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

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.

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Ventilation-perfusion relationship during high-frequency ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1984.56.2.454 ◽

1984 ◽

Vol 56 (2) ◽

pp. 454-458 ◽

Cited By ~ 13

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).

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Resonant amplification of delivered volume during high-frequency ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1986.60.3.885 ◽

1986 ◽

Vol 60 (3) ◽

pp. 885-892 ◽

Cited By ~ 21

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.

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

Journal of Applied Physiology ◽

10.1152/jappl.1989.66.5.2462 ◽

1989 ◽

Vol 66 (5) ◽

pp. 2462-2467 ◽

Cited By ~ 4

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.

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