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Technique to Determine Inspiratory Impedance during Mechanical Ventilation: Implications for Flow Limited Patients (1999)

Kaczka, David W. ; Ingenito, Edward P. ; Lutchen, Kenneth R.

Springer

Annals of biomedical engineering 27 (1999), S. 340-355

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ISSN: 1573-9686

Keywords: Mechanical ventilation ; Inspiratory resistance ; Inspiratory elastance ; Enhanced ventilator waveform ; Flow limitation

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Abstract We present the design of an enhanced ventilator waveform (EVW) for routine measurement of inspiratory resistance (R) and elastance (E) spectra in ventilator-dependent and/or severely obstructed flow-limited patients. The EVW delivers an inspiratory tidal volume of fresh gas with a flow pattern consisting of multiple sinusoids from 0.156 to 8.1 Hz and permits a patient-driven exhalation to the atmosphere or positive end-expiratory pressure. Weighted least-squares estimates of the coefficients in a sinusoidal series approximation of the EVW inspirations yielded inspiratory R and E spectra. We first validated the EVW approach using simulated pressure and flow data under different physiological conditions, noise levels, and harmonic distortions. We then applied the EVW in four intubated patients during anesthesia and paralysis: two with mild airway obstruction and two with severe emphysema and flow limitation. While the level of inspiratory R was similar in both groups of patients, the inspiratory E of the emphysematous patients demonstrated a pronounced frequency-dependent increase consistent with severe peripheral airway obstruction. We conclude that the EVW offers a potentially practical and efficient approach to monitor lung function in ventilator-dependent patients, especially those with expiratory flow limitation. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8780-y

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1114/1.146

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Assessment of time-domain analyses for estimation of low-frequency respiratory mechanical properties and impedance spectra (1995)

Kaczka, David W. ; Barnas, George M. ; Suki, Bela ; [et al.]

Springer

Annals of biomedical engineering 23 (1995), S. 135-151

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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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