Nonuniformity of canine lung washout by high-frequency ventilation

Ethane washout during low tidal volume (25–100 ml) high-frequency (3–40 Hz) ventilation (HFV) was studied in seven excised dog lungs. The lungs were initially equilibrated with 1% ethane, and then the concentration of ethane was monitored by mass spectrometry from multiple anatomic sites along the tracheobronchial tree during washout. We observed that the lung changed from a uniform distribution of ethane concentrations to a nonuniform distribution by a three-phase process. The first phase was nearly complete within the first 15 s and probably corresponds to concentration gradients being established in the central airways. During the second phase of washout, which lasted for several minutes, the concentrations in the various alveolar regions diverged. In the final phase, the regional concentrations remained at fixed ratios, and washout from all sites in the lung was at a constant fractional rate. These data are consistent with a model in which the duration of the second phase and the magnitude of the regional concentration differences established in this phase are dependent on both the magnitude of differences between regional transport paths and the nature of regional coupling by a common transport path to the airway opening.

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Airway pressures in an asymmetrically branched airway model of the dog respiratory system

Journal of Applied Physiology ◽

10.1152/jappl.1984.57.4.1222 ◽

1984 ◽

Vol 57 (4) ◽

pp. 1222-1230 ◽

Cited By ~ 8

Author(s):

Andrew C. Jackson ◽

Mehrdad Tabrizi ◽

Michael I. Kotlikoff ◽

Jon R. Voss

Keyword(s):

Respiratory System ◽

High Frequency ◽

High Frequency Ventilation ◽

Tissue Properties ◽

Pressure Distributions ◽

Lumped Parameter ◽

Airway Opening ◽

Frequency Ventilation ◽

Lung Periphery ◽

Airway Model

A computer model of the mechanical properties of the dog respiratory system based on the asymmetrically branching airway model of Horsfield et al. (11) is described. The peripheral ends of this airway model were terminated by a lumped-parameter impedance representing gas compression in the alveoli, and lung and chest wall tissue properties were derived from measurements made in this laboratory. Using this model we predicted the respiratory system impedance and the distribution of pressures along the airways in the dog lung. Predicted total respiratory system impedances for frequencies between 4 and 64 Hz at three lung volumes were found to compare quite closely to measured impedances in dogs. Serial pressure distributions were found to be frequency-dependent and to result in higher pressures in the lung periphery than at the airway opening at some frequencies. The implications of this fading for high-frequency ventilation are discussed. impedance; high-frequency ventilation; central airway resistance; respiratory system resistance; airway pressure distribution; distribution of ventilation Submitted on November 14, 1983 Accepted on May 8, 1984

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Alveolar pressure nonhomogeneity during small-amplitude high-frequency oscillation

Journal of Applied Physiology ◽

10.1152/jappl.1984.57.3.788 ◽

1984 ◽

Vol 57 (3) ◽

pp. 788-800 ◽

Cited By ~ 116

Author(s):

J. J. Fredberg ◽

D. H. Keefe ◽

G. M. Glass ◽

R. G. Castile ◽

I. D. Frantz

Keyword(s):

Resonant Frequency ◽

High Frequency ◽

Small Amplitude ◽

Regional Distribution ◽

High Frequency Oscillation ◽

High Frequency Ventilation ◽

Tissue Impedance ◽

Spatial Homogeneity ◽

Airway Opening ◽

Frequency Ventilation

In six excised canine lungs, regional alveolar pressures (PA) were measured during small-amplitude high-frequency oscillations applied at the airway opening. Both the regional distribution of PA's and their relationship to pressure excursions at the airway opening (Pao) were assessed in terms of amplitude and phase. PA was sampled in several capsules glued to the pleural surface and communicating with alveolar gas via pleural punctures. Pao and PA were measured over the frequency (f) range 1–60 Hz, at transpulmonary pressures (PL) of 5, 10, and 25 cmH2O. The amplitude of PA excursions substantially exceeded Pao excursions at frequencies near the resonant frequency. At resonance the ratio [PA/Pao] was 1.9, 2.9, and 4.8 at PL's of 5, 10, and 25 cmH2O, respectively. Both spatial homogeneity and temporal synchrony of PA's between sampled lung regions decreased with f and increased with PL. Interregional variability of airway impedance [(Pao - PA)/Vao] and tissue impedance (PA/Vao) tended to be larger than differences due to changing PL but not as large as between-dog variability. These data define the baseline nonhomogeneity of the normal canine lung and also suggest that there may be some advantage in applying high-frequency ventilation at frequencies at least as high as lung resonant frequency.

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Hemodynamic Response to High-Frequency Ventilation in Infants Following Cardiac Surgery

PEDIATRICS ◽

10.1542/peds.73.4.426 ◽

1984 ◽

Vol 73 (4) ◽

pp. 426-430

Author(s):

Robert N. Vincent ◽

Ann R. Stark ◽

Peter Lang ◽

Richard H. Close ◽

William I. Norwood ◽

...

Keyword(s):

Cardiac Surgery ◽

High Frequency ◽

Pulmonary Arterial Pressure ◽

Hemodynamic Response ◽

Conventional Ventilation ◽

High Frequency Ventilation ◽

Tracheal Pressure ◽

Airway Opening ◽

Frequency Ventilation ◽

Pulmonary Arterial

The hemodynamic response to high-frequency ventilation was compared with conventional ventilation in six infants following cardiac surgery. While undergoing high-frequency ventilation, adequate gas exchange was maintained in all infants. High frequency ventilation allowed a reduction of peak ventilatory pressure at the airway opening by 19%, and peak tracheal pressure by 42%. No clinically important changes in heart rate, systemic and pulmonary arterial pressure, cardiac index, or systemic and pulmonary vascular resistance were noted when high-frequency ventilation was compared with conventional ventilation.

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High-frequency ventilation of ducks and geese

Journal of Applied Physiology ◽

10.1152/jappl.1987.63.1.413 ◽

1987 ◽

Vol 63 (1) ◽

pp. 413-417 ◽

Cited By ~ 6

Author(s):

R. H. Hastings ◽

F. L. Powell

Keyword(s):

Gas Exchange ◽

High Frequency ◽

Minute Ventilation ◽

Control Ventilation ◽

High Frequency Ventilation ◽

Opening Pressure ◽

Arterial Pco2 ◽

Bias Flow ◽

Airway Opening ◽

Frequency Ventilation

We studied gas exchange in anesthetized ducks and geese artificially ventilated at normal tidal volumes (VT) and respiratory frequencies (fR) with a Harvard respirator (control ventilation, CV) or at low VT-high fR using an oscillating pump across a bias flow with mean airway opening pressure regulated at 0 cmH2O (high-frequency ventilation, HFV). VT was normalized to anatomic plus instrument dead space (VT/VD) for analysis. Arterial PCO2 was maintained at or below CV levels by HFV with VT/VD less than 0.5 and fR = 9 and 12 s-1 but not at fR = 6 s-1. For 0.4 less than or equal to VT/VD less than or equal to 0.85 and 3 s-1. less than or equal to fR less than or equal to 12 s-1, increased VT/VD was twice as effective as increased fR at decreasing arterial PCO2, consistent with oscillatory dispersion in a branching network being an important gas transport mechanism in birds on HFV. Ventilation of proximal exchange units with fresh gas due to laminar flow is not the necessary mechanism supporting gas exchange in HFV, since exchange could be maintained with VT/VD less than 0.5. Interclavicular and posterior thoracic air sac ventilation measured by helium washout did not change as much as expired minute ventilation during HFV. PCO2 was equal in both air sacs during HFV. These results could be explained by alterations in aerodynamic valving and flow patterns with HFV. Ventilation-perfusion distributions measured by the multiple inert gas elimination technique show increased inhomogeneity with HFV. Elimination of soluble gases was also enhanced in HFV as reported for mammals.(ABSTRACT TRUNCATED AT 250 WORDS)

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Augmented diffusion in the airways can support pulmonary gas exchange

Journal of Applied Physiology ◽

10.1152/jappl.1980.49.2.232 ◽

1980 ◽

Vol 49 (2) ◽

pp. 232-238 ◽

Cited By ~ 119

Author(s):

J. J. Fredberg

Keyword(s):

Gas Exchange ◽

Tidal Volume ◽

High Frequency ◽

Molecular Diffusion ◽

Minute Ventilation ◽

Turbulent Dispersion ◽

High Frequency Ventilation ◽

Ventilation Efficiency ◽

Airway Opening ◽

Frequency Ventilation

Bohn et al. (J Appl. Physiol.: Respirat. Environ. Exercise Physiol, 48: 710-716, 1980) reported that paralyzed beagle dogs maintained normal gas exchange for 6 h or more when small tidal volumes at high breathing rates were maintained at the airway opening (15 ml tidal volume at 15 breaths/s). These tidal volumes were 25% of dead space and thereby were too small to permit convective gas exchange with pulmonary air spaces. I have used a semiempirical analysis to show that augmented diffusion in the central airways, akin to Taylor's turbulent dispersion (Proc. R. Soc. Ser. A 223: 446-468, 1954) combined with molecular diffusion in the periphery of the lung, can account for most if not all of the observed gas transport during small tidal volume, high-frequency ventilation. Ventilation efficiency (alveolar ventilation/minute ventilation) is approximately 2-5% and is insensitive to the combination of frequency and tidal volume giving rise to the minute ventilation.

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