Contratilidade

Contractility: Still Searching After All These Years
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Aqui
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The term contractility refers to the intrinsic contractile capacity of the heart, so that its measurement should ideally be independent of the specific external loading conditions placed on the pump. This load insensitivity of contractility measurement has proved to be an elusive goal.
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First, similar to the ventricular myocardium, the atrial myocardium exhibits length-dependent activation, so that increased preload to the atrium is associated with increased atrial contraction with consequent greater pre-systolic lengthening of any ventricular segment. Consequently, the increased systolic shortening of the same ventricular segment is to be expected as a direct consequence of the increased end-diastolic fiber length due to length-dependent activation. In this sense, the pre-systolic lengthening is just a surrogate measure of the preload (end-diastolic segment length). This was evident in the proportionate increase in pre-systolic lengthening and systolic shortening with increased preload, with the consequence that the slope of the relationship was not significantly altered. Nevertheless, the R2 value of 0.67 suggests that pre-systolic segment stretch is a relatively weak surrogate for end-diastolic segment length.
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Avaliar a contratilidade sem levar em consideração a pré e pós carga é ruim para qualquer metodologia. O ecocardiografista sabe que com a queda da pós carga, a fração de ejeção aumenta e o inverso também. Assim como a pré carga, como vemos no texto acima, de forma diretamente relacionada. Apesar de ser trabalhoso, coletar a pressão atrial esquerda e a resistência periférica parecem fundamentais para o estudo da contratilidade.