Physiological measurement
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Physiological measurement · Feb 2001
Analysis by mathematical model of haemodynamic data in the failing Fontan circulation.
Several late complications jeopardize the clinical performance of recipients of the Fontan operation. The underlying causes have been referred to disturbed flow dynamics in the cavopulmonary connections. Presumably, the large pressure drops occurring in the inferior and superior connections play a pivotal role in the pressure level of the entire circulation, especially in the venous. ⋯ In the patients with failing Fontan, pressure in the venae cavae was found to be significantly higher, especially at the inferior cava (19.3 +/- 2.2 versus 12.5 +/- 2.3 mmHg) with the pressure drop at the inferior cavopulmonary connection significantly increased (4.7 +/- 3.1 versus 0.33 +/- 0.82 mmHg). The proposed mathematical model permits us to clearly relate the pressure increase in the venae cavae to an increased resistance in the cavopulmonary connections. Therefore, the present analysis confirms that, to avoid possible congestion of venous circulation, the definitive palliation of univentricular heart should not cause pressure drops at the cavopulmonary connections.
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Physiological measurement · Feb 2001
Comparative StudyVariability in the cardiac EIT image as a function of electrode position, lung volume and body position.
A study was conducted using the Sheffield electrical impedance tomography (EIT) portable system DAS-01 P to determine the change in the cardiac image with electrode position, lung volume and body position. Sixteen electrodes were positioned in three transverse planes around the thorax at the level of the second intercostal space, at the level of the xiphisternal joint, and midway between upper and lower locations. Data were collected at each electrode level with the breath held at end expiration and after inspiring 0.5, 1 and 1.5 l of air with the subject in both the supine and sitting position. ⋯ The pattern of variability with electrode position was not consistent among subjects. In one subject MRI images were obtained to compare actual structures with those seen in the EIT image. The results suggest that using these electrode locations reliable and consistent data, which could be used in clinical applications, cannot be obtained.
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Physiological measurement · Feb 2001
Progress in non-invasive respiratory monitoring using uncalibrated breathing movement components.
The theory for optimal linear combination of uncalibrated breathing movements was developed and applied in non-invasive respiratory monitoring situations for assessment. 16 patients were monitored overnight for respiratory depression during postoperative pain treatment. Intranasal/extra-oral airway pressure monitoring and pulse oximetry signals were recorded at 50 Hz. Respiratory inductive plethysmography (RIP) provided guidance to nurses regarding sensitivity settings of the pressure device during slow, shallow breathing, and vital information about breathing movements to help distinguish central from obstructive apnoeas. ⋯ The necessary signal combination and linearcalibration model background is reviewed for this simple formulation, which arises from component analysis and least squares regression. The methods are illustrated for definitive non-invasive postoperative monitoring and calibration situations. Theoretical and physiological reasons for preferring the use of balanced ribcage and abdomen contributions to overall tidal volume are presented that also help clarify the greater limitations of traditional RIP monitoring practices.