TIDAL VOLUME DEAD-SPACE RELATIONSHIP DURING HIGH-FREQUENCY VENTILATION

Tidal volumes used in high-frequency ventilation (HFV) may be smaller than anatomic dead space, but since gas exchange does take place, physiological dead space (VD) must be smaller than tidal volume (VT). We quantified changes in VD in three dogs at constant alveolar ventilation using the Bohr equation as VT was varied from 3 to 15 ml/kg and frequency (f) from 0.2 to 8 Hz, ranges that include normal as well as HFV. We found that VD was relatively constant at tidal volumes associated with normal ventilation (7–15 ml/kg) but fell sharply as VT was reduced further to tidal volumes associated with HFV (less than 7 ml/kg). The frequency required to maintain constant alveolar ventilation increased slowly as tidal volume was decreased from 15 to 7 ml/kg but rose sharply with attendant rapid increases in minute ventilation as tidal volumes were decreased to less than 7 ml/kg. At tidal volumes less than 7 ml/kg, the data deviated substantially from the conventional alveolar ventilation equation [f(VT - VD) = constant] but fit well a model derived previously for HFV. This model predicts that gas exchange with volumes smaller than dead space should vary approximately as the product of f and VT2.

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Gas exchange during high-frequency ventilation of the chicken

Journal of Applied Physiology ◽

10.1152/jappl.1982.53.6.1418 ◽

1982 ◽

Vol 53 (6) ◽

pp. 1418-1422 ◽

Cited By ~ 9

Author(s):

R. B. Banzett ◽

J. L. Lehr

Keyword(s):

Gas Exchange ◽

Tidal Volume ◽

Dead Space ◽

High Frequency ◽

Conventional Mechanical Ventilation ◽

High Frequency Ventilation ◽

Tracheal Cannula ◽

Bias Flow ◽

Frequency Ventilation ◽

Co2 Elimination

Recent studies have shown that high-frequency ventilation (HFV) at 1–30 Hz is capable of maintaining adequate gas exchange in humans and dogs even when tidal volumes are substantially less than dead space. We evaluated the effectiveness of HFV in roosters by comparing CO2 elimination during various frequencies and tidal volumes of HFV with CO2 elimination during conventional mechanical ventilation. Sinusoidal oscillations were applied at the tracheal cannula. A bias flow provided fresh gas at the top of the tracheal cannula. Three conclusions emerge from the data. 1) HFV enhances gas transport in the chicken as it does in mammals. 2) At low oscillatory flows (amplitude X frequency) CO2 elimination depends on both frequency and tidal volume, whereas at higher flows CO2 elimination depends more strongly on tidal volume. The flow at which this transition occurs is relatively lower than in humans and much lower than in dogs. 3) HFV at volumes below dead space is usually not capable of maintaining adequate gas exchange in the chicken in contrast to results in dogs and humans.

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Gas transport during high-frequency ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1983.55.2.472 ◽

1983 ◽

Vol 55 (2) ◽

pp. 472-478 ◽

Cited By ~ 15

Author(s):

V. Brusasco ◽

T. J. Knopp ◽

K. Rehder

Keyword(s):

Stroke Volume ◽

Dead Space ◽

High Frequency ◽

Oscillation Frequency ◽

High Frequency Ventilation ◽

Dead Space Volume ◽

Entire Lung ◽

Frequency Ventilation ◽

Gas Volume ◽

Space Volume

During high-frequency small-volume ventilation (HFV), the transport rate of gas from the mouth to a lung region is a function of two conductances (conductance is the transfer rate of a gas divided by its partial pressure difference): regional longitudinal gas conductance along the airways (Grlongi) and gas conductance between lung regions (Ginter). Grlongi per unit regional lung (gas) volume [Grlongi/(Vr beta g)] was determined during HFV in 11 anesthetized paralyzed dogs lying supine. The distribution of Grlongi/(Vr beta g) was nearly uniform during HFV when stroke volumes were less than approximately two-thirds of the Fowler dead-space volume. By contrast, the distribution of Grlongi/(Vr beta g) was nonuniform when the stroke volume exceeded approximately two-thirds of the Fowler dead-space volume and the oscillation frequency was 5 Hz. Gas conductance along the airways per unit lung gas volume [average Glongi/(V beta g)], for the entire lung, increased with stroke volume at all frequencies, but for a given product of oscillation frequency and stroke volume, the average Glongi/(V beta g) was greater when stroke volume was large and oscillation frequency was low. The average Glongi/(V beta g) increased with frequency up to a maximal value; the frequency at which the maximum occurred depended on the kinematic viscosity of the inspired gas mixture.

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Tidal Volume and Frequency Dependence of Carbon Dioxide Elimination by High-Frequency Ventilation

Survey of Anesthesiology ◽

10.1097/00132586-198210000-00024 ◽

1982 ◽

Vol 26 (5) ◽

pp. 277-278

Author(s):

T. H. ROSSING ◽

A. S. SLUTSKY ◽

J. L. LEHR ◽

P. A. DRINKER ◽

R. KAMM ◽

...

Keyword(s):

Carbon Dioxide ◽

Tidal Volume ◽

Frequency Dependence ◽

High Frequency ◽

High Frequency Ventilation ◽

Carbon Dioxide Elimination ◽

Frequency Ventilation

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1826 TRANSTHORACIC IMPEDANCE AS A METHOD OF MEASURING TIDAL VOLUME DURING HIGH FREQUENCY VENTILATION

Pediatric Research ◽

10.1203/00006450-198504000-01844 ◽

1985 ◽

Vol 19 (4) ◽

pp. 415A-415A

Author(s):

Kenneth L Sandberg ◽

Elizabeth P Krueger ◽

Daniel P Lindstrom ◽

Hakan Sundell ◽

Robert B Cotton

Keyword(s):

Tidal Volume ◽

High Frequency ◽

High Frequency Ventilation ◽

Transthoracic Impedance ◽

Frequency Ventilation

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Moderately high frequency ventilation with a conventional ventilator allows reduction of tidal volume without increasing mean airway pressure

Intensive Care Medicine Experimental ◽

10.1186/2197-425x-2-13 ◽

2014 ◽

Vol 2 (1) ◽

Cited By ~ 2

Author(s):

Ricardo Luiz Cordioli ◽

Marcelo Park ◽

Eduardo Leite Vieira Costa ◽

Susimeire Gomes ◽

Laurent Brochard ◽

...

Keyword(s):

Tidal Volume ◽

High Frequency ◽

Airway Pressure ◽

High Frequency Ventilation ◽

Mean Airway Pressure ◽

Frequency Ventilation

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Effects of respiratory variables on regional gas transport during high-frequency ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1988.64.5.2108 ◽

1988 ◽

Vol 64 (5) ◽

pp. 2108-2118 ◽

Cited By ~ 20

Author(s):

J. G. Venegas ◽

Y. Yamada ◽

J. Custer ◽

C. A. Hales

Keyword(s):

Tidal Volume ◽

High Frequency ◽

Transport Mechanism ◽

Gas Transport ◽

Substantial Effect ◽

High Frequency Ventilation ◽

Regional Effects ◽

Functional Images ◽

Tracer Isotope ◽

Frequency Ventilation

The regional effects of tidal volume (VT), respiratory frequency, and expiratory-to-inspiratory time ratio (TE/TI) during high-frequency ventilation (HFV) were studied in anesthetized and paralyzed dogs. Regional ventilation per unit of lung volume (spVr) was assessed with a positron camera during the washout of the tracer isotope 13NN from the lungs of 12 supine dogs. From the washout data, functional images of the mean residence time (MRT) of 13NN were produced and spVr was estimated as the inverse of the regional MRT. We found that at a constant VT X f product (where f represents frequency), increasing VT resulted in higher overall lung spV through the local enhancement of the basal spVr and with little effect in the apical spVr. In contrast, increasing VT X f at constant VT increased overall ventilation without significantly affecting the distribution of spVr values. TE/TI had no substantial effect in regional spVr distribution. These findings suggest that the dependency of gas transport during HFV of the form VT2 X f is the result of a progressive regional transition in gas transport mechanism. It appears, therefore, that as VT increases, the gas transport mechanism changes from a relative inefficient dispersive mechanism, dependent on VT X f, to the more efficient mechanism of direct fresh gas convection to alveoli with high regional tidal volume-to-dead-space ratio. A mathematical model of gas transport in a nonhomogeneous lung that exhibits such behavior is presented.

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