Alveolar ventilation during high-frequency oscillation: core dead space concept

1984 ◽  
Vol 56 (3) ◽  
pp. 700-707 ◽  
Author(s):  
D. Isabey ◽  
A. Harf ◽  
H. K. Chang
Keyword(s):  
Tidal Volume ◽  
Dead Space ◽  
High Frequency ◽  
Alveolar Ventilation ◽  
High Frequency Oscillation ◽  
High Frequency Ventilation ◽  
Frequency Oscillation ◽  
Simple Physical Model ◽  
Small Tube ◽  
The Dead

To assess the role of direct alveolar ventilation during high-frequency ventilation, we studied convective gas mixing during high-frequency oscillation with tidal volumes close to the dead space volume in a simple physical model. A main conduit representing a large airway was connected with a rigid sphere (V = 77, 517, and 1,719 cm3) by a small circular tube (d = 0.3 and 0.5 cm; L = 5, 10, and 20 cm). The efficiency of sinusoidal oscillations (f = 5, 20, and 40 Hz) applied at one end of the main conduit was assessed from the washout of a CO2 mixture from the sphere; to flush CO2 from the main fluid line, a constant flow of air was used. The decay in CO2 concentration measured in the sphere was exponential and therefore characterized by a measured time constant (tau m). Taking the small tube volume as the ventilatory dead space (VD), an effective tidal volume (VT*) was computed from tau m and compared with the tidal volume (VT) obtained separately from the pressure variation in the sphere. The discrepancy between these two tidal volumes has been found to be uniquely dependent on the ratio VT/VD within the range of VT/VD studied (0.5–2.2). For VT/VD less than 1.2, VT* was larger than VT, indicating that the conventional concept of alveolar ventilation does not apply. From the partition of the oscillatory flow in the small tube into two regions, the core and the unsteady boundary layer, we theoretically computed the proportions of the sinusoidal flow (or tidal volume) and the dead space for each region.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological dead space during high-frequency ventilation in dogs

1984 ◽  
Vol 57 (3) ◽  
pp. 881-887 ◽  
Author(s):  
G. G. Weinmann ◽  
W. Mitzner ◽  
S. Permutt
Keyword(s):  
Gas Exchange ◽  
Tidal Volume ◽  
Dead Space ◽  
High Frequency ◽  
Minute Ventilation ◽  
Alveolar Ventilation ◽  
High Frequency Ventilation ◽  
Physiological Dead Space ◽  
Frequency Ventilation ◽  
Normal 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.

High-frequency ventilation in dogs with three gases of different densities

1991 ◽  
Vol 70 (5) ◽  
pp. 2188-2192 ◽  
Author(s):  
M. J. Jaeger
Keyword(s):  
Tidal Volume ◽  
High Frequency ◽  
Kinematic Viscosity ◽  
Blood Gases ◽  
High Frequency Oscillation ◽  
High Frequency Ventilation ◽  
Gas Mixture ◽  
Frequency Oscillation ◽  
Frequency Ventilation ◽  
Arterial Po2

Dogs were ventilated with a high-frequency oscillation device varying the frequency (5-15 Hz), the tidal volume (25-100 ml), and the resident gas (He, N2, SF6). Tidal volume was measured with a body plethysmograph. Blood gases were measured after a quasi-steady state was established. The kinematic viscosity of the breathing gas mixture, which changed by 1,700%, was found to have little effect on arterial PO2 and PCO2. The results are consistent with findings in a branched model that consisted of tubes with a diameter of 1 cm and with the theory of Taylor-type diffusion in turbulent flow. In addition, experiments were performed reducing and increasing the equipment dead space. This resulted in changes of PO2 and PCO2 that were appreciably less than those resulting from variations of tidal volume of the same magnitude.

A new system for ventilating with high-frequency oscillation

1982 ◽  
Vol 53 (6) ◽  
pp. 1638-1642 ◽  
Author(s):  
Y. K. Ngeow ◽  
W. Mitzner
Keyword(s):  
Tidal Volume ◽  
High Frequency ◽  
Airway Pressure ◽  
Ventilation System ◽  
High Frequency Oscillation ◽  
High Frequency Ventilation ◽  
Mean Airway Pressure ◽  
Frequency Oscillation ◽  
Frequency Ventilation ◽  
New System

We describe simple high-frequency oscillation systems that incorporate a CO2 absorber and supply O2 on a need basis. These systems have the advantage of easy control of mean airway pressure and airway hydration and negligible loss of oscillatory tidal volume. Experiments done at constant tidal volume showed that as frequency (and hence total ventilation) increased, arterial CO2 tension (PaCO2) decreased. The fall in PaCO2 occurred until frequency reached approximately 20 Hz; above 20 Hz further increases in frequency had little or no effect on PaCO2. Because of their practical advantages the techniques described here may be quite useful in a clinical setting where an oscillator, rather than jet-type high-frequency, ventilation system is desired.

High frequency oscillation: paradigm of inhomogeneous alveolar ventilation

1989 ◽  
Vol 33 ◽  
pp. 13-21 ◽  
Author(s):  
P. P. LUNKENHEIMER ◽  
G. FRIELING ◽  
F.-J. MERSCH ◽  
K. REDMANN ◽  
A. LUNKENHEIMER ◽  
...  
Keyword(s):  
High Frequency ◽  
Alveolar Ventilation ◽  
High Frequency Oscillation ◽  
Frequency Oscillation

Mechanically Induced Pendelluft Flow in a Model Airway Bifurcation During High Frequency Oscillation

1991 ◽  
Vol 113 (3) ◽  
pp. 342-347 ◽  
Author(s):  
K. C. High ◽  
J. S. Ultman ◽  
S. R. Karl
Keyword(s):  
Tidal Volume ◽  
High Resistance ◽  
High Frequency ◽  
Volume Fraction ◽  
Reynolds Numbers ◽  
High Frequency Oscillation ◽  
Optimal Frequency ◽  
Frequency Oscillation ◽  
Parameter Values ◽  
Airway Bifurcation

A single bifurcation with adjustable branch compliances, resistances and inertances was used to study the generation of pendelluft flows during ventilation at tidal volumes of 5–15 ml and frequencies of 6–26 Hz, corresponding to parent branch Reynolds numbers of 400–8000 and Womersley parameter values of 12–25. Pendelluft was quantified by the ratio of tidal volume sum in sibling branches to tidal volume in the parent branch. This tidal volume fraction being greater than one in all experiments where an asymmetry in branch mechanics was imposed, indicated that some degree of pendelluft was always present. Asymmetries in compliance and in inertance produced much greater pendelluft than an asymmetry in resistance. The largest tidal volume fraction, equal to 2.75, was recorded when inertance in both sibling branches was high, resistance was low, and compliances differed by a factor of five. Tidal volume fraction always peaked at an optimal frequency between 12–24 Hz, similar to the frequencies at which physiologic transport optima have previously been observed.

Gas exchange during high-frequency ventilation of the chicken

1982 ◽  
Vol 53 (6) ◽  
pp. 1418-1422 ◽  
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.

Measurement of tidal volume using a pneumotachometer during high-frequency oscillation

1990 ◽  
Vol 18 (6) ◽  
pp. 651-653 ◽  
Author(s):  
SHERRY E. COURTNEY ◽  
KAYE R. WEBER ◽  
WILLIAM A. SPOHN ◽  
SETH W. MALIN ◽  
CHARLES V. BENDER ◽  
...  
Keyword(s):  
Tidal Volume ◽  
High Frequency ◽  
High Frequency Oscillation ◽  
Frequency Oscillation

Unanesthetized dogs with increased respiratory dead space

1960 ◽  
Vol 15 (5) ◽  
pp. 838-842 ◽  
Author(s):  
Thomas B. Barnett ◽  
Richard M. Peters
Keyword(s):  
Tidal Volume ◽  
Respiratory Rate ◽  
Dead Space ◽  
Minute Volume ◽  
Alveolar Ventilation ◽  
Physiologic Dead Space ◽  
Consistent Change ◽  
The Dead ◽  
Animal Preparation ◽  
Respiratory Dead Space

A method is described for maintaining a permanent tracheostomy in dogs. This animal preparation has been used to study the effects of artificially increased respiratory dead space. Trained dogs with tracheostomies have made possible measurements of ventilation without anesthesia. It has been found that additions to the respiratory dead space in the form of tubing of frac34 in. i.d. result in an increase in physiologic dead space of the same magnitude as the volume of tubing added. Increasing the dead space in this manner resulted in an increased minute volume which was accomplished principally by an increase in tidal volume without a significant or consistent change in respiratory rate. Alveolar ventilation remained unchanged even with large additions to the dead space (20–30 cc/kg of animal wt.). Arterial pCO2 was significantly higher in these animals than in the controls. The CO2 tension was similarly elevated when extra dead space of lesser volume (5–20 cc/kg) was allowed to remain on the dogs for more than 48 hours. Submitted on April 13, 1960

TIDAL VOLUME DEAD-SPACE RELATIONSHIP DURING HIGH-FREQUENCY VENTILATION

The Lancet ◽  
1983 ◽  
Vol 322 (8363) ◽  
pp. 1360 ◽  
Author(s):  
J.G. Whitwam ◽  
M.K. Chakrabarti ◽  
G. Gordon
Keyword(s):  
Tidal Volume ◽  
Dead Space ◽  
High Frequency ◽  
High Frequency Ventilation ◽  
Frequency Ventilation
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