Biomedical sciences instrumentation
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The use of sidestream capnometers, with a sampling rate of 150-250 cc/min, as a means of measuring a patient's expired CO2 (ETCO2) and respiratory rate, has been a common practice for many years. However, in recent years, there has been a focus on lower flow rate sampling sidestream systems due to the benefits of less loss of tidal volume for patients, such as infants or neonates. When developing a sidestream system, four principle issues must be considered; 1) The signal fidelity of the gas sample must be sufficiently maintained from the sampling site to the measurement site. 2) Condensate from a patient's breath, as well as blood, mucus, or other contaminates often pose problems for sidestream systems and requires mitigation. 3) The mechanics of transporting a gas sample at a constant flow rate through the sampling system, regardless of atmospheric or clinical conditions must be developed. 4) The physics of handling CO2 gas throughout the transport process must be understood in order to ensure accurate readings. These issues lead to a complex web of interrelations that are explored in the development of a low flow rate sidestream capnometer.
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Clinical Trial Controlled Clinical Trial
Assessment of heart rate variability during alterations in stress: complex demodulation vs. spectral analysis.
Complex demodulation (CDM) has been proposed as a method for the analysis of high- and low-frequency variabilities of heart rate and blood pressure under non-stationary conditions. In contrast to power spectral analysis, CDM provides time-dependent changes in signal amplitude and frequency on a continuous basis and may yield insights into short-term alterations in autonomic regulation. In particular, CDM may be uniquely suited for quantifying changes in respiratory sinus arrhythmia (RSA) at the onset of acute physical or mental stress conditions. ⋯ Compared to CDM, power spectral analysis results were less informative since they did not allow the disentangling of unique contributions of distinct amplitudes and frequencies at different time points. Our analyses indicate that CDM provides a powerful means of continuously assessing time-dependent changes in RSA during varying physical or mental stress. CDM may also hold promise for a range of physiological and environmental non-steady state conditions where rapid dynamic alterations in autonomic control are likely to occur.