Gas Transport Mechanisms during High Frequency Ventilation

2015 ◽  
pp. 157-160
Author(s):  
H. K. Chang
Keyword(s):  
High Frequency ◽  
Gas Transport ◽  
High Frequency Ventilation ◽  
Transport Mechanisms ◽  
Frequency Ventilation

Effects of mean airway pressure on gas transport during high-frequency ventilation in dogs

1986 ◽  
Vol 61 (5) ◽  
pp. 1896-1902 ◽  
Author(s):  
Y. Yamada ◽  
J. G. Venegas ◽  
D. J. Strieder ◽  
C. A. Hales
Keyword(s):  
Lung Volume ◽  
High Frequency ◽  
Airway Pressure ◽  
Gas Transport ◽  
Blood Gases ◽  
Co2 Production ◽  
High Frequency Ventilation ◽  
Mean Airway Pressure ◽  
Arterial Blood ◽  
Frequency Ventilation

In 10 anesthetized, paralyzed, supine dogs, arterial blood gases and CO2 production (VCO2) were measured after 10-min runs of high-frequency ventilation (HFV) at three levels of mean airway pressure (Paw) (0, 5, and 10 cmH2O). HFV was delivered at frequencies (f) of 3, 6, and 9 Hz with a ventilator that generated known tidal volumes (VT) independent of respiratory system impedance. At each f, VT was adjusted at Paw of 0 cmH2O to obtain a eucapnia. As Paw was increased to 5 and 10 cmH2O, arterial PCO2 (PaCO2) increased and arterial PO2 (PaO2) decreased monotonically and significantly. The effect of Paw on PaCO2 and PaO2 was the same at 3, 6, and 9 Hz. Alveolar ventilation (VA), calculated from VCO2 and PaCO2, significantly decreased by 22.7 +/- 2.6 and 40.1 +/- 2.6% after Paw was increased to 5 and 10 cmH2O, respectively. By taking into account the changes in anatomic dead space (VD) with lung volume, VA at different levels of Paw fits the gas transport relationship for HFV derived previously: VA = 0.13 (VT/VD)1.2 VTf (J. Appl. Physiol. 60: 1025–1030, 1986). We conclude that increasing Paw and lung volume significantly decreases gas transport during HFV and that this effect is due to the concomitant increase of the volume of conducting airways.

Gas concentration profiles along airways of dog lungs during high-frequency ventilation

1984 ◽  
Vol 56 (6) ◽  
pp. 1491-1499 ◽  
Author(s):  
T. Kaethner ◽  
J. Kohl ◽  
P. Scheid
Keyword(s):  
High Frequency ◽  
Gas Transport ◽  
Total Concentration ◽  
Relative Concentration ◽  
Inert Gases ◽  
High Frequency Ventilation ◽  
Gas Mixing ◽  
Upper Airways ◽  
Alveolar Region ◽  
Frequency Ventilation

Following equilibration with inert gases (He and SF6), dog lungs were partially washed out, either by high-frequency ventilation (HFV) or by conventional mechanical ventilation (CMV), to varied inert gas clearance levels, at which expirograms were recorded by mass spectrometry. Relative alveolar slopes were distinctly positive for HFV and tended to increase with lung clearance; they were, however, smaller than those of CMV and were smaller for He than for SF6 during both ventilatory modes. Fowler dead space was smaller for HFV than for CMV, with significant differences between test gases only during CMV. Plots of concentration against linear distance between measuring site and alveolar region showed that most of the total concentration drop during HFV occurred, with nearly linear slope, along the endotracheal tube and the upper airways, with no difference between He and SF6. In the alveolar region, on the other hand, relative concentration gradients were similar for HFV and CMV, both showing separation of He and SF6. The data suggest that gas transport in the upper airways during HFV is not diffusion limited. Gas mixing in alveolar regions, although more complete for HFV than for CMV, is limited by diffusion; however, this incomplete gas mixing does not appreciably limit overall gas transport during HFV.

Corrigenda, Vol. 60

1986 ◽  
Vol 60 (6) ◽  
pp. 2166-t-2166-t
Keyword(s):  
High Frequency ◽  
Gas Transport ◽  
High Frequency Ventilation ◽  
Dimensionless Equation ◽  
Frequency Ventilation

Page 1025: J. G. Venegas, C. A. Hales, and D. J. Strieder. “A general dimensionless equation of gas transport by high-frequency ventilation.” Page 1027: substitute corrected Fig. 1 (see PDF).

Gas transport in branched airways during high-frequency ventilation

1984 ◽  
Vol 12 (4) ◽  
pp. 385-405 ◽  
Author(s):  
P. W. Scherer ◽  
F. R. Haselton ◽  
J. R. Seybert
Keyword(s):  
High Frequency ◽  
Gas Transport ◽  
High Frequency Ventilation ◽  
Frequency Ventilation

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

1988 ◽  
Vol 64 (5) ◽  
pp. 2108-2118 ◽  
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.

Regional mapping of gas transport during high-frequency and conventional ventilation

1989 ◽  
Vol 66 (3) ◽  
pp. 1209-1218 ◽  
Author(s):  
Y. Yamada ◽  
C. Burnham ◽  
C. A. Hales ◽  
J. G. Venegas
Keyword(s):  
High Frequency ◽  
Gas Transport ◽  
Central Area ◽  
Lung Ventilation ◽  
Local Effect ◽  
Conventional Ventilation ◽  
High Frequency Ventilation ◽  
Positron Emission ◽  
Partial Pressure Of Co2 ◽  
Frequency Ventilation

The effects of changing tidal volume (VT) and frequency (f) on the distribution of ventilation during high-frequency ventilation (HFV) were assessed from the washout of nitrogen-13 by positron emission tomography. Six dogs, anesthetized and paralyzed, were studied in the supine position during conventional ventilation (CV) and during HFV at f of 3, 6, and 9 Hz. In CV and HFV at 6 Hz, VT was selected to achieve eucapnic arterial partial pressure of CO2 (37 +/- 3 Torr). At 3 and 9 Hz, VT was proportionally changed so that the product of VT and f remained constant and equal to that at 6 Hz. Mean residence time (MRT) of nitrogen-13 during washout was calculated for apical, midheart, and basal transverse sections of the lung and further analyzed for gravity-dependent, cephalocaudal and radial gradients. An index of local alveolar ventilation per unit of lung volume, or specific ventilation (spV), was calculated as the reciprocal of MRT. During CV vertical gradients of regional spV were seen in all sections with ventral (nondependent) regions less ventilated than dorsal (dependent) regions. Regional nonuniformity in gas transport was greatest for HFV at 3 and 6 Hz and lowest at 9 Hz and during CV. During HFV, a central region at the base of the lungs was preferentially ventilated, resulting in a regional time-averaged tracer concentration equivalent to that of the main bronchi. Because the main bronchi were certainly receiving fresh gas, the presence of this preferentially ventilated area, whose ventilation increased with VT, strongly supports the hypothesis that direct convection of fresh gas is an important mechanism of gas transport during eucapnic HFV. Aside from the local effect of increasing overall lung ventilation, this central area probably served as an intermediate shuttle station for the transport of gas between mouth and deeper alveoli when VT was less than the anatomic dead space.

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