Physiological measurement
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Physiological measurement · Oct 2004
Clinical TrialThe effect of contacting force on photoplethysmographic signals.
Photoplethysmography (PPG) has been used in oxygen saturation measurement, heart rate monitoring, and the assessment of peripheral circulation and large artery compliance. However, the waveform of the photoplethysmographic signal may be affected by the contacting force between the sensor and the measurement site. The aim of this study is to investigate the change in pulse amplitude (AC), DC amplitude, ratio of AC/DC and normalized pulse area of the reflective photoplethysmographic signals with increasing contacting force, from 0.2 N to 1.8 N. ⋯ For different subjects, the pulse amplitude and the ratio of AC/DC peaked at different contacting forces, from 0.2 N to 1.0 N, and most of the subjects achieved their maximum pulse amplitude within 0.2-0.4 N. Over the range of contacting force between 0.2 N and 0.8 N, the DC amplitude and the normalized pulse area had significant changes (p < 0.001). The results suggest that the effects of contacting force should be carefully examined in the design of photoplethysmography-based health care devices.
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Physiological measurement · Aug 2004
Clinical TrialQuantifying agitation in sedated ICU patients using heart rate and blood pressure.
Agitation is a significant problem in the intensive care unit (ICU), affecting 71% of sedated adult patients during 58% of ICU patient-days (Fraser and Riker 2001 NY Health-Syst. Pharm. 20 17-24). Subjective scale-based assessment methods are currently used to assess the level of patient agitation, but are limited in their accuracy and resolution. ⋯ Proof of concept clinical trials on 13 normal subjects and 5 ICU patients has been performed to verify the validity of this approach in comparison with agitation graded by nursing staff using the Riker sedation-agitation scale (SAS). Results show good correlation with medical staff assessment with no false positive results during calm periods. Clinically, this initial agitation measurement method promises the ability to consistently and objectively quantify patient agitation to enable better management of sedation and agitation through optimized drug delivery leading to reduced length of stay.
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Physiological measurement · Aug 2004
Cortical entropy changes with general anaesthesia: theory and experiment.
Commonly used general anaesthetics cause a decrease in the spectral entropy of the electroencephalogram as the patient transits from the conscious to the unconscious state. Although the spectral entropy is a configurational entropy, it is plausible that the spectral entropy may be acting as a reliable indicator of real changes in cortical neuronal interactions. Using a mean field theory, the activity of the cerebral cortex may be modelled as fluctuations in mean soma potential around equilibrium states. ⋯ These predictions were compared with experimental results in which electrocorticograms and brain concentrations of propofol were recorded in seven sheep during induction of anaesthesia with intravenous propofol. The observed changes in spectral entropy agreed with the theoretical predictions. We conclude that spectral entropy may be a sensitive monitor of the consciousness-unconsciousness transition, rather than a progressive indicator of anaesthetic drug effect.
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Physiological measurement · Jun 2004
Comparative Study Clinical Trial Controlled Clinical TrialAssessment of the hypoxic-ischemic encephalopathy in neonates using non-invasive near-infrared spectroscopy.
This paper introduces a method of monitoring cerebral oxygenation for healthy neonates and neonates with hypoxic-ischemic encephalopathy (HIE) using near-infrared spectroscopy. The object of this study was to investigate whether or not there were differences between the HIE group and the healthy group in terms of NIRS parameters. The subjects were all term neonates, their age ranging from 2 to 18 days. ⋯ The result shows that: (1) the mean+/-SD of rSO2 for the healthy group was 62 +/- 4% in the frontal region under the quiet sleep condition, but the mean+/-SD of rSO2 for the HIE group was 53 +/- 3%. (2) As all subjects inhaled pure oxygen in 21 min(-1) for a period of 60 s, rSO2 for the healthy group increased rapidly, with the increase in rSO2 (deltarSO2) being 7 +/- 2.3%, but the increase in rSO2 for the HIE neonates was 3 +/- 1.5%. After inhaling oxygen, deltaHbO2 and deltaHb between the two groups were also significantly different. (3) During all the experiments SpO2 was monitored, the value of SpO2 was not significantly different between the two groups. The above observations suggest that the rSO2 in quiet condition and the values of change of rSO2, HbO2 and Hb during the inhalation of oxygen may be used as the parameters to discover and assess the HIE infants.
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Physiological measurement · Nov 2003
Clinical TrialMacrocirculation is not the sole determinant of respiratory induced variations in the reflection mode photoplethysmographic signal.
Photoplethysmography (PPG) is a non-invasive optical technique sensitive to variations in blood volume and perfusion in the tissue. Reflection mode PPG may have clinical advantages over transmission mode PPG. To improve clinical usefulness and further development of the reflection mode PPG, studies on factors that modify the signal are warranted. ⋯ In spontaneously breathing patients the coherence was high, but the phases between the signals were changed. During inspiration, ABP decreased slightly before CVP, followed by a decrease in RIIV and PVP. The phase relation between RIIV and respiratory induced variation in macrocirculation changed with ventilatory mode, but not in a uniform way, indicating the influence of mechanisms other than macrocirculation involved in generating the RIIV signal.