Inability to separate airway from tissue properties by use of human respiratory input impedance

1990 ◽  
Vol 68 (6) ◽  
pp. 2403-2412 ◽  
Author(s):  
K. R. Lutchen ◽  
C. A. Giurdanella ◽  
A. C. Jackson
Keyword(s):  
Input Impedance ◽  
Acoustic Resonance ◽  
Element Model ◽  
Tissue Properties ◽  
Rigid Tube ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
Alveolar Tissue ◽  
High Frequency Resonance ◽  
Gas Volume

Respiratory input impedance (Zrs) from 2.5 to 320 Hz displays a high-frequency resonance, the location of which depends on the density of the resident gas in the lungs (J. Appl. Physiol. 67: 2323-2330, 1989). A previously used six-element model has suggested that the resonance is due to alveolar gas compression (Cg) resonating with tissue inertance (Iti). However, the density dependence of the resonance indicates that is associated with the first airway acoustic resonance. The goal of this study was to determine whether unique properties for tissues and airways can be extracted from Zrs data by use of models that incorporate airway acoustic phenomena. We applied several models incorporating airway acoustics to the 2.5- to 320-Hz data from nine healthy adult humans during room air (RA) and 20% He-80% O2 (HeO2) breathing. A model consisting of a single open-ended rigid tube produced a resonance far sharper than that seen in the data. To dampen the resonance features, we used a model of multiple open-ended rigid tubes in parallel. This model fit the data very well for both RA and HeO2 but required fewer and longer tubes with HeO2. Another way to dampen the resonance was to use a single rigid tube terminated with an alveolar-tissue unit. This model also fit the data well, but the alveolar Cg estimates were far smaller than those expected based on the subject's thoracic gas volume. If Cg was fixed based on the thoracic gas volume, a large number of tubes were again required. These results along with additional simulations show that from input Zrs alone one cannot uniquely identify features indigenous to alveolar Cg or to the respiratory tissues.

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.

T model partition of lung and respiratory system impedances

1995 ◽  
Vol 78 (3) ◽  
pp. 938-947 ◽  
Author(s):  
M. Rotger ◽  
R. Farre ◽  
R. Peslin ◽  
D. Navajas
Keyword(s):  
Respiratory System ◽  
Frequency Range ◽  
Tissue Impedance ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
The Mean ◽  
Gas Volume ◽  
Mean Compliance ◽  
Gas Compressibility ◽  
Shunt Impedance

The aim of this work was to demonstrate that the three compartments of the lung T network and the chest wall impedance (Zcw) can be identified from input and transfer impedances of the respiratory system if the pleural pressure is recorded during the measurements. The method was tested in six healthy volunteers in the range of 8–32 Hz. The impedances resulting from the decomposition confirm the adequacy of the monoalveolar structure commonly used in healthy subjects. Indeed, the T shunt impedance is well modeled by a purely compliant element, the mean compliance [0.038 +/- 0.081 (SD) l/kPa], which coincides within 9.5 +/- 6.3% of the alveolar gas compressibility derived from thoracic gas volume (0.036 +/- 0.011 l/kPa). The results obtained provide experimental evidence that the alveolar gas compression is predominantly isothermal and that lung tissue impedance is negligible throughout the whole frequency range. The shape of Zcw is consistent with a low compliance-low inertance pathway in parallel with a high compliance-high inertance pathway. We conclude that the proposed method is able to reliably identify the T network featuring the lung and Zcw.

Partitioning of airway and respiratory tissue mechanical impedances by body plethysmography

1998 ◽  
Vol 84 (2) ◽  
pp. 553-561 ◽  
Author(s):  
R. Peslin ◽  
C. Duvivier
Keyword(s):  
Body Plethysmography ◽  
Tissue Resistance ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
Airway Opening ◽  
Elastic Loading ◽  
Gas Volume ◽  
The Relationship ◽  
Respiratory Tissue ◽  
Good Agreement

Peslin, R., and C. Duvivier. Partitioning of airway and respiratory tissue mechanical impedances by body plethysmography. J. Appl. Physiol. 84(2): 553–561, 1998.—We have tested the feasibility of separating the airway (Zaw) and tissue (Zti) components of total respiratory input impedance (Zrs,in) in healthy subjects by measuring alveolar gas compression by body plethysmography (Vpl) during pressure oscillations at the airway opening. The forced oscillation setup was placed inside a body plethysmograph, and the subjects rebreathedbtps gas. Zrs,in and the relationship between Vpl and airway flow (Hpl) were measured from 4 to 29 Hz. Zaw and Zti were computed from Zrs,in and Hpl by using the monoalveolar T-network model and alveolar gas compliance derived from thoracic gas volume. The data were in good agreement with previous observations: airway and tissue resistance exhibited some positive and negative frequency dependences, respectively; airway reactance was consistent with an inertance of 0.015 ± 0.003 hPa ⋅ s2 ⋅ l−1and tissue reactance with an elastance of 36 ± 8 hPa/l. The changes seen with varying lung volume, during elastic loading of the chest and during bronchoconstriction, were mostly in agreement with the expected effects. The data, as well as computer simulation, suggest that the partitioning is unaffected by mechanical inhomogeneity and only moderately affected by airway wall shunting.

Frequency dependence of plethysmographic measurement of thoracic gas volume

1984 ◽  
Vol 57 (6) ◽  
pp. 1865-1871 ◽  
Author(s):  
R. Brown ◽  
A. S. Slutsky
Keyword(s):  
Frequency Dependence ◽  
Normal Subjects ◽  
Lung Capacity ◽  
Airways Obstruction ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
Mouth Pressure ◽  
Extrathoracic Airway ◽  
Shunt Capacitor ◽  
Gas Volume

With airways obstruction, panting frequency affects plethysmographically determined thoracic gas volume (Vtg) because the extrathoracic airway acts as a shunt capacitor. Stanescu et al. (19) suggested that in the calculation of Vtg, use of esophageal (delta Pes) rather than mouth pressure (delta Pm) swings might eliminate the problem. We measured total lung capacity (TLC) plethysmographically in 10 subjects with chronic airways obstruction (CAO) and in four normal subjects. TLC (using delta Pm) was derived from Vtg obtained from slow-(approximately 1 Hz) and fast- (approximately 4 Hz) panting frequencies. In the normal subjects and four subjects with CAO, TLC was also obtained using delta Pes. In these subjects abdominal gas compression and decompression did not contribute significantly to the frequency dependence of TLC. In CAO, TLC was frequency dependent in direct proportion to the severity of obstruction. Although the frequency dependence was greater using delta Pm to calculate Vtg, it also occurred using delta Pes. Thus it could not be explained entirely by the shunt capacitor effect of the extrathoracic airways. The residual and significant overestimations of TLC (reflected by frequency dependency of TLC derived from Vtg calculated from delta Pes) may be explained by interregional nonhomogeneities during the panting maneuver.

Respiratory tissue properties derived from flow transfer function in healthy humans

1997 ◽  
Vol 82 (4) ◽  
pp. 1098-1106 ◽  
Author(s):  
W. Tomalak ◽  
R. Peslin ◽  
C. Duvivier
Keyword(s):  
Transfer Function ◽  
Upper Airway ◽  
Tissue Impedance ◽  
Tissue Properties ◽  
Healthy Humans ◽  
Volume Curve ◽  
Thoracic Gas Volume ◽  
Gas Volume ◽  
Flow Transfer ◽  
Respiratory Tissue

Tomalak, W., R. Peslin, and C. Duvivier. Respiratory tissue properties derived from flow transfer function in healthy humans. J. Appl. Physiol. 82(4): 1098–1106, 1997.—Assuming homogeneity of alveolar pressure, the relationship between airway flow and flow at the chest during forced oscillation at the airway opening [flow transfer function (FTF)] is related to lung and chest wall tissue impedance (Zti): FTF = 1 + Zti/Zg, where Zg is alveolar gas impedance, which is inversely proportional to thoracic gas volume. By using a flow-type body plethysmograph to obtain flow rate at body surface, FTF has been measured at oscillation frequencies ( f os) of 10, 20, 30 and 40 Hz in eight healthy subjects during both quiet and deep breathing. The data were corrected for the flow shunted through upper airway walls and analyzed in terms of tissue resistance (Rti) and effective elastance (Eti,eff) by using plethysmographically measured thoracic gas volume values. In most subjects, Rti was seen to decrease with increasing f os and Eti,eff to vary curvilinearly with f os 2, which is suggestive of mechanical inhomogeneity. Rti presented a weak volume dependence during breathing, variable in sign according to f os and among subjects. In contrast, Eti,eff usually exhibited a U-shaped pattern with a minimum located a little above or below functional residual capacity and a steep increase with decreasing or increasing volume (30–80 hPa/l2) on either side. These variations are in excess of those expected from the sigmoid shape of the static pressure-volume curve and may reflect the effect of respiratory muscle activity. We conclude that FTF measurement is an interesting tool to study Rti and Eti,eff and that these parameters have probably different physiological determinants.

Influence of panting frequency on plethysmographic measurements of thoracic gas volume

1982 ◽  
Vol 52 (3) ◽  
pp. 739-747 ◽  
Author(s):  
A. B. Bohadana ◽  
R. Peslin ◽  
B. Hannhart ◽  
D. Teculescu
Keyword(s):  
High Frequency ◽  
Healthy Subjects ◽  
Airflow Obstruction ◽  
Gastric Balloon ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
Mouth Pressure ◽  
Before And After ◽  
Flow Pressure ◽  
Gas Volume

Using an integrated flow pressure-corrected body plethysmograph we obtained total lung capacities (TLC) derived from thoracic gas volumes measured at low, medium, and high panting frequencies in 10 healthy men and in 13 patients with chronic airflow obstruction before and after an aerosol of albuterol. Using a gastric balloon we also assessed gastric-to-mouth pressure ratios (delta Pga/delta Pm). In patients before albuterol, estimated TLC remained unchanged from low to medium and increased (not significantly) from medium to high frequency. Healthy subjects and patients after albuterol showed a significant decrease in TLC from low to medium panting frequencies, which persisted after correcting the data for abdominal gas compression using observed delta Pga/delta Pm. In patients after albuterol the results may be explained, at least in part, by intrathoracic airway compliance and mechanical inhomogeneity of the lung. In healthy subjects a remote possibility is the association of mechanical inhomogeneity and nonuniform pleural pressure.

Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter

1997 ◽  
Vol 83 (5) ◽  
pp. 1517-1521 ◽  
Author(s):  
O. F. Pedersen ◽  
T. F. Pedersen ◽  
M. R. Miller
Keyword(s):  
Peak Expiratory Flow ◽  
Wave Speed ◽  
Vital Capacity ◽  
Added Resistance ◽  
Alveolar Pressure ◽  
Healthy Men ◽  
Gas Compression ◽  
Thoracic Gas Volume ◽  
Expiratory Flow ◽  
Gas Volume

Pedersen, O. F., T. F. Pedersen, and M. R. Miller. Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter. J. Appl. Physiol. 83(5): 1517–1521, 1997.—It has recently been shown (O. F. Pedersen T. R. Rasmussen, Ø. Omland, T. Sigsgaard, P. H. Quanjer, and M. R. Miller. Eur. Respir. J. 9: 828–833, 1996) that the added resistance of a mini-Wright peak flowmeter decreases peak expiratory flow (PEF) by ∼8% compared with PEF measured by a pneumotachograph. To explore the reason for this, 10 healthy men (mean age 43 yr, range 33–58 yr) were examined in a body plethysmograph with facilities to measure mouth flow vs. expired volume as well as the change in thoracic gas volume (Vb) and alveolar pressure (Pa). The subjects performed forced vital capacity maneuvers through orifices of different sizes and also a mini-Wright peak flowmeter. PEF with the meter and other added resistances were achieved when flow reached the perimeter of the flow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 ± 1.5 to 10.3 ± 1.4 (SD) l/s ( P < 0.001), Pa increased from 6.7 ± 1.9 to 9.3 ± 2.7 kPa ( P < 0.001), an increase equal to the pressure drop across the meter, and caused Vb at PEF to decrease by 0.24 ± 0.09 liter ( P < 0.001). We conclude that PEF obtained with an added resistance like a mini-Wright PEF meter is a wave-speed-determined maximal flow, but the added resistance causes gas compression because of increased Pa at PEF. Therefore, Vb at PEF and, accordingly, PEF decrease.

Impact of frequency range and input impedance on airway-tissue separation implied from transfer impedance

1993 ◽  
Vol 74 (3) ◽  
pp. 1089-1099 ◽  
Author(s):  
K. R. Lutchen ◽  
J. R. Everett ◽  
A. C. Jackson
Keyword(s):  
Prior Knowledge ◽  
Input Impedance ◽  
Upper Airway ◽  
Element Model ◽  
Frequency Range ◽  
Tissue Properties ◽  
Transfer Impedance ◽  
Tissue Separation ◽  
Enhanced Sensitivity ◽  
Tissue Resistance

In humans, application of the DuBois (DuBois et al. J. Appl. Physiol. 8: 587–594, 1956) six-element model to respiratory transfer impedance (Ztr) data has been proposed as a means to noninvasively estimate airway and tissue properties. This approach requires prior knowledge of alveolar gas compressibility (Cg). With input impedance (Zin), prior knowledge of Cg is not required, but the data do not support a reliable separation of airway from tissue properties. In this study, we investigated the separation of airway and tissue properties when Ztr and Zin data are measured and analyzed simultaneously over a larger frequency range than usual. In 10 healthy adults, we measured Ztr and Zin from 2 to 64 Hz. Zin was measured using both the standard approach with oscillations directly into the airway opening (Zst) and the head generator approach (Zhg) with oscillations applied around the head. With Ztr data alone, we found that the airway resistance and inertance estimates were reliable with only 2- to 32-Hz data and were unaffected by including the additional 32- to 64-Hz data. Conversely, the estimates of tissue resistance and inertance were highly unreliable unless the 32- to 64-Hz data are included. Because of enhanced sensitivity of Ztr to Cg from 32 to 64 Hz, inaccuracies in the assigned Cg will distort the estimated tissue but not airway properties. The Ztr-based parameters predicted Zhg data far better than Zst data, which is consistent with Zhg data being less influenced by upper airway shunting over this frequency range. There was no apparent advantage to combining Ztr and Zhg data during parameter estimation. With Cg unfixed, the estimated Cg was 50–100% higher than expected from an independent measurement of functional residual capacity. These results confirm that Ztr alone can provide a reliable distinction of lumped respiratory airway and tissue properties that are little influenced by upper airway wall shunting but only if 2- to 64-Hz data are analyzed. This distinction, however, requires an accurate prior measurement of Cg, and this requirement cannot be removed by combining Ztr and Zin data.

Density dependence of respiratory system impedances between 5 and 320 Hz in humans

1989 ◽  
Vol 67 (6) ◽  
pp. 2323-2330 ◽  
Author(s):  
A. C. Jackson ◽  
C. A. Giurdanella ◽  
H. L. Dorkin
Keyword(s):  
Respiratory System ◽  
Cylindrical Tube ◽  
Acoustic Resonance ◽  
Element Model ◽  
Acoustic Properties ◽  
Parameter Estimates ◽  
Resonant Frequencies ◽  
Tissue Properties ◽  
Tissue Compliance ◽  
Breathing Room

For respiratory system impedance (Zrs), the six-element model of DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956) suggests three resonant frequencies (f1,f2,f3), where f1 is the result of the sum of tissue and airway inertances and tissue compliance and f2 is the result of alveolar gas compression compliance (Cg) and tissue inertance (Iti). Three such resonant frequencies have been reported in humans. However, the parameter estimates resulting from fitting this model to the data suggested that f2 and f3 were not associated with Cg and Iti but with airway acoustic properties. In the present study, we measured Zrs between 5 and 320 Hz in 10 healthy adult humans breathing room air or 80% He-20% O2 (HeO2) to gain insight as to whether airway or tissue properties are responsible for the f2 and f3. When the subjects breathed room air, f2 occurred at 170 +/- 16 (SD) Hz, and when they breathed HeO2 it occurred at 240 +/- 24 Hz. If this resonance were due to Cg and Iti it should not have been affected to this extent by the breathing of HeO2. We thus conclude that f2 is not due to tissue elements but that it is an airway acoustic resonance. Furthermore, application of the six-element model to analyze Zrs data at these frequencies is inappropriate, and models incorporating the airway acoustic properties should be used. One such model is based on the concept of equivalent length, which is defined as the length of an open-ended, cylindrical tube that has the same fundamental acoustic resonant frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

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