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Biomedical subjects

R L Lieber

Publications and source records attributed to R L Lieber.

113 records · Page 7Linked to original sources
PubMed1980

Theory of light diffraction by single skeletal muscle fibers.

A theoretical discussion is presented describing the diffraction of laser light by a single fiber of striated muscle. The complete three-dimensional geometry of the fiber has been taken into consideration. The basic repeated unit is taken as the sarcomere of a single myofibril, including its cylindrical geometry. The single fiber is considered as the sum of myofibrils up to the fiber dimensions. When proper phasing is taken into account, three cases of interest are analyzed. (a) When the adjacent myofibrils are totally aligned with respect to their index of refraction regions (e.g., A and I bands), then the diffraction pattern reflects that of a larger striated cylinder with the dimensions of the fiber. (b) When a particular skew plane develops for the myofibril elements, additional Bragg reflection occurs at certain specific sarcomere lengths, and intensity asymmetry amongst the diffracted orders occurs. (c) When the myofibril phasing changes in a random fashion, while all sarcomeres remain at the same length, then intensity decrease is directly related to the phase deviation from a reference phase point. This condition may well describe a fiber undergoing active isometric contraction.

Chemical Phenomena↗
PubMedDate not supplied

Direct memory access of diffraction patterns from striated muscle--a software view.

Complete software support has been developed for a direct memory access microprocessor system used to store and analyze diffraction data from striated muscle. These studies are based on the premise that the regularly alternating light and dark regions of the fiber behave like a phase grating to incident laser light. A knowledge of the position of a diffracted order can thus be used to determine striation spacing. Since these striations are directly associated with the force generating components of the muscle, diffraction data can provide insights into the mechanism of force generation in muscle. In our system, a charge-coupled device (CCD) is used to detect diffracted order, position, and intensity. In addition, a high speed muscle puller and tension transducer are used to characterize or alter the mechanical state of the muscle. The software has been designed to allow the inexperienced user to perform sophisticated diffraction experiments. The user may present several experimental parameters: magnitude and direction of puller movement; number of frames of data to be taken; and delay of puller or scan. This has been accomplished by interleaving DMA and control loop cycles. System performance indicates that the full 256 point analog output of the CCD can be digitized and stored in about 2 ms. The data can be transferred directly from the CCD to memory leaving the CPU free for experimental control or closed-loop processing.

Animals↗
PubMedDate not supplied

Decompression of an experimental compartment syndrome in dogs with hyaluronidase.

The treatment of compartment syndromes in which elevation of intracompartmental pressure occurs is by surgical fasciotomy. This is a relatively simple procedure but may be associated with complications. This study aimed at developing an alternative method to decompress a compartment by use of the enzyme hyaluronidase. Autologous plasma was infused into the anterolateral leg compartments of six dogs to simulate compartment syndromes of 80 mmHg. Pressure decay after pressurization was recorded. The compartment pressures were then again raised to 80 mmHg by subfascial injections of 1500 units hyaluronidase in 2 ml saline injected into one compartment and 2 ml saline only into the control side. Pressure decay was again recorded. On the experimental side, a significantly faster decay rate occurred after hyaluronidase injection than after initial pressurization; 8.0 +/- 1.3 (S.E.M.) versus 3.4 +/- 0.4 (S.E.M.) mmHg/min (p less than .01). Pressure decay after hyaluronidase injection was significantly faster than after the same volume injection on the control side, over both a four-minute period (8.0 +/- 1.3 [S.E.M.] versus 4.1 +/- 0.6 [S.E.M.] mmHg/min [p less than .03]) and a 25-minute period (2.1 +/- 0.3 [S.E.M.] versus 1.3 +/- 0.1 [S.E.M.] mmHg/min [p less than .03]). Hyaluronidase removes hyaluronic acid molecules from the leg compartment fascia and, by facilitating fluid flow from the compartment, causes decompression. Hyaluronidase may then have a place in the prophylaxis and treatment of compartment syndrome, thus avoiding anesthesia and surgery.

Animals↗
PubMedDate not supplied

Skeletal muscle architecture: implications for muscle function and surgical tendon transfer.

Skeletal muscles have mechanical properties that are well-described by the length-tension relationship (for isometric contractions) and the force-velocity relationship (for isotonic contractions). These two intrinsic properties are scaled for a given muscle based on its architectural properties. Muscle active force-generating range is determined by muscle fiber length, while maximum muscle force is determined by physiologic cross-sectional area. These and other architectural properties should be matched between muscles when planning surgical tendon transfers in order to closely match donor and recipient muscles. Finally, the fiber length/moment arm ratio of a muscle-joint combination must be considered when describing strength because strength is a manifestation of both muscle and joint properties and not either alone. Unfortunately, detailed description of normal musculoskeletal design or optimal transfer strategy cannot be made until more basic science studies of the musculoskeletal system are conducted.

Finger Injuries↗