[Effects of negative extra-thoracic pressure ventilation on respiratory system and hemodynamics in normal dogs]

The effects of negative extra-thoracic pressure ventilation (NETPV) on respiratory system and hemodynamics were examined in ten normal dogs. Changes of the parameters obtained during intermittent NETPV (INETPV), and NETPV with negative end-expiratory pressure (CNETPV) were compared with those during IPPV and CPPV. Animals' chests and upper abdomens were confined in an acryl box. In INETPV and CNETPV, the dogs were ventilated with the negative extra-thoracic pressure ventilator (Kimura, OKT-100). Positive and negative pressure ventilation was carefully matched for tidal volume and the increase in FRC obtained with PEEP and the end-expiratory negative extra-thoracic pressure (EENETP). EENETP of -11.6 cmH2O produced the same FRC change as PEEP of 10.6 cmH2O did. Gas exchanges did not differ in any modes. INETPV did not change any hemodynamic parameters without PAP. In CNETPV, heart rate increased, and CVP, cardiac index (CI) and stroke volume (SV) decreased significantly (P less than 0.05), but tmCVP and tmPCWP did not change. The decreases of CI and SV (100----89.1, 88.8%) in CNETPV were significantly smaller when compared with CPPV (100----78.8, 74.5%). In CPPV, meanBP, CVP, tmCVP, tmPCWP, CI, SV changed significantly. The mechanisms of the decrease of CI and SV by CNETPV seemed to be different from those by CPPV.