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Chapter 2 – Intensive care: mechanical ventilation and HFPV
2.3.1 Principles of HFPV
One of several controversial aspects surrounding modes of high frequency ventilation (HFV)
is that there is no universally accepted classification or defined nomenclature for these various
methods [Froese AB, 1984] Depending on the frequency used, the maneuvers may be divided
into high frequency jet ventilation (HFJV) and its variant, high frequency flow interruption
(HFFI), high frequency oscillation (HFO) and high frequency positive pressure ventilation
(HFPPV). Basically, HFPPV uses lower frequencies (60-300 cycles/min), while HFO uses
higher frequencies (60-2400 cycles/min). However, this classification does not take into
account that HFO can also use low working frequencies. Technically, all modes of HFV share
at least 3 basic elements: a high pressure flow generator, a safety valve, and a breathing
circuit connected to the patient [Gioia et al, 1985] [Branson, 1995]. HFPV may be defined as
flow-regulated time-cycled ventilation that creates controlled pressure and delivers a series of
high frequency subtidal volumes in combination with low frequency breathing cycles. The
only system that delivers HFPV is the VDR® 4 (Volumetric Diffusive Respiration). The
system may be defined as a time-cycled pressure-controlled ventilator equipped with a high
frequency flow generator connected to a device (the phasitron) that provides the interface
between the patient and the machine
2.3.2 General characteristics of HFPV system
Figure 2.6 Schematic diagram of the HFPV system.
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