addition to these changes in known markers, comparison of 500-800 cytosolic and 750-1000 membrane associated polypeptides showed that roughly 4-10% of the polypeptides were undergoing quantitative changes of at least 4-fold during these stages of hepatocarcinogenesis. Thirty (10 cytosolic and 20 membrane) polypeptides were significantly down-regulated while 22 (7 cytosolic and 15 membrane) polypeptides were up-regulated in both preneoplastic and neoplastic nodules. In all cases the direction and magnitude of change were the same in both preneoplastic and neoplastic nodules with the exception of three polypeptides.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectral characteristics of air and bone conduction transducers used to record the auditory brain stem response

This study sought to determine differences in the acoustic spectra of five different transducers commonly used for stimulus presentation to record the auditory brain stem response (ABR). The outputs of three commercially available bone conduction vibrators (Radioear B-70A, B-71 and B-72), a TDH-49 earphone, and an insert receiver were measured by applying a 0.1 msec rectangular electrical pulse to each transducer. The resultant output for each transducer was converted to one-third octave band data and plotted against reference threshold levels. Results demonstrated relatively flat acoustic spectra and high output levels for the two air conduction receivers. In contrast, each of the bone oscillators had its greatest concentration of energy in the 2000 Hz region with the spectrum characterized by a precipitous decrease in output at frequencies above and below this resonance peak. Maximum output never exceeded 35 dB HL for any of the three bone conduction devices. Of the three oscillators, however, the B-70A appeared to provide the highest output before reaching saturation. Results are discussed relative to the limitations for recording the auditory brain stem response to bone conducted transient signals.

Auditory and vestibular function in hyperbaric oxygen

The therapeutic value of high partial pressures of oxygen is limited by the toxicity of oxygen. Pulmonary damage, visual impairment, and convulsions are known hazards during hyperoxic exposure, but dose-effect relationships have not been quantified for specific organs or functions. As part of an integrated study of organ oxygen tolerance in man (Predictive Study V of the Institute for Environmental Medicine), auditory and vestibular function was evaluated in man before, during, and after exposure to 100% oxygen at 3 atmospheres absolute pressure for 2 to 3.5 hours. No alterations in hearing or equilibrium were detected, suggesting that ototoxicity is not a factor that would limit exposure under these conditions.