Journal of medical engineering & technology
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Clinical Trial
MR-based measurement of spinal cord motion during flexion of the spine: implications for intradural spinal cord stimulator systems.
This study develops a means of delivering electrical stimuli directly to the pial surface of the spinal cord for treatment of intractable pain. This intradural implant must remain in direct contact with the cord as it moves within the spinal canal. ⋯ Following flexion of the back, the mean change in the pedicle-to-spinal cord dorsal root entry zone distance at the T10-11 level was (8.5 ± 6.0) mm, i.e. a 71% variation in the range of rostral-caudal movement of the spinal cord across all patients. There will be a large spectrum of spinal cord strains associated with this observed range of rostral-caudal motions, thus calling for suitable axial compliance within the electrode bearing portion of the intradural implant.
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Respiratory variation in the arterial blood pressure and photoplethysmographic (PPG) waveforms have both been shown to predict the haemodynamic response to volume administration. Whether or not the two can be considered interchangeable is controversial. Twenty-three patients undergoing spine surgery received both a 20 gauge intra-arterial catheter and a Masimo adult adhesive SpHb sensor connected to a Radical-7 monitor. ⋯ The agreement between respiratory variation in the arterial blood pressure and PPG waveforms is poor and these two should not be considered interchangeable. Changes in PPV are unrelated to changes in PVI. The data, combined with recently published work from other authors, suggests that the low frequency oscillations in the PPG waveform are not related to the low frequency oscillation in the systemic arterial blood pressure tracing and may be related to changes in venous pressure, peripheral tone or other physiologic phenomena yet to be described.
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Heart sounds and murmurs provide crucial diagnosis information for several heart diseases such as natural or prosthetic valve dysfunction and heart failure. Many pathological conditions of the cardiovascular system cause murmurs and aberrations in heart sounds. ⋯ This paper presents an algorithm for the detection of heart sounds (the first and second sounds, S1 and S2) and heart murmurs. The segmentation algorithm is based on the detection of the envelope of the phonocardiogram signal by the Hilbert transform technique, which is used to extract a smooth envelogram which enable one to apply the tests necessary for temporal localization of heart sounds and heart murmurs.
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Respiratory variation in the systemic arterial blood pressure tracing is predictive of the change in cardiac output following volume administration. However, significant inter-individual variability exists. Animal data suggest that systemic arterial respiratory variation loses its predictive ability in the setting of right ventricular failure. ⋯ The correlation between SPoR(pulmonary) and SPoR(radial) was stronger than the correlation between either measure of respiratory variation and any of the ventilatory parameters (r = 0.342, p < 0.001). Respiratory variation in the pulmonary arterial tracing does not appear to be closely related to ventilatory parameters and is more closely related to systemic arterial respiratory variation, a well-validated estimate of volume status. The observed respiratory variation in the pulmonary arterial pressure tracing may be related to cyclical changes in pre-load or after-load that occur with mechanical ventilation and may affect the predictive power of systemic arterial respiratory variation.
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The Tensys T-line uses tonometry to reproduce the arterial blood pressure tracing non-invasively. The purpose of this study was to assess the agreement between estimates of the T-line and an intra-arterial catheter (for both mean arterial pressure [MAP] and pulse pressure variation [PPV]) in the setting of spine surgery. Continuous blood pressure data were collected for 7507 minutes from 25 patients. ⋯ The mean bias for mean, diastolic and systolic blood pressure ranged from 3.4-6.4, 3.1-7.1 and 0.1-0.8 mmHg and 6.5-11.8% for PPV. Ninety-five per cent confidence intervals for mean, diastolic and systolic blood pressure ranged from 24-28, 23.1-24.7 and 33.4-35.6 mmHg for 14-21% for PPV. The limits of agreement preclude the use of the T-line for reliable estimation of MAP or PPV in spine surgery.