Physiological measurement
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Physiological measurement · Feb 1999
Tomographic reconstruction of the retina using a confocal scanning laser ophthalmoscope.
Retinal imaging with a confocal scanning laser ophthalmoscope (cSLO) involves scanning a small laser beam over the retina and constructing an image from the reflected light. By applying the confocal principle, tomographic images can be produced. However, the thickness of such slices, when compared with the retinal thickness, is too large to give useful 3D retinal images. ⋯ From the fitted curve, topographic images and novel thickness images of the retina can be generated. The technique has been applied to three normal volunteers and seven patients with macular pathology (cystoid macular oedema and macular hole) demonstrating the clinical value of the technique. The improvement in accuracy achieved by using a double rather than a single Gaussian is also demonstrated.
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Physiological measurement · Aug 1998
ReviewAssessment of cerebral pressure autoregulation in humans--a review of measurement methods.
Assessment of cerebral autoregulation is an important adjunct to measurement of cerebral blood flow for diagnosis, monitoring or prognosis of cerebrovascular disease. The most common approach tests the effects of changes in mean arterial blood pressure on cerebral blood flow, known as pressure autoregulation. A 'gold standard' for this purpose is not available and the literature shows considerable disparity of methods and criteria. ⋯ Dynamic testing overcomes several limitations of static methods but it is not clear whether the two approaches are interchangeable. Classification of autoregulation performance using dynamic methods has been based on mathematical modelling, coherent averaging, transfer function analysis, crosscorrelation function or impulse response analysis. More research on reproducibility and inter-method comparisons is urgently needed, particularly involving the assessment of pressure autoregulation in individuals rather than patient groups.
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Physiological measurement · Feb 1998
Clinical TrialThe variability of the photoplethysmographic signal--a potential method for the evaluation of the autonomic nervous system.
The heart rate variability is composed of low- and high-frequency fluctuations, which are mediated by the sympathetic and the parasympathetic nervous systems. The baseline and the amplitude of the photoplethysmographic (PPG) signal also show fluctuations in the same frequencies. In the current study, PPG examinations were performed on the fingers of normal subjects and diabetic patients, and three parameters were derived from each PPG pulse: the baseline of the pulse, its amplitude and its period (which is equal to the heart period). ⋯ The curves of the baseline and the amplitude of the PPG signal for the non-diabetic subjects showed high correlation between the left and the right hands. For most of the diabetic patients the right-left correlation coefficients were significantly lower than those for the non-diabetic subjects. Our initial results have shown that the variability of the PPG parameters shows promise for the assessment of the function of the autonomic nervous system.
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Physiological measurement · Nov 1997
Comparative Study Clinical TrialNon-invasive assessment of cardiac output during exercise in chronic obstructive pulmonary disease: comparison of the CO2-rebreathing method and electrical impedance cardiography.
In exercise testing of patients with chronic obstructive pulmonary disease (COPD), non-invasive assessment of stroke volume (SV) and cardiac output (CO) would be valuable. Electrical impedance cardiography (EIC) has proved to be a valid and reliable instrument in healthy subjects. In this study it is investigated whether this also applies to patients with COPD. ⋯ CO was closely correlated to oxygen uptake using the CO2-rebreathing as well as the EIC method; the slope of the regression line was closer to what has been reported in the literature with EIC. Results were better with the EIC-ht than with the EIC-135 and EIC-150 methods. It is concluded that EIC is a reliable and valid method for measurements of SV and CO in COPD during exercise.
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Physiological measurement · Aug 1997
An assessment of infrared tympanic thermometers for body temperature measurement.
This article provides an experimental assessment of three commercially available clinical thermometers, using different thermal infrared sensors. This kind of thermometer measures body temperature by detecting infrared radiation from the tympanic membrane. These thermometers are growing in popularity thanks to their simplicity of use, rapid response and minimal distress to the patient. The purpose of the laboratory tests presented here was to assess the effect of varying ambient temperature and varying simulated patient temperature on the performance of the three infrared tympanic thermometers.