Canine Pulmonary Input Impedance Measured by Transient Forced Oscillations

1978 ◽  
Vol 100 (2) ◽  
pp. 67-71 ◽  
Author(s):  
J. J. Fredberg ◽  
R. S. Sidell ◽  
M. E. Wohl ◽  
R. G. DeJong
Keyword(s):  
Input Impedance ◽  
Forced Oscillations ◽  
Acquisition Time ◽  
Data Channel ◽  
Airway Opening ◽  
Line Theory ◽  
Lossy Transmission ◽  
Data Acquisition Time ◽  
Airway Walls ◽  
Lossy Transmission Line

We describe a transient forced oscillation method for measurement of the input impedance of excised canine lungs. The technique employs a single uncalibrated data channel to record short duration pressure transients incident upon and reflected from the airway opening, from which the input impedance up to 10,000 Hz is computed using lossy transmission line theory. Data acquisition time is less than 10 ms. The lung responses exhibit numerous resonances and anti-resonances below 10,000 Hz, and exhibit lung volume dependence. The branching structure of the airways and response of the airway walls appear to be important factors in the lung response.

Upper airway walls impedance measured with head plethysmograph

1984 ◽  
Vol 57 (2) ◽  
pp. 596-600 ◽  
Author(s):  
R. Peslin ◽  
C. Duvivier ◽  
P. Jardin
Keyword(s):  
Upper Airway ◽  
Normal Subjects ◽  
Forced Oscillations ◽  
Respiratory Impedance ◽  
Respiratory Compliance ◽  
Airway Opening ◽  
Positive Frequency Dependence ◽  
Airway Walls ◽  
Extrathoracic Airway ◽  
Positive Frequency

Respiratory input impedance (Zrs) measured by forced oscillations needs to be corrected for the motion of extrathoracic airway walls. Two methods of obtaining the impedance of this shunt pathway [upper airway impedance (Zuaw)] were compared in six normal subjects. In the first, flow was measured at the airway opening during Valsalva maneuvers, as described by Michaelson et al. (10). In the second, motions of upper airway walls were directly assessed during respiratory impedance measurements by use of a head plethysmograph. Larger upper airway impedance values were found during Valsalva maneuvers, corresponding to a larger upper airway resistance (Ruaw) (at 20 Hz, Ruaw = 9.1 +/- 4.7 compared with 7.0 +/- 2.1 cmH2O X 1–1 X s with the second method) and inertance (Iuaw) (Iuaw = 0.053 +/- 0.036 vs. 0.025 +/- 0.008 cmH2O X 1–1 X s2, P less than 0.05) and a lower upper airway compliance (Cuaw) (Cuaw = 0.78 +/- 0.33 vs. 1.15 +/- 0.15 ml X cmH2O–1, P less than 0.05). Active contraction of facial muscles during Valsalva maneuvers may be responsible for this finding. As a consequence, respiratory impedance values are undercorrected when using the Valsalva method, leading in normal subjects to an overestimation of respiratory compliance by 30% and an underestimation of inertance by 16% (P less than 0.05) and promoting positive frequency dependence of respiratory resistance. Substantial errors may be avoided by using a head plethysmograph, which permits measuring Zrs and Zuaw simultaneously.

scholarly journals Lossy-Transmission-Line Analysis of Frequency Reconfigurable Rectangular-Ring Microstrip Antenna

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Bambang Setia Nugroho ◽  
Fitri Yuli Zulkifli ◽  
Eko Tjipto Rahardjo
Keyword(s):  
Transmission Line ◽  
Input Impedance ◽  
Microstrip Antenna ◽  
Reconfigurable Antenna ◽  
Resonant Frequencies ◽  
Rf Switches ◽  
Rectangular Patch ◽  
Full Wave ◽  
Lossy Transmission ◽  
Lossy Transmission Line

An analytical model for a frequency reconfigurable rectangular-ring microstrip antenna is proposed. The resonant frequencies and input impedance of the reconfigurable antenna are analyzed using a lossy-transmission-line (LTL) model. By making use of Y-admittance matrices, a formulation for the input impedance is analytically derived. The structure of the frequency reconfigurable antenna consists of a rectangular-ring shaped microstrip antenna which is loaded with a rectangular patch in the middle of the rectangular-ring antenna and fed by a microstrip line. RF switches are applied to connect the load to the antenna in order to reconfigure the operating frequencies. By modeling the antenna into a multiport equivalent circuit, the total input impedance is analytically derived to predict the resonant frequencies. To verify the analysis, the model input impedance and reflection coefficient calculation have been compared with the full-wave simulation and measurement results. The proposed model shows good agreement with full-wave simulated and measured results in the range of 1–3 GHz.

Input impedance and peripheral inhomogeneity of dog lungs

1992 ◽  
Vol 72 (1) ◽  
pp. 168-178 ◽  
Author(s):  
Z. Hantos ◽  
B. Daroczy ◽  
B. Suki ◽  
S. Nagy ◽  
J. J. Fredberg
Keyword(s):  
Input Impedance ◽  
Lung Model ◽  
Forced Oscillations ◽  
Lung Structure ◽  
Tracheal Pressure ◽  
Frequency Independent ◽  
Airway Opening ◽  
Slight Elevation ◽  
Experimental Findings ◽  
Control State

Tracheal pressure, central airflow, and alveolar capsule pressures in cardiac lobes were measured in open-chest dogs during 0.1- to 20-Hz pseudorandom forced oscillations applied at the airway opening. In the interval 0.1–4.15 Hz, the input impedance data were fitted by four-parameter models including frequency-independent airway resistance and inertance and tissue parts featuring a marked negative frequency dependence of resistance and a slight elevation of elastance with frequency. The models gave good fits both in the control state and during histamine infusion. At the same time, the regional transfer impedances (alveolar pressure-to-central airflow ratios) showed intralobar and interlobar variabilities of similar degrees, which increased with frequency and were exaggerated during histamine infusion. Results of simulation studies based on a lung model consisting of a central airway and a number of peripheral units with airway and tissue parameters that were given independent wide distributions were in agreement with the experimental findings and showed that even an extremely inhomogeneous lung structure can produce virtually homogeneous mechanical behavior at the input.

Influence of Bifurcations on Forced Oscillations in an Airway Model

1992 ◽  
Vol 114 (2) ◽  
pp. 216-221
Author(s):  
D. A. Bunk ◽  
W. J. Federspiel ◽  
A. C. Jackson
Keyword(s):  
Input Impedance ◽  
Forced Oscillations ◽  
Straight Tube ◽  
Axial Distance ◽  
Direct Role ◽  
Branch Segment ◽  
Airway Opening ◽  
Flow Impedance ◽  
The Individual ◽  
Individual Tube

Forced oscillations is a technique to determine respiratory input impedance from small amplitude sinusoidal pressure excursions introduced at the airway opening. Models used to predict respiratory input impedance typically ignore the direct effect of bifurcations on the flow, and treat airway branches as individual straight tubes placed appropriately in parallel and series. The flow within the individual tubes is assumed equivalent to that which would occur in infinitely long tubes. In this study we examined the influence of bifurcations on impedance for conditions of the forced oscillatory technique. We measured input impedance using forced oscillations in straight tubes and in an anatomically-relevant, four generation physical model of a human airway network. The input impedance measured experimentally compared well to that obtained theoretically using model predictions. The predictive scheme was based on appropriate parallel and series combinations of theoretically computed individual tube impedances, which were computed from solutions to oscillatory flow of a compressible gas in an infinitely long rigid tube. The agreement between experimental measurements and predictions indicates that bifurcations play a relatively minor direct role on the flow impedance for conditions of the forced oscillations technique. These results are explained in terms of the small tidal volumes used, whereby the axial distance traveled by a fluid particle during an oscillation cycle is appreciably smaller than branch segment lengths. Accordingly, only a small fraction of fluid particles travel through the bifurcation region, and the remainder experience an environment approaching flow in an infinite straight tube. The relevance of the study to the prediction of impedances in the human lung during forced oscillations is discussed.

Human respiratory input impedance from 4 to 200 Hz: physiological and modeling considerations

1988 ◽  
Vol 64 (2) ◽  
pp. 823-831 ◽  
Author(s):  
H. L. Dorkin ◽  
K. R. Lutchen ◽  
A. C. Jackson
Keyword(s):  
Input Impedance ◽  
Element Model ◽  
Forced Oscillations ◽  
Parameter Estimates ◽  
Tissue Resistance ◽  
Thoracic Gas Volume ◽  
Reliable Parameter ◽  
Quarter Wave ◽  
Lumped Element Model ◽  
Gas Volume

Recent studies on respiratory impedance (Zrs) have predicted that at frequencies greater than 64 Hz a second resonance will occur. Furthermore, if one intends to fit a model more complicated than the simple series combination of a resistance, inertance, and compliance to Zrs data, the only way to ensure statistically reliable parameter estimates is to include data surrounding this second resonance. An additional question, however, is whether the resulting parameters are physiologically meaningful. We obtained input impedance data from eight healthy adult humans using discrete frequency forced oscillations from 4 to 200 Hz. Three resonant frequencies were seen: 8 +/- 2, 151 +/- 10, and 182 +/- 16 Hz. A seven-parameter lumped element model provided an excellent fit to the data in all subjects. This model consists of an airway resistance (Raw), which is linearly dependent on frequency, and airway inertance separated from a tissue resistance, inertance, and compliance by a shunt compliance (Cg) thought to represent gas compressibility. Model estimates of Raw and Cg were compared with those suggested by measurement of Raw and thoracic gas volume using a plethysmograph. In all subjects the model Raw and Cg were significantly lower than and not correlated with the corresponding plethysmographic measurement. We hypothesize that the statistically reliable but physiologically inconsistent parameters are a consequence of the distorting influence of airway wall compliance and/or airway quarter-wave resonance. Such factors are not inherent to the seven-parameter model.

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