A Preliminary Report on Experimental Studies of Continuous Positive-pressure Ventilation (CPPV) and High-frequency Positive-pressure Ventilation (HFPPV)

Abstract

In a previous study on dogs the ventilatory pattern of a conventional respirator (SV-900) was compared with that produced by a prototype system for volume-controlled high-frequency positive-pressure ventilation (HFPPV). At comparable arterial carbon dioxide tensions the intratracheal peak and mean pressures and the total peripheral vascular resistance (TPR) were higher but cardiac output (CO), stroke volume (SV) and oxygen flux (OF) lower during ventilation with SV-900 at a ventilatory frequency of 20/min than during HFPPV at a ventilatory frequency of 60/min.

In the present study on 10 dogs, using ventilatory frequencies (f) of 20, 40, 50 and 60, the experimental conditions were light pentobarbital anaesthesia and normoventilation. With a prototype system (system H), functionally with no compression volume, the tidal volume of the ventilator system (V_TTOT) was equal to the effective tidal volume (V_TE) and by increasing f to 60/min, V_TE could be reduced to only 65% of that at f=20/min and the peak and mean airway pressures were consequently reduced.

The alveolar gas distribution was studied by mass-spectrometric analyses of pulmonary nitrogen clearance curves in terms of nitrogen clearance ratio (NCR). With ventilator system H, functionally with no compression volume, the alveolar gas distribution was significantly improved in comparison with the conditions with the conventional respirator system (SV-900). It seems, therefore, that ventilation with a ventilator which has a negligible compression volume and therefore can be set at a high ventilatory frequency, may cause less interference with cardio-circulatory function, and with the improved intrapulmonary gas distribution which it implies, offers advantages in the critically ill patient.