Research

Chest wall mechanics during pressure support ventilation

Andrea Aliverti¹ , Eleonora Carlesso² , Raffaele Dellac๠, Paolo Pelosi³ , Davide Chiumello⁴ , Antonio Pedotti¹ and Luciano Gattinoni^2,4

¹Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy

²Università degli Studi, Milano, Italy

³Dipartimento Ambiente, Salute e Sicurezza, Universita' degli Studi dell'Insubria, Varese, Italy

⁴Istituto di Anestesia e Rianimazione, Fondazione IRCCS, Ospedale Maggiore Policlinico Mangiagalli Regina Elena, Milano, Italy

author email corresponding author email

Critical Care 2006, 10:R54doi:10.1186/cc4867

Published:	31 March 2006

Abstract

Introduction

During pressure support ventilation (PSV) a part of the breathing pattern is controlled by the patient, and synchronization of respiratory muscle action and the resulting chest wall kinematics is a valid indicator of the patient's adaptation to the ventilator. The aim of the present study was to analyze the effects of different PSV settings on ventilatory pattern, total and compartmental chest wall kinematics and dynamics, muscle pressures and work of breathing in patients with acute lung injury.

Method

In nine patients four different levels of PSV (5, 10, 15 and 25 cmH₂O) were randomly applied with the same level of positive end-expiratory pressure (10 cmH₂O). Flow, airway opening, and oesophageal and gastric pressures were measured, and volume variations for the entire chest wall, the ribcage and abdominal compartments were recorded by opto-electronic plethysmography. The pressure and the work generated by the diaphragm, rib cage and abdominal muscles were determined using dynamic pressure-volume loops in the various phases of each respiratory cycle: pre-triggering, post-triggering with the patient's effort combining with the action of the ventilator, pressurization and expiration. The complete breathing pattern was measured and correlated with chest wall kinematics and dynamics.

Results

At the various levels of pressure support applied, minute ventilation was constant, with large variations in breathing frequency/ tidal volume ratio. At pressure support levels below 15 cmH₂O the following increased: the pressure developed by the inspiratory muscles, the contribution of the rib cage compartment to the total tidal volume, the phase shift between rib cage and abdominal compartments, the post-inspiratory action of the inspiratory rib cage muscles, and the expiratory muscle activity.

Conclusion

During PSV, the ventilatory pattern is very different at different levels of pressure support; in patients with acute lung injury pressure support greater than 10 cmH₂O permits homogeneous recruitment of respiratory muscles, with resulting synchronous thoraco-abdominal expansion.