High frequency oscillation: paradigm of inhomogeneous alveolar ventilation

Heterogeneous activity of pulmonary vagal receptors during high-frequency oscillation ventilation

“…The heterogeneity of both SAR and RAR discharge patterns, which occurs during HFO but not during static lung inflation and deflation, indicates that the mechanical conditions in different parts of the lung during HFO are heterogeneous. The suggestion of different mechanical conditions in different parts of the lung is supported by the finding of heterogeneity of mean alveolar pressure [1] and of inhomogeneous alveolar ventilation [15] during HFO. During static lung inflation or deflation, all parts of the lung are distended or deflated evenly and the conditions for the stimulation of pulmonary receptors are similar in all parts.…”

High Frequency Ventilation and Regional Compliance

“…When increasing the exciting frequency ( fig. 5) from 3.14 to 62.4 Hz by a rotating valve tube ventilator [13] we obtained modulations of segmental length oscillations and in mean segmental length which were different between measuring sites. Clinically, unequal distribution [28] of gas filling cannot be expressed in terms of FRC and cannot be assessed by measurement of chest circumference [5].…”

“…What basic findings contribute to the particular gas mixing procedure during High Frequency Ventilation? Observations on lungs ventilated in the open chest and multifocal pressure measurements in the subpleural compartment [12,13] confirm that not only does alveolar ventilation become non-homogeneous during monofrequent excitation above 10 Hz, but there is also a non-symmetrical distribution of the gas content within the lungs [28]. Some zones tend to remain motionless and collapse, whilst others are well inflated and follow the excitation.…”

“…With periodic insufflation at frequencies exceeding 7 Hz, a frequency-dependent excitation of individual gas conduits and the attached parenchyma appears to occur [11,12]. With each change in the excitation frequency, the distribution of the oscillating bronchi changes, and it has been suggested that all the regions of the lung could be ventilated by systematically varying the exciting frequency [13].…”

“…There are five possible ancilliary mechanisms: (i) There may be gas transfer from "high pressure" to "low pressure" areas (collateral flow) [13]. Interalveolar windows, ascribed to (but not described first by) Kohn (1893), may function as one pathway for "one-way" gas flow.…”