Flap Dynamics Research Articles

Repair of Defects on Nasal Sebaceous Skin

Reconstructive procedures performed on sebaceous nasal skin are prone to partial flap necrosis, scar spread and inversion, and tissue mismatch. An ideal repair would optimize vascular integrity, minimize closure tension, and use adjacent tissue. The purpose of this article is to describe a flap design and dynamics that permit satisfactory reconstruction of small- to medium-sized defects on nasal sebaceous tissue. A modified advancement flap is described that may be used on central and off-midline defects of the nasal tip. Use of the modified advancement flap resulted in good cosmetic results with few adverse postsurgical events. The modified advancement flap satisfies the requirements of a hardy blood supply, minimization of closure tension, and use of adjacent tissue. The surgical results are predictable and rarely associated with complications.

Solution Structure of the Mature HIV-1 Protease Monomer: INSIGHT INTO THE TERTIARY FOLD AND STABILITY OF A PRECURSOR

We present the first solution structure of the HIV-1 protease monomer spanning the region Phe1-Ala95 (PR1-95). Except for the terminal regions (residues 1-10 and 91-95) that are disordered, the tertiary fold of the remainder of the protease is essentially identical to that of the individual subunit of the dimer. In the monomer, the side chains of buried residues stabilizing the active site interface in the dimer, such as Asp25, Asp29, and Arg87, are now exposed to solvent. The flap dynamics in the monomer are similar to that of the free protease dimer. We also show that the protease domain of an optimized precursor flanked by 56 amino acids of the N-terminal transframe region is predominantly monomeric, exhibiting a tertiary fold that is quite similar to that of PR1-95 structure. This explains the very low catalytic activity observed for the protease prior to its maturation at its N terminus as compared with the mature protease, which is an active stable dimer under identical conditions. Adding as few as 2 amino acids to the N terminus of the mature protease significantly increases its dissociation into monomers. Knowledge of the protease monomer structure and critical features of its dimerization may aid in the screening and design of compounds that target the protease prior to its maturation from the Gag-Pol precursor.

Stability and Control of a Parametrically Excited Rotating Beam

In this paper the stability and control of a parametrically excited, rotating flexible beam is considered. The equations of motion for such a system contain time periodic coefficients. Floquet theory and a numerical integration are used to evaluate the stability of the linearized system. Stability charts for various sets of damping, parametric excitation, and rotation parameters are obtained. Several resonance conditions are found and it is shown that the system stability can be significantly changed due to the rotation. Such systems can be used as preliminary models for studying the flap dynamics and control of helicopter rotor blades and flexible mechanisms among other systems. To control the motion of the system, an observer based controller is designed via Lyapunov-Floquet transformation. In this approach the time periodic equations are transformed into a time invariant form, which are suitable for the application of standard time invariant controller design techniques. Simulations for several combinations of excitation and rotation parameters are shown.

Nasal reconstruction with the cheek island pedicle flap

Background: Reconstruction of the lower third of the nose can be challenging. Maintaining the nasal subunit symmetry and providing good tissue match with regard to color, sebaceous quality, and thickness is essential. For extensive defects in this area, paramedian forehead flaps are often considered. Objective: Our purpose was to develop the technique of preparing and executing the cheek island pedicle flap, as well as to define the limitations and “pitfalls” of the flap. Methods: The cheek island pedicle flap is described. Results: The cheek island pedicle flap can provide excellent cosmetic results in reconstructing defects of the lower third of the nose. The flap dynamics are predictable, and anticipated complications are described. Conclusion: The cheek island pedicle flap provides an excellent alternative to the paramedian forehead flap for reconstruction of extensive defects of the lower third of the nose.

Rhomboid flap dynamics.

The rhomboid flap is a reliable, versatile, and widely used tool in head and neck surgery. Although its geometry is well described, the mechanics of the flap have not been scientifically investigated. For example, there is disagreement whether the maximum tension is located at the closure of the donor site or at the tip of the flap. An experimental model using piglets and stabilized force gauges has been developed to measure the distribution of tension in a standard Limberg flap (60 degrees rhomboid). Variables evaluated include the size of the rhomboid, the amount of undermining, and the position of the flap on the animal. Consistent measurements show tension at the closure of the donor site to represent the majority of tension around the flap (58% average); the size of the rhomboid and degree of undermining do not change relative tensions. A composite figure discloses the relationship of the initially outlined flap to the final result and quantifies the observable changes in the length of sides.