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Biomedical subjects

M D Graham

Publications and source records attributed to M D Graham.

At least 19 recordsLinked to original sources
PubMed2004

Transient and sustained changes in myofilament sensitivity to Ca2+ contribute to the inotropic effects of sevoflurane in rat ventricle.

BACKGROUND: The volatile anaesthetics isoflurane and sevoflurane induce both negative and positive inotropic effects in ventricular myocytes, the mechanisms of which are not fully understood. Previous data suggest that changes in myofilament Ca(2+) sensitivity contribute to their sustained negative inotropic effects. In this study, the role of changes in myofilament Ca(2+) sensitivity in both positive and negative inotropic effects of these agents was examined in intact ventricular myocytes. METHODS: Contractility and cytosolic Ca(2+) (fura-2) were recorded optically in ventricular myocytes stimulated electrically (1 Hz) at 30 degrees C. Myofilament Ca(2+) sensitivity was assessed from plots of cell length against fura-2 fluorescence ratio (Fr) from individual twitches at various points before, during and after a 1 or 4 min exposure to 0.6 mM anaesthetic. RESULTS: Isoflurane reduced mean (sd) myofilament Ca(2+) sensitivity from 10.3 (1.9) to 5.9 (1.6) microm Fr(-1) (P<0.001) throughout a 1 min exposure, which returned to control on removal. In contrast, on initial exposure to sevoflurane, Ca(2+) sensitivity was reduced from 10.8 (1.3) to 4.3 (0.9) microm Fr(-1) (P<0.001) but this recovered partially towards control over 3 min. On removal, sensitivity was increased above control (to 17.7 (2.2) microm Fr(-1); P<0.001) before preanaesthetic levels were restored. CONCLUSIONS: These data show that both isoflurane and sevoflurane reduce apparent myofilament Ca(2+) sensitivity at steady state. However, sevoflurane (but not isoflurane) induced transient changes in apparent myofilament Ca(2+) sensitivity, which would contribute to its inotropic profile.

Actin Cytoskeleton↗
PubMed2004

Conformation and dynamics of single DNA molecules in parallel-plate slit microchannels.

The conformation and diffusion of a single DNA molecule confined between two parallel plates are examined using both single molecule experiments and Brownian dynamics simulations accounting for hydrodynamic interactions. The degree of chain stretching and the diffusivity are characterized as a function of the chain confinement and the channel geometry. Good agreement is found between the simulations, experiments, and scaling theory predictions.

Computer Simulation↗
PubMed2000

Solitary coherent structures in viscoelastic shear flow: computation and mechanism.

Starting from stationary bifurcations in Couette-Dean flow, we compute nontrivial stationary solutions in inertialess viscoelastic circular Couette flow. These solutions are strongly localized vortex pairs, exist at arbitrarily large wavelengths, and show hysteresis in the Weissenberg number, similar to experimentally observed "diwhirl" patterns. Based on the computed velocity and stress fields, we elucidate a heuristic, fully nonlinear mechanism for these flows. We propose that these localized, fully nonlinear structures comprise fundamental building blocks for complex spatiotemporal dynamics in the flow of elastic liquids.

Journal Article↗
PubMed1999

Closed tympanomastoidectomy.

The role of closed tympanomastoidectomy in the treatment of chronic ear disease continues to be a subject of debate. This article reviews the position of closed tympanomastoidectomy in the armamentarium of the otolaryngologist. In this article the technique is described and indications are reviewed. A brief history of closed tympanomastoidectomy and the issue of outcome from surgery are also addressed.

Cholesteatoma, Middle Ear↗
PubMed1997

Professional associations and managed care. How four provider groups are helping their members.

Managed care is facilitating rapid change in the day-to-day practice of many addiction treatment and mental health professionals. It is only natural, therefore, that the associations representing the various disciplines in behavioral healthcare should seek to present short- and long-term plans, advice, and programs for their members. We have asked leaders from four prominent groups to present what their organizations are doing today to assist professionals in adapting to the new realities of the healthcare system. The comments below are by no means conclusive, and are representative of a few efforts and thoughts. It is our mission at Behavioral Healthcare Tomorrow to provide an independent platform for dialogue in the world of mental health and addiction treatment. It is our hope that the proposals and ideas published here stimulate even more planning amongst providers as managed care assertively enters public sector services.

Ethics, Medical↗
PubMed1997

Bilateral Meniere's disease. Treatment with intramuscular titration streptomycin sulfate.

Most patients with bilateral Meniere's disease treated with streptomycin sulfate titration therapy and followed over the long term have either improvement or relief of their disabling vertigo. Although persistent post-treatment disequilibrium occurs not infrequently, it is mild in the most patients. Stabilization or improvement of hearing occurs in most patients, and the authors have not encountered hearing loss to date as a result of streptomycin sulfate titration therapy. There seems to be considerable separation between the vestibulotoxic and cochleotoxic doses of streptomycin sulfate intramuscularly when administered in humans.

Antibiotics, Antitubercular↗
PubMed1996

Mechanical versus CO2 laser occlusion of the posterior semicircular canal in humans.

The purpose of this study was to compare the effectiveness of mechanical and laser-assisted posterior semicircular canal occlusion (PCO) for the treatment of intractable benign paroxysmal positional vertigo (BPPV). Twelve consecutive patients with intractable BPPV underwent PCO by three surgeons, six with mechanical PCO and six with CO2 laser-assisted PCO. PCO eliminated positional vertigo in all patients treated with the laser and five of six patients treated without the laser. Dysequilibrium was present in all patients immediately postoperatively. This resolved in all patients treated with the CO2 laser but in only two of six patients treated without the laser (p = 0.03). Patients were hospitalized for dysequilibrium for an average of 5.2 and 2.8 days for the mechanical and laser-assisted groups, respectively. Preoperative and postoperative hearing was not significantly different between the groups. No clinically significant postoperative hearing loss was encountered in either group. These results suggest that PCO is an effective treatment for intractable BPPV. The incidence of dysequilibrium that persists following PCO may be reduced by using the CO2 laser to seal the membranous canal prior to occluding the bony canal.

Adult↗
PubMed1996

Temporal bone encephalocele and cerebrospinal fluid leaks.

Nineteen cases of temporal bone brain herniation and cerebrospinal fluid (CSF) leaks in 17 adult patients since 1987 are reviewed. Of these 19 cases, 11 were spontaneous CSF leaks, 6 were related to chronic otitis media, and 2 were posttraumatic. Among the 10 women and 7 men, the average age was 51.2 years, with average follow-up time of 2 years, 7 months. Two cases were repaired by a middle fossa craniotomy approach, 1 case by a transmastoid approach, and 16 by a combined transmastoid and middle fossa approach. Ten cases utilized the preferred technique of fascia-bone-fascia to repair the defects. The diagnosis was made on clinical grounds in 18 of the 19 cases, with ancillary diagnostic test providing little useful information. There were no postoperative surgery-related complications, and definitive repair was accomplished in one stage in all cases.

Adult↗
PubMed1995

Meatal facial nerve decompression in acoustic neuroma resection.

Delayed facial palsy occurs after approximately 15% of acoustic neuroma resections. Whereas in most cases facial nerve function recovers satisfactorily, in about 12% of cases delayed facial palsy may have a poor functional recovery. The fate of facial nerve function was studied in 55 consecutive translabyrinthine acoustic neuroma resections, 23 of whom underwent meatal facial nerve decompression (MFND) at the time of tumor resection. The facial nerve results also were reviewed in 19 middle cranial fossa resections, of whom 14 underwent MFND. There was a bimodal distribution of the delayed palsies, with one group having the onset of palsy within hours to 2 days after surgery and the second group having onset of palsy up to 17 days after surgery. The poorest recoveries were seen in the first group. Although the effect was not statistically significant due to the small sample size, the chance of facial weakness in patients who underwent MFND after translabyrinthine surgery was about 40% less than in those who did not undergo decompression. The apparent protective effect of MFND was increased when the confounding factors of tumor size and degree of resection were taken into account, although the effect was not statistically significant. The duration of palsy was shorter and ultimate recovery better among the patients who underwent facial nerve decompression than in those who did not. Of the translabyrinthine patients who underwent MFND, 100% had House-Brackmann grade I-II function at 2 years, whereas 87% of patients who did not have MFND had grade I-II function and 13% had grade III-IV function. Without MFND, 57% of translabyrinthine patients whose onset of facial palsy was within 2 days of surgery had grade III-IV facial nerve function.

Facial Nerve↗
PubMed1994

Selective embolization of glomus jugulare tumors.

Four patients with grade C or D(1) glomus jugulare tumors who underwent preoperative highly selective embolization followed by infratemporal fossa removal of their tumors were compared to three patients undergoing surgery alone with respect to intraoperative blood loss, operative time, cranial nerve palsy, length of hospitalization, and perioperative complications. Embolized patients demonstrated a marked reduction in blood loss (650 vs 1375 cc) compared with the nonembolized group. Operative time was shortened (by 51 minutes). Facial nerve function did not appear related to embolization but was directly related to intraoperative nerve manipulation. Hospital stay, perioperative complications, and lower cranial nerve palsies were not related to embolization.

Journal Article↗
PubMed1994

Labyrinthectomy. Indications and surgical technique.

Surgical intervention is considered for patients whose disabling vertigo fails to respond to appropriate medical therapy. Topics discussed in this article include indications, preoperative assessment, and surgical techniques. Fifteen case studies supplement the text, followed by a discussion.

Adult↗
PubMed1994

Facial nerve outcome in acoustic tumor surgery.

Seventy-three procedures involving 70 acoustic tumors were carried out over 3 years. The majority of tumors (65) were removed by the translabyrinthine approach. Tumor size ranged from 0.5 through 5.0 cm. All patients underwent intraoperative facial nerve monitoring: 22 patients developed immediate facial palsy (House-Brackmann grades II-VI); 11 patients recovered completely; 11 patients (15.7%) had persistent paralysis. The incidence of long-term, poor outcome (H-B grade IV-VI) was 5.7 percent. The overall incidence of facial palsy was not found to be related to tumor size; however, facial paralysis associated with large tumors exhibited a poorer House-Brackmann grade compared to small and medium lesions. The use of intraoperative facial monitoring has enhanced the surgeon's ability to preserve facial nerve function by reducing the overall incidence of postoperative facial paralysis.

Cranial Nerve Neoplasms↗