Physiological measurement
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Pulse oximetry has been one of the most significant technological advances in clinical monitoring in the last two decades. Pulse oximetry is a non-invasive photometric technique that provides information about the arterial blood oxygen saturation (SpO(2)) and heart rate, and has widespread clinical applications. When peripheral perfusion is poor, as in states of hypovolaemia, hypothermia and vasoconstriction, oxygenation readings become unreliable or cease. ⋯ The limitations of this technique are also discussed leading to the proposed development of the oesophageal pulse oximeter. In the majority, the report will be focused on the description of a new oesophageal photoplethysmographic/SpO(2) probe, which was developed to investigate the suitability of the oesophagus as an alternative monitoring site for the continuous measurement of SpO(2) in cases of poor peripheral circulation. The article concludes with a review of reported clinical investigations of the oesophageal pulse oximeter.
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Physiological measurement · Jan 2006
A longitudinal study of breath isoprene in healthy volunteers using selected ion flow tube mass spectrometry (SIFT-MS).
Thirty volunteers (19 males, 11 females) were recruited for a 6-month study of the volatile compounds in their exhaled breath using the selected ion flow tube mass spectrometry (SIFT-MS) analytical technique. Volunteers provided weekly breath samples between 8:45 am and 1 pm (before lunch), and the concentrations of several trace compounds were obtained. In this paper, we focus on the isoprene in alveolar breath, which was monitored by SIFT-MS using NO(+) precursor ions. ⋯ Isoprene levels increased immediately after moderate exercise, but returned to normal within 2-3 min for those few volunteers that were investigated. Cholesterol levels analysed for only three of the subjects were not obviously correlated with isoprene concentration in breath. Differences in isoprene levels were not directly correlated to gender, age or body mass index.
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Physiological measurement · Jan 2006
The influence of flow rate on breathing circuit compliance and tidal volume delivered to patients in mechanical ventilation.
Assessment of the gas volume that actually reaches the airways during mechanical ventilation appears to be a difficult task because of the presence of the breathing circuit. Most ventilators measure tidal volume at ventilator level making the determination of circuit compliance a critical factor in estimating the actual tidal volume. ⋯ The dependence of the compliance on the inspiratory flow is experimentally assessed, and differences of about 20% on the measured value in the common flow range utilized in infant ventilation have been found, with consequent estimation errors of the volume delivered. Experimental tests show that the correct value of the tidal volume actually delivered to the patient can be reliably estimated from measurements performed at the ventilator level if the circuit compliance is determined with the same flow rates that will be utilized in mechanical ventilation.