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  • American Physiological Society  (14)
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  • American Physiological Society  (14)
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  • 1
    Online Resource
    Online Resource
    Dynamic elastance and tissue resistance of isolated liquid-filled rat lungs
    American Physiological Society ; 1995
    In:  Journal of Applied Physiology Vol. 79, No. 5 ( 1995-11-01), p. 1595-1600
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 79, No. 5 ( 1995-11-01), p. 1595-1600
    Abstract: The effect of the surface forces of the alveolar air-liquid interface on the dynamic behavior of lung tissue was investigated in five isolated liquid-filled rat lungs. The lungs were subjected to 0.04-Hz sinusoidal oscillation (1.5-ml tidal volume) at lung volume (VL) levels ranging from volume at zero pressure (V0) + 4 ml to V0 + 10 ml. Oscillations were performed at each VL after inflation of the lungs from V0. Alveolar pressure (PA) was measured with an alveolar capsule attached to the visceral pleura. Dynamic elastance (Edyn), tissue resistance (Rti), and hysteresivity [eta = Rti omega/Edyn, where omega is angular frequency (2 pi x frequency)] were computed from PA and VL changes. Edyn was 59.6 +/- 4.3 Pa/ml at V0 + 4 ml and varied little up to V0 + 7 ml. Thereafter, Edyn increased markedly with VL, reaching 102 +/- 16 Pa/ml at V0 + 10 ml. No significant difference was found between elastance computed from PA and that computed from pressure recorded at the airway opening. Rti was 35.2 +/- 3.6 Pa.s.ml-1 and exhibited a VL dependence similar to that of Edyn. As a result, eta was 0.16 and did not vary significantly in the explored VL range. We conclude that PA can be reliably measured in the liquid-filled lung by means of alveolar capsules. In the liquid-filled lung, Edyn was smaller than and eta was similar to values reported for air-filled lungs. Hence, surface tension accounts for a considerable part of elastance and Rti of the air-filled lung within the volume range of normal breathing.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1995.79.5.1595
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1995
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 2
    Online Resource
    Online Resource
    Effect of body posture on respiratory impedance
    American Physiological Society ; 1988
    In:  Journal of Applied Physiology Vol. 64, No. 1 ( 1988-01-01), p. 194-199
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 64, No. 1 ( 1988-01-01), p. 194-199
    Abstract: The effects of posture on the mechanics of the respiratory system are not well known, particularly in terms of total respiratory resistance. We have measured respiratory impedance (Zrs) by the forced random noise excitation technique in the sitting and the supine position in 24 healthy subjects. Spirometry and lung volumes (He-dilution technique) were also measured in both postures. The equivalent resistance (Rrs), compliance (Crs), and inertance (Irs) were also calculated by fitting each measured Zrs to a linear series model. When subjects changed from sitting to the supine position, the real part of Zrs increased over the whole frequency band. The associated equivalent resistance, Rrs, increased by 28.2%. The reactance decreased for frequencies lower than 18 Hz and increased for higher frequencies. Consequently, Crs decreased by 38.7% and Irs increased by 15.6%. All of these parameter differences were significant (P less than 0.001). A covariance analysis showed that a significant amount of the postural change in Rrs and Crs can be explained by the reduction of functional residual capacity (FRC). This indicates that the observed differences on Zrs can in part be explained be a shift of the operating point of the respiratory system induced by the decrease in the FRC.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1988.64.1.194
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1988
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Confidence intervals of respiratory mechanical properties derived from transfer impedance
    American Physiological Society ; 1991
    In:  Journal of Applied Physiology Vol. 70, No. 6 ( 1991-06-01), p. 2432-2438
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 70, No. 6 ( 1991-06-01), p. 2432-2438
    Abstract: Short-term intraindividual variability of the parameters derived from respiratory transfer impedance (Ztr) measured from 4 to 32 Hz was studied in 10 healthy subjects. The corresponding 95% confidence intervals (CIo) were compared with those computed from a single set of data (CIL) according to Lutchen and Jackson (J. Appl. Physiol. 62: 403-413, 1987). Ztr was analyzed with the six-coefficient model of DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956), which includes airway resistance (Raw) and inertance (Iaw), tissue resistance (Rti), inertance (Iti), and compliance (Cti), and alveolar gas compressibility (Cg). The lowest variability was seen for Iaw (CIo = 11.1%), closely followed by Raw (14.3%) and Cti (14.8%), and the largest for Rti and Iti (24.6 and 93.6%, respectively). Using a simpler model, where Iti was excluded, significantly decreased the variability of Iaw (P less than 0.01) and Rti (P less than 0.05) but was responsible for a systematic decrease of Raw and Iaw and increase of Rti. Except for Raw with both models and Iaw with the simpler model, CIL was greater than CIo. Whatever the model, a high correlation between both sets of confidence intervals was found for Rti and Iaw, whereas no correlation was seen for Raw. This suggests that the variability of the former coefficients mainly reflects experimental noise, whereas that of the latter is largely due to biological variability.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1991.70.6.2432
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1991
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 4
    Online Resource
    Online Resource
    Respiratory input impedance in anesthetized paralyzed patients
    American Physiological Society ; 1990
    In:  Journal of Applied Physiology Vol. 69, No. 4 ( 1990-10-01), p. 1372-1379
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 69, No. 4 ( 1990-10-01), p. 1372-1379
    Abstract: Respiratory impedance (Zrs) was measured between 0.25 and 32 Hz in seven anesthetized and paralyzed patients by applying forced oscillation of low amplitude at the inlet of the endotracheal tube. Effective respiratory resistance (Rrs; in cmH2O.l-1.s) fell sharply from 6.2 +/- 2.1 (SD) at 0.25 Hz to 2.3 +/- 0.6 at 2 Hz. From then on, Rrs decreased slightly with frequency down to 1.5 +/- 0.5 at 32 Hz. Respiratory reactance (Xrs; in cmH2O.l-1.s) was -22.2 +/- 5.9 at 0.25 Hz and reached zero at approximately 14 Hz and 2.3 +/- 0.8 at 32 Hz. Effective respiratory elastance (Ers = -2pi x frequency x Xrs; in cmH2O/1) was 34.8 +/- 9.2 at 0.25 Hz and increased markedly with frequency up to 44.2 +/- 8.6 at 2 Hz. We interpreted Zrs data in terms of a T network mechanical model. We represented the proximal branch by central airway resistance and inertance. The shunt pathway accounted for bronchial distensibility and alveolar gas compressibility. The distal branch included a Newtonian resistance component for tissues and peripheral airways and a viscoelastic component for tissues. When the viscoelastic component was represented by a Kelvin body as in the model of Bates et al. (J. Appl. Physiol. 61: 873-880, 1986), a good fit was obtained over the entire frequency range, and reasonable values of parameters were estimated. The strong frequency dependence of Rrs and Ers observed below 2 Hz in our anesthetized paralyzed patients could be mainly interpreted in terms of tissue viscoelasticity. Nevertheless, the high Ers we found with low volume excursions suggests that tissues also exhibit plasticlike properties.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1990.69.4.1372
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1990
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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    Online Resource
  • 5
    Online Resource
    Online Resource
    Airways impedance during single breaths of foreign gases
    American Physiological Society ; 1991
    In:  Journal of Applied Physiology Vol. 71, No. 5 ( 1991-11-01), p. 1813-1821
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 71, No. 5 ( 1991-11-01), p. 1813-1821
    Abstract: The changes in airways resistance (Raw) and inertance (Iaw) during single inspirations of pure methane, helium, neon, and ethane at a flow of 0.1 l/s were measured in six healthy subjects by use of a forced-oscillation technique. Raw and Iaw were computed from respiratory transfer impedance obtained at a frequency of 20 Hz by applying pressure oscillations at the chest and measuring flow at the mouth with a bag-in-box system. Compared with the air data, the changes of Iaw after inhalation of 500 ml of gas averaged -41.1% with methane, -82.8% with helium, -25.8% with neon, and +4.8% with ethane. These changes were slightly less than the changes in gas density (-45%, -86%, -31%, and +5%, respectively). The inhaled volumes at which 50% of the changes had occurred (V50) did not differ significantly among gases and were approximately 100 ml. For Raw the data were more noisy than for Iaw; they were discarded in two subjects because of a strong and irreproducible volume dependence in air. Consistent differences were seen between the remaining subjects, one of whom exhibited a predominant viscosity dependence of Raw, one a predominant density dependence, and two an intermediate pattern. V50s were larger for Raw than for Iaw, indicating a more peripheral distribution of Raw. For Raw, V50s were lower with helium than with methane, in agreement with the notion that density-dependent resistance is located mainly in the large airways. The results suggest that some information on the serial distribution of Raw and Iaw may be derived from impedance measurements with foreign gases.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1991.71.5.1813
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1991
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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    Online Resource
  • 6
    Online Resource
    Online Resource
    Density dependence of respiratory input and transfer impedances in humans
    American Physiological Society ; 1988
    In:  Journal of Applied Physiology Vol. 65, No. 2 ( 1988-08-01), p. 928-933
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 65, No. 2 ( 1988-08-01), p. 928-933
    Abstract: Total respiratory input (Zin) and transfer (Ztr) impedances were obtained from 4 to 30 Hz in 10 healthy subjects breathing air and He-O2. Zin was measured by applying pressure oscillations around the head to minimize the upper airway shunt and Ztr by applying pressure oscillations around the chest. Ztr was analyzed with a six-coefficient model featuring airways resistance (Raw) and inertance (Iaw), alveolar gas compressibility, and tissue resistance, inertance, and compliance. Breathing He-O2 significantly decreased Raw (1.35 +/- 0.32 vs. 1.74 +/- 0.49 cmH2O.l-1.s in air, P less than 0.01) and Iaw (0.59 +/- 0.33 vs. 1.90 +/- 0.44 x 10(-2) cmH2O.l-1.s2), but, as expected, it did not change the tissue coefficients significantly. Airways impedance was also separately computed by combining Zin and Ztr data. This approach demonstrated similar variations in Raw and Iaw with the lighter gas mixture. With both analyses, however, the changes in Iaw were more than what was expected from the change in density. This indicates that factors other than gas inertance are included in Iaw and reveals the short-comings of the six-coefficient model to interpret impedance data.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1988.65.2.928
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1988
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
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  • 7
    Online Resource
    Online Resource
    Respiratory input impedance up to 256 Hz in healthy humans breathing foreign gases
    American Physiological Society ; 1993
    In:  Journal of Applied Physiology Vol. 75, No. 1 ( 1993-07-01), p. 307-320
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 75, No. 1 ( 1993-07-01), p. 307-320
    Abstract: Currently available data concerning respiratory input impedance (Zrs) at frequencies up to 300 Hz indicate that Zrs is determined mainly by the airways and, in particular, the gas compressibility in the airways and the airway wall compliance. Hence, measurements of Zrs when breathing gases with different physical properties would be useful in investigating airway mechanics and the role of acoustic propagation. Zrs measured with a standard generator (Zst) and corrected for the upper airway shunt (Zrs*) were measured in nine healthy subjects breathing air or a gas mixture consisting of 20% O2 and 80% He or SF6. The frequency band was extended up to 256 Hz for air and He-O2 and up to 128 Hz for SF6-O2. Zrs exhibited a similar pattern for the three gases, with a shift toward low frequencies as the gas density increased. Moreover, the resonance peaks tended to be narrower and higher as the gas density increased. The second frequency of resonance for He-O2, air, and SF6-O2 were 220, 180, and 50 Hz, respectively, for Zrs* and were systematically higher for Zst. Zrs* and Zst data were interpreted in terms of a tricompartmental model that partitioned the airways into two segments: a central one featuring the acoustic propagation in the airways and a peripheral one that included bronchial wall elasticity (Farre et al. J. Appl. Physiol. 67: 1973–1981, 1989). The model was able to interpret the gas dependence of Zrs* but not that of Zst. The influence of the gas physical properties on both Zrs* and Zst confirms that total Zrs at high frequencies is basically that of the airways and that the second resonance is related mainly to the gas compressibility in the airways.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1993.75.1.307
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1993
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
    Location Call Number Limitation Availability
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    Online Resource
  • 8
    Online Resource
    Online Resource
    Optimized estimation of respiratory impedance by signal averaging in the time domain
    American Physiological Society ; 1992
    In:  Journal of Applied Physiology Vol. 73, No. 3 ( 1992-09-01), p. 1181-1189
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 73, No. 3 ( 1992-09-01), p. 1181-1189
    Abstract: The spontaneous breathing of a subject during measurements of respiratory impedance (Zrs) by the forced oscillation technique (FOT) induces errors that result in biased impedance estimates, especially at low frequencies. Although in standard measurements this bias may be avoided by using special impedance estimators, there are two applications of FOT for which such estimators are not useful: when a head generator is used and when measurements are made during intubation. In this paper we describe a data-processing procedure for unbiased impedance estimation for all FOT setups. The proposed estimator (Z) was devised for pseudorandom excitation and is based on time-domain signal averaging before frequency analysis. The performance of estimator Z was first analyzed by computer simulation of a head generator setup and a setup including an endotracheal tube to measure (2–32 Hz) a resistance-inertance-elastance model mimicking Zrs of a healthy subject. Second, Z was assessed during real measurements in 16 healthy subjects. The results obtained in the simulation (e.g., error in elastance was reduced from 15.6% with most conventional estimators to 3.3% with Z in simulation of head generator setup) and in the measurements in subjects (differences of less than 1.6% between Z and a reference) confirmed the theoretical lack of bias of Z and its practical suitability for the different FOT setups. In addition to its applicability in the situations in which no other unbiased estimators are available, estimator Z is also advantageous in most conventional applications of FOT, since it requires much less computing time and thus allows on-line Zrs measurements.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1992.73.3.1181
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1992
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
    Location Call Number Limitation Availability
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    Online Resource
  • 9
    Online Resource
    Online Resource
    Assessment of respiratory pressure-volume nonlinearity in rabbits during mechanical ventilation
    American Physiological Society ; 1996
    In:  Journal of Applied Physiology Vol. 80, No. 5 ( 1996-05-01), p. 1637-1648
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 80, No. 5 ( 1996-05-01), p. 1637-1648
    Abstract: The volume dependence of respiratory elastance makes it difficult to recognize actual changes in lung and chest wall elastic properties in artificially ventilated subjects. We have assessed in six anesthetized, tracheotomized, and paralyzed rabbits whether reliable information on the static pressure-volume (PV) curve could be obtained from recordings performed during step variations of the end-expiratory pressure without interrupting mechanical ventilation. Pressure and flow data recorded during 5- and 10-hPa positive-pressure steps were analyzed in the time domain with a nonlinear model featuring a sigmoid PV curve and with a model that, in addition, accounted for tissue viscoelastic properties. The latter fitted the data substantially better. Both models provided reasonably reproducible coefficients, but the PV curves obtained from the 5- and 10-hPa steps were systematically different. When the PV curves were used to predict respiratory effective elastance, the best predictor was the curve derived from the 10-hPa step with the viscoelastic model: unsigned differences averaged 8.6 +/- 11.1, 26.9 +/- 36.4, and 5.5 +/- 5.8% at end-expiratory pressures of 0, 5, and 10 hPa, respectively. This approach provides potentially useful, although not highly accurate, estimates of respiratory effective elastance-volume dependence.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1996.80.5.1637
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1996
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
    Location Call Number Limitation Availability
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    Online Resource
  • 10
    Online Resource
    Online Resource
    Effect of expiratory flow limitation on respiratory mechanical impedance: a model study
    American Physiological Society ; 1996
    In:  Journal of Applied Physiology Vol. 81, No. 6 ( 1996-12-01), p. 2399-2406
    Details
    In: Journal of Applied Physiology, American Physiological Society, Vol. 81, No. 6 ( 1996-12-01), p. 2399-2406
    Abstract: Peslin, R., R. Farré, M. Rotger, and D. Navajas.Effect of expiratory flow limitation on respiratory mechanical impedance: a model study. J. Appl. Physiol. 81(6): 2399–2406, 1996.—Large phasic variations of respiratory mechanical impedance (Zrs) have been observed during induced expiratory flow limitation (EFL) (M. Vassiliou, R. Peslin, C. Saunier, and C. Duvivier. Eur. Respir. J. 9: 779–786, 1996). To clarify the meaning of Zrs during EFL, we have measured from 5 to 30 Hz the input impedance (Zin) of mechanical analogues of the respiratory system, including flow-limiting elements (FLE) made of easily collapsible rubber tubing. The pressures upstream (Pus) and downstream (Pds) from the FLE were controlled and systematically varied. Maximal flow (V˙max) increased linearly with Pus, was close to the value predicted from wave-speed theory, and was obtained for Pus-Pds of 4–6 hPa. The real part of Zin started increasing abruptly with flow (V˙) 〉 85%V˙max and either further increased or suddenly decreased in the vicinity of V˙max. The imaginary part of Zin decreased markedly and suddenly above 95%V˙max. Similar variations of Zin during EFL were seen with an analogue that mimicked the changes of airway transmural pressure during breathing. After pressure andV˙ measurements upstream and downstream from the FLE were combined, the latter was analyzed in terms of a serial (Zs) and a shunt (Zp) compartment. Zs was consistent with a large resistance and inertance, and Zp with a mainly elastic element having an elastance close to that of the tube walls. We conclude that Zrs data during EFL mainly reflect the properties of the FLE.
    Type of Medium: Online Resource
    ISSN: 8750-7587 , 1522-1601
    URL: Article
    DOI: 10.1152/jappl.1996.81.6.2399
    RVK:
    WA 15000
    RVK:
    XA 52094
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1996
    detail.hit.zdb_id: 1404365-8
    SSG: 12
    SSG: 31
    Location Call Number Limitation Availability
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    Online Resource
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