Physiological measurement
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Physiological measurement · Jul 2006
Comment LetterComments on 'The influence of cardiac preload and positive end-expiratory pressure on the pre-ejection period'.
The pre-ejection period (PEP) has been described as a potential parameter for monitoring cardiac preload in deeply sedated mechanically ventilated patients. Other authors have recently suggested that PEP is not sensitive to the changes in intravascular volume status in mechanically ventilated pigs which underwent acute hemorrhage. The present comment is an analysis of this recent animal investigation.
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Physiological measurement · Jul 2006
Comparative StudyA longitudinal study of methanol in the exhaled breath of 30 healthy volunteers using selected ion flow tube mass spectrometry, SIFT-MS.
Selected ion flow tube mass spectrometry, SIFT-MS, has been used to monitor the volatile compounds in the exhaled breath of 30 volunteers (19 male, 11 female) over a six-month period. Volunteers provided breath samples each week between 8:45 am and 1 pm (before lunch), and the concentrations of several trace compounds were obtained. In this paper the focus is on methanol in breath. ⋯ Breath methanol is not correlated with age, breath ethanol or ethanol consumed in the previous 24 h, but there was an inverse correlation with body mass index (BMI) for the cohort of volunteers recruited for this study. Observed breath methanol levels are well compatible with the previously published blood methanol levels. Some tentative suggestions are made concerning the origin of endogenous methanol.
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Physiological measurement · Jun 2006
The increase of breath ammonia induced by niacin ingestion quantified by selected ion flow tube mass spectrometry.
The ingestion of relatively large doses of the vitamin niacin by healthy volunteers results in a reddening of the skin, a skin 'flush'. Thus, we have carried out a study of the breath metabolites of two healthy volunteers following (i) the ingestion of 200 mg of immediate-release niacin, (ii) as (i) but preceded by the ingestion of 325 mg of aspirin that diminishes the skin 'flush', (iii) ingestion of 500 mg of slow-release niacin. On-line breath analysis was carried out using selected ion flow tube mass spectrometry, SIFT-MS. ⋯ The slow-release niacin (iii) did not result in a flush and the breath ammonia levels increased more slowly and did not reach the higher levels produced by (i) and (ii). The results of these experiments demonstrate that breath ammonia levels are dependent on the blood/plasma levels of niacin, but are not directly related to the flushing phenomenon, and that the observed increases in blood/breath ammonia levels are consistent with current knowledge of the metabolic pathways of niacin. The parallel measurements of breath isoprene are presented, which demonstrate the quality of breath analyses that can be achieved using SIFT-MS.
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Physiological measurement · May 2006
Clinical TrialParametric EIT for monitoring cardiac stroke volume.
The bio-impedance technique appears appropriate for non-invasive cardiac stroke volume (SV) measurement, as the thoracic conductivity distribution is altered during the cardiac cycle due to the heart contraction and blood perfusion. In the present work, the feasibility of a parametric electrical impedance tomography (EIT) for assessing the cardiac SV was studied. An impedance model of the thorax was constructed from segmented axial MRI images along 19 phases of the cardiac cycle. ⋯ The simulation results were compared to physical data, collected with a portable EIT system (PulmoTrace, CardioInspect). The validation study was employed for a group of N = 28 healthy patients, and a comparison with impedance cardiography measurements (BioZ, Cardiodynamics) was made, showing a correlation of r = 0.86 (p = 4 x10(-9)). The preliminary results demonstrate that parametric EIT has the potential to measure SV, and may be applicable for both clinical and home environment usage.
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Electrical impedance tomography (EIT) attempts to reconstruct the internal impedance distribution in a medium from electrical measurements at electrodes on the medium surface. One key difficulty with EIT measurements is due to the position uncertainty of the electrodes, especially for medical applications, in which the body surface moves during breathing and posture change. In this paper, we develop a new approach which directly reconstructs both electrode movements and internal conductivity changes for difference EIT. ⋯ A one-step regularized imaging algorithm is then implemented based on the augmented Jacobian and smoothness constraint. Images were reconstructed using the algorithm of this paper with data from simulated 2D and 3D conductivity changes and electrode movements, and from saline phantom measurements. Results showed good reconstruction of the actual electrode movements, as well as a dramatic reduction in image artefacts compared to images from the standard algorithm, which did not account for electrode movement.