Technical aspects of the latissimus dorsi myocutaneous flap in breast reconstruction

The authors review the technical refinements that have come about through their increased use of the latissimus dorsi flap for reconstruction of the female breast following mastectomy, referring to over 90 of their cases. These refinements involve careful selection of patients in whom the flap is used; planning the flap, including determination of the limits of the muscle; and the location and shape of the skin island. Placement of the patient on the table and the position of her arms and hips are discussed. The dissection and transfer of the flap, as well as closure of the donor defect, can present particular problems, which are outlined. Implant placement, wound closure, and postoperative care of the patient are also discussed.     

Performance analysis of a retransmission control algorithm for local area networks

Algorithms for the control of the transmission procedure in multiaccess schemes must ensure simplicity in the implementation, stability of the system operation and high efficiency for all traffic conditions. A control algorithm suitable for slotted multiaccess schemes based on monitoring the channel transmissions is proposed. A model is presented and the algorithm is analysed in detail. The performance of the algorithm is evaluated, and comparisons are made with multiaccess protocols.     

Effects of gravity on tracheal mucus transport rates in normal subjects and in patients with cystic fibrosis

A noninvasive, radionuclide imaging technique for measuring the rate of mucus clearance in the trachea (RT), was used to study gravitational effects on mucus clearance in 13 patients with cystic fibrosis (CF), average age 17 years; 7 normal, nonsmoking adults, average age 26 years; and a normal subject who was recovering from an acute upper respiratory tract infection (URTI). In the upright position, nine of the CF patients and the subject with URTI demonstrated abnormal tracheal mucus clearance which approached normal when they were placed in 25 degrees headdown position. The normal subjects and two of the CF patients showed no significant difference in the RT measured in the two positions. The results of the study indicate that the force of gravity can be a major influence on tracheal mucus clearance in CF and URTI subjects. This conclusion supports the use of postural drainage as an effective form of therapy in patients with cystic fibrosis.     

The monitoring of heparin activity during extracorporeal circulation

Heparin activity was assessed in 11 patients who underwent extracorporeal circulation for open-heart surgery. The activated partial thromboplastin time (A-PTT), thrombin time, protamine sulphate titration and factor Xa inhibition assay were used. The patients received heparin 3 mg/kg body weight, and 20 mg/450 ml blood was added to the pump. When the operative procedure was extended beyond 100 minutes patients received an additional 1,5 mg heparin/kg body weight. Protamine sulphate in a dose of 1,5 mg/1 mg heparin, was given to neutralize the heparin activity. The A-PTT was the easiest test which gave reliable results. The factor Xa inhibition assay measured heparin levels most precisely and mirrored the A-PTT results in all but one instance. These results indicate that the protocol employed produced adequate anticoagulation for the bypass procedure in all the patients. Protamine sulphate failed to neutralize heparin adequately after bypass in the 3 patients who received additional heparin during the surgical procedure. The monitoring of heparin activity during and after extracorporeal circulation is a desirable addition to open-heart surgical treatment.     

Surgical procedure for modifying the duodenum in cattle to measure bile flow and the diurnal variation in biliary manganese, iron, copper and zinc excretion

A surgical procedure is described for modifying the duodenum of cattle so that bile can be sampled and its rate of flow measured for long periods. In 12 steers, aged three months to three years and weighing between 50 and 650 kg, bile flow ranged from 2 to 12 ml per minute, the rate of flow increasing with bodyweight. The rate of flow expressed as ml per minute per 100 kg bodyweight decreased as bodyweight increased, the regression equation being in (ml per minute per 10 kg) = 1.65-0.0022 x where x = bodyweight (kg), r = 0.871. The mean concentrations of copper, iron, manganese and zinc in bile were 8.2, 6.2, 17.1 and 3.3 mumol per litre respectively. The concentration of iron was the least variable between the steers. The average total cholate concentration was 100 mmol per litre and total solids ranged from 5.4 to 7.2 per cent. Diurnal patterns in bile flow and trace element excretion were measured in four adult steers during a period of 38.5 hours. Although the rate of excretion of iron, zinc and copper and bile flow varied throughout the period, changes could not be associated with feeding or time of day. The concentration of manganese in bile and its excretion rate varied in a reproducible manner which may be related to feeding activity. The mean output of the four trace elements in bile from the four steers during 24 hours was, copper 37.7 mumol, iron 68.0 mumol, manganese 80.3 mumol and zinc 59.6 mumol.     

GPU-accelerated FDTD modeling of radio-frequency field-tissue interactions in high-field MRI

The analysis of high-field RF field-tissue interactions requires high-performance finite-difference time-domain (FDTD) computing. Conventional CPU-based FDTD calculations offer limited computing performance in a PC environment. This study presents a graphics processing unit (GPU)-based parallel-computing framework, producing substantially boosted computing efficiency (with a two-order speedup factor) at a PC-level cost. Specific details of implementing the FDTD method on a GPU architecture have been presented and the new computational strategy has been successfully applied to the design of a novel 8-element transceive RF coil system at 9.4?T. Facilitated by the powerful GPU-FDTD computing, the new RF coil array offers optimized fields (averaging 25% improvement in sensitivity, and 20% reduction in loop coupling compared with conventional array structures of the same size) for small animal imaging with a robust RF configuration. The GPU-enabled acceleration paves the way for FDTD to be applied for both detailed forward modeling and inverse design of MRI coils, which were previously impractical.     

Long-term environmental fate of perfluorinated compounds after accidental release at Toronto airport

Perfluorooctane sulfonate (PFOS; a perfluorinated compound or PFC), its salts, and perfluorooctane sulfonyl fluoride have recently been listed in Annex B of the Stockholm Convention due to their widespread presence, persistence, and toxicity. Because of the persistent nature of PFCs, it is generally presumed that the impact of direct discharges of these chemicals on a receiving environment would be long-lasting. However, long-term environmental fate studies based on field measurements are rare. We examined spatial and long-term (9 year) temporal trends of PFCs in water, sediment, fish, and fish liver collected in 2003, 2006, and 2009 from 10 locations spanning ～20 km in Etobicoke and Spring Creeks, where an accidental release of fire fighting foam containing PFOS from nearby Toronto International Airport occurred in 2000. Even a decade after the spill, sediment PFOS concentrations are still elevated in Spring Creek Pond which received the foam discharge; however, the major impact is relatively localized likely due to the stormwater management nature of the pond and the diluting effect of Etobicoke Creek. Fish and fish liver PFOS concentrations at a Spring Creek location downstream of Spring Creek Pond declined by about 70 and 85%, respectively, between 2003 and 2009. PFOS in water at locations further downstream in Etobicoke Creek have declined by >99.99% since the spill; however, the 2009 water and fish levels were ～2-10 times higher than upstream locations likely due to the long-term impact of the spill as well as urbanization. The decrease in the upstream PFOS concentrations likely reflects the reduction of PFOS sources due to phased out production by 3M and regulations on the use of PFOS in fire fighting foams. Field-based sediment/water distribution coefficients (K(D)) and bioaccumulation factors (BAF) were calculated from environmental measurements. Log K(D) values were 0.54-1.65 for perfluoroalkyl sulfonates (PFASs) and 1.00-1.85 for perfluorocarboxylates (PFCAs). Log BAF(fish) ranged from 1.85 to 3.24 for PFASs and 0.88-3.47 for PFCAs, whereas log BAF(fish liver) ranged from 2.1-4.3 for PFASs and 1.0-5.0 for PFCAs.