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Biomedical subjects

D M Stevens

Publications and source records attributed to D M Stevens.

18 recordsLinked to original sources
PubMed1996

Survival of normothermic microvascular flaps after prolonged secondary ischemia: effects of hyperbaric oxygen.

Although hyperbaric oxygen has been shown to improve the survival rate of ischemic grafts and flaps of many types, it has not been studied extensively in free tissue transfer. This study was designed to evaluate the effect of hyperbaric oxygen on flap survival when exposed to critical combinations of primary ischemia, reperfusion, and secondary ischemia times. Unilateral abdominal adipocutaneous island flaps based on the superficial inferior epigastric vessels were raised in 133 Sprague-Dawley rats. Primary normothermic ischemia was induced by applying a microvascular clamp to the vascular pedicle for 6 hours. The clamp was removed for 2 hours of reperfusion and then reapplied for a 6-, 10-, or 14-hour period of secondary ischemia. After completion of the secondary ischemia time, the clamp was removed, and the animals were randomly assigned to one of three treatment regimens. The control animals breathed normobaric air, and the others breathed normobaric 100% oxygen or hyperbaric oxygen (100% oxygen at the equivalent of 33 feet of seawater, 2.0 atmospheres absolute), respectively, for two periods of 90 minutes for 7 days. Flap survival was assessed at postoperative day 7 and was found to be an all-or-none phenomenon. Maximum likelihood-derived survival curves were fitted to the data and used to calculate the secondary ischemic time at which 50% of the flaps survived (D50). The D50 for the air and 100% oxygen groups was 6 hours, whereas that for the hyperbaric oxygen group was 10 hours. This difference in D50 was found to be statistically significant (analysis of variance, p < 0.05). Chi-squared statistical evaluation of pooled data reaffirmed a statistically significant increase in flap survival of the animals treated with hyperbaric oxygen vs. those treated with air or 100% oxygen (p < 0.03 and p < 0.01, respectively). Hyperbaric oxygen enhances the tolerance of normothermic, microvascular flaps to prolonged secondary ischemia. A similar effect was not noted in the 100% oxygen group; therefore the additional expense and technology of a hyperbaric chamber system is necessary to achieve this effect.

Animals↗
PubMed1995

Vestibulo-ocular reflex gain as a measure of vestibular function in guinea pigs while in a recompression chamber: apparatus design and effects of nitrogen narcosis.

There are several mechanisms whereby alteration of barometric pressure can produce vertigo in divers or aviators. Development of a reliable measure of vestibular function in an animal model is the first requirement for further study of these mechanisms. This report presents the development of a rotatory table device capable of evoking the vestibulo-ocular reflex (VOR) of a guinea pig while in a hyperbaric chamber. To assess the reproducibility of this response, eight animals were monitored by electronystagmography during rotations at three table velocities (62.4, 83.3, and 100 degrees/s). Two test sessions were performed on each animal with a 6-hour interval between sessions. The VOR gain was calculated by dividing the average peak velocity of the slow phase component of the nystagmus by the peak stimulus velocity. At least eight observations per test speed were averaged; calibration of eye movement was performed prior to each session by forced ocular abduction. Multifactorial analysis of variance revealed no significant differences (p > .05) between the differing rotation speeds nor between test sessions for individual animals. However, there was a significant difference in VOR gain between animals (p < .002). The VOR gain was then measured, using the same techniques, in another group of seven animals before, during, and after an air dive to the equivalent of 200 feet of seawater (7.06 atmospheres absolute) to assess the effects of nitrogen narcosis. Pre- and post-dive VOR gains were significantly greater than those measured at depth (p < .05). These results are consistent with the slow processing model of nitrogen narcosis and the controversial theory that central nervous system depressants decrease the VOR gain. The results also demonstrate the ability of this inexpensive apparatus to provide a sensitive measure of pressure-induced changes of vestibular function in guinea pigs.

Analysis of Variance↗
PubMed1994

Computer-assisted assessment of cochlear nerve fibers.

Quantitative assessment of cochlear nerve fibers, with statistical analysis of histologic specimens, is facilitated by the application of computer image processing techniques. Three algorithms, developed for the evaluation of cochlear sections, are presented, MANUAL, AIDED, and AUTO, in order of increasing degree of automation and decreasing requirement for operator intervention. All three algorithms demonstrate high accuracy and consistency in identifying cochlear nerve fibers and quickly provide statistics regarding the target nerve fiber population. These algorithms have potential utility in the study of cochlear nerve pathologic alterations, as for example, with intracochlear electrical stimulation.

Animals↗
PubMed1993

Complement activation during saturation diving.

In this study, the levels of activated complement fragments C3a and C5a were measured on 11 U.S. Navy divers as they performed a 28-day saturation dive to a pressure equivalent of 1,000 feet of seawater (fsw, 31.3 atm abs). Two subjects developed symptoms consistent with the high pressure nervous syndrome (HPNS) and three were treated for type I DCS (joint pain only). These events allowed us to test two hypotheses: a) alterations in C3a or C5a levels during compression are related to the occurrence of HPNS and b) increases in complement fragments are an indicator of decompression stress associated with type I DCS. There was no correlation between changes in C3a and C5a levels during compression and the diagnosis of HPNS. Our results suggest that an increase in C3a and C5a levels during saturation diving correlates with decompression stress and the clinical diagnosis of type I DCS.

Analysis of Variance↗
PubMed1992

Endoscopic carpal tunnel release: a cadaveric study.

Five surgeons performed endoscopic (Dyonics) carpal tunnel releases on 24 fresh cadaver wrists. In 50% of the specimens, transection of the transverse carpal ligament was incomplete. The average amount of incomplete release was 31% (range, 0% to 53%). Three types of incomplete release were noted: (1) release of Guyon's canal release--one, (2) incomplete distal ligament release--five, and (3) incomplete central or superficial release--six. Other technical errors were noted in nine of 24 specimens. There were no nerve lacerations. Endoscopic carpal tunnel release is either a technically demanding procedure, commonly results in incompletely released ligaments, or both. Proper training, followed by practice on several cadaver specimens before its clinical use, is recommended.

Anthropometry↗
PubMed1992

Management of herniated intervertebral disks during saturation dives: a case report.

During research saturation dives at 5.0 and 5.5 atm abs, 2 divers developed an acute herniation of the nucleus pulposus of the L5-S1 intervertebral disk. In both cases the pain was severe enough to require intravenous morphine or intramuscular meperidine. Although the symptoms presented by these divers are frequently considered to be an indication for immediate surgical consultation, we decided that emergency decompression posed an unacceptable risk that decompression sickness (DCS) would develop in the region of acute inflammation. In both cases strict bedrest and medical therapy were performed at depth. In the first case, 12 h was spent at depth before initiating a standard U.S. Navy saturation decompression schedule with the chamber partial pressure of oxygen elevated to 0.50 atm abs. In the second case, a conservative He-N2-O2 trimix decompression schedule was followed to the surface. In both cases, no initial upward excursion was performed. The required decompression time was 57 h 24 min from 5.5 atm abs and 55 h 38 min from 5.0 atm abs. During the course of decompression, the first diver's neurologic exam improved and he required decreasing amounts of intravenous narcotic; we considered both to be evidence against DCS. The second diver continued to have pain and muscle spasm throughout decompression, however he did not develop motor, reflex, or sphincter abnormalities. Both divers have responded well to nonsurgical therapy.

Adult↗
PubMed1992

Morphologic and electrophysiologic effects of cochlear implantation and electrical stimulation.

The nondeafened guinea pig model was utilized in this study to assess the functional and morphologic effects of cochlear implantation and electrical stimulation. Auditory brainstem responses (ABRs) were recorded prior to and following intrascalar implantation of a 3M-House cochlear electrode (n = 41 ears), as well as after electrical stimulation (n = 23 ears). The experimental population was divided into the following groups according to implantation and stimulation parameters: 200 microA for 3 hours (group I); 200 microA for 24 hours (group II); 400 microA for 3 hours (group III); implanted, but not stimulated (group IV); and nonimplanted, not stimulated ears (group V). Of those cochleae that sustained the trauma of implantation, 32 percent had no detectable ABR to 110 dB SPL clicks, while only 7 percent additionally failed to respond to 130 dB SPL clicks. No significant difference (one-way ANOVA with repeated measures at the 95 percent confidence limit) could be detected when comparing those ears that retained ABRs according to experimental grouping. Morphologic analysis was performed on 29 cochleae. Spiral ganglion "packing densities" were not found to be significantly different among the groups (ANOVA). The status of the organ of Corti was significantly better in groups II and V in comparison to the other groups (Kruskal-Wallis test with pairwise comparisons, p less than 0.05); there was no discernible dose-response relationship. Morphologic and electrophysiologic changes correlated with insertion trauma and infection rather than with electrical stimulation at the levels tested in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1985

The effects of estrogen and progesterone on glycogen and the enzymes involved in its metabolism in the cat uterus.

In the endometrium of the spay cat, estradiol treatment causes a drastic reduction in glycogen content. The initiation of simultaneous progesterone treatment causes a replenishment of glycogen with the levels surpassing those observed in the spayed animal. The effect of the hormones on glycogen synthetase I follows the same pattern as the changes in glycogen content, while the effect on phosphorylase a is the mirror image. The total content of glycogen synthetase and phosphorylase do not show appreciable changes with the same hormone treatment. The possible reproductive role of these changes in glycogen content are discussed.

Animals↗
PubMed1978

The glucagonoma syndrome.

The glucagonoma syndrome is characterized by necrolytic migratory erythema, glossitis, ungual dystrophy, diabetes mellitus, anemia, weight loss, elevated plasma glucagon levels and an alpha-cell glucagon-secreting neoplasm of the pancreas. We are reporting a case of this syndrome in a middle-aged woman, in whom the first complaints and signs were cutaneous. The recognition of the distinctive skin manifestations of the syndrome led to early diagnosis and treatment of the underlying malignant pancreatic tumor.

Adenoma, Islet Cell↗
PubMed1977

Ulcers of the leg in thalassemia.

Four patients had thalassemia and leg ulcers. In three patients the hematologic diagnosis of thalassemia had not been previously made; the presenting symptom was the leg ulcer. The diagnosis of thalassemia should be considered in patients who have unexplained chronic leg ulcers; the incidence of this complication of thalassemia may be higher than previously reported.

Adult↗
PubMedDate not supplied

Marketing and commercial challenges for anticancer products.

Traditional marketing techniques that are employed by pharmaceutical manufacturers are not adequate in the oncology setting. Many unique characteristics of this therapeutic area create challenges to the marketing and sales teams responsible for selling anticancer and cancer-therapy support products. There is a high burden on those marketing oncology products to provide vast amounts of information about their products, in a timely manner, to various groups of health care providers, while functioning within established legal boundaries. Pharmaceutical companies, through their sales and marketing efforts, are working to provide the information health care providers need to make patient management decisions and prevent the health care environment from restricting physician and patient choices.

Antineoplastic Agents↗