Biomechanics of the sarcolemma and costameres in single skeletal muscle fibers from normal and dystrophin-null mice.

We studied the biomechanical properties of the sarcolemma and its links through costameres to the contractile apparatus in single mammalian myofibers of Extensor digitorum longus muscles isolated from wild (WT) and dystrophin-null (mdx) mice. Suction pressures (P) applied through a pipette to the sarcolemma generated a bleb, the height of which increased with increasing P. Larger increases in P broke the connections between the sarcolemma and myofibrils and eventually caused the sarcolemma to burst. We used the values of P at which these changes occurred to estimate the tensions and stiffness of the system and its individual elements. Tensions of the whole system and the sarcolemma, as well as the maximal tension sustained by the costameres, were all significantly lower (1.8-3.3 fold) in muscles of mdx mice compared to WT. Values of P at which separation and bursting occurred, as well as the stiffness of the whole system and of the isolated sarcolemma, were ~2-fold lower in mdx than in WT. Our results indicate that the absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises the mechanical stability of costameres and their connections to nearby myofibrils.

Sequential analysis for quality control in the neonatal intensive care unit.

OBJECTIVE: This article describes a novel application of a statistical technique for continuous quality assurance in the NICU. METHODS: We used prospective analysis of rates of survival to 28 days of life, without major IVH in ELBW infants in a single tertiary NICU, before and after the introduction of an evidence-based treatment protocol. By using the CUSUM function, each infant's results were sequentially plotted, and significant changes in outcomes were noted when the plot crossed predetermined boundary lines. RESULTS: Significant changes in outcomes were evident with this method sooner than traditional analyses on the basis of year-end or other arbitrary intervals. The introduction of the ELBW protocol was temporally associated with significant improvement in intact short-term survival. CONCLUSION: Sequential analysis techniques are useful tools for ongoing quality assurance; deviations in outcomes may be detected more quickly, which should assist in the identification of improvements or decrements in performance of the NICU.