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  • 1
    Electronic Resource
    Electronic Resource
    Automated system for detailed measurement of respiratory mechanics (1996)
    Springer
    Journal of clinical monitoring and computing 12 (1996), S. 61-67 
    Details
    ISSN: 1573-2614
    Keywords: Lung ; mechanics: resistance ; compliance ; elastance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Objective. The mechanical properties of the respiratory system (i.e., elastance and resistance) depend on the frequency, tidal volume, and shape of the flow waveform used for forcing. We developed a system to facilitate accurate measurements of elastance and resistance in laboratory and clinical settings at the frequencies and tidal volumes in the physiologic range of breathing.Methods. A personal computer (PC) is used to drive a common clinically used ventilator while simultaneously collecting measurements of airway flow, airway pressure, and esophageal pressure from the experimental subject or animal at different frequencies and tidal volumes. Analysis analogous to discrete Fourier transform at the fundamental frequency (i.e., ventilator setting) is used to calculate elastances and resistances of the total respiratory system and its components, the lungs and the chest wall. We have shown that this analysis is independent of the high-frequency harmonics that are present in the waveform from clinical ventilators.Results. The system has been used successfully to make measurements in anesthetized/paralyzed dogs and awake or anesthetized human volunteers in the laboratory, and in anesthetized humans in the operating room and intensive care unit. Elastances and resistances obtained with this approach are the same as those obtained during more controlled conditions, e.g., sinusoidal forcing. Conclusions. Accurate, standardized measurements of lung and chest wall properties can be obtained in many settings with relative ease with the system described. These properties, and their frequency and tidal volume dependences in the physiologic range, provide important information to aid in the understanding of changes in respiratory function caused by day-to-day conditions, clinical intervention and pathologies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02025312
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  • 2
    Electronic Resource
    Electronic Resource
    Response Time Studies of a New, Portable Mass Spectrometer (1997)
    Springer
    Journal of clinical monitoring and computing 13 (1997), S. 181-189 
    Details
    ISSN: 1573-2614
    Keywords: Gas measurement ; critical care ; instrument comparison
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract Objective. Mass spectrometers are frequently used by anesthesiologistsperioperatively to monitor patients’ respiratory function and levels ofinhaled anesthetics. Due to size, complexity and expense, they are typicallyused in a time-sharing manner which degrades their performance. We assessedthe accuracy of the Random Access Mass Spectrometer (RAMS, MarquetteElectronics) which is small enough to be dedicated to a single patient.Methods. We compared the 10–90% rise times for O2,CO2, N2O and isoflurane for the RAMS withdifferent catheter configurations to those of a MedSpect mass spectrometer(Allegheny International Medical Technology) operating under ideal conditions.For CO2 the lag of the RAMS relative to the MedSpect was alsomeasured. Next, perioperative conditions were simulated by ventilatinganesthetized dogs with a variety of inhalatory gases and ventilatoryparameters, and the interchangability of the two devices was assessed.Results. When fitted with a catheter with minimal dead space the MedSpect hadrise times of 0.11–0.12 sec while the RAMS had rise times of0.07–0.12 sec and a delay of 0.19 sec compared to the MedSpect. The risetimes and delay of the RAMS increased when using a larger catheter and watertrap. Although there were statistically significant differences in some valuesfor inhaled and end-tidal gases under simulated perioperative conditions,particularly at the higher frequencies, these differences were small and formost purposes not clinically significant. Conclusions. Our results demonstratethat the RAMS configured for clinical conditions performs nearly as well asthe MedSpect under ideal conditions. The small differences between the two,confined almost entirely to their end-tidal CO2 values, couldbe due to differences in instrument calibration, by the larger samplingcatheter commonly used in clinical settings, or by a combination of bothfactors. Therefore the RAMS is sufficiently accurate for clinical use andwould alleviate problems associated with time-shared mass spectrometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007353818448
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  • 3
    Electronic Resource
    Electronic Resource
    Assessment of time-domain analyses for estimation of low-frequency respiratory mechanical properties and impedance spectra (1995)
    Springer
    Annals of biomedical engineering 23 (1995), S. 135-151 
    Details
    ISSN: 1573-9686
    Keywords: Respiratory impedance ; Ventilator ; Real-time estimation ; Intensive care unit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Time-domain estimation has been invoked for tracking of respiratory mechanical properties using primarily a simple single-compartment model containing a series resistance (R rs) and elastance (E rs). However, owing to the viscoelastic properties of respiratory tissues,R rs andE rs exhibit frequency dependence below 2 Hz. The goal of this study was to investigate the bias and statistical accuracy of various time-domain approaches with respect to model properties, as well as the estimated impedance spectra. Particular emphasis was placed on establishing the tracking capability using a standard step ventilation. A simulation study compared continuous-timeversus discrete-time approaches for both the single-compartment and two-compartment models. Data were acquired in four healthy humans and two dogs before and after induced severe pulmonary edema while applying sinusoidal and standard ventilator forcing.R rs andE rs were estimated either by the standard Fast Fourier Transform (FFT) approach or by a time-domain least square estimation. Results show that the continuous-time model form produced the least bias and smallest parameter uncertainty for a single-compartment analysis and is quite amenable for reliable on-line tracking. The discrete-time approach exhibits large uncertainty and bias, particularly with increasing noise in the flow data. In humans, the time-domain approach produced smooth estimates ofR rs andE rs spectra, but they were statistically unreliable at the lower frequencies. In dogs, both the FFT and time-domain analysis produced reliable and stable estimates forR rs orE rs spectra for frequencies out to 2 Hz in all conditions. Nevertheless, obtaining stable on-line parameter estimates for the two-compartment viscoelastic models remained difficult. We conclude that time-domain analysis of respiratory mechanics should invoke a continuous-time model form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368321
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