Introduction: Positive pressure ventilation (PPV) is common in life support, however, the use of positive intrapulmonary pressure differs from the physiological pressure regimen, which has adverse consequences on ventilation-perfusion (V/Q) matching. While negative pressure ventilation (NPV) resembles to physiological conditions, its effect on the V/Q matching has not been elucidated.

Methods: Anaesthetized rats (n=8) were ventilated using PPV at positive end-expiratory pressures of 0, 3, 6 and 9 cmH₂O. NPV then was initiated by placing the rats in a sealed chamber and generating cyclic negative pressure changes around the body, with maintaining identical pressure regimes and tidal volumes (VT) than those generated under PPV. End tidal CO₂ (ETCO₂), volume of exhaled CO₂ (VCO₂), phase 3 (S3V), and phase 2 slopes (S2V), anatomical deadspace fraction (VDF), and physiological deadspace fractions according to Bohr (VDB) and Enghoff (VDE) were established by volumetric capnography.

Results: Lack of difference in VT or ETCO₂ was associated with higher S2V (p=0.008) and lower S3V (p<0.001) under NPV than PPV. At low end-expiratory pressures, significantly lower VDF (p=0.01) and VDB (p<0.05), and greater VCO₂ (p<0.01) were obtained under NPV. Ventilation mode had no effect on VDE.

Conclusions: Application of physiological pressure regimes during NPV ameliorates CO₂ clearance, thereby diminishing anatomical and physiological deadspace fractions. These findings may propose the benefit of NPV in improving V/Q matching, however further studies are required to reveal the underlying mechanisms.

Funding: OTKA-NKFIH K138032 and FK134274