Shunt effect of gas compression inside pneumotachographs during forced oscillations

1991 ◽  
Vol 70 (1) ◽  
pp. 143-151 ◽  
Author(s):  
B. Louis ◽  
A. Harf ◽  
H. Lorino ◽  
D. Isabey
Keyword(s):  
Frequency Response ◽  
High Frequency ◽  
Forced Oscillation ◽  
Series Resistance ◽  
Forced Oscillations ◽  
Respiratory Impedance ◽  
Gas Compression ◽  
Normal Humans ◽  
Oscillation Method

Determination of the frequency response of pneumotachographs is needed whenever they are used to measure high-frequency flows, such as in the forced oscillation method. When screen and capillary pneumotachographs are calibrated using an adiabatic compression in a closed box as a reference impedance, they can be adequately described by a series of inertial-resistive elements. However, this type of reference impedance strongly differs from the actual respiratory impedance (ZL). We studied the frequency response of pneumotachographs up to 250 Hz in reference to the impedance of a compressible gas oscillating in a long tube, taken as a more generalizable model of actual ZL. We found that, with this device, the series resistance-inertance models fail to describe the frequency response of the pneumotachograph. However, when compressible effects in the pneumotachograph are taken into account by adding to the resistive models a compliance (Cpn) corresponding to the compression in half of the inner volume of the pneumotachograph, the agreement with experiments becomes satisfactory. Gas compression-related phenomena were demonstrated to be negligible only when the parameter omega Cpn magnitude of ZL is much smaller than 1 (omega pulsation). Results obtained in normal humans have shown that such a correction is required above 100 Hz. Similar correction at lower frequency might also be necessary in cases of large respiratory impedance (e.g., babies, subjects with pathological lungs, and intubated subjects).

Respiratory resistance by end-inspiratory occlusion and forced oscillations in intubated patients

1996 ◽  
Vol 80 (4) ◽  
pp. 1105-1111 ◽  
Author(s):  
L. Beydon ◽  
P. Malassine ◽  
A. M. Lorino ◽  
C. Mariette ◽  
F. Bonnet ◽  
...  
Keyword(s):  
Forced Oscillation ◽  
Forced Oscillations ◽  
Forced Oscillation Technique ◽  
Respiratory Impedance ◽  
Respiratory Resistance ◽  
Airway Occlusion ◽  
Residual Capacity ◽  
Occlusion Technique ◽  
Air Compression ◽  
Good Agreement

Measurement of respiratory impedance by the forced oscillation technique (FOT) in intubated patients requires corrections for the flow-dependent resistance, inertance, and air compression inside the endotracheal tube (ETT). Recently, we published a method to correct respiratory impedance for the mechanical contribution of the ETT. To validate this correction, we compared the respiratory resistance obtained with this method (Rfo) to the intrinsic (Rmin) and total resistances (RT) measured by the airway-occlusion technique (OCT) in 16 intubated sedated paralyzed ventilated patients. The FOT was applied at functional residual capacity in the 4- to 32-Hz frequency range, whereas the OCT was performed at the end of a normal constant-flow inspiration. Rmin corrected with Rfo measured at 16 and 32 Hz [Rfo(16) = 1.10 x Rmin + 0.10 cmH2O.s.l-1, r = 0.96, P < 0.001; Rfo(32) = 0.93 x Rmin + 0.72 cmH2O.s.l-1, r = 0.97, P < 0.001]. RT corrected with Rfo at 4 Hz [Rfo(4) = 1.11 x RT - 1.48 cmH2O.s.l-1; = 0.92; P < 0.001]. We conclude that the FOT improved by correction for the behavior of the ETT is in good agreement with the OCT in intubated patients.

Respiratory impedance and volume flow at high frequency in dogs

1961 ◽  
Vol 16 (3) ◽  
pp. 439-443 ◽  
Author(s):  
Wayland Elroy Hull ◽  
Ernest Croft Long
Keyword(s):  
High Frequency ◽  
Damping Ratio ◽  
Simultaneous Recording ◽  
Volume Flow ◽  
Total Resistance ◽  
Respiratory Impedance ◽  
Static Compliance ◽  
Tissue Resistance ◽  
Zero Phase

Sinusoidal forcing at frequencies up to 11 cycle/sec was applied to the anesthetized, apneic dog in a body respirator. Using an oscilloscope and the Lissajous patterns displayed by the simultaneous recording of driving pressure and volume flow, the frequency (resonant; mean, 5.4 cycle/sec) at which there was zero phase shift was determined. By analogy with an inductance-resistance-capacitance network, inertance (mean, .041 cm H2O/liter/sec2) was derived from static compliance (mean, .022 liter/cm H2O) and resonant frequency. Impedance at each frequency and damping ratio (mean, 1.57) was calculated. Tissue resistance was found to be 19% of the total resistance (mean, 4.3 cm H2O/liter/sec). A nomogram was constructed to facilitate the determination of inertance and the coding of data as electrical analogues. Submitted on September 16, 1960

Modifications to Willmore's method for calibrating seismographs using a maxwell bridge

1970 ◽  
Vol 60 (6) ◽  
pp. 2015-2022
Author(s):  
R. E. White
Keyword(s):  
Frequency Response ◽  
High Frequency ◽  
Bridge Circuit ◽  
Direct Method ◽  
Accurate Determination ◽  
High Frequency Response ◽  
Transient Methods

Abstract The substitution of an oscilloscope as detector into a Willmore bridge circuit allows a simple, accurate, and direct method of calibration for seismometer systems. An example of the method is given and its modification for a seismometer having appreciable inductance is discussed. It is also shown that transient methods do not allow an accurate determination of high-frequency response.

scholarly journals Evaluation of a forced oscillation method to measure thoracic gas volume

1998 ◽  
Vol 84 (3) ◽  
pp. 862-867 ◽  
Author(s):  
R. Peslin ◽  
C. Duvivier
Keyword(s):  
Forced Oscillation ◽  
Forced Oscillations ◽  
Strongly Correlated ◽  
Thoracic Gas Volume ◽  
Peripheral Airway ◽  
Multiple Frequencies ◽  
Gas Conditioning ◽  
Gas Volume ◽  
The Relationship

The purpose of this study was to test a plethysmographic method of measuring thoracic gas volume (TGV) that, contrary to the usual panting method, would not require any active cooperation from the subject. It is based on the assumption that the out-of-phase component of airway impedance varies linearly with frequency. By using that assumption, TGV may be computed by combining measurements of total respiratory impedance (Zrs) and of the relationship between the plethysmographic signal (Vpl) and airway flow (V˙) during forced oscillations at several frequencies. Zrs and Vpl/V˙were measured at 10 noninteger multiple frequencies ranging from 4 to 29 Hz in 15 subjects breathing gas in nearlybtps conditions. Forced oscillation measurements were immediately followed by determination of TGV by the standard method. The data were analyzed on different frequency ranges, and the best agreement was seen in the 6- to 29-Hz range. Within that range, forced oscillation TGV and standard TGV differed little (3.92 ± 0.66 vs. 3.83 ± 0.73 liters, n = 77, P < 0.05) and were strongly correlated ( r = 0.875); the differences were not correlated to the mean of the two estimates, and their SD was 0.35 liter. In seven subjects the differences were significantly different from zero, which may, in part, be due to imperfect gas conditioning. We conclude that the method is not highly accurate but could prove useful when, for lack of sufficient cooperation, the panting method cannot be used. The results of computer simulation, however, suggest that the method would be unreliable in the presence of severe airway inhomogeneity or peripheral airway obstruction.

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