Resonant amplification of delivered volume during high-frequency ventilation

1986 ◽  
Vol 60 (3) ◽  
pp. 885-892 ◽  
Author(s):  
V. Brusasco ◽  
K. C. Beck ◽  
M. Crawford ◽  
K. Rehder
Keyword(s):  
Stroke Volume ◽  
Endotracheal Tube ◽  
High Frequency ◽  
Gas Flow ◽  
High Frequency Ventilation ◽  
Frequency Ventilation ◽  
Anesthetized Dogs ◽  
Gas Volume

The volume of gas delivered from a high-frequency ventilation (HFV) circuit was measured with an ultrasonic flowmeter. The measurements were done in vitro (20-liter air-filled glass bottle) and in vivo (9 anesthetized dogs lying supine) at oscillation frequencies ranging from 4 to 23 Hz and stroke volumes of the pump ranging from 36 to 150 ml. We varied the length and diameter of the tube connecting the pump with the endotracheal tube, the length and diameter of the bias outflow tube, the diameter of the endotracheal tube, and the stroke volume of the pump. Both in vitro and in vivo, there was resonant amplification of the delivered gas volume; i.e., the delivered gas volume exceeded the stroke volume at certain frequencies. Altering the dimensions of connecting tube, endotracheal tube, bias outflow tube, or stroke volume, i.e., changing the resistance to gas flow, gas compliance, and/or gas inertance in these elements, altered the ratio of gas delivered to stroke volume that could be predicted by an electric analog. These data indicate that the delivered gas volume during HFV depends critically on the configuration of the HFV circuit, the size of the endotracheal tube, the oscillation frequency, and the pump stroke volume. Knowledge of the delivered gas volume during HFV and appreciation of the phenomenon of resonant amplification of the delivered gas volume will permit a more accurate description of factors contributing to gas transport during HFV.

Gas transport during high-frequency ventilation

1983 ◽  
Vol 55 (2) ◽  
pp. 472-478 ◽  
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.

Respiratory and inert gas exchange during high-frequency ventilation

1982 ◽  
Vol 52 (3) ◽  
pp. 683-689 ◽  
Author(s):  
H. T. Robertson ◽  
R. L. Coffey ◽  
T. A. Standaert ◽  
W. E. Truog
Keyword(s):  
Gas Exchange ◽  
High Frequency ◽  
Gas Flow ◽  
Inert Gases ◽  
Inert Gas ◽  
High Frequency Ventilation ◽  
Physiological Dead Space ◽  
Volume Ventilation ◽  
Frequency Ventilation ◽  
Carrier Gases

Pulmonary gas exchange during high-frequency low-tidal volume ventilation (HFV) (10 Hz, 4.8 ml/kg) was compared with conventional ventilation (CV) and an identical inspired fresh gas flow in pentobarbital-anesthetized dogs. Comparing respiratory and infused inert gas exchange (Wagner et al., J. Appl. Physiol. 36: 585--599, 1974) during HFV and CV, the efficiency of oxygenation was not different, but the Bohr physiological dead space ratio was greater on HFV (61.5 +/- 2.2% vs. 50.6 +/- 1.4%). However, the elimination of the most soluble inert gas (acetone) was markedly enhanced by HFV. The increased elimination of the soluble infused inert gases during HFV compared with CV may be related to the extensive intraregional gas mixing that allows the conducting airways to serve as a capacitance for the soluble inert gases. Comparing as exchange during HFV with three different density carrier gases (He, N2, and Ar), the efficiency of elimination of Co2 or the intravenously infused inert gases was greatest with He-O2. However, the alveolar-arterial partial pressure difference for O2 on He-O2 exceeded that on N2-O2 by 5.4 Torr during HFV. The finding agrees with similar observations during CV, suggesting that this aspect of gas exchange is not substantially altered by HFV.

High-frequency ventilation lengthens expiration in the anesthetized dog

1983 ◽  
Vol 55 (2) ◽  
pp. 329-334 ◽  
Author(s):  
R. Banzett ◽  
J. Lehr ◽  
B. Geffroy
Keyword(s):  
Lung Volume ◽  
High Frequency ◽  
Blood Gases ◽  
Abdominal Muscle ◽  
High Frequency Ventilation ◽  
Maximal Response ◽  
Variable Effect ◽  
Frequency Ventilation ◽  
Anesthetized Dogs ◽  
Arterial Po2

We tested the response of nine barbiturate-anesthetized dogs to high-frequency ventilation (HFV) (40-55 ml tidal volumes at 15 Hz) while measuring and controlling lung volume and blood gases. When lung volume and PCO2 were held constant, six of the nine responded to HFV by lengthening expiration. In each of these six dogs the maximal response was apnea. The response was immediate. In submaximal responses only expiration was changed; inspiratory time and peak diaphragmatic electrical activity were unaffected. There was a variable effect on abdominal muscle activity. If mean expiratory lung volume was allowed to increase at the onset of HFV, the Hering-Breuer inflation reflex added to the response. The strength of the response depended on level of anesthesia and arterial PO2. Vagotomy abolished the response in all cases. We conclude that oscillation of the respiratory system reflexly prolongs expiration via mechanoreceptors, perhaps those in the lungs.

Ventilation-perfusion relationship during high-frequency ventilation

1984 ◽  
Vol 56 (2) ◽  
pp. 454-458 ◽  
Author(s):  
V. Brusasco ◽  
T. J. Knopp ◽  
E. R. Schmid ◽  
K. Rehder
Keyword(s):  
Mechanical Ventilation ◽  
High Frequency ◽  
Conventional Mechanical Ventilation ◽  
Regional Perfusion ◽  
High Frequency Ventilation ◽  
Regional Ventilation ◽  
Frequency Ventilation ◽  
Anesthetized Dogs

The efficiency of oxygenation and the uniformity of the distribution of regional ventilation (Vr) to regional perfusion (Qr) along the vertical and horizontal axes was compared in anesthetized dogs between conventional mechanical ventilation (CMV) and high-frequency ventilation (HFV) at 5.8, 15.0, and 29.8 Hz. Both CMV and HFV were adjusted to result in similar arterial CO2 tensions. The distribution of Vr/Qr during HFV at 5.8 Hz tended to be more uniform than during HFV at 15.0 or 29.8 Hz or during CMV. Consistent with this observation, arterial O2 tension (PaO2) tended to be higher during HFV at 5.8 Hz (means +/- SD, 90 +/- 9 Torr) than during HFV at 15.0 Hz (83 +/- 9 Torr) or 29.8 Hz (78 +/- 10 Torr); PaO2 was significantly higher during HFV at 5.8 Hz than during CMV (83 +/- 7 Torr).

“Closing volume” during high-frequency ventilation in anesthetized dogs

1988 ◽  
Vol 32 (2) ◽  
pp. 140-146 ◽  
Author(s):  
T. Haghenberg ◽  
M. Wendt ◽  
J. Meyer ◽  
K. Wrenger ◽  
P. Lawin
Keyword(s):  
High Frequency ◽  
High Frequency Ventilation ◽  
Closing Volume ◽  
Frequency Ventilation ◽  
Anesthetized Dogs

Gas mixing during high-frequency ventilation: an improved model

1984 ◽  
Vol 57 (2) ◽  
pp. 493-506 ◽  
Author(s):  
M. C. Khoo ◽  
A. S. Slutsky ◽  
J. M. Drazen ◽  
J. Solway ◽  
N. Gavriely ◽  
...  
Keyword(s):  
High Frequency ◽  
Gas Flow ◽  
Molecular Diffusion ◽  
Elimination Rate ◽  
Effective Diffusivity ◽  
High Frequency Ventilation ◽  
Cross Sectional ◽  
Bias Flow ◽  
Frequency Ventilation ◽  
Improved Model

A model for gas transport during high-frequency ventilation incorporating recently derived empirical forms for the effective diffusivity in oscillatory gas flow through a symmetrical branching network is proposed. The model accounts for the movement of gas among airways with changing cross-sectional area by using a moving-reference-frame analysis. The analysis technique incorporates the convective purging of the bias flow at the airway opening. The model predicts that although the cycle-averaged CO2 elimination rate (VCO2) depends most strongly on the product of frequency and tidal volume (VT), VT has an effect on its own, a finding consistent with published observations. This “VT effect” is due primarily to the oscillatory movement of gas from more central regions into peripheral regions where large cross-sectional areas promote efficient CO2 transport by molecular diffusion. Although the VT effect exists independent of the presence of a bias flow, placing the bias flow near the main carina can enhance the VT effect substantially. As VT is increased to values in the range of ordinary tidal breaths, VCO2 predicted by the model achieves close agreement with VCO2 deduced from conventional gas exchange theory.

High-frequency ventilation-induced apnea: interaction of frequency, volume, FRC, and CO2

1989 ◽  
Vol 66 (5) ◽  
pp. 2462-2467 ◽  
Author(s):  
P. W. Davenport ◽  
D. J. Dalziel
Keyword(s):  
High Frequency ◽  
Blood Gas Analysis ◽  
Gas Analysis ◽  
High Frequency Ventilation ◽  
Emg Activity ◽  
Bipolar Electrodes ◽  
Residual Capacity ◽  
Frequency Ventilation ◽  
Anesthetized Dogs ◽  
End Tidal

Apnea is often observed during high-frequency oscillatory ventilation (HFOV). This study on anesthetized dogs varied the oscillator frequency (f) and determined the stroke volume (SV) at which apnea occurred. Relaxation functional residual capacity (FRC) and the eupneic breathing end-tidal CO2 level were held constant. Airway pressure and CO2 were measured from a side port of the tracheostomy cannula. An arterial cannula was inserted for blood gas analysis. Diaphragm electromyogram (EMG) was recorded with bipolar electrodes. Apnea was defined as the absence of phasic diaphragm EMG activity for a minimum of 60 s. During HFOV, SV was increased at each f (5–40 Hz) until apnea occurred. The apnea inducing SV decreased as f increased. SV was minimal at 25–30 Hz. Frequencies greater than 30 Hz required increased SV to produce apnea. The f-SV curve was defined as the apneic threshold. Increased FRC resulted in a downward shift (less SV at the same f) in the apneic threshold. Elevated CO2 caused an upward shift (more SV at the same f) in the apneic threshold. These results demonstrate that the apnea elicited by HFOV is dependent on the interaction of oscillator f and SV, the FRC, and CO2.

Pressure-flow relationships of endotracheal tubes during high-frequency ventilation

1985 ◽  
Vol 59 (1) ◽  
pp. 3-11 ◽  
Author(s):  
N. Gavriely ◽  
J. Solway ◽  
S. H. Loring ◽  
J. P. Butler ◽  
A. S. Slutsky ◽  
...  
Keyword(s):  
High Frequency ◽  
Pressure Fluctuations ◽  
Flow Equation ◽  
High Frequency Ventilation ◽  
Pressure Flow ◽  
Pressure Drops ◽  
Endotracheal Tubes ◽  
Frequency Ventilation

We studied the pressure-flow relationships of various endotracheal tubes (ETT) at frequencies (f) and tidal volumes (VT) in the range used for high-frequency ventilation (HFV) (f: 2–32 Hz, VT: 15–100 ml). Sinusoidal flows were applied to ETT inserted into a rigid bottle or into the tracheae of three anesthetized paralyzed dogs, while pressure fluctuations were measured both proximal and distal to the ETT. The pressure drops in the ETT were nonlinearly related to the peak flow rate and were VT dependent, suggesting that turbulent frictional head loss and convective acceleration were important. The pressure drops measured in vitro were found to be in good agreement with the predictions of a nonlinear oscillatory pressure-flow equation (derived herein), which incorporate the effects of turbulent frictional losses, convective acceleration, inertance, and compliance. The pressure drops measured in situ were 30–50% higher than with the corresponding f-VT combinations in vitro. Possible explanations of these differences are junctional losses at the tip of the ETT or the nonrigid character of the trachea.

Frequency and amplitude effects during high-frequency vibration ventilation in dogs

1989 ◽  
Vol 66 (3) ◽  
pp. 1127-1135 ◽  
Author(s):  
Y. Shabtai ◽  
N. Gavriely
Keyword(s):  
High Frequency ◽  
Gas Flow ◽  
Vertical Displacement ◽  
High Frequency Ventilation ◽  
Input Amplitude ◽  
Frequency Ventilation ◽  
Vibrating Table ◽  
Peak Pressures ◽  
Arterial Po2 ◽  
Tracheal Carina

High-frequency external body vibration, combined with constant gas flow at the tracheal carina, was previously shown to be an effective method of ventilation in normal dogs. The effects of frequency (f) and amplitude of the vibration were investigated in the present study. Eleven anesthetized and paralyzed dogs were placed on a vibrating table (4–32 Hz). O2 was delivered near the tracheal carina at 0.51.kg-1.min-1, while mean airway pressure was kept at 2.4 +/- 0.9 cmH2O. Table vertical displacement (D) and acceleration (a), esophageal (Pes), and tracheal (Ptr) peak-to-peak pressures, and tidal volume (VT) were measured as estimates of the input amplitude applied to the animal. Steady-state arterial PCO2 (PaCO2) and arterial PO2 (PaO2) values were used to monitor overall gas exchange. Typically, eucapnia was achieved with f greater than 16 Hz, D = 1 mm, a = 1 G, Pes = Ptr = 4 +/- 2 cmH2O, and VT less than 2 ml. Inverse exponential relationships were found between PaCO2 and f, a, Pes, and Ptr (exponents: -0.69, -0.38, -0.48, and -0.54, respectively); PaCO2 decreased linearly with increased displacement or VT at a fixed frequency (17 +/- 1 Hz). PaO2 was independent of both f and D (393 +/- 78 Torr, mean +/- SD). These data demonstrate the very small VT, Ptr, and Pes associated with vibration ventilation. It is clear, however, that mechanisms other then those described for conventional ventilation and high-frequency ventilation must be evoked to explain our data. One such possible mechanism is forcing of flow oscillation between lung regions (i.e., forced pendelluft).

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