Effects of continuous negative extrathoracic pressure ventilation on left ventricular dimensions and hemodynamics in dogs.

It has been reported that continuous negative extrathoracic pressure ventilation (CNETPV) depresses cardiac output less than continuous positive pressure ventilation (CPPV) does, and this difference may be related to the different effects of two ventilatory modes on preload. We performed simultaneous measurements of hemodynamics and left ventricular short axis dimensions by transesophageal echocardiography (TEE) to evaluate left ventricular preload and function during CNETPV and CPPV in normal dogs. Hemodynamic measurements and simultaneous TEE recording were performed at 5 successive periods; 1) the first control period of intermittent positive pressure ventilation (IPPV1), 2) CNETPV with negative end-expiratory pressure (NEEP) of -10 cmH2O (CNET10), 3) CNETPV with NEEP of -15 cmH2O (CNET15), 4) the second control period of IPPV (IPPV2), and 5) CPPV with PEEP of 15 cmH2O (CPPV15). Left ventricular end-systolic and end-diastolic dimension (LVESD and LVEDD), ejection fraction (EF) and fractional shortening (FS) were measured from TEE recordings. Both CNET10 and CNET15 induced no significant changes in hemodynamics and left ventricular dimensions, compared with those during IPPV1. However, CPPV15 reduced cardiac output and stroke volume (SV) and increased heart rate significantly, compared with IPPV2. CPPV15 significantly decreased LVEDD compared with IPPV2. Neither EF nor FS showed any significant change throughout the experiment. These results indicate that CNETPV preserved cardiac output because it maintained the preload and the left ventricular function.