Published in:
01-03-2004 | Experimental
Dynamic elastic pressure-volume loops in healthy pigs recorded with inspiratory and expiratory sinusoidal flow modulation
Relationship to static pressure-volume loops
Authors:
Ulrika Bitzén, Björn Drefeldt, Lisbet Niklason, Björn Jonson
Published in:
Intensive Care Medicine
|
Issue 3/2004
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Abstract
Objective
The objective was to analyse relationships between inspiratory and expiratory static and dynamic elastic pressure-volume (Pel/V) curves in healthy pigs.
Design
The modulated low flow method was developed to allow studies also of the expiratory Pel/V curves. Static Pel/V (Pel,st/V) and dynamic Pel/V (Pel,dyn/V) loops were studied in healthy pigs.
Setting
Animal research laboratory in a university hospital.
Material
Ten healthy anaesthetised and paralysed pigs.
Interventions and measurements
A computer controlled a Servo Ventilator 900C with respect to respiratory rate, inspiratory flow and expiratory pressure to achieve a sinusoidal modulation of inspiration and expiration for determination of Pel,dyn/V loops from zero end-expiratory pressure (ZEEP) and from a positive end-expiratory pressure (PEEP) of 6 cmH2O to 20, 35 and 50 cmH2O. The same system was used for studies of Pel,st/V loops with the flow-interruption method from ZEEP and PEEP to 35 cmH2O. Recordings were analysed with an iterative technique.
Results
The feasibility of automated determination of Pel,dyn/V loops was demonstrated. Differences between Pel,dyn/V and Pel,st/V loops were explained by viscoelastic behaviour. Pel,st/V loops recorded from PEEP to 35 cmH2O showed no significant hysteresis, indicating a non-significant surface tension hysteresis. Pel,dyn/V loops from PEEP and both Pel,st/V and Pel,dyn/V loops from ZEEP to 35 cmH2O showed hysteresis. This indicates that lung collapse/re-expansion caused Pel/V loop hysteresis which, in Pel,dyn/V loops, was augmented by viscoelastic behaviour.
Conclusions
Viscoelasticity influences Pel,dyn/V curves. Hysteresis caused by surface tension merits re-evaluation. Lung collapse and re-expansion may be indicated by hysteresis of Pel/V loops.