Test of wave-speed theory of flow limitation in elastic tubes

Elliott, E. A.; Dawson, Stanley V.

doi:10.1152/jappl.1977.43.3.516

Cited by 75 publications

(59 citation statements)

References 6 publications

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“…It was shown further, that in all instances flow limitation was eliminated with PEEP as low as 5 cmH 2 O, indicating that low lung V was the main determinant of flow limitation. The existence of flow limitation invalidates the calculation of expiratory resistance using the difference between alveolar and mouth pressures [9]. In flow-limited patients, upstream airway resistance at a specific V should be calculated by dividing the difference between alveolar pressure and total pressure head at the choke point by the corresponding V9 [23].…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, it has been shown that mechanically-ventilated patients with ARDS may exhibit flow limitation during tidal expiration [8]. In which case the endotracheal tube resistance (Rtube), as well as the expiratory ventilator circuit, may not affect the expiratory flow and, thus, the rate of lung emptying [9,10]. It follows that calculating the ters without knowing if expiratory flow at the volume of interest is or is not limited might be misleading.…”

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confidence: 99%

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Lung emptying in patients with acute respiratory distress syndrome: effects of positive end-expiratory pressure

Kondili¹,

Prinianakis²,

Athanasakis³

et al. 2002

Eur Respir J

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The pattern of lung emptying was studied in 10 mechanically-ventilated patients with acute respiratory distress syndrome.At four levels of positive end-expiratory pressure (PEEP) (0, 5, 10 and 15 cmH 2 O) tracheal (Ptr) and airway pressures (Paw), flow (V9) and volume (V) were continuously recorded. Tidal volume was set between 0.5-0.6 L and V9/V curves during passive expiration were obtained. Expired volume was divided into five equal volume slices and the time constant (te) and effective deflation compliance (Crs eff ) of each slice was calculated by regression analysis of V/V9 and postocclusion V/Ptr relationships, respectively. In each slice, the presence or absence of flow limitation was examined by comparing V9/V curves with and without decreasing Paw. For a given slice, total expiratory resistance (Rtot) (consisting of the respiratory system (Rrs), endotracheal tube (Rtube) and ventilator circuit (Rvent)) was calculated as the te/Crs eff ratio. In the absence of flow limitation Rrs was obtained by subtracting Rtube and Rvent from Rtot, while in the presence of flow limitation Rrs equaled Rtot. The te of the pure respiratory system (ters) was calculated as the product of Rrs and Crs eff .At zero PEEP, ters increased significantly towards the end of expiration (52¡31%) due to a significant increase in Rrs (46¡36%). Application of PEEP significantly decreased Rrs at the end of expiration and resulted in a faster and relatively constant rate of lung emptying.In conclusion, without positive end-expiratory pressure the respiratory system in patients with acute respiratory distress syndrome deflates with a rate that progressively decreases, due to a considerable increase in expiratory resistance at low lung volumes. Application of positive end-expiratory pressure decreases the expiratory resistance, probably by preventing airway closure, and as a result modifies the pattern of lung emptying.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Lung emptying in patients with acute respiratory distress syndrome: effects of positive end-expiratory pressure

Kondili¹,

Prinianakis²,

Athanasakis³

et al. 2002

Eur Respir J

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show abstract

“…The We will interpret our measurements partitioning the pressure drops and resistances upstream from the site of flow limitation to describe the mechanisms setting Vmax on each gas. We will try to integrate our results with the intuitive approaches of Mead et al (4) and Pride et al (5) as well as the mncathemiiatical approaclh described by the wave-speed theorv (6,13). Fturthermore, we will use equations derived from the previouis canine study (3) and apply them to the data found in the excised human lungs.…”

Section: Discussionmentioning

confidence: 99%

“…A more rigorous explanation of how Pfr/Ptot would reduce Vmax can be derived from the wave-speed theory of flow limitation (3,6,13). According to the theory, Vmax occurs when at a point in the airway, the choke point, linear velocity equals the speed ofpropagation of the pressure pulse waves.…”

Section: Discussionmentioning

confidence: 99%

How does HeO2 increase maximum expiratory flow in human lungs?

Mink¹,

Wood²

1980

J. Clin. Invest.

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A B S T R A C T We used the retrograde catheter techni(que to investigate the effect of HeO2 on resistance to maximum expiratory flow (Vmax) in airways stubsegments between alveoli and the equtal pressuire point (EPP), and between EPP and the flow-limiting segment (FLS). FLS were found at the same airway site in sublobar bronchi (i.d., 0.54+0.13 cm) on both air and HeO2 in the six human excised lungs studied. Static elastic recoil pressure (5±1 cm H20) and the lateral pressuire at FLS (critical transmural airway pressuire -6+3 cm H20) were not different on the two gases. AVmax averaged 37±8.9% and was similar to the valuie fouind in healthy subjects of similar age (66+10 yr). EPP were located on HeO2 in peripheral airways (i.d., 0.33±0.03 cm), and EPP on air were located more downstream. Resistance between EPP and FLS was highly density dependent. Resistance between alveoli and EPP behaved as if it were density independent, due in part to Poisecuille flow in the peripheral airways and in part to the consequent narrowing of peripheral airways on HeO2. This density-independent behavior in peripheral airways reduced AVmax on HeO2 from its predicted maximal amount of 62%. Asstuming that FLS is the "choke point" these findings are consistent with wavespeed theory of flow limitationi modified to include futnctionially density-independent pressure losses in peripheral airways. These restults and concltusions are similar to those fouind in living dogs. They question previous interpretation of /Vmax as an index of peripheral airway obstruction, and demonstrate the utility of the wave-speed theory in explaining complicated mechanisms of expiratory flow limitation.

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“…The V, , , of liquid from the lung is limited by the wave speed of the fluid (8)(9)(10). Furthermore, diffusion of C02 into FC-80 is approximately 2500 times slower (7) than diffusion of COz in air and is gradient limited (PVco, 1'46 mm Hg and PA^^,= 40 mm Hg).…”

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confidence: 99%

Fluorocarbon Ventilation: Maximal Expiratory Flows and CO2 Elimination

1988

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ABSTRACT. Elimination of C02 during liquid ventilation is dependent on flow, diffusion, and the 1.iquid's capacitance for C02. Maximum expiratory flow (V, . , ) and diffusion dead space were measured in vivo in 12 young cats during liquid fluorocarbon (FC-80) ventilation to determine the effect of breathing frequency on maximum CO2 elimina- f) when tidal volume was adjusted appropriately during steady state liquid ventilation. Predicted maximum C 0 2 elimination (VcoZmax) determined from V, . , and VDdia was 24 ml/min at a f of 3-3.5 breathslmin. The maximum was found to be strongly dependent on f with much less dependency on fixed dead space (anatomic plus equipment) and wave shape characteristics. Elimination of C02 decreased at low values off due to inadequate ventilation and at high values o f f due to inadequate diffusion time. From a comparison of experimentally determined steady state Vco, to theoretically predicted VcoZmax, the results demonstrate a f-related functional reserve capacity for CO2 elimination during liquid ventilation. These findings suggest that by optimizing the liquid ventilatory pattern it should be possible to maintain adequate CO2 elimination and

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Test of wave-speed theory of flow limitation in elastic tubes

Cited by 75 publications

References 6 publications

Lung emptying in patients with acute respiratory distress syndrome: effects of positive end-expiratory pressure

Lung emptying in patients with acute respiratory distress syndrome: effects of positive end-expiratory pressure

How does HeO2 increase maximum expiratory flow in human lungs?

Fluorocarbon Ventilation: Maximal Expiratory Flows and CO2 Elimination

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