IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Oct 2009
An enhanced automatic algorithm for estimation of respiratory variations in arterial pulse pressure during regions of abrupt hemodynamic changes.
We describe an improved automatic algorithm to estimate the pulse-pressure-variation (PPV) index from arterial blood pressure (ABP) signals. This enhanced algorithm enables for PPV estimation during periods of abrupt hemodynamic changes. Numerous studies have shown PPV to be one of most specific and sensitive predictors of fluid responsiveness in mechanically ventilated patients. ⋯ We report validation results comparing the proposed algorithm against a commercial system (pulse contour cardiac output, PICCO) with continuous PPV monitoring capabilities. Both systems were assessed during periods of abrupt hemodynamic changes against the "gold-standard" PPV, calculated and manually annotated by experts. Our results indicate that the proposed algorithm performs considerably better than the PICCO system during regions of abrupt hemodynamic changes.
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IEEE Trans Biomed Eng · Oct 2009
Stochastic population model for electrical stimulation of the auditory nerve.
We have developed a biophysical model of a population of electrically stimulated auditory nerve fibers. It can be used to interpret results from physiological and behavioral experiments with cochlear implants and propose novel stimulation strategies. Our model consists of myelinated internodes described by a passive resistor-capacitor network, membrane capacitance, and leakage current at the nodes of Ranvier, as well as stochastic representations of nodal voltage-dependent channels. ⋯ Using our model, we have replicated the following properties within 10 % of the reported feline single-fiber measurements: relative spread (5.8 %), spike latency (630 micros), jitter (93 micros), chronaxie (238 micros), relative refractory period (4.6 ms), and conduction velocity (14 m/s). Moreover, we have successfully matched response characteristics of a population of fibers with the same number of diameter-distributed model fibers, enabling us to simulate responses of the entire AN. To demonstrate the performance of our model, we compare responses of a population of ANs stimulated with two speech encoding strategies, Continuous Interleaved Sampling and Compressed Analog.