Parallel imaging performance as a function of field strength--an experimental investigation using electrodynamic scaling.

In this work, the dependence of parallel MRI performance on main magnetic field strength is experimentally investigated. Using the general framework of electrodynamic scaling, the B0-dependent behavior of the relevant radiofrequency fields at a single physical field strength of 7 T is studied. In the chosen implementation this is accomplished by adjusting the permittivity and conductivity of a homogeneous spherical phantom. With different mixing ratios of decane, ethanol, purified water, N-methylformamide, and sodium chloride, field strengths in the range of 1.5 to 11.5 T are mimicked. Based on sensitivity maps of an eight-coil receiver array, the field-dependent performance of parallel imaging is assessed in terms of the geometry factor g, which reflects noise enhancement in parallel imaging reconstruction. At low field strengths the SNR penalty was nearly independent of B0 and favorably low for 1D reduction factors up to between 3 and 4. At higher field strengths the transition between favorable and prohibitive parallel imaging conditions was found to shift toward higher feasible reduction factors. These findings are in good agreement with previous theoretical predictions. From this agreement it is concluded that parallel MRI at high B0 benefits specifically from onsetting far-field behavior of the involved radiofrequency fields.     

Chondromyxoid fibroma involving the entire metacarpal: a case report

The occurrence of chondromyxoid fibroma in the hand is rare. We report a case of chondromyxoid fibroma involving the whole fourth metacarpal that was treated by curettage and cancellous bone allograft.     

Effects of positive end-expiratory pressure on ventilatory and oxygenation parameters during pressure-controlled one-lung ventilation

OBJECTIVES: The purpose of this study was to investigate the effects of PEEP on oxygenation and airway pressures during PCV-OLV. DESIGN: Randomized, crossover, clinical study. SETTING: University hospital. PARTICIPANTS: Twenty-five patients undergoing thoracotomy. INTERVENTIONS: During the first 5 minutes of OLV, all patients were ventilated with VCV (PEEP: 0) (VCV-ZEEP). Afterward, ventilation was changed to PCV with PEEP: 0 (PCV-ZEEP) or PEEP: 4 cmH2O (PCV-PEEP) for 20 minutes. In the following 20 minutes, PCV-PEEP and PCV-ZEEP were applied in reverse sequence. MEASUREMENTS AND MAIN RESULTS: At the end of VCV-ZEEP airway pressures (peak airway pressure, plateau airway pressure, mean airway pressure, and pause airway pressure) were recorded. At the end of PCV-PEEP and PCV-ZEEP airway pressures, PaO2 and Qs/Qt were recorded. Ppeak and Pplat were significantly lower with PCV-PEEP compared with VCV-ZEEP (eg, Ppeak: 33.4+/-4.2, 28.3+/-4.1, and 28.9+/-3.7 cmH2O in VCV-ZEEP, PCV-ZEEP, and PCV-PEEP, respectively; p<0.05 for PCV-ZEEP v VCV-ZEEP and PCV-PEEP v VCV-ZEEP). PCV-PEEP was associated with an increased PaO2 (230.3+/-69.8 v 189.0+/-54.8 mmHg, p<0.05) and decreased Qs/Qt (33.4%+/-7.3% v 38.4%+/-5.7%, p<0.05) compared with PCV-ZEEP (mean+/-SD). Eighty-eight percent of the patients have benefited from PEEP. CONCLUSION: During OLV, PCV with a low level of PEEP leads to improved oxygenation with lower airway pressures.     

Experience with Autogenous Arteriovenous Access for Hemodialysis in Children and Adolescents

The National Kidney Foundation’s DOQI-NKF recommendation to construct an autogenous arteriovenous access (AAVA) for chronic hemodialysis whenever possible can be a challenge in the pediatric population. This report reviews recent surgical experience in this patient subgroup. From March 1999 to April 2004, 47 consecutive children requiring permanent vascular access had construction of AAVA. There were 16 girls and 31 boys, with a mean age of 14.6 years (range 5-20). The surgeon preoperatively mapped veins with ultrasound in all patients. Access sites were radial-cephalic (n = 16), upper arm brachial-cephalic (n = 15), transposed upper arm brachial-basilic (n = 7), and transposed femoral vein (n = 9). An operating microscope was used to construct three radial-cephalic accesses in individuals with small arteries. Three forearm cephalic veins were transposed (one at the original surgical procedure and two postoperatively). Five upper arm cephalic veins were transposed (three at the original surgical procedure and two postoperatively). Femoral vein accesses were constructed for either exhausted access in the upper extremities (n = 7) or patient preference (n = 2). Primary patency at 1 and 2 years was 100% and 96%, respectively. Secondary patency at 1 and 2 years was 100%. One individual with a radial-cephalic AAVA and severe radial artery calcification required an inflow procedure. Thirty-five accesses are currently in use (functionally patent), eight are in individuals with successful renal transplants, and two are maturing; one individual declines using the access. Two accesses are secondarily patent (thrombosed and repaired 12 and 29 months after construction, respectively), and one access thrombosed after 27 months (abandoned). Construction of an AAVA is possible in virtually all pediatric age individuals if attention is given to preoperative vein mapping, selective use of an operating microscope, and creation of a transposed femoral vein when upper extremity access is neither possible nor desired.Presented at the Twenty-second Annual Meeting of the Southern California Vascular Surgical Society, April 30-May 2, 2004.     

Risk factors for stroke following coronary artery bypass operations

BACKGROUND: Although the overall complication rates have been decreased significantly in recent years, stroke rates still remain high in patients undergoing coronary bypass operations. This study is designed to evaluate the risk factors for stroke in patients who had undergone coronary artery bypass surgery in an 8-year period in our clinic. METHODS: Between 1995 and 2003, 8547 coronary artery operations under cardiopulmonary bypass were performed. Retrospective analysis of the patient files revealed that 75 (0.9%) patients had stroke in the early postoperative period. RESULTS: Mean age of these patients was 62.3 +/- 9.5 years, and 54 (72%) were males. Stroke rate was 1.2% between 1995 and 1998 and this was significantly higher from the stroke rate (0.7%) of the period 1998 to 2003 (p = 0.03). Major technical differences between these two periods were the routine application of preoperative carotid arteries Doppler evaluation and intraoperative epiaortic echocardiography after 1998. Higher age (p = 0.000), female sex (p = 0.005), smoking (p = 0.03), presence of diabetes mellitus (p = 0.01), hypertension (p = 0.008), and left main coronary artery disease (p = 0.001), carotid surgery (p = 0.000), and peripheral vascular disease (p = 0.049) were identified as important risk factors in univariate analysis for stroke development. Higher age (p = 0.000; OR = 21.38), left main coronary artery disease (p = 0.007; OR = 7.26), peripheral vascular disease (p = 0.050; OR = 3.08), and operation date before 1998 (p = 0.012; OR = 6.33) were identified as important risk factors in logistic regression analysis. According to intraoperative epiaortic ultrasonography, operative strategy was changed in 9% of patients. Thirty-seven (49.3%) of the stroke patients died. Female sex (p = 0.023; OR = 5.18) and preoperative hypertension (p = 0.045; OR = 4.03) were observed as significant risk factors for mortality after stroke. CONCLUSION: Development of stroke is one of the major reasons of mortality after coronary artery bypass operations. It is essential to take all the measures to prevent this complication, especially in patients with known risk factors. Evaluation of carotid arteries prior to operation and application of routine intraoperative epiaortic echocardiography may in part eliminate stroke.     

The incidence and risk factors of difficult mask ventilation

Purpose The ability to ventilate and oxygenate a patient using a bag-mask breathing system may be lifesaving in the case of failure of the initial intubation attempt. In this study, we aimed to determine the incidence of difficult mask ventilation (DMV) and to find preoperative risk factors for this procedure.Methods Based on methods used for overcoming some difficulties with bag-mask ventilation (MV), classification has been made into four categories: easy MV, awkward MV, difficult MV, and impossible MV. A univariate analysis was performed to identify potential risk factors predicting DMV, followed by a stepwise forward binary logistic regression, and the odds ratio and 95% confidence interval were calculated.Results A total of 576 patients were studied. Incidence of easy MV, awkward MV, and difficult MV were found to be 75.5% (n = 435), 16.7% (n = 96), and 7.8% (n = 45), respectively. Height, weight, age, male gender, increased Mallampati class, history of snoring, lack of teeth, and beard were found to be DMV risk factors (P < 0.05). Using a multivariate analysis, Mallampati class 4, male, history of snoring, age, and weight were found to be significantly associated with DMV. Although the incidence of DMV in general was 7.8% (n = 45), the incidence of DMV among patients with difficult intubation (n = 123) was found to be 15.5% (n = 19).Conclusions Mallampati class 4, male patients, history of snoring, increasing age, and increasing weight were found to be risk factors for DMV in our study.     

Malaria epidemic and drug resistance, Djibouti

Analysis of Plasmodium falciparum isolates collected before, during, and after a 1999 malaria epidemic in Djibouti shows that, despite a high prevalence of resistance to chloroquine, the epidemic cannot be attributed to a sudden increase in drug resistance of local parasite populations.     

Allothetic orientation and sequential ordering of places is impaired in early stages of Alzheimer's disease: corresponding results in real space tests and computer tests

Spatial disorientation and learning problems belong to the integral symptoms of Alzheimer's disease (AD). A circular arena for human subjects (2.9 m diameter, 3 m high) was equipped with a computerized tracking system, similar to that used in animals. We studied navigation in 11 subjects diagnosed with early stages of Alzheimer's disease (AD), 27 subjects with subjective problems with memory or concentration, and 10 controls. The task was to locate one or several unmarked goals using the arena geometry, starting position and/or cues on the arena wall. Navigation in a real version and a computer map view version of the tests yielded similar results. The AD group was severely impaired relative to controls in navigation to one hidden goal in eight rotated positions. The impairment was largest when only the cues on the wall could be used for orientation. Also, the AD group recalled worse than controls the order of six sequentially presented locations, though they recalled similarly to controls the positions of the locations. The group with subjective problems was not impaired in any of the tests. Our results document the spatial navigation and non-verbal episodic memory impairment in the AD. Similar results in real and map view computer tests support the use of computer tests in diagnosis of cognitive disturbances.     

The role of bcl-2 family of genes during kindling

PURPOSE: Several experimental models of human temporal lobe epilepsy have shown that apoptotic death of neurons is an important part of this degenerative disease. However, the role of apoptotic regulators is not clear during the epileptogenesis. Therefore we investigated the expression pattern of bcl-2 family of genes during the formation of kindling model of epilepsy in rats. METHODS: We examined the expression pattern of bax, bcl-2, bcl-xL, mtd, and bcl-w both at messenger RNA (mRNA) and protein level in the brain tissues during the formation of epilepsy with kindling model in adult rats, which has been the most acceptable form of experimental model of human epilepsy. We also assessed the onset of DNA fragmentation by using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. RESULTS: Animals have started to have epileptic discharges after day 10 of kindling model. Recurrent subthreshold electrical stimuli induced not only epileptic foci but also the expression of bax, an inducer of apoptosis, in this time period. Conversely, bcl-xL, which is an inhibitor of apoptosis, had an opposite pattern of expression both at mRNA and protein level during the formation of epilepsy. We did not observe DNA fragmentation by TUNEL staining. CONCLUSIONS: Our study shows differential expression of Bax and Bcl-xL at the CA1 region during the formation of hippocampal kindling model. The absence of DNA fragmentation during this period suggests that epileptic changes in neurons have the potential to induce DNA fragmentation by altering the expression levels of Bax and Bcl-xL.