Development of a time-cycled volume-controlled pressure-limited respirator and lung mechanics system for total liquid ventilation

Abstract

Total liquid ventilation can support gas exchange in animal models of lung injury. Clinical application awaits further technical improvements and performance verification. Our aim was to develop a liquid ventilator, able to deliver accurate tidal volumes, and a computerized system for measuring lung mechanics. The computer-assisted, piston-driven respirator controlled ventilatory parameters that were displayed and modified on a real-time basis. Pressure and temperature transducers along with a lineal displacement controller provided the necessary signals to calculate lung mechanics. Ten newborn lambs (<6 days old) with respiratory failure induced by lung lavage, were monitored using the system. Electromechanical, hydraulic, and data acquisition/analysis components of the ventilator were developed and tested in animals with respiratory failure. All pulmonary signals were collected synchronized in time, displayed in real-time, and archived on digital media. The total mean error (due to transducers, analog-to-digital conversion, amplifiers, etc.) was less than 5% compared with calibrated signals. Components (tubing, pistons, etc.) in contact with exchange fluids were developed so that they could be readily switched, a feature that will be important in clinical settings. Improvements in gas exchange and lung mechanics were observed during liquid ventilation, without impairment of cardiovascular profiles. The total liquid ventilator maintained accurate control of tidal volumes and the sequencing of inspiration/expiration. The computerized system demonstrated its ability to monitor in vivo lung mechanics, providing valuable data for early decision making.

A Liquid Ventilator Prototype for Total Liquid Ventilation Preclinical Studies

“…In addition, the maximal PaO 2 of 234 mmHg obtained herein is similar to the PaO 2 value of 201 mmHg previously reported in healthy newborn lambs by others (Hirschl et al, 1995;Larrabe et al, 2001;Stavis et al, 1998, www.intechopen.com Progress in Molecular and Environmental Bioengineering -From Analysis and Modeling to Technology Applications 336 Cox et al 2003). Beyond their low cost and simplicity of use, the present study clearly shows that bubble oxygenators can be highly efficient during TLV.…”

“…A decrease in the oxygen flow rate through the oxygenator is not a suitable solution, since they it compromises the PaCO 2 , before any effect on PaO 2 reduction. The choice of a bubble oxygenator could be seen as a limitation, since most research groups use membrane oxygenators with TLV (Corno et al 2003;Cox et al 2003;Hirschl et al, 1995;Larrabe et al, 2001;Parker et al, 2009;Pohlmann et al, 2011;Tredici et al, 2004). On the contrary, we strongly believe that bubble oxygenators are quite suitable for TLV.…”

“…However, the insertion of a pressure sensor in the mouth can be problematic in a clinical context, thus the main issue is to adapt this pressure controlled mode without a pressure sensor in the trachea. Many efficient demonstrations of TLV have been performed with different prototypes (Corno et al 2003;Cox et al 2003;Degraeuwe et al, 2000a;Hirschl et al, 1995;Larrabe et al, 2001;Meinhardt et al, 2000;Parker et al, 2009;Pohlmann et al, 2011;Sekins et al, 1999;Tredici et al, 2004). With O 2 saturated PFC and limited to low minute ventilations (comparatively to CMV), they obtained acceptable ventilation.…”

“…Research teams in TLV have mainly used bubble oxygenators Sekins et al, 1999;Tissier et al, 2009), commercial membrane oxygenators (Corno et al 2003;Larrabe et al, 2001;Hirschl et al, 1995;Wolfson et al, 1999Wolfson et al, , 2008 or have developed membrane oxygenators specifically for TLV (Tredici et al, 2004). However, the requirements for extracorporeal blood oxygenation appear irrelevant in TLV, since there is no mechanical stress to the blood (hemolysis) or bubble infusion in the blood (Iwahashi et al, 2004).…”

Long-Term Tidal Liquid Ventilation in Premature Lambs: Physiologic, Biochemical and Histological Correlates

“…In this way, lung volumes are tightly controlled during tidal liquid ventilation. Other experimental works with tidal liquid ventilators include evaluation of a time-cycled volume-controlled pressure-limited ventilator with lung mechanics measurement capabilities [41]; evaluating the distribution of mechanical loads in the lungs during tidal liquid ventilation [42], and the use of a feedback controller to maintain FRC during tidal liquid ventilation [43].…”