Effective Pulmonary Ventilation with Small-Volume Oscillations At High Frequency

Slutsky, A. S.; Drazen, FM; Ingram, R. H.; Kamm, R. D.; Shapiro, A. H.; Fredberg, J. J.; Loring, S. H.; Lehr, John L.

doi:10.1126/science.6771872

Cited by 163 publications

(52 citation statements)

References 7 publications

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“…8) to regional gas exchange during HFV is unclear. An early theoretical study (34) predicted and later experimental studies (35)(36)(37)(38) confirmed that overall gas exchange during HFV would depend upon the product of f and VT, rather than each individually, in the limit when VT'S were infinitesimally small compared with dead space, and that there would be an independent influence of VT upon gas exchange when VT's approached appreciable fractions of the dead space, i.e., when bulk convection would become significant relative to gas mixing phenomena. It has also been speculated that the independent VT effect might be due to direct ventilation 'of nearby alveoli in the asymmetrical airway tree (39), due to complexities in characterizing the gas concentration boundary conditions at the airway opening and at the alveolus (36,40), due to streaming flows (41), and due to the physics of compartmental mixing (42).…”

Section: Resultsmentioning

confidence: 99%

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

Allen¹,

Frantz²,

Fredberg³

1985

J. Clin. Invest.

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We measured pressure excursions at the airway opening and at the alveoli (PA) as well as measured the regional distribution of PA during forced oscillations of six excised dog lungs while frequency (f12-32 Hzj), tidal volume (VT 15-80 ml]), and mean transpulmonary pressure (PL 125, 10, and 6 cm H20) were varied. PA'S were measured in four alveolar capsules glued to the pleura of different lobes. The apex-to-base ratio of PA'S was used as an index of the distribution of dynamic lung distension. At low ; there was slight preferential distension of the lung base which was independent of VT, but at higher f, preferential distension of the lung apex was found when VT's were small, whereas preferential distension of the lung base was found when VT's approached or exceeded dead space. These V1-related changes in distribution at high frequencies seem to depend upon the branching geometry of the central airways and the relative importance of convective momentum flux vs. unsteady inertia of gas residing therein, which, in this study, we showed to be proportional to the ratio VT/VD*, where VD* is an index of dead space. Furthermore, they imply substantial alteration in the distribution of ventilation during high frequency ventilation as f VT, and PL vary. The data also indicate that alveolar and airway opening pressure costs per unit flow delivered at the airway opening exhibit weakly nonlinear behavior and that resonant amplification of PA's, which has been described previously for the case of very small

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Section: Resultsmentioning

confidence: 99%

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

Allen¹,

Frantz²,

Fredberg³

1985

J. Clin. Invest.

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“…Recently, however, this traditional concept has been challenged by experimental observations demonstrat-ing that effective alveolar ventilation can occur with VT considerably less than dead-space volume provided that the ventilatory frequencies are sufficiently large (1)(2)(3)(4)(5). Although this has by now been well established by a number of studies, the physical mechanisms that account for the observed gas exchange are not known with certainty.…”

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confidence: 91%

“…To confirm that during an experimental run of HFV the oscillations did not introduce an artifact, we measured the integral of the CO2 concentration from the bias flow using a constant CO2 source in place of the dog while oscillatory frequency and stroke volume were varied and found this integral to be constant. In dogs 3-6, whose data were presented in part in our previous paper (5), and in dogs 8 and 9, we corrected the integral of CO2 concentration for a small systematic error (7 ml/min) in our CO2 analyzer calibration. This problem was eliminated for the experiments in dogs 10-16. We found that changes in the fractional alveolar CO2 concentration (FACO2) resulted in a change in VCo2 at any Vosc.…”

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confidence: 99%

Effects of frequency, tidal volume, and lung volume on CO2 elimination in dogs by high frequency (2-30 Hz), low tidal volume ventilation.

Slutsky¹,

Kamm²,

Rossing³

et al. 1981

J. Clin. Invest.

123

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A B S T R A C T Recent studies have shown that effective pulmonary ventilation is possible with tidal volumes (VT) less than the anatomic dead-space if the oscillatory frequency (f) is sufficiently large. We systematically studied the effect on pulmonary CO2 elimination (VCO2) of varying f (2-30 Hz) and VT (1-7 ml/kg) as well as lung volume (VL) in 13 anesthetized, paralyzed dogs in order to examine the contribution of those variables that are thought to be important in determining gas exchange by high frequency ventilation. All experiments were performed when the alveolar PCO2 was 40±+1.5 mm Hg. In all studies, VCO2 increased monotonically with f at constant VT. We quantitated the effects of f and VT on VCo2 by using the dimensionless equation VCO2/ Vosc = a(VT/VTO)b(f/fo)c where: Vosc = f x VT, VTO = mean VT, fo = mean f and a, b, c, are constants obtained by multiple regression. The mean values of a, b, and c for all dogs were 2.12 x 10-3, 0.49, and 0.08, respectively. The most important variable in determining VCO2 was Vosc; however, there was considerable variability among dogs in the independent effect of VT and f on VCO2, with a doubling of VT at a constant Vosc causing changes in VCO2 ranging from -13 to + 110% (mean = +35%). Increasing VL from functional residual capacity (FRC) to the lung volume at an airway opening minus body surface pressure of 25 cm H20 had no significant effect on VCO2.

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“…These results suggest that using the high frequency ventilator tested, to minimize alveolar barotrauma one should choose the highest frequency where gas exchange is adequate. (Pediatr Res 19: 162-166,1985) Abbreviations HFV, high frequency-low tidal volume ventilation HFV is currently under investigation as a new technique for treatment of adults and infants with respiratory failure (2,3,6,8,10,15). Its major advantage is the potential for adequate gas exchange with lower dynamic pressures within the airways.…”

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confidence: 99%

Alveolar Pressure Swings during High Frequency Ventilation in Rabbits

Frantz

1985

Pediatr Res

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ABSTRAm. In order to understand the pressures and volumes delivered during ventilation with the Emerson flow-interrupting high frequency ventilator, we have measured dynamic and mean pressures at the airway opening, trachea, and alveoli as well as delivered volumes in vivo in closed-chest adult rabbits ventilated at rates of 2-37.5 Hz. To measure alveolar pressure we opened the chest, glued an alveolak capsule to the visceral pleural surface, punctured the pleura and lung surface through the capsule, inserted a pressure transducer into the capsule and closed the chest. We measured delivered volume with a pressure plethysmograph. Alveolar pressure swings fell with increasing frequency, as did delivered volume. Alveolar pressure swings were always lower than those at the airway opening or in the trachea. Removal of the rib cage resulted in a decrease in alveolar pressure swings although muscle paralysis had little effect. Mean pressures were equal at the airway opening, trachea, and alveoli at all frequencies. These results suggest that using the high frequency ventilator tested, to minimize alveolar barotrauma one should choose the highest frequency where gas exchange is adequate. (Pediatr Res 19: 162-166,1985) Abbreviations HFV, high frequency-low tidal volume ventilation HFV is currently under investigation as a new technique for treatment of adults and infants with respiratory failure (2,3,6,8,10,15). Its major advantage is the potential for adequate gas exchange with lower dynamic pressures within the airways. While there is evidence that dynamic pressure in the trachea may be lower during HFV than during conventional ventilation (6), data from our laboratory demonstrate that under conditions of low oscillatory flow and pressure amplitudes, alveolar pressure swings may exceed those at the airway opening near the resonant frequency of the respiratory system (1, 7). Although these data provide important physiologic information, they do not have direct clinical relevance since the experiments were camed out using dynamic pressures at the airway opening which were very much lower than those used for HFV. Furthermore, excised lungs were studied, eliminating effects of the chest wall. The objectives of this study were to measure dynamic pressure within the alveoli in vivo in response to pressure oscillations generated

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Effective Pulmonary Ventilation with Small-Volume Oscillations At High Frequency

Cited by 163 publications

References 7 publications

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

Regional alveolar pressure during periodic flow. Dual manifestations of gas inertia.

Effects of frequency, tidal volume, and lung volume on CO2 elimination in dogs by high frequency (2-30 Hz), low tidal volume ventilation.

Alveolar Pressure Swings during High Frequency Ventilation in Rabbits

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