Mohammed El-Shahat

n/a

We conduct a complete analysis of the effect of digit redundancy in adders on their delay, power, energy, and energy-delay product. To our knowledge, this is the first such detailed analysis. We discuss the hybrid signed digit representations that offer a continuum of choices from two's complement representation on one extreme, all the way to a fully signed digit representation on the other extreme. Power and time delay reductions are achieved as a result of algorithmic level changes. Our analysis using TSMC 1.8μm technology indicates that the increment in power over the whole range from two's complement to fully signed representation is relatively small (52.174%), while the reduction in speed is much larger (95.455%). The best designs from the energy and energy-delay product points of view are the most redundant. We also present a new Modified Hybrid Signed Digit(MHSD) adder that leads to greater improvements. Compared to the Hybrid Signed Digit(HSD) adder, MHSD adder shows power decrement of 1.653% and speed increment of 17.716%.

BACKGROUND: The pectoralis major myocutaneous pedicle flap (PMMPF) has been considered to be the "workhorse" of pedicled flaps in head and neck reconstruction. Several series of PMMPF procedures in head and neck reconstruction have been reported in the literature. Even with the worldwide use of free flaps, the flap is still considered the mainstay head and neck reconstructive procedures in many centers. However, the flap is usually associated with a high incidence of complications in addition to its large bulk compared with the free fasciocutaneous flaps. Also the final functional and the aesthetic results are not comparable to free flaps head and neck reconstruction.

AIM OF THE STUDY: The aim of the study is to evaluate the reliability of such flap in selected cases of head and neck reconstruction. The indications, technique, complications and the functional as well as the aesthetic results of the flap utilization were evaluated.

PATIENTS AND METHODS: Between May 2002 and May 2005 a 26 consecutive head and neck reconstruction procedures using the PMMPF were carried out on 25 patients at the Department of Surgery, National Cancer Institute, Cairo University. The indications for the flap use were defects due to resection of stage II-IV cancer in the head and neck region. The site, stage of the disease and the presence or absence of distant metastasis were assessed. Also preoperative assessment included the fitness of patients for such an extensive procedure. The total operative time, the need for blood transfusion, the postoperative complications, were all documented. The length of hospital stay, the follow-up of patients as well as the incidence of local recurrence underneath the flap were all evaluated.

RESULTS: Pectoralis major myocutaneous pedicled flap reconstructions were used to reconstruct defects in the following sites: oral cavity (10 patients); oropharynx/ hypopharynx, (5 patients); and neck or face (10 patients). Of the 26 PMMPF reconstructions, 22 flaps were carried out as primary reconstructive procedures, whereas 4 flaps were "salvage" procedures (reconstruction after fistula, free flap failure, coverage of exposed mandibular prosthesis). Fifteen patients (60%) had complications such as wound dehiscence, infection, hematoma, seroma, partial flap failure, total flap failure, fistula, and donor site complications. A higher complication rates were associated with the utilization of the flap as a salvage procedure, number of co morbidities, and in oral cavity reconstructions.

CONCLUSION: Although the PMMPF is a versatile flap in head and neck reconstruction, being in the proximity of the region with good reach to different areas of the face, oral cavity, and the pharynx; the flap is fraught with a high complication rate. The wide use and the reliability of free flaps in head and neck reconstruction have superseded the use of the PMMPF flap in comparable circumstances. However, the flap still has a place in head and neck reconstruction, particularly after resection of locally advanced tumours. Also the flap can be still used as a salvage procedure after free flaps failure or when there is a shortage of the microsurgery facility.