Physiological measurement
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Physiological measurement · Jun 2012
Hemodynamic evaluation in pregnancy: limitations of impedance cardiography.
Impedance cardiography (ICG) has been proposed to estimate the stroke volume (SV) and cardiac output (CO) in various medical indications. The aim of this study was to explore the reliability of ICG during pregnancy with respect to SV and CO measurements. Blood pressure, heart rate and thoracic impedance were monitored during the course of pregnancy and related ICG patterns analyzed. ⋯ These results were confirmed for fixed R-R interval at a constant value across the repeated measurements. Based on beat-to-beat analysis of the main components of non-invasive SV estimation by ICG, measured repeatedly throughout normal pregnancy, we conclude that SV calculations render invalid data. Our findings strongly suggest that CO cannot be reliably assessed with ICG in pregnant women.
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Physiological measurement · Jun 2012
Improvement of signal-to-interference ratio and signal-to-noise ratio in nerve cuff electrode systems.
Cuff electrodes are effective for chronic electroneurogram (ENG) recording while minimizing nerve damage. However, the ENG signals are usually contaminated by electromyogram (EMG) activity from the surrounding muscles, stimulus artifacts produced by the electrical stimulation and noise generated in the first stage of the neural signal amplifier. ⋯ Furthermore, a new low-noise amplifier was proposed to improve the signal-to-noise ratio. The circuit was designed based on a noise analysis to minimize the noise, and the results show that the total noise of the amplifier was below 1 μV for a cuff impedance of 1 kΩ and a frequency bandwidth of 300 to 5000 Hz.