Cardiovascular engineering
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The search for a load-independent index of myocardial contractility has been a focus for nearly 100 years. Nearly all of the parameters developed have yielded insight into cardiac function but their clinical utility has been limited. A new index, dsigma*/dt (max), has been proposed to be useful in the clinic. ⋯ There was also a significant correlation between dsigma*/dt (max) and dP/dt (max). With a strong correlation between the values of dsigma*/dt (max), dP/dt (max), and EDV in all five subjects, dsigma*/dt (max) is not load independent in the canine heart when preload is altered by a VCO. Further evaluation of this index is required to delineate the situations where dsigma*/dt (max) can be accurately applied.
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A frequency domain distributed 55 segment arterial model was constructed from the reflection perspective to predict pressure waveforms in the large systemic arteries. At any node, the predicted pressure waveform was the combination of a forward propagating waveform and a number of repeatedly reflected waveforms from any possible sites. This approach ensured that any single reflected waveform could be traced back to its origin, and thus the causal-effect relation would be precisely known. ⋯ It was found that the model predicted pressure waveforms were most sensitive to the branch reflection coefficient, and this led to the adoption of the zero-forward reflection assumption at branches. The model-predicted pressure waveforms compared favorably with realistic blood pressure waveforms, especially in the upper limbs. For lower limbs, finer segmentation could further improve the predictions.