Medical & biological engineering & computing
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Med Biol Eng Comput · May 2007
ReviewLaser Doppler perfusion monitoring and imaging: novel approaches.
Laser Doppler flowmetry (LDF) is a non invasive method enabling the monitoring of microvascular blood flow, a very important marker of tissue health. This article gives an overview on the concept of LDF for microvascular perfusion monitoring and imaging. It first describes the theoretical background of the technique. ⋯ For that purpose, a work providing the determination of the velocities relative contribution in physiologically relevant units (mm/s) is presented. Imaging perfusion is also reviewed through methods based on laser speckle. The most prominent disadvantage of the latter devices being the time needed to produce a perfusion image, solutions are proposed in the last part of the paper.
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Med Biol Eng Comput · May 2006
Model-based evaluation of the short-circuited tripolar cuff configuration.
Recordings of neural information for use as feedback in functional electrical stimulation are often contaminated with interfering signals from muscles and from stimulus pulses. The cuff electrode used for the neural recording can be optimized to improve the S/I ratio. In this work, we evaluate a model of both the nerve signal and the interfering signals recorded by a cuff, and subsequently use this model to study the signal to interference ratio of different cuff designs and to evaluate a recently introduced short-circuited tripolar cuff configuration. The results of the model showed good agreement with results from measurements in rabbits and confirmed the superior performance of the short-circuited tripolar configuration as compared with the traditionally used tripolar configuration.
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Med Biol Eng Comput · Apr 2006
Global versus local linear beat-to-beat analysis of the relationship between arterial pressure and pulse transit time during dynamic exercise.
Global linear analysis has been traditionally performed to verify the relationship between pulse transit time (PTT) and systolic arterial pressure (SAP) at the level of their spontaneous beat-to-beat variabilities: PTT and SAP have been plotted in the plane (PTT,SAP) and a significant linear correlation has been found. However, this relationship is weak and in specific individuals cannot be found. This result prevents the utilization of the SAP-PTT relationship to derive arterial pressure changes from PTT measures on an individual basis. ⋯ This local approach was applied to PTT and SAP series derived from 13 healthy humans during incremental supine dynamic exercise (at 10, 20 and 30% of the nominal individual maximum effort) and compared to the global approach. While global approach failed in some subjects, local analysis allowed the extraction of the gain of the SAP-PTT relationship in all subjects both at rest and during exercise. When both local and global analyses were successful, the local SAP-PTT gain is more negative than the global one as a likely result of noise reduction.
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Med Biol Eng Comput · Nov 2005
Unconstrained cardiorespiratory and body movement monitoring system for home care.
An unconstrained respiratory rate (RR) and heart rate (HR) monitoring system to be used during sleeping is proposed. The system consisted of eight polyvinylidene fluoride cable sensors, charge amplifiers and measuring software, together with an analogue-to-digital converter unit. The cable sensors were horizontally embedded into a textile sheet on a bed surface covering the upper half of the body. ⋯ The results showed that the mean frame-by-frame difference ranged from -1.2 to 0.2 beats min(-1) for the HR and, for RR, ranged from -0.8 to 1.4 breath min(-1) during the short-term recordings. Similar differences were obtained during the first 2 h of overnight recordings. The proposed system is feasible for the combined long-term monitoring of a person's RR and HR with sleep posture changes and may be helpful for practical use in the home.
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The study's goal was to determine if cardiac output (CO), obtained by impedance cardiography (ICG), would be improved by a new equation N, implementing a square root transformation for dZ/dtmax/Z0, and a variable magnitude, mass-based volume conductor Vc. Pulmonary artery catheterisation was performed on 106 cardiac surgery patients pre-operatively. Post-operatively, thermodilution cardiac output (TDCO) was simultaneously compared with ICG CO. dZ/dtmax/Z0 and Z0 were obtained from a proprietary bioimpedance device. ⋯ By contrast, CO calculated using K (3.70 +/- 1.53 l min(-1)), S (4.16 +/- 1.83 l min(-1)) and SB (4.37 +/- 1.82 l min(-1)) was significantly less than TDCO. Bland-Altman analysis showed poor agreement between TDCO and K, S and SB, but not between TDCO and N. Compared with TDCO, equation N, using a square-root transformation for dZ/dtmax/Z0, and a mass-based Vc, was superior to existing transthoracic impedance techniques for SV and CO determination.