Constancy of physiological dead space during high-frequency ventilation

1982 ◽  
Vol 47 (1) ◽  
pp. 39-49 ◽  
Author(s):  
P.R. Fletcher ◽  
R.A. Epstein
Keyword(s):  
Dead Space ◽  
High Frequency ◽  
High Frequency Ventilation ◽  
Physiological Dead Space ◽  
Frequency Ventilation

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.

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.

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.

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

Model of gas transport during high-frequency ventilation

1985 ◽  
Vol 58 (6) ◽  
pp. 1956-1970 ◽  
Author(s):  
S. Permutt ◽  
W. Mitzner ◽  
G. Weinmann
Keyword(s):  
Standard Deviation ◽  
Gas Exchange ◽  
Dead Space ◽  
High Frequency ◽  
Mean Transit Time ◽  
High Frequency Ventilation ◽  
Transit Times ◽  
Frequency Ventilation ◽  
In Series ◽  
The Dead

We analyze gas exchange during high-frequency ventilation (HFV) by a stochastic model that divides the dead space into N compartments in series where each compartment has a volume equal to tidal volume (V). We then divide each of these compartments into alpha subcompartments in series, where each subcompartment receives a well-mixed concentration from one compartment and passes a well-mixed concentration to another in the direction of flow. The number of subcompartments is chosen on the basis that 1/alpha = (sigma t/-t)2, where -t is mean transit time across a compartment of volume, and sigma t is standard deviation of transit times. If (sigma t/-t)D applies to the transit times of the entire dead space, the magnitude of gas exchange is proportional to (sigma t/-t)D, frequency, and V raised to some power greater than unity in the range where V is close to VD. When V is very small in relation to VD, gas exchange is proportional to (sigma t/-t)2D, frequency, and V raised to a power equal to either one or two depending on whether the flow is turbulent or streamline, respectively. (sigma t/-t)D can be determined by the relation between the concentration of alveolar gas at the air outlet and volume expired as in a Fowler measurement of the volume of the dead space.

Pneumothorax and pulmonary intersticial emphysema: treatment with selective bronchial occlusion and high frequency ventilation

1998 ◽  
Vol 74 (5) ◽  
pp. 411-5 ◽  
Author(s):  
Marcus A.J. Oliveira ◽  
Antônio C. P. Ferreira ◽  
João S. Oliveira ◽  
José S. Oliveira ◽  
Yara G. Silva
Keyword(s):  
High Frequency ◽  
High Frequency Ventilation ◽  
Frequency Ventilation
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