Model of gas transport during high-frequency ventilation

S. Permutt, W. Mitzner, G. Weinmann

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Abstract

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 α 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/α = (σ(t)/t̄)2, where t̄ is mean transit time across a compartment of volume, and σ(t) is standard deviation of transit times. If (σ(t)/t̄)(D) applies to the transit times of the entire dead space, the magnitude of gas exchange is proportional to (σ(t)/t̄)(D), frequency, and V raised to some power greater than unity in the range where V is close to V(D). When V is very small in relation to V(D), gas exchange is proportional to (σ(t)/t̄)(D)2, frequency, and V raised to a power equal to either one or two depending on whether the flow is turbulent or streamline, respectively. (σ(t)/t̄)(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.

Original languageEnglish (US)
Pages (from-to)1956-1970
Number of pages15
JournalJournal of applied physiology
Volume58
Issue number6
StatePublished - Jan 1 1985

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ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

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