Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference
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Conf Proc IEEE Eng Med Biol Soc · Jan 2009
Estimation of the aortic pressure waveform from a radial artery pressure waveform via an adaptive transfer function: Feasibility demonstration in swine.
We previously proposed a new technique to estimate the physiologically and clinically more relevant central aortic pressure (AP) waveform from a conveniently and safely measured peripheral artery pressure (PAP) waveform distorted by wave reflections. In contrast to conventional generalized transfer function (GTF) techniques, the technique is able to adapt the transfer function relating PAP to AP to the inter-patient and temporal variability of the arterial tree by defining it through a tube model and invoking the fact that aortic flow is negligible during diastole to estimate the unknown model parameters. We conducted feasibility testing of this adaptive transfer function technique here with respect to radial artery pressure (RAP) waveforms, for the first time, as well as femoral artery pressure (FAP) waveforms from four swine instrumented with AP catheters during several hemodynamic conditions. Our results showed that the AP waveforms estimated by the technique from the RAP and FAP waveforms were in superior agreement to the measured AP waveforms (overall respective errors of 4.1 and 4.8 mmHg) than the two unprocessed PAP waveforms (9.1 and 8.1 mmHg) and a previous GTF technique trained on a subset of the same data (5.0 and 5.8 mmHg).
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Conf Proc IEEE Eng Med Biol Soc · Jan 2009
Reduction of the onset response in high frequency nerve block with amplitude ramps from non-zero amplitudes.
High frequency alternating current (HFAC) waveforms reversibly block conduction in mammalian peripheral nerves. The initiation of the HFAC produces an onset response in the nerve before complete block occurs. An amplitude ramp, starting from zero amplitude, is ineffective in eliminating this onset response. ⋯ However, an amplitude ramp was successful in eliminating this onset. This was always possible for the ramps up from 50%, 75 % and 90% block threshold amplitude, but never from 0% or 25% of the block threshold amplitude. This maneuver can potentially be used to maintain complete nerve block, transition to partial block and then resume complete block without initiating another onset.
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Conf Proc IEEE Eng Med Biol Soc · Jan 2009
Combined direct current and high frequency nerve block for elimination of the onset response.
Nerve conduction in peripheral mammalian nerves can be blocked by high frequency alternating current (HFAC) waveforms. However, one of the disadvantages of HFAC block is that it produces an intense burst of firing in the nerve when the HFAC is first turned on. This is a significant obstacle to the clinical implementation of HFAC block. ⋯ This method was experimentally evaluated in an in-vivo mammalian model. Successful no-onset HFAC block was obtained using a DC block of 200 microA and an HFAC block of 30 kHz at 10 Vp-p. This may allow HFAC block to be used in clinical applications for pain relief.
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BIS monitoring is a processed electroencephalogram (EEG) technology that is designed to follow the effects that anesthetics and sedatives have on cerebral function. Much is know about the technology, it's utility and limitations. The economic case for widespread utilization of this technology is weak. ⋯ Total cost to the heath care system would approach one billion US dollars per year, just for use during general anesthetics. More appropriate use of already available drugs and technology would most likely decrease the incidence of IR as effectively, although individual patients who are at high risk for IR may benefit from this technology. However, based on current health care economic standards general use of BIS monitoring does not seem warranted and appears not to be cost-effective.