Detection of Expiratory Flow Limitation During Experimental Mechanical Ventilation
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Pneumon 1999;12(2):84-92
SUMMARY In the present study, a new technique for the detection of expiratory flow limitation (EFL) during experimental artificial ventilation is proposed, based upon a specific analysis of the driving pressure (Pao), the volume (V) and the flow (V΄) signals in eight tracheotomized and intubated rabbits. EFL was provoked by application of negative expiratory pressure or/and intravenous infusion of Histamine. EFL was detected by application of: Additional negative expiratory pressure (ANEP) and b) Forced oscillations. Two equal volume paired points have been chosen, that correspond to 10% and 90% of the expiratory tidal volume. The recorded pressure gradient (ΔP) between these paired points may be considered as totally consumed for the development of the corresponding flow difference (ΔV΄). The comparative evaluation of the ‘differential’ resistance (ΔR=ΔP/ΔV΄) expressed by the index: ΔR90%VTexp- ΔR10%Vtexp x100/ΔR10%VTexp permitted the EFL detection with absolute specificity and sensitivity. The observed high values of the proposed index (mean value: 60.6 ± 9.23), at the presence of EFL, express the significant increase of ΔR90%VTexp. On the contrary, the low values of the index (mean value 4.5 ± 15.26), in the absence of EFL, are related to the relative stability of ΔR during the whole respiratory cycle. The proposed method is simple, noninvasive, it does not require any change of the ventilator settings and is offered for continuous monitoring. Pneumon 1999, 12 (2): 84-92
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