Physiological measurement
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Physiological measurement · Nov 1996
Gravity-dependent phenomena in lung ventilation determined by functional EIT.
Gravity exerts an effect on the distribution of intrapulmonary ventilation. A study on the detection of gravity-dependent inhomogeneity of ventilation by a functional EIT technique is presented. The study was performed on five human subjects, whose ventilation distribution was modified by changes in body position. ⋯ The qualitative and quantitative analysis of the functional EIT images revealed that the ventilation is higher in the dependent lung regions when compared with the non-dependent ones. These EIT findings correspond to current knowledge of the physiological behaviour of the lungs as derived from the radioactive-gas methods and raise the possibility of applying the less complicated functional EIT in future studies on ventilation distribution in the lungs. This may be of major interest in the monitoring of intensive care patients with severe pulmonary disorders.
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Physiological measurement · Aug 1996
Improvement of cardiac imaging in electrical impedance tomography by means of a new electrode configuration.
Until now, electrical impedance tomography (EIT) has been used for cardiac imaging with the electrodes attached transversally at the level of the fourth intercostal space at the anterior side. However, the results obtained with this electrode configuration have been disappointing. The aim of the present study was to improve the measurement design of EIT for cardiac imaging. ⋯ The increase in impedance change during exercise compared with rest was 34 +/- 13% (20-59%) for the oblique plane and 68 +/- 57% (13-140%) for the transverse plane. From these results we infer that the stroke volume is assessed more accurately by using the oblique plane. From these findings, we conclude that the oblique plane improved the cardiac measurements, because (i) a better spatial separation of the heart compartments is obtained, (ii) the results are more reliable and (iii) measurements during exercise are more accurate with the electrodes attached in an oblique plane.
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Physiological measurement · Feb 1996
Comparative StudyThe performance of a variable-flow indirect calorimeter.
Indirect calorimetry estimates energy expenditure from measurement of respiratory gas exchange volumes. This paper considers the design and evaluation of an indirect calorimeter, the Europa GEM, suitable for use in nutritional research. The calorimeter is of the ventilated hood, flow-through type and is intended for use with spontaneously breathing patients. ⋯ Performance was assessed in a laboratory simulation using reference gas injections (n = 24) producing a mean error of 0.3 +/- 2% in oxygen consumption (VO2), 1.8 +/- 1% in carbon dioxide production (VCO2) and 1.4 +/- 1.5% in respiratory quotient (RQ). In order to investigate the effect of FeCO2 on error multiplication a further subdivision (n = 8) of tests at FeCO2 = 0.5%, 0.75% and 1% was made by modulating the air flow through the hood. However, the predicted increase in system accuracy with increasing FeCO2 was not apparent in practice.
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Physiological measurement · Feb 1996
The lowering of stroke volume measured by means of impedance cardiography during endexpiratory breath holding.
Impedance cardiography is a reliable method for estimating stroke volume (SV). Breathing, however, causes artefacts, which can be avoided by measuring during breath holding. This study investigated whether SV determination is accurate during breath holding. ⋯ This indicates that the SV decrease was not caused by a Valsalva-like manoeuvre. The mean SV value calculated by means of impedance cardiography for the total breath hold period was significantly lower than the SV during breathing, both at rest (91.7 +/- 2.4%) and at 100 W (90.5 +/- 7.0%). From this study it can be concluded that averaging of the impedance signal, measured while the subject is breathing, is preferential to measuring during breath holding, because the latter condition systematically underestimates SV.
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Physiological measurement · Aug 1995
Clinical TrialA new non-invasive approach for monitoring respiratory movements of sleeping subjects.
We have developed a minimally intrusive system to monitor respiratory movements of sleeping subjects. This system is based on a pressure transducer which measures the changes in air pressure inside an inflatable mattress on which the subject sleeps. Using a mechanical filter to protect the transducer against the large pressure changes due to sudden movements and subject weight, we can detect the more subtle movements of the subject's chest. This paper discusses the design of the monitoring system, including the design and modelling of the mechanical filter.