Influence of Ventilatory Frequencies and Ventilator Volume/Pressure Quotients on Pulmonary Ventilation Using a Tidal Volume Ventilator

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Abstract
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 VDphys/VTexpratio was greater at f = 30 than at f = 10.3 cycles/min. This could be related to a significant increase in the VDanat/VTexpratio at f = 30, while VDc/VTexpand VDlav/VTexpwere unchanged at both frequencies. With regional bronchial obstruction and f = 30, the regional ventilation and perfusion within the obstructed pulmonary field were reduced, compared to the values at f = 10.3 cycles/min. With Cvent20 ml/kPa, the tidal volumes were insufflated in a shorter time and with a higher initial tracheal peak pressure than with Cvent80 ml/kPa. Following bronchial obstruction, VA, RQ and Pao2were greater with Cvent20 than with Cvent80 ml/kPa. With Cvent20, 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 Cvent80. Ventilation at Cvent20 showed no essential advantage over Cvent80. Only in lungs extremely difficult to ventilate and with ventilatory frequencies over 50 cycles/min could possible indications for Cvent20 be seen.