Optimal control of diffuser shapes for non-uniform flow.

A simplified model is used to identify the diffuser shape that maximises pressure recovery for several classes of non-uniform inflow. We find that optimal diffuser shapes strike a balance between not widening too soon, as this accentuates the non-uniform flow, and not staying narrow for too long, which is detrimental for wall drag. Three classes of non-uniform inflow are considered, with the axial velocity varying across the width of the diffuser entrance. The first case has inner and outer streams of different speeds, with a velocity jump between them that evolves into a shear layer downstream. The second case is a limiting case when these streams are of similar speed. The third case is a pure shear profile with linear velocity variation between the centre and outer edge of the diffuser. We describe the evolution of the time-averaged flow profile using a reduced mathematical model that has been previously tested against experiments and computational fluid dynamics models. The model consists of integrated mass and momentum equations, where wall drag is treated with a friction factor parameterisation. The governing equations of this model form the dynamics of an optimal control problem where the control is the diffuser channel shape. A numerical optimisation approach is used to solve the optimal control problem and Pontryagin's maximum principle is used to find analytical solutions in the second and third cases. We show that some of the optimal diffuser shapes can be well approximated by piecewise linear sections. This suggests a low-dimensional parameterisation of the shapes, providing a structure in which more detailed and computationally expensive turbulence models can be used to find optimal shapes for more realistic flow behaviour.

High frequency bone conduction auditory evoked potentials in the guinea pig: Assessing cochlear injury after ossicular chain manipulation.

Permanent high frequency (>4 kHz) sensorineural hearing loss following middle ear surgery occurs in up to 25% of patients. The aetiology of this loss is poorly understood and may involve transmission of supra-physiological forces down the ossicular chain to the cochlea. Investigating the mechanisms of this injury using animal models is challenging, as evaluating cochlear function with evoked potentials is confounded when ossicular manipulation disrupts the normal air conduction (AC) pathway. Bone conduction (BC) using clinical bone vibrators in small animals is limited by poor transducer output at high frequencies sensitive to trauma. The objectives of the present study were firstly to evaluate a novel high frequency bone conduction transducer with evoked auditory potentials in a guinea pig model, and secondly to use this model to investigate the impact of middle ear surgical manipulation on cochlear function. We modified a magnetostrictive device as a high frequency BC transducer and evaluated its performance by comparison with a calibrated AC transducer at frequencies up to 32 kHz using the auditory brainstem response (ABR), compound action potential (CAP) and summating potential (SP). To mimic a middle ear traumatising stimulus, a rotating bur was brought in to contact with the incudomalleal complex and the effect on evoked cochlear potentials was observed. BC-evoked potentials followed the same input-output function pattern as AC potentials for all ABR frequencies. Deterioration in CAP and SP thresholds was observed after ossicular manipulation. It is possible to use high frequency BC to evoke responses from the injury sensitive basal region of the cochlea and so not rely on AC with the potential confounder of conductive hearing loss. Ongoing research explores how these findings evolve over time, and ways in which injury may be reduced and the cochlea protected during middle ear surgery.

Sudden hearing loss following non-petrous craniotomy.

We present two patients with known otosclerosis undergoing craniotomy for conditions unrelated to the temporal bone who experienced sudden sensorineural hearing loss. In both patients, the hearing loss was noted immediately post-operatively and there was no subsequent recovery. Sudden hearing loss is a rare complication of non-otologic, non-cardiopulmonary bypass surgery. To our knowledge it has not been described in patients with otosclerosis undergoing craniotomy. This is a rare event that may occur in patients with vulnerable ears, such as those with otosclerosis or pre-existing sensorineural hearing loss.

Poor hormone receptor expression in East African breast cancer: evidence of a biologically different disease?

BACKGROUND: Few studies have examined breast cancer hormone receptor expression in Africans. We report on the hormone receptor profile of breast cancer in East Africans in the largest prospective study for this region. METHODS: Consecutive breast cancer presentations to a hospital in Kijabe (2001-2007) were included. Demographic, clinical, and test data were collected. ER/PR and Her2 testing was based on immunohistochemistry (IHC). RESULTS: There were 129 subjects (median 47 years), most had invasive ductal cancer and locally advanced disease and/or metastases. ER/PR testing was done in 120: 24% had ER-positive tumours, 34% were ER- and/or PR-positive, 10% were ER-negative but PR-positive tumours, and 66% were negative for ER and PR. ER/PR positivity was not associated with stage (P = 0.28) and was not related to age, parity, menopausal status, or node metastases. Increasing tumour grade was associated with PR expression (P = 0.02) with decreasing frequency of PR positive tumours as histological grade increased; there was weak evidence of an association between grade and ER expression (P = 0.06). Of cases tested, 26.5% overexpressed Her2. CONCLUSIONS: Breast cancer in Kijabe is an advanced-stage disease, comprised mainly of poorly differentiated cancers that are less likely to be hormone sensitive (across all stages of disease). ER/PR testing of all those affected by breast cancer should be supported as a global priority in cancer control. International and inter-African research collaborations are needed to allow genetic detailing of tumours in indigenous Africans to assess possible racial heterogeneity in the biology of breast cancer.

Prospective evaluation of magnetic resonance imaging and physical examination findings in patients with greater trochanteric pain syndrome.

OBJECTIVE: This study examined patients with greater trochanteric pain syndrome (GTPS) to determine the prevalence of gluteus medius pathology by utilizing magnetic resonance imaging (MRI), and to evaluate the presence of Trendelenburg's sign, pain on resisted hip abduction, and pain on resisted hip internal rotation as predictors of a gluteus medius tear in this group of patients. METHODS: Twenty-four subjects with clinical features consistent with GTPS were recruited. A standard physical assessment was performed at study entry, including assessment of the 3 specific physical signs. Following this initial assessment, MRI of the affected hip was performed. A 1.5T whole body MRI system was utilized, with T1 and T2 fast spin-echo sequences performed in the coronal and axial planes. All MR images were reviewed in random order by a single radiologist. In 12 patients, the 3 physical signs were assessed at study entry and at 2 months by the same observer and the intraobserver reliability for each of the signs was calculated. RESULTS: All subjects were women (median age 58 years, range 36-75 years). The median duration of symptoms was 12 months (range 12-60 months). MRI findings were as follows: 11 patients (45.8%) had a gluteus medius tear, 15 patients (62.5%) had gluteus medius tendinitis (pure tendinitis in 9 patients and tendinitis with a tear in 6 patients), 2 patients had trochanteric bursal distension, and 1 patient had avascular necrosis of the femoral head. Trendelenburg's sign was the most accurate of the 3 physical signs in predicting a tendon tear, with a sensitivity of 72.7% and a specificity of 76.9%. Moreover, Trendelenburg's sign was the most reliable measure, with a calculated intraobserver kappa of 0.676 (95% confidence interval 0.270-1.08). CONCLUSION: The results support the hypothesis that gluteus medius tendon pathology is important in defining GTPS. In this series, trochanteric bursal distension was uncommon and did not occur in the absence of gluteus medius pathology. The physical findings suggest that Trendelenburg's sign is the most sensitive and specific physical sign for the detection of gluteus medius tears, with an acceptable intraobserver reliability. Further delineation with MRI, especially in patients with a positive Trendelenburg's sign, is recommended prior to any consideration of surgery in this group of patients. Finally, with the pathology of this condition defined, the challenge will be to devise and assess, by randomized controlled trial, an appropriate treatment strategy for this group of patients.

Questioning the sensitivity of magnetic resonance imaging in early septic spondylodiscitis.

Septic spondylodiscitis is an uncommon disease, but one with serious complications and potentially high morbidity and mortality. The diagnosis is sometimes delayed, particularly in those patients with an insidious mode of onset and nonspecific symptoms. Several imaging methods are available to facilitate the early diagnosis of septic spondylodiscitis, and of these methods magnetic resonance imaging (MRI) has been reported to be the most sensitive, revealing abnormalities earlier than plain x-ray, gallium scan and bone scan. We report a case of septic spondylodiscitis in which MRI did not demonstrate evidence of discitis after a symptom period of seven days. The diagnosis was later confirmed by bone scan and repeat MRI. We suggest that a negative or equivocal MRI cannot exclude infective spondylodiscitis, especially in the early stages of the disease process. In such cases, it is important to note that the addition of a short tau-inversion recovery sequence will increase the sensitivity of MRI, and, additionally, gadolinium should be administered if the magnetic resonance study is negative and a strong clinical suspicion of spondylodiscitis exists.

Using the CLARION cochlear implant in cochlear ossification.

This paper is a retrospective review of 5 patients with various degrees of cochlear ossification who were implanted with the CLARION Multi-Strategy Cochlear Implant. Preoperative computed tomography scans, intraoperative findings, surgical technique, and hearing outcomes are discussed in a case report format. Full implantation was achieved in all cases by a systematic approach that included drill-through of proximal obstruction (2 cases), scala vestibuli insertion (2 cases), and complete drill-out (1 case). The only complication was delayed wound healing in a patient with sickle cell disease, chronic active hepatitis, and steroid dependency on antimetabolite therapy. Early results show that the 4 patients with at least 3 months of experience have a mean open-set sentence recognition score of 55% and a mean open-set word recognition score of 24%. The conclusion is that implantation of the Clarion device in ossified cochleas can be successful in all degrees of ossification and can provide significant hearing benefit.

Cochlear reimplantation.

OBJECTIVE: A small number of multichannel cochlear implant (CI) recipients require reimplantation. This study describes the causes of failure, surgical technique, and hearing outcomes in a consecutive series of 16 patients undergoing reimplantation of multichannel devices. We hypothesize that reimplantation is safe and that hearing results are at least as good as those measured following primary implantation. STUDY DESIGN: Retrospective analysis of consecutive clinical series. METHODS: Chart analysis of 191 consecutive CI operations performed at the University of Miami Ear Institute between 1990 and 1997 revealed 16 patients who received a second multichannel device. All but one had a minimum follow-up of 1 year after reimplantation. Ten of these patients had initial implantation performed by us, and six were initially operated on elsewhere. Main outcomes of the initial procedure were compared with those of the reimplantation, including electrode insertion length, number of channels programmed, and audiometric results. In addition, cause of failure and relevant surgical findings at the second procedure are described. RESULTS: There were no surgical complications after reimplantation surgery. Device failure was the most frequent cause for reimplantation. Time between initial implantation and failure ranged from 0 to 46 months (mean, 22.4 mo; median, 23 mo). Common intraoperative findings include mastoid fibrosis, bone growth at the cochleostomy, and skin flap breakdown. Following reimplantation, mean length of insertion, number of channels actively programmed, and speech recognition scores were at least as good as findings before initial implant failure. CONCLUSION: CI reimplantation is safe and effective.

Hearing results with deep insertion of cochlear implant electrodes.

OBJECTIVE: This study aimed to investigate the relationship of electrode insertion length and speech recognition in patients using Nucleus-22 cochlear implants. STUDY DESIGN: The study design was a retrospective review of a consecutive clinical series. SETTING: The study was conducted at an academic medical center. PATIENTS: Thirty-one postlingually deafened adults with at least 6 months' experience with a Nucleus-22 cochlear implant using Spectra-22 processor and SPEAK strategy participated. MAIN OUTCOME MEASURES: Open-set speech recognition scores for words and sentences were measured. RESULTS: Insertion length ranged from 22 rings (estimated 17 mm) to 32 rings (estimated 25 mm). Mean word recognition score was 35%. Mean sentence score was 69.6%. Statistical analysis showed no correlation between insertion depth and word or sentence scores. CONCLUSION: Insertion of the Nucleus-22 array beyond 22 rings does not improve performance in speech recognition. This finding cannot be generalized to other electrodes or processing strategies.

Surgical technique for implantation of the totally ossified cochlea.

OBJECTIVES: Among the technical challenges of cochlear implant surgery is electrode insertion into the fully ossified cochlea. Earlier drill-out techniques have two significant drawbacks: 1. up to one half fail when the electrode pulls away from the cochlea; and 2. extended radical mastoidectomy, abdominal fat graft for obliteration, and closure of the external auditory meatus are required. A simplified technique is described that allows positive fixation of the cochlear implant electrode and in selected cases avoids a radical cavity with obliteration. STUDY DESIGN: Technical description with case reports and hearing outcomes. METHODS: Ten cadaver temporal bones were dissected to determine middle ear landmarks that overlie the basal turn of the cochlea from the transcanal approach and to establish the feasibility of the intact canal wall procedure. Surgery was performed on four patients who had preoperative imaging evidence of full ossification, two with the canal wall down, and two with canal wall up. Standard measures of speech recognition were used to evaluate hearing. RESULTS: Critical surgical landmarks are the round window, carotid artery, cochleariform process, and oval window. The procedure was successfully performed on four patients and open-set speech recognition is present in each. CONCLUSIONS: This canal wall up procedure allows long electrode insertion without radical cavity/obliteration in patients with fully ossified cochleas and prevents distraction of the electrode from the cochlea. While open-set word recognition was achieved by all subjects, results are poorer than expected for patients with limited or no ossification.

Functional laparoscopic reversal of a long gastroplasty.

Gastroplasty operations for obesity occasionally require surgical reversal. A laparoscopic technique is described for the successful functional reversal of a case who had a Long vertical gastroplasty.

Endosurgical treatment for spontaneous pneumothorax.

When spontaneous pneumothorax is recurrent or persistent, an open pleurodesis with excision or ligation of the bullae is the procedure of choice but can lead to significant morbidity. Thorascopic surgery for the management of spontaneous pneumothorax was first introduced in 1937 but this has become a useful technique only since the introduction of video-controlled thorascopic surgery and the availability of suitable endothoracic instrumentation. A review was made of nine patients having endosurgery for recurrent (six) or persistent (three) pneumothorax. At surgery the bullae were ligated with an endoloop (four) or excluded with an endostapler (five). Pleurodesis was obtained by a combination of strip pleurectomy, diathermy and installation of an alcohol iodine solution. The early results are similar to those following an open operation with considerably reduced hospital stay and morbidity.

Haemodialysis-induced leucopenia and activation of complement: effects of different membranes.

The effects on neutrophil count and complement activity of five different haemodialysis membranes were studied. There was no correlation between the degree of neutropenia and intensity of complement activation. With cuprophan membrane both occurred simultaneously but to unrelated degrees; polyacronitrile induced mild, not significant neutropenia but marked activation of complement; polycarbonate membranes induced severe neutropenia without detectable complement activation. Where complement activation occurred it was via the alternative pathway. Haemodialysis induced neutropenia may have many causes and complement activation is probably not the major responsible factor.