Influence of ventilatory frequencies and ventilator volume/pressure quotients on pulmonary ventilation using a tidal volume ventilator.

The influence of ventilatory frequency and the ventilator's "internal state of gas compression" (Cvent) on mechanics of ventilation, pulmonary ventilation, gas distribution, gas exchange and lung perfusion was studied with free airway and experimental regional airway obstruction in 10 piglets (7-12 kg b. w. ), using a tidal volume ventilator. The VDphy/VTexp ratio was greater at f = 30 than at f = 10.3 cycles/min. This could be related to a significant increase in the VDanat/VTexp ratio at f = 30, while VDc/VTexp and VDlav/VTexp were unchanged at both frequencies. With regional ventilation and perfusion within the obstructed pulmonary field were reduced, compared to the values at f = 10.3 cycles/min. With Cvent 20 ml/kPa, the tidal volumes were insufflated in a shorter time and with a higher initial tracheal peak pressure than with Cvent 80 ml/kPa. Following bronchial obstruction, VA, RQ and Pao2 were greater with Cvent 20 than with Cvent 80 ml/kPa. With Cvent 20, the ventilation of the lung bases was reduced, which was compensated for by a large increase in ventilation within the apical areas of the lungs, while gas distribution within the unobstructed areas was more evenly distributed with Cvent 80. Ventilation at Cvent 20 showed no essential advantage over Cvent 80. Only in lungs extremely difficult to ventilate and with ventilatory frequencies over 50 cycles/min could possible indications for Cvent 20 be seen.